Lathe-Type 3D Printer

LATHE-TYPE 3D PRINTER ME3 DMT FINAL REPORTGROUP 27 ALEXANDROS KENICH MATTHIEU BURNAND-GALPIN ERWAN ROLLAND YOUSSEF IBRAHIM

LATHE-TYPE 3D PRINTER

ERWAN ROLLAND Project Manager

ME3 DMT FINAL REPORT MATTHIEU BURNAND MATTHIEU GALPIN BURNAND GALPIN

PEOPLE DMT Team Name

Head of Control Head of Control and Structure

Contact Number

Email

ERWAN ROLLAND

07 906 478 467

[email protected]

MATTHIEU BURNAND-GALPIN

07 824 967 269

[email protected]

ALEXANDROS KENICH

07 857 781 592

[email protected]

YOUSSEF IBRAHIM

07 896 669 666

ALEX KENICH Head of Programming

[email protected]

Supervising Team Name

Contact Number

Email

Room

DR SHAUN CROFTON

02 075 947 085

[email protected]

551

DR PAUL HOOPER

02 075 947 128

[email protected]

393

DR DANIEL PLANT

02 075 947 128

[email protected]

002

YOUSSEF IBRAHIM Head of Mechanical Design

GROUP 27 Supervis ing Team

VERSION 1.3 DMT Team Lathe Type 3D Printer

Checked: E.R, M.B, Y.I 04/06/2013

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ABSTRACT This final report documents the design, making and testing of a novel lathe-type 3D printer. The prototype produced makes use of Fused Deposition Modelling and presents a viable alternative to Cartesian 3D printers currently in use. Methods were developed to generate G-Code machine commands which are used to produce these parts. The main objectives of the project were met; parts can be printed with good accuracy and with minimal effort. Through efficient management and organisation, the project was completed on time and under budget at £527. The additive lathe prototype is capable of printing parts exhibiting complex geometries exclusive to cylindrical 3D printers. Parts previously impossible to create using additive manufacturing such as springs and propellers can be made with ease. The infill and aspect of cylindrical components can be controlled more precisely than is possible on a conventional 3D printer, and filament can be interwoven to improve mechanical properties. The project could be extended by adding supplementary features to the software used to control the printer. In particular, writing code for a custom slicing procedure could streamline the generation of G-Code starting from a solid model. The printer provides an excellent foundation for these innovations to be implemented.

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TABLE OF CONTENTS I. BACKGROUND ................................................................................................................................................1 I.1 INTRODUCTION ...............................................................................................................................................1 I.2 TECHNOLOGY REVIEW ....................................................................................................................................2 I.3 GROUP CONTRIBUTIONS .................................................................................................................................5 II. PROJECT PLANNING .....................................................................................................................................6 II.1 PRODUCT DESIGN SPECIFICATION .................................................................................................................6 II.2 GANTT CHART ...............................................................................................................................................8 II.3 QUALITY MANAGEMENT .................................................................................................................................9 III. DESIGN PROCESS ......................................................................................................................................10 III.1 DESIGN EVOLUTION ...................................................................................................................................10 III.3 STRUCTURAL DESIGN .................................................................................................................................13 III.4 CONTROL AND TRANSMISSION ....................................................................................................................16 III.5 MECHANICAL DESIGN .................................................................................................................................20 III.5 ELECTRONICS AND PROGRAMMING .............................................................................................................23 IV. MANUFACTURING AND ASSEMBLY ........................................................................................................30 IV.1 PERSPEX STRUCTURE ...............................................................................................................................30 IV.2 PRINTED PARTS.........................................................................................................................................31 IV.3 MACHINED PARTS ......................................................................................................................................32 IV.3 ASSEMBLY.................................................................................................................................................33 V.4 CALIBRATION ..............................................................................................................................................37 V. TESTING ........................................................................................................................................................38 V.1 TESTING THE PRINTER PROTOTYPE .............................................................................................................38 V.2 G-CODE GENERATION ................................................................................................................................41 V.3 TESTING THE PRINTED PARTS .....................................................................................................................45 VI. COSTING AND PURCHASING ....................................................................................................................47 VII DISCUSSION ................................................................................................................................................49 VII.1 SHORTCOMINGS AND POTENTIAL IMPROVEMENTS .......................................................................................49 VII.2 UTILITY OF THE CYLINDRICAL PRINTER AND POTENTIAL APPLICATIONS ..........................................................50 VII.3 PLANNING AND CONDUCT OF TASK ............................................................................................................51 VIII. CONCLUSION ............................................................................................................................................52 IX. REFERENCES ..............................................................................................................................................53 X. ACKNOWLEDGEMENTS ..............................................................................................................................53 APPENDICES ....................................................................................................................................................54 APPENDIX A1: STRUCTURAL AND CONTROL CALCULATIONS ................................................................................54 APPENDIX A2: DETAILED BILL OF MATERIALS .....................................................................................................59 APPENDIX A4: DETAILED DRAWINGS ..................................................................................................................60 APPENDIX A5: INDIVIDUAL CRITIQUES ................................................................................................................61

III

DMT 27: Lathe-type 3D Printer

Department of Mechanical Engineering

I. BACKGROUND I.1 Introduction Fused Deposition Modelling 3D printers have recently garnered significant attention due to simplifications in design, leading to cheaper and more widely available printers. However, some limitations are associated to this technology, and several attempts have been made to overcome these [1]. The aim of the project described in this report is exploring one such possibility. A 3D printer was developed that, unlike a standard printer operating in Cartesian co-ordinates, operates in cylindrical co-ordinates. This is analogous to a lathe where material is deposited on a rotating cylinder rather than cut away. Efforts were also made to investigate the advantages of using a cylindrical printer over its Cartesian counterpart, exploring aspects such as the facilitation of creating certain geometries and the ability to control the disposition of the filament used to produce a printed part.

Figure 1: The Airwolf 3D printer operating in Cartesian coordinates

The report begins by introducing the topic of additive manufacturing and reviewing current 3D printing technology. Following this background information, the project plan used to conduct this project is briefly introduced. The design is explained in depth by exploring initial concepts and detailed features present in the final design. The design decisions concerning software and electronics are also presented. Manufacturing considerations and the assembly process are then outlined, followed by information relating to the assessment and testing of the finalised prototype and the parts it can produce. The project costing is then presented followed by a discussion of the project, including its main achievements and potential areas of improvement.

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I.2 Technology Review Increased interest in additive manufacturing methods has been accompanied by a popularisation of 3D printers. The applications of these devices range from rapid prototyping to specialist applications in medicine or aeronautics. While 3D printers are often grouped as single technology, they often operate using a variety of methods, and utilise a myriad of materials [1]. One of the most prominent 3D printing techniques is known as Fused Deposition Modelling (FDM). This method uses use thermoplastics such as ABS, polycarbonate and PLA, and has gathered considerable interest, as it is conceptually simple and relatively cheap. Material is fed into a heated nozzle, and laid upon a print bed while melted. As the layers solidify, a solid object is formed.

Heated Nozzle

Deposited material

Print bed Figure 2: Diagram of Fused Deposition Modelling (FDM)

[1]

The team decided to conduct a short literature review to understand the basics of 3D printing, and to identify some of the shortcomings which could be overcome with a cylindrical printer. Additionally, past attempts to design cylindrical 3D printers were reviewed in order for our project to build upon their limitations. Much of the on-going development surrounding FDM printers is concentrated around the RepRap Project (Replicating Rapid Prototyping Machine). The main advantage of these machines is that they can be built with standard components, and extensively customised. For these reasons, RepRap-type printers provide a good framework in which innovative features can be implemented with minimal cost and effort. These machines operate in Cartesian coordinates; the print head can move in the X and Z directions, while the printbed is free to move in the Y direction using stepper motors. A picture of a typical RepRap machine is shown in figure 3.

Z Axis motor

Print head

Print bed X Axis motor

Printed Fixtures

Control electronics

Figure 3: A typical RepRap 2.0 Mendel Printer

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The range of geometries obtainable by these printers is limited by the use of Cartesian coordinates. One of these limitations is the difficulty of producing parts with large overhangs. This can be remedied by using a second material as a support, which can be removed once the part is completed. However, this method is significantly more costly and more complex. Similarly, traditional FDM printers are often unable to create curved shapes with high accuracy. The smoothness of a circular part is limited by the step size on the motors. One of the shapes difficult to make on a Cartesian 3D printer is shown in figure 4 below. Z Z

Θ X

No overhangs

X Y

Large overhangs

Figure 4: Complex shape in on a Cartesian print bed (left) and cylindrical print bed (right)

Cylindrical-type 3D Printers One of the attempts made to further 3D printer technology is the additive lathe. Unlike a traditional lathe, the exact angular position of the cylindrical printbed can be controlled using a stepped motor. Material can be deposited on the rotating print bed using a print head which moves in the X direction.

Extruder Assembly

X Rails

Chuck Rotating Print Bed

Figure 5: Sketches of shapes difficult to make on a Cartesian printer

[2]

The additive lathe was created mainly as a proof of concept, and demonstrates the possibility of using a rotating print bed in a 3D printer with cylindrical coordinates [2]. Its main drawback stems from the omission of vertical mobility. As such, the range of parts that can be created is severely

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reduced. Components with overhangs which could be created in cylindrical coordinates cannot be made on this printer. Additionally, although a chuck is included, the design of the transmission does not enable the rotating print bed to be swapped for one with a different shape or material. Finally, this prototype cannot make use of existing software, and relies on custom electronics with reduced functionality. Only very simple parts can be produced by this printer, making it difficult to assess the increase in quality which can be offered by cylindrical printers. Furthermore, the design offers no upgradability, which would be desirable in order for a variety of print beds and materials to be tested. Some of the aspects related to cylindrical printing have recently been patented [3]. The patent gives a very general overview of the systems which could be involved in such a machine, but gives minor indications on how these features could be implemented. A diagram of this machine is presented in figure 6 below.

Deposited material Printhead

Rotating bit

Electronics

Figure 6: Diagram of a cylindrical printer

[3]

Conclusion While there have been some attempts to create a cylindrical 3D printer, most have been experimental, and no complex parts have been printed. As a result, many of the features which seem to be made possible with cylindrical printing are still hypothetical. The priority of the project is to construct a prototype which demonstrates some of these novel features. Another significant challenge is to integrate electronics and software with the printer. The main shortcomings of past projects which must be resolved with the project are presented in figure 7 below.

Implementation of a vertical axis

Integration of electronics

Feature interchangeable printbeds

Create more complex parts

Identify main limitations of concept

Show overhangs can be avoided

Show viability of overhangs

Figure 7: Main objectives of the DMT prototype

Show off interweaving

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I.3 Group contributions The group benefitted from excellent team cohesion and maintained well-distributed responsibilities and work amongst team members. While all team members contributed to the overall design, problem solving and report writing, each team member focused on particular aspects of the project. ERWAN: PROJECT MANAGER As project manager, Erwan coordinated the team’s efforts and scheduled meetings. He was a driving force in maintaining the team’s motivation high and ensured deadlines were met. Erwan played a pivotal role in the Electronics and Programming aspects of the project, as he was responsible for selecting and implementing hardware and software solutions for the printer. He was also in charge of modifying and tweaking the printer’s firmware to adapt it to cylindrical coordinates. As project manager, Erwan also held the responsibility for ensuring the quality of the reports. He was in charge of assembling the reports, unifying the formatting and final editing. MATTHIEU: HEAD OF CONTROL AND STRUCTURE As Head of Control, Matthieu worked on obtaining the best possible printing accuracy. To this effect, he was responsible for selecting the motors and designing the transmission while minimising backlash. He was also in charge of designing the print bed assembly and all the components that relate to it. He was also the main architect of the CAD model and ensured the overall design was coherent. As such, he played a vital role in the manufacturing process and ensured quality control. Matthieu was also in charge of the acrylic sheets, from purchase to the design. He conducted and evaluated the impact of the laser cutter on the Perspex sheet and updated the CAD file accordingly. Matthieu also played a significant role in programming; he developed and tested the MATLAB program. Finally, along with Erwan, he was responsible for editing and proofreading the reports. YOUSSEF: HEAD OF MECHANICAL DESIGN In the design process, Youssef held responsibility for the design of the X and Z axis components. He adapted standard RepRap x and z axis components for cylindrical printing. He distinguished himself in the manufacturing and assembly process. He played a key role in manufacturing and used his technical abilities to fix problems during the assembly process. Once the printer was assembled, he contributed heavily to increasing the practicality and aesthetic appeal of the printer. Along with Matthieu, he was an important contributor to the CAD. Finally, he generated innovative ideas for the poster. ALEX: HEAD OF ELECTRONICS AND PROGRAMMING Alex played varied roles as part of the team. As head of electronics and programming, Alex contributed to the programming through his expert knowledge of C. Possessing clear artistic skills; he was in charge of visual representation and photography of the printer. His skills in scene setting and lighting ensured aesthetic and precise representations of the printer and test parts. Alex also brought forward his image processing skills to design the poster. He also made subtle modifications to the CAD file, and was the driving force behind the assembly drawing. Finally he kept track of the teams spending and budgeting.

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II. PROJECT PLANNING One of the main aims of the project was to demonstrate the viability of the cylindrical 3D printer concept. As such, the team’s approach to the project was relatively unrestrained and free of commercial considerations. One limitation however was the project budget, which could not exceed £600. As a result of these criteria, the group prioritised innovation over cost-effectiveness, exploring different methods and perspectives towards the realisation of the end product.

II.1 Product Design Specification Starting from the project brief, a Product Design Specification (PDS) was produced in order to identify the key requirements which our project would need to satisfy. Additionally, these objectives were quantified in order to provide a framework for the design process. The criteria outlined below are of varying importance to the success of the project and a weighting from 1 (low importance) to 6 (high importance) was assigned to each criterion. Table 1: Product Design Specification: Performance and Safety

Aspect

Criteria High precision printing Homogeneous deposition

Performance

Quality

Robustness

Safety

Efficiency

Low risk to user

Objective

Testing

4

<0.5mm

Print a part with intricate details

5

Large printing volume

3

Use mains power

6

No large vibrations Easy STL to GCode translation Seldom breaks down

Reliability

Weight

3 3

Smooth and even At least 200x200x150 mm 220V Standard <3mm displacement Less than 5min

Print a part with smooth features Print a large part Plug into socket Print while on a hard surface Record time to process STL

3

-

Focus Group Evaluation

2

At least 10 hours

Print for 10 hours without maintenance

4

At least 20min

Print for at least 20 minutes continuously

3

Up to 100N

Place 10kg mass on printer

3

At least 10 parts

Print 10 parts consecutively

3

0.1cm3/s

Print cylinder and perform simple calculations

1

Less than 50

Check with bill of materials

Heat protection

4

Heat insulated

Check temperature in vicinity of heater during operation

Electrical Protection

5

Safe disposal

1

Use of safe materials

1

No sharp edges

2

Long life Can be used for lengthy jobs Must withstand light loads Must resist regular use Prints parts quickly Minimal number of parts

Electrically insulated Relevant Standards Relevant standards -

Focus Group Evaluation Focus Group Evaluation Focus Group Evaluation Focus Group Evaluation

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Table 2: Product Design Specification: Ergonomics and User Appeal

Aspect

Ergonomics

Size and Weight

Usability

Criteria

Weight

Target

Testing

Reasonably compact

1

Less than 500x500x500mm

Measure Dimensions

Moderate weight

1

Less than 20kg

Weigh printer

Compact addons and tools

2

User testing


Easy to set up

3

User testing


4

Clear and concise


2

-


3

No physical strain


2

Less than 60dB


3

Design Review


Accessible controls and features Good visibility of printing process Minimal effort to operate Low noise

Maintenance

User Appeal

Manufacturing

Easily serviceable parts Use cheap processes Use FDM printer for parts Easy to manufacture Within budget

Cost

Proof of Concept

Low operating costs Features interweaving Faster printing of some shapes Accurate GCode and path

2 1

Within costing budget For standard components

Focus Group Evaluation Print parts from Cartesian printer

2

Design Review


6

Less than £600

Calculate cost of project

1

Less than £10/kg

Check cost of filament

4

Prototype testing

Print cylindrical part with interweaving

3

20% Reduction

Compare to Cartesian printer

3

No construction errors

Compare accuracy of parts to Cartesian printer

Following the construction of the PDS, a Quality Function Deployment matrix (QFD) was produced in order to relate engineering requirements to the functions the printer would need to fulfil. This matrix was instrumental in establishing key features the printer would need to accommodate. Additionally, the relative importance of each function was used to determine which tasks would need to be prioritised. The result of this analysis was used to allocate the team’s time and resources.

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II.2 Gantt chart The time allocations for tasks and milestones in the project are illustrated in a Gantt chart. This chart was updated at various stages to reflect modifications in the project. In order to ensure that each task was completed within the allocated time frame, individual team members were assigned responsibility for specific tasks. Their role was also to ensure the task was delivered on time. Peer review sessions were also marked on the chart to ensure that all deliverables could be checked before their deadline. The most recent Gantt chart (21/04/2013) is shown in table 3 below. Table 3: Gantt chart Section

Name

Description

October

Team 1

8

15

Initial research and understanding

Planning

Project plan report Progress report Poster design

Programming

Log book

Control Mechanical Purchasing Manufacturing

All

Background reading on 3D printers

All

Writing of the project plan report

E&Y

Writing of the progress report

A&M

Brainstorming for poster ideas and poster design Keeping track of new ideas and progress in a log book

Seminar preparation

Preparing for the presentation of the project

Y

In-depth understanding of

Understanding CAM software, G-code,

software

Arduino… Selecting open source and intercompatible

cylindrical coordinates

software Modifying the CAM and slicer softwares to allow for cylindrical printing Simulation of G-code and verification of its

Understanding the

good functioning Understanding what components are

requirements Selecting adapted

necessary to ensure control of the actuators Selecting the relevant chipboards and servos

components

all while minimisimg cost Design concepts and general arrangement of

General ideas Finalising design 3D modelling of the printer Determining parts to buy Purchasing of parts

the printer Finalising the design of the printer Solidworks modelling of the printer with all the standard parts From part requirements and assembly choose parts to purchase Passing orders to purchase the parts, allowing plenty of time for reception

Receiving of parts

Reception and quality testing of parts

Manufacture of parts using

From the CAD model, print parts for the

the existing RepRap

building of the cylindrical printer Manufacture of other parts required for the

Manufacture of other parts Assembly Testing Calibrating Modifying Printing an object

Key

printer Mechanical assembly of the printer and linking it to the electronics Testing of quality of assembly, response to command Calibrating printer parameters to optimise printing speed From built device, make modifications to parts to optimise printing Printing test specimens to prove that the printer is functioning correctly

Completed task:

12

19

26

December 3

10

17

24

January 31

Christmas Holidays

7

14

21

Design Review

Febuary 28

4

11

18

Progress report

March 25

1

8

15

April 22

1

8

15

Easter Holidays

May 22

29

6

Exams

13

20

June 27

3

Seminar Review

10

17

Seminar

Final report, log book and poster presentation hand in

E E&M

Adapting the software to

5

A

Drafting, writing and editing of the final report

Analysis and corrections

Testing

Form a group and choose a project

Final report

Software selection

November 29

Project plan report

Milestones DMT project selection

22

A&E E A A M E M M&Y Y All A M M Y E M A E Y

Incomplete task:

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II.3 Quality Management To ensure the quality of the project and to guarantee the planning was respected, the group adopted the Total Quality Management (TQM) philosophy of management. This process revolves around eight main points adapted to this project. These are shown in figure 8 below. Crossfunctional Product Design

Supervisor Involvment

Strategic Planning

Process Management

Supplier quality management

Comitted Leadership

Team Involvement

Figure 8: Total Quality Management criteria

Information and Feedback

[4]

These eight points were central to the elaboration of the quality tables, inspired by Deming’s PlanDo-Check-Act (PDCA) cycle. Team members were given responsibility for the completion of different stages of each task. The outcome was then checked by a different member to ensure quality and to avoid errors. The quality tables constructed for this purpose are shown in the project plan report [4]. Meetings with all group members present were scheduled three times a week. This was done to ensure that everyone was up to date with the status of the project, and to enable external input to be incorporated in tasks conducted individually. During these sessions running roughly two hours, team members were able to work on their tasks together. This was an effective way to ensure consistent quality and good communication between group members. These gatherings were supplemented with weekly supervisor meetings. These sessions brought to light any issues with the design, and enabled the team to check whether the direction and scope of the project were consistent with expectations. Suggestions from the supervising team to amend the design were implemented by the appropriate members delegated in the quality plan. A timetable of a typical week is shown in figure 9 below.

Afternoon

Morning

Monday

Tuesday

Wednesday

Thrursday

Friday

Lectures and study

Lectures and study

Supervisor Meeting

Session 1: Set tasks for week

Lectures and study

Lectures and study

DMT Project Work

Session 2: Check task progress

DMT Project Work

Session 3: Results and feedback

Figure 9: Typical Weekly DMT timetable

Finally, two formal peer-reviews were planned to assess the quality of the final design and seminar. These were conducted with two fellow students from other DMT groups. This provided an external perspective and additional ideas for dealing with shortcomings in the design and constructive criticism for the presentation of the seminar.

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III. DESIGN PROCESS A large amount of time was voluntarily dedicated to the design process, in order to ensure the final design fulfilled or exceeded engineering requirements. The first section of this chapter shows the elaboration of conceptual designs, culminating in the finalised design of the printer. Subsequent sections showcase the main features of the printer, as well as key design decisions. A more complete explanation of the design choices is explored in the Progress Report [5]. Finally, an assembly drawing of the printer is presented along with the bill of materials.

III.1 Design Evolution Initial designs were drafted informally during the first weeks of the project. Team members’ contributions were unhindered; to ensure all design possibilities were equally considered. A list of advantages and disadvantages was compiled for each concept in order to distinguish them, and to ensure subsequent iterations would build upon their failings. III.1.1 FIRST CONCEPT This design is inspired by the RepRap Mendel printer, which allows for most components to be acquired easily. The X and Z axes are similar to the Mendel, while the Y axis is modified to support a cylindrical print bed operating on a pulley system. Using a bevel gear transmission, a flat print bed can be added on removable rails to allow for Cartesian printing. Enables Cartesian and cylindrical printing Structure could lack stability Original Mendel dimensions leave little space for a cylindrical print bed

Figure 10: Sketch and Evaluation of the First Concept

[5]

III.1.2 SECOND CONCEPT Deviating from RepRap models, this design was elongated to make more room for the cylindrical print bed. The print head would only move in the X direction while the print bed would be made to rotate and move in the Y direction. This design could also be made to accept a flat print bed. Large print bed and printing volume Perspex sheets on edges improve stability Z Axis not included The print bed is only supported at one end (risk of deflection) Figure 11: Sketch and Evaluation of the Second Concept

[5]

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III.1.3 THIRD CONCEPT This design involved fixing the cylindrical print bed to a movable support, allowing for the whole print bed to move in the Y-axis using a threaded rod linear drive system. The print head is fixed on vertical supports and moves up and down in the Z-axis as well as laterally in the X-axis. This idea was based around exploring the choice of which axes can be fixed.

Printhead can move both in X and Z directions Print bed supported on both sides Hot end and sharp edges are in the open (safety hazard) Cartesian printing is not included Print head support lacks lateral stiffness Figure 12: Sketch and Evaluation of the Second Concept

[5]

III.1.4 FINAL CONCEPT Combining the best features from the initial ideas, this finalised concept was produced. The whole assembly is housed between two end plates and rests on a base. The print head is mounted on a carriage and allowed to move up and down on the Z axis and laterally on the X-axis. The print bed is fixed in the centre of the assembly, and can be interchanged with several different sized print beds. A support is added on the non-driven end of the print bed to prevent any sagging or axial deflection during printing.

Figure 13: Sketch of the Final Concept

[5]

The idea for a Cartesian flat print bed was abandoned as it was deemed unnecessarily complex, and deviated from the original direction of the project. While promising, 4 axis designs were abandoned as they were too complex to be incorporated effectively in a timely manner.

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III.1.5 FINAL DESIGN Starting from the final concept, a detailed design was drafted over a period of 10 weeks. In order to streamline this process, design tasks were divided into four sections; structural, control, mechanical and electronics & programming. These tasks were conducted in tandem to ensure the design was coherent, and fit requirements. The figure below shows the main features of the printer, and indicates in which section of the report they are explained in more detail.

Vertical axis clamps (III.4): These clamps are used to hold the vertical rails. They are printed parts from a conventional FDM printer.

Print head (III.4): The extruder head deposits molten polymer onto the cylindrical bed in successive layers to produce printed parts.

Fixtures (III.4): LM8UU linear bearings enable smooth vertical motion. This allows for accurate displacement in the vertical direction.

Vertical axis rails (III.4): These steel rods are threaded which enables movement of the extruder head in the vertical axis.

Print bed (III.4): The print bed is held in a chuck so that it can rotate while printing. The print bed can be changed by unloading the chuck and inserting any cylinder with appropriate dimensions. The print bed is covered in polyamide tape for adherence.

Perspex body (III.3): Perspex is the selected body material because it is a cheap alternative to metal, more aesthetic and does not compromise the structural integrity of the printer.

Pulley system (III.5): This system uses the appropriate gears and belt to provide sufficient step-down in motor speed while also limiting any backlash.

Power supply (III.6): The power pack supplies the power to the motors, the Arduino and the heating element. It is placed in a slot under the print bed for proximity to the motors to keep wiring neat and for safety of the operator.

Arduino and RAMPS (III.6): These elements take the instructions provided by the user on the PC and convert them to motor instructions

Figure 14: CAD Rendering of the final design

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III.3 Structural Design The structure encompasses the components that support and locate the functional elements of the printer. This mainly comprises of the Perspex body panels, which were carefully designed. Indeed, as they are relatively brittle, they cannot be reworked or modified once sent to the laser cutter. This section explores the overall frame design, develops a more specific design rationale behind the motor plate and discusses fits and tolerances used in this structure. III.3.1 BODY PANELS The body panels provide both support and location for the printer’s components. This structure must also limit the vibration that can be caused by moving parts. Perspex is a material that meets these requirements. It can easily be manufactured with high tolerances using a laser cutter. This is important for precisely locating printer components as this process is highly accurate and repeatable. Other options such as sheet metal and medium density fibre (MDF) were disregarded because they were either hard to manufacture or presented low durability. Perspex provides an elegant solution combining structural stiffness and ease of manufacture, while allowing good visibility during printing. The structure is formed by six Perspex sheets, which form a pocket under the main printing area. This pocket was implemented in response to supervisor feedback in order to enhance the overall stability of the printer. Vibrations caused by moving parts are reduced further by using 10mm thick Perspex sheets. This pocket also acts as storage for electronic components and the power supply, with cooling provided by ventilation holes. These features are shown in figure 15. Slot for plastic filament feed

Z axis motor slot

Top plate

Ventilation holes Base plate

Holes for wires and cables

Shear plate Figure 15: Main features of the Perspex Structure

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The plates are locked into place using a slotting system and fastened using bolts. A more detailed description of the fastening methods can be found in the next section. Clearance holes are cut to fix motors and other components. Motor Plate: Design for Manufacture The design of the motor plate is extremely important to the design, as it locates components essential to the alignment of the print bed and its transmission. Like the other body panels, this component was designed specifically to be laser cut. As such, nominal dimensions were adapted using data obtained by conducting tests on the laser cutter. These tests were necessary to achieve the tight tolerances necessary to locate critical components such as the motor and bearings. These precautions were crucial to obtain the printing precision accuracy set in the PDS.

Filleted edges

Slot for the top plate boss

Clearance hole for M4 bolt

Bearing housing hole

Slot for locating the rotational axis motor

Slot for the base plate

Slot for the shear plate boss

Bottom plate boss

Figure 16: Design of the motor support plate

The shape of the plate is designed to accommodate the supported parts while minimising the use of material. All exposed corners are filleted, in order to reduce stress concentrations and crack formation characteristic of acrylic sheets. This implementation was also deemed necessary from a safety perspective. Corners in contact with other components were left square to promote stability. III.3.2 FASTENING Proper fastening is paramount to ensure a perfectly rigid structure, and is essential to the quality of printed parts. This is provided in part by slotting the panels together tightly, as shown in figure 17 overleaf.

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Figure 17: Body panels slotting system

Additional fastening is provided by standard M4 bolts located fitted in clearance holes. Square cuts through the body panels enable nuts to be attached and tightened. The conjunction of these two methods the body panels are rigidly secured without imparting excessive bending stresses or sharp cracks in the Perspex. Bolts were preferred to self-tapping screws, which were dismissed due to the brittle nature of Perspex.

Square hole containing nut

Bolt

Figure 18: Perspex fastening method

For further stability, adhesives are also used between the constituent panels due to Perspex’s compatibility with glue. This forms very strong bonds that eliminate any residual gaps between the panels. III.3.3 FITS AND TOLERANCES The connecting slots between the Perspex sheets require tight dimensional accuracy and hence precise dimensions for the Perspex sheet are evaluated. The 10mm sheet is of actual thickness 9.51mm and of satisfactory uniformity (±0.04mm). Slots between acrylic sheets are designed to have transition fits. This type of fit ensures minimal movement between the parts whilst allowing for the plates to be assembled manually. The transition fits are made such that the nominal sizes of both mating parts are equal. The width of cut of the laser cutting machine is used to compensate the parts before the cut. This ensures the resulting parts are of the required dimension. The cut by the laser also generates a taper; the cut surface is not perpendicular to the sheet. This is incorporated into the design by orientating the parts during manufacturing to facilitate the assembly of the slotted parts.

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III.4 Control and Transmission Control and transmission components are key in ensuring high printing accuracy. Motors and transmission methods are carefully selected to minimise backlash. In this section, the reasons behind the selection of the motors are explored in detail as well as an explanation of the transmission design. Finally, the design rationale of the print bed assembly is explained. III.4.1.1 MOTOR SELECTION The printer is operated using 5 stepper motors. One is used for the main rotational axis, another for the horizontal X axis, and two are required for the Z axis. Stepper motors are selected as they natively incorporate feedback and have high angular precision. Two different motors are used in the printer, their characteristics and the reasons they were selected are detailed below. The rotational axis has a separate NEMA 23, high accuracy motor. The requirements for the rotational axis are unique to this printer axis, and precise calculations were necessary to specify the required motor characteristics. The maximum printing radius is 50mm and the required precision of the nozzle is of 0.2mm. From this, the required angular accuracy θ of the print bed is then:

Stepper motors generally come with step sizes of 1.8° or 0.9°, so a 0.9° step motor was selected to ⁄ minimize gear reduction. This corresponds to a minimal gear reduction of . To ensure quick displacement of the print bed and the nozzle head, an arbitrary minimal angular acceleration of 100rad.s-2 was set. From this, the minimal motor torque M was calculated (with the mass moment of inertia Ig=0.005 kg.m-2, calculated from the chuck and print bed):

The Nanotec ST5709S1208-B (NEMA 23) fulfils these requirements and has a dynamic torque of 1.06N.m. This is higher than the required torque but can be useful to overcome friction in bearings as well as other factors that may increase the required moment [4]. The requirements for the other motors necessary in this project are identical to those in the Mendel RepRap printer. As such, the choice of X and Z axis motors is inspired by those of other RepRap printers. Therefore, FL42STH47-1206AC (NEMA 17) motors are selected. They are rated with an angular accuracy of 1.8° and a torque of 0.44N.m. A picture of the motors is presented in figure 19. NEMA 23

NEMA 17

Figure 19: Selected Stepper Motors

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Detailed calculations pertaining to motor selection are presented in Appendix A1. III.4.1 TRANSMISSION DESIGN The main transmission of the Y-axis is comprised of a pulley system using a timing belt. The main advantage of this setup over traditional gears is the minimisation of backlash. Indeed, any clearance between mating components would cause an error in the angular position of the print bed. The belt selected is specifically designed to contend with frequent changes of direction, which is particularly relevant for this application. The choice of using a belt also gave the team more flexibility during the design process, as the distance between the pinion and gear could be varied. A rendering of the Y-axis transmission is shown in figure 20 below.

Pulley

Timing Belt

NEMA23 Motor

Pinion

Figure 20: Belt and pulley arrangement for transmission between the motor and print bed

The transmission is designed so that a minimum of 6 teeth are meshed at all times. This implementation is included in order to reduce backlash. The size and module of the transmission and pinion are balanced to satisfy the requirement while limiting the inertial forces caused by large gears. As such, a 15 tooth pinion and a 60 tooth pulley with a module of 3mm were chosen, resulting in a reduction factor of 4. Detailed calculations for the length of the belt are shown in Appendix A1. III.4.2 PRINT BED ASSEMBLY The print bed assembly is constituted of multiple components, which together fulfil the requirements set by the PDS. The components of the print bed assembly are matched to the engineering requirements of the printer in figure 21 below.

Figure 21: Main Requirements and Parts for the Print Bed Assembly

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The print bed was effectively designed as two separate parts; the bearing housing and the mobile support, shown in figure 22. The former connects the print bed to the transmission, while the latter provides location and support at the other end. Bearing Housing Assembly

Mobile Support Assembly

Figure 22: Bearing Housing Assembly (left) and Mobile Support (right)

Bearing Housing The power from the motor is transmitted through a belt to a pulley as shown in figure 22. To obtain high precision printing, the shaft’s only degree of freedom is rotation. As thermal expansion was identified to be negligible, axial displacement of the shaft was restricted in both directions using a step in the shaft and a bolt and washer. Torque is transmitted from the pulley to the shaft from the pulley using a square key. This solution was preferred to a grub screw, which would be less reliable at relatively high torques. The shaft is mounted on radial ball bearings enclosed in a bearing housing. This bearing housing guarantees both bearings are aligned. This is crucial to ensure precise rotation of the print bed, as inaccuracies in the bearing alignment are amplified by the length of the print bed. The bearing housing is designed to be manufactured in one session on the same lathe to ensure the bearing bores at both ends are concentric. This arrangement is shown in figure 23 below.

Bearing housing

Pulley

Chuck

Bolt

Shaft Flange Bearing housing support

Perspex

Figure 23: Section view of rotational axis transmission

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The bearing housing is supported by the Perspex sheet on one side and by a special support which also axially locates the housing. The bearings are axially located by a specially printed flange as well as steps in the bearing housing. Finally, the chuck is fastened to the shaft using a thread and a bolt. Another option considered was to use a Morse taper and collar to secure the chuck. However, using a thread and bolt provides a more compact solution, as the morse taper is long and heavy. Additionally, the Morse taper requires a relatively strong axial force, typically present in lathes. Mobile support assembly The chuck is fixed onto the shaft with a thread and a bolt which fits inside the chuck. This reduces the movement of the chuck and prevents it from rotating on the shaft thread. At its other end, the print bed is supported by the live centre in the mobile support. The printer is designed to accommodate print beds with a maximum diameter of 100mm. To ensure all print beds can be fitted, these all incorporate a 15mm boss at the end held by the chuck. Live Centre Slide Rails

Print Bed

Adjustable screws Figure 24: Live Centre Support

The print bed is supported at one end by a live centre placed on a mobile support. The purpose of the live support is to limit the deflection of the print bed without hindering the rotation of the print bed. The mobile support the live centre is placed on is free to slide axially, which enables print beds of different lengths to be used with the printer. In order to obtain perfect alignment of the live centre with the chuck holding the print bed, the deflection of the guide rails is kept to a minimum. This is achieved by using 8mm thick steel rods, and by reducing the weight of the mobile support with a large hole. These implementations lead to a maximum deflection of 0.25mm in the worst case scenario. Detailed calculations for the deflection of the rails are shown in Appendix A1.

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III.5 Mechanical Design III.5.1 PRINT HEAD CARRIAGE Movement of the print head in the horizontal and vertical directions is achieved through the print head carriage. The carriage is controlled with 3 stepper motors; two for the Z direction and one for the X direction. The mounts and fixtures employed are all designed to be 3D printed, which is necessary to create complex shapes in a minimal time frame. Two stepper motors performing exactly the same movements are required for the Z axis to ensure the carriage remains level. Alternatively, a belt system could have been used, but this can easily introduce levelling issues due to backlash and frictional losses.

Z-axis Motors

Threaded Rod

Carriage End Fixtures

Figure 25: Print Head Assembly

The Z axis stepper motors employ a worm gear system where the carriage mounts ride onto two threaded shafts connected to the stepper motors via rigid shaft couplers. Rotation of the motors translates into linear vertical motion of the carriage through nuts fitted inside the mounts. To add rigidity and locational restraint, two guide rails are clamped to the end Perspex plates. Linear bearings are pressed into the carriage end fixtures. The bearings ride onto the vertical guide rails, contributing to the levelling the assembly. X axis control is achieved through a stepper motor mounted onto one of the carriage end fixtures. A belt and pulley system translates the rotation of the motor into linear lateral movement of the print head. The belt runs from on fixture to the other, looping around the stepper pulley at one end and bearings at the other. This belt is clamped onto the print head mid length. X-axis Motor

Z axis nuts

Print Head Assembly

Belt Belt Clamps

Z-Rail Linear Bearings

End Fixture

Pulley Bearings

Figure 26: Print Head Carriage

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III.5.2 PRINT HEAD ASSEMBLY The print head consists of and extruder and a hot end (nozzle) assembly. The extruder employs an additional stepper motor that, via a double bevel gear system, pulls in filament from the spool into the nozzle. The double bevel gears are necessary to reduce backlash, which would lead to uneven extrusion of the printing material. A spring and bearing system applies tangential force onto the incoming filament against a hobbed bolt. The hobbed bolt is rotated by the stepper motor, pulling in or reversing the filament through the use of sharp teeth cut into the bolt. Spring pressure system

Hobbed Bolt

Wade Extruder

Gripping Teeth Hot end

Figure 27: Extruder Features

The filament is forced into the hot end where it melts on contact with the heated brass nozzle. The nozzle is heated by a resistive heater, and temperature control is achieved through feedback from a thermistor fixed into a recess in the nozzle. The nozzle is threaded onto a PEEK (Poly-etherether-ketone) polymer hollow shaft through which the filament passes before melting in the nozzle. A PTFE (poly-tetra-floro-ethene) tube fixed inside the PEEK shaft acts as a filament guide as it can withstand the heat without melting and provides a sleek, no stick surface.

Filament Filament inlet

Hobbed Bolt

Extruder Stepper Motor

Double bevel gear system

Mounting plate PEEK Mount

PTFE Sleeve

Brass Nozzle

Figure 28: Hot End Assembly

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Printing starts when the nozzle reaches the required temperature and filament flow is controlled by the extruder stepper motor. In addition to forcing the filament into the nozzle for extrusion, the extruder assembly can also reverse and pull the filament back, preventing the polymer melt from dripping while the print head rapidly moves from one position to the other. III.4.4 PRINT MATERIAL SELECTION Selecting an appropriate printing material is an important decision as it has an influence on certain components of the printer such as the print head, extruder gears and the print bed. While the design can be used with a variety of print materials, one was prioritised for the sake of the design. The first consideration for material selection is the availability of the material in filament form. Only PLA and ABS are readily available and for a reasonable price. Table 4 draws a list of the pros and cons of both materials to determine the most adequate one for cylindrical printing. These are weighted and scored with a maximum weighted total of 1000. Table 4: Criteria and importance for material selection

Criteria PLA Description Weight Description Warping Resistance 8 High Cost of Material 2 Inexpensive Heat Settings Required 2 Lower; 160-220⁰C Extrusion Facility 4 High force required Mechanical Properties 4 Mediocre Weighted Total

ABS Score Description Score 50 Low 5 35 Inexpensive 35 25 10 Higher; 215-250⁰C 15 Moderate force 25 15 Superior 30 640‰ Weighted Total 350‰

Table 4 stresses the importance of the material stability at different temperatures. Choosing ABS would require a heated print bed, adding complexity to the project. Printing an ABS part on a cold bed would result in significant warping and the possibility of the printed object falling off the print bed during the printing process. From this analysis PLA is chosen as the printing material thanks to its limited warping and lower glass transition temperature. The printer is designed to accommodate for PLA, however ABS can still be used if necessary by tweaking the slicing software parameters. The PLA filament is wound around an overhung spool mounted onto a simple bearing system to ensure continuous, unhindered delivery of the filament. The filament is then guided via adhesive clamps attached to the Perspex frame, through a slot cut into the top plate and into the extruder assembly.

Figure 29: PLA Spool mount

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III.5 Electronics and Programming Unlike the mechanical and structural design, much of the electronics and software aspects of the project are constructed using pre-existing solutions. On top of this, several modifications are implemented to tailor the equipment to the specifics of the project. The flowchart below presents the key tasks and deliverables that must be fulfilled by the electronics and software. Alternatives considered during the design process are also presented, and accompanied with requirements and modifications unique to our project. This is presented in figure 30. .STL file

Main Components

.GCode File

Commands

Slicing Software

Slic3r (Pearl)

Alternatives

Printer Commands

Signal

Printer Interface

Pronterface, Reoplicator G

Microcontroller

Circuit Board

Arduino Mega, Duo or Uno (C)

RAMPS (Marlin, Sprinter)

(Interchangeable)

Sanguinolu (Intergrated)

Skeinforge (Python)

Corresponding Modifications

Edit slicing code for cylindrical coordinates

Manually modify Gcode to adapt to geometry

Rewrite firmware to adapt to cylindrical coordinates

Calibrate motor drivers and thermistors

Figure 30: Electronics and Programming Overview

The hardware and software can be divided into 3 main sections; PC software, printer hardware, and printer firmware. These aspects are presented below, along with key design decisions. III.5.1 PC SOFTWARE The first task fulfilled by the PC software is the conversion of an .STL file to G-Code which can be sent and processed by the printer firmware. While a variety of software packages can fulfil this role, an additional objective of the project is to explore the feasibility of a custom slicing procedure to enable printing in cylindrical coordinates. In order to fulfil these two objectives, the printer uses two different software; Skeinforge and Slic3r. An interaction matrix was used to highlight the differences between these two programs, while showing the uses best adapted to each one. Table 5: Software Selection Matrix

Criteria Description Programming Language Options

Weight

Skeinforge Description

Score

Slic3r Description

Score

5

Python

35

Perl

50

3

Exhaustive

45

Basic

25

Support

2

User Forum

30

User+Developer Forum

40

Access

3

Files on Github Weighted Total

30 700‰

Open Source File Weighted Total

40 730‰

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As demonstrated, Skeinforge presents more flexibility due to the variety of built in options. Conversely, Slic3r offers much less functionality, but has a simple coding structure which can be edited more easily. For these reasons, Skeinforge was primarily used to generate G-Code, while Slic3r was also used to explore the possibility of implementing a cylindrical slicing procedure by editing the program’s source code. The main functionalities of Slic3r are presented in figure 31.

Orientati on errors can be quickly spotted in the preview

Multiple parts can processed at once

Print settings are easily stored and managed

Figure 31: Slic3r user interface and settings

A separate program is used to send the G-Code file created by the slicing program directly to the printer. This is achieved using Printrun (Pronterface). Unlike its alternatives, Printrun is not constructed with a particular model of 3D Printer in mind, meaning that many more settings are left to the user. A key feature is that G-Code files sent to the printer can be overridden at any time simply by typing G-Code commands into the user interface. A variety of common G-Code commands were gathered to enable small mistakes to be corrected and without stopping the printer to re-upload a new G-Code file. A screenshot of the Printrun interface is presented figure 32. Printhead trajectory can be visualised beforehand

Estimation of print duration GCode can be sent manually to the printer Figure 32: Printrun interface and settings

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III.5.2 HARDWARE SELECTION The main role fulfilled by the hardware on the printer is to receive and interpret G-Code commands to control the motors and heating element using feedback from the endstops and thermistors. These tasks are fulfilled by combining an Arduino Mega microcontroller to a RAMPS module (RepRap Mega Pololu Shield). The Arduino is used to relay commands from the PC to the RAMPS. The RAMPS is fitted with stepper motor drivers and connected to a power source in order to control the printer. This setup is shown in figure 33 below.

USB connection to Arduino

Straight-fin heat sink

Stepper motor drivers

Power Supply to RAMPS

Figure 33: Arduino and RAMPS setup

The RAMPS is fitted to a 12V 360W power supply to power to stepper motor drivers and heating element. Although our calculations showed that the RAMPS would draw no more than 13A at peak operation, and that a 240W source would have been sufficient, higher capacity was selected to ensure fans and additional motors could be added if necessary in the future. In particular, the possibility of adding a small blow heater was considered as an alternative to the heated print beds in traditional 3D printers. One of the specificities of our design compared to Cartesian 3D printers is that the range in the Y direction (print bed rotation) is virtually unlimited. In some components, the print bed is rotated continuously during the entire printing job. For this reason, the Y axis motor is typically active for extensive amounts of time. In order to prevent the stepper motors from overheating due to this phenomenon, these were fitted with straight-fin heat sinks using thermal tape, as shown in figure 34 below. Current can be adjusted with a screw

Straight-fin heat sink

Figure 34: Stepper Motor Driver

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The setup outlined above was chosen over a Sanguinolu, a cheaper all-in-one alternative designed specifically for 3D printers. However, the Sanguinolu can only hold 4 stepper motor drivers. Given that one of these drivers must be used to control the extruder motor, and that two motors are needed for the Z-Axis, this limitation rules out the possibility of creating a 4-axis machine. Although a 4-axis machine was not strictly necessary given the design specifications, the Sanguinolu offered fewer options for overall upgradability and flexibility. Furthermore, although buying a Sanguinolu could save us £20, the cost of the Arduino and RAMPS was well within our costing plan, and would present a more versatile basis for potential upgrades in the future. III.5.3 WIRING AND SETUP A schematic of the RAMPS wiring to the printer components is presented in figure 35 below. Although the endstop for the Y axis (rotation of the print bed) is not needed for location purposes, leaving it out would have caused several conflicts in the Arduino firmware.

Figure 35: Wiring Plan for the RAMPS

III.5.4 PRINTER FIRMWARE The firmware used to control the printer is stored on the Arduino and written in C. The main role of this firmware is to interpret G-Code commands to control the motors and heating elements while incorporating feedback from thermistors and endstops. This role is fulfilled by the open-source firmware Marlin, which is used with many traditional 3D printers. Unlike some firmware developed specifically for commercial 3D printers, a large amount of settings used by Marlin can be changed by editing the firmware code. Given that one of the main challenges associated to this project is to adapt Cartesian coordinated into cylindrical ones, this aspect of the firmware is fundamental.

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The Marlin software was chosen over the firmware used by the other 3D printer in the Polymer Processing lab, Sprinter. Although Sprinter has many of the advantages associated to Marlin outlined above, some underlying settings in its coding give printed parts a different aspect. The choice to use Marlin was done by printing two identical parts using both firmware. These parts are shown in figure 36 below.

Printed with Sprinter: uneven surface

Printed with Marlin: smooth surface

Figure 36: Identical parts printed with Sprinter (left) and Marlin (right)

As shown above, parts printed with Marlin have a superior surface finish compared to parts printed with the Sprinter firmware. Additionally, the irregular surface of the latter was identified as a source of embrittlement, and an overall lower quality. Given the similar format between the two firmware codes, a separate version of Sprinter was kept up to date with the latest settings as a backup. III.5.5 SOFTWARE MODIFICATION One of the objectives set by the team at the start at the project was to explore the possibility of writing a custom slicing procedure for cylindrical coordinates. While this implementation was not required for the purpose of the project, it would prove essential for the cylindrical printer to be used on a regular basis. A diagram comparing traditional (Cartesian) and cylindrical slicing is shown in figure 37 [6].

Figure 37: Comparison of Cartesian and Cylindrical Slicing

[6]

The preferred method to achieve this goal was to edit Slic3r source code to accommodate cylindrical coordinates. The first task undertaken to this effect was to divide the source code into main functional blocks, in order to identify which portions of the code would need to be edited or revised.

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The Slic3r program accesses the Slic3r.pm module in order to carry out the main functions delivered by the program. These “main” modules are the ones which slice the solid model into a physical trajectory. Additionally, post-processing modules are used to create the G-Code, while incorporating user settings such as filament width and extruders speed. Finally, test files are used for development purposes to assess the performance of these modules on an individual basis. A simplified layout of the Slic3r source constructed for this purpose is shown in figure 38 below.

Figure 38: Slic3r Source Code Architecture

The sections of the code requiring modification form a large proportion of the main modules, and to a lesser extent, some of the post-processing modules. These are outlined in orange in figure 38 above. In particular, the elements determining the geometry and extrusion path would require most attention. A modified slicing procedure was outlined conceptually. This procedure was inspired by literature on Cartesian slicing, as well as a variety of papers on novel slicing methods. The method is based on iteration: each layer is processed separately, and “flattened out” onto a Cartesian plane. Once the polygons for this layer have been constructed, the extrusion path is computed, and projected onto a surface of radius R. This operation is repeated for each successive layer as the projection radius is increased, in order to form a cylindrical shape. This method is only valid since the solid model is deconstructed into relatively thin layers (less than δ=1mm). One key consideration is that as R is incremented, the total printing surface is increased by a factor 2πδ, and the amount of material deposited must be varied accordingly. The main advantage of this approach is that it can make use of many of the existing features in available slicing programs, since most operations are carried out in a Cartesian plane. A simplified flowchart of this procedure is presented in figure 39 overleaf.

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Figure 39: Cylindrical Coordinates Slicing procedure (REF)

Upon inspection of the source code, many of the new functions which need to be implemented necessitate the modification of several subroutines forming part of the Slic3r program. One of these subroutines is presented in figure 40 below.

Variables are set as part of the subroutine

Routines linked together

are

Figure 40: Excerpt of Perl Code for one of the Slic3r Subroutines from Geometry.

This particular subroutine participates to the elaboration of a polygon map. The Slic3r program is constructed in a way in which all programs are interdependent, and changes made to one section of the code must be adapted to all its linked routines. The changes needed to use cylindrical coordinates are fundamental in nature, and our examination of the code revealed that their implementation would require more modification than could be achieved through tweaking. In light of these observations, the custom slicing procedure drafted cannot be easily included into the existing code. While this would be possible in theory, a more efficient approach would be to rewrite a program from scratch. This time investment would allow creating a program specifically for this purpose. Alternatively, software used for CNC lathes could be used as a more adapted starting point. However, the source code for these programs is not openly available. As a result, for the purpose of this project, cylindrical parts are constructed by constructing extrusion paths using alternative methods, rather than by using a cylindrical slicing procedure. These methods are outlined in section V.2.

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IV. MANUFACTURING AND ASSEMBLY While a substantial amount of the parts were purchased, unique components such as the Perspex plates and those relating to the print bed assembly were manufactured. This section gives an account of how the parts used in the printer were manufactured. Explanations relating to the assembly and calibration of the printer are also presented.

IV.1 Perspex Structure One of the key parts to be manufactured was the Perspex structure. As they provide both support and location for many of the printer’s components, the Perspex sheets required high precision manufacturing. The Perspex sheets fit together using slots with tightly toleranced transition fits. LASER CUTTING TESTS One concern was that the width of the laser in the laser cutting machine would increase the actual size of cut and increase clearances. To evaluate the laser width, three test samples were cut and measured. The data and calculations related to these tests are presented in Appendix A1. The first test was carried out on a Perspex sheet of thickness 6mm. The aim of this test was to evaluate how repeatable the laser cutter was and to get an idea of the surface finish that could be achieved. The width of the laser cutter was determined by comparing the actual dimension of the cuts to the one set in the solid model. The cutting accuracy was determined to be 0.27mm. A second test was carried out, this time on the sheet used for the printer. Two test parts that slot into each other were made in order to test the transition fit. The test yielded a laser width of 0.43mm which was different from the previous results. This was attributed to the fact that a new Perspex sheet with slightly different material properties and thickness was used.

Burn marks

Figure 41: Laser Cutter Test Part 1

Following these tests, the laser cutter broke down and the lens was replaced. Due to the high tolerances required for the transition fit, a final test was undertaken to evaluate the impact of this change. This time a simple slot and fit were made. The fit was tight and worked correctly. However, the laser width now changed to 0.28mm. This was the value that was retained for the final design and is compensated for on the solid model that was sent for manufacture. All test parts confirmed the need for compensating however the cutter was very repeatable (±0.03mm). The test parts also displayed the evidence of a tap of around 0.05mm throughout the 10mm thick Perspex. The final parts were cut in order to use this tap to facilitate manual assembly. PERSPEX SHEET LAYOUT Given the high price of the Perspex sheets, an optimal layout was determined to minimise the

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amount of Perspex necessary to print all the parts. Additional space was added to enable parts to be recut if any errors were made. This resulted in the purchasing of a 1000×750x10mm sheet.

IV.2 Printed Parts The required printed parts were initially to be purchased as they are usually sold in sets. However access to the 3D printers on campus provided the added design flexibility of printing custom parts tailored to the cylindrical printer. Shown below are some of the .STL files used to print the required parts.

Figure 42: .STL files of various parts used in the assembly

Another aspect to consider was the material from which the parts could be made. PLA and ABS plastics are the most widely used polymers as they are ideally suited for 3D printing. ABS, having slightly better mechanical properties than PLA, is preferable for parts subjected to high stresses. Due to limited access to ABS printing filament, the only option of obtaining highly stressed parts was through purchasing. The parts that were not easily available for purchasing online were made using a printer provided by the Imperial College Robotics Society (ICRS). All remaining parts were printed using PLA with the printer in the Polymer Processing Laboratory (PPL) in the Mechanical Engineering Department. Figure 43 below shows a summary of how the printed parts were obtained and from which polymer they were printed. Figure 43: Origin of 3D printed parts

Printed Part Carriage Z-Clamp Z-Clamp (Short) Clamp Top Endstop Mount Bearing Flange Guide Rail Washer X-Belt Clamp X-Belt Guide X-Belt Tensioner X-Carriage Mount X-Carriage Mount (Motor) Extruder Assembly

Material ABS ABS ABS ABS ABS PLA PLA ABS ABS PLA ABS ABS PLA

Acquisition Printed by ICRS Printed by ICRS Printed by ICRS Printed by ICRS Printed by ICRS Printed in PPL Printed in PPL Printed by ICRS Printed by ICRS Printed in PPL Printed by ICRS Printed by ICRS Purchased Online

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IV.3 Machined Parts The components requiring higher precision and strength than could be achieved with 3D printing were machined from aluminium and mild steel. These were mainly the components associated with the print bed assembly. In order to ensure the print bed was held perfectly level, the live centre mount, chuck mount and bearing housing were machined using very tight tolerances. Power transmission parts, such as the chuck shaft and pulleys, were machined from steel. Additionally, the guide rails were also machined from mild steel as flexural rigidity and surface hardness are important to ensure smooth linear bearing operation. Larger parts, such as the live centre mount, chuck mount and print bed, were machined from aluminium. These parts are bolted onto the Perspex directly and so the main limiting factor is weight. The aluminium parts are lighter, and so impose minimum bending stresses on the base plate. A slot was drilled into the live centre to further reduce its weight. Furthermore, washers and spacers that required precise dimensional control, as well as pins used in the extruder assembly, were also machine out of mild steel to ensure proper fitting.

Figure 44: All components prior to assembly

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IV.3 Assembly IV.3.1 PERSPEX FRAME Assembly began with setting up the Perspex frame by bolting the laser cut Perspex panels together. Due to the size and shape of the body panels, it proved difficult to drill the perpendicular bolt holes into the end faces of the panels. A hand drill was subsequently used to drill the required holes. Consequently, the brittle Perspex suffered a few minor fractures, all of which were fixed with Perspex adhesive. The laser cutter created thermal stresses in some of the Perspex panels, leading to significant warping of the top base plate. The warping introduced an intolerable misalignment of the live centre and drill chuck that would lead to the print bed failing to remain perfectly level. The warping was subsequently eliminated through the use of a heat gun and the application of uniform pressure onto the heated plate for a period of time until the plate was flattened out.

Cracks

Figure 45: Assembly induced cracks in the Perspex

Due to the nature of the laser cutter, all cuts made had a very slight taper. This wasn’t of much concern when considering the edges of the Perspex panels, but contributed significantly to the locating slots that were used to correctly align the panels in place. The layout of the panels on to the original Perspex sheet from which they were cut ensured that the tapers created on the locating slots were advantageous. The tapered slots could accept their corresponding square protrusions from only one side and provided a tight press fit that eliminated any potential wobble between the panels. Taper

Press fit

Figure 46: Effect of Tapered locating slots

To further stabilise the frame, four adhesive rubber mounts were added to the bottom base plate onto which the whole printer is supported. This provides vibration isolation as well as preventing the printer from sliding out of place due to the rapid movement of the print head.

Figure 47: Adhesive rubber Mounts

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IV.3.2 PRINT BED ASSEMBLY The print bed assembly consisted mainly of machined parts due to the need for tighter tolerances and structural rigidity. The design of the assembly revolved around ensuring perfect alignment between the constituent parts. Despite this however, a few extra spacers were needed to accomplish the task.

Spacers are added to ensure the chuck is perpendicular to the shaft Main Shaft

Chuck Figure 48: Chuck Assembly

The figure above illustrates the need for spacers between the chuck and the main shaft. This is due to the fact that the shaft is only partially threaded to allow space for the bearing that sits directly behind the chuck. As the internal threads on the chuck meet the end of the threaded portion of the main shaft, the chuck is very slightly deflected off to an angle and is no longer concentric with the shaft. Adding spacers in the area indicated above remedies the problem as the inner face of the chuck contacts the spacers before reaching the end of the thread. IV.3.3 PRINT HEAD ASSEMBLY The print head assembly is mounted on a carriage and is made to move in the X and Z directions. The carriage frame was first assembled separately by press fitting two steel guide rods into the printed fixtures on both ends, with the inclusion of linear bearings mounted on the rails. The print head carriage was then rested on to the linear bearings and the X axis belt system was attached Printed Parts

Belt Clamps X-axis Stepper

L8MUU Bearings

Figure 49: Print Head Carriage Mount

The extruder was purchased as a complete preassembled unit with bearings fitted in place. The hot end assembly was also purchased as a unit, but required fitting of the heater and temperature sensor to the nozzle. The hot end and extruder assemblies were then mounted onto the print head

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carriage. This required adjusting the alignment to ensure the nozzle coincided perfectly with the central axis of the print bed cylinder. IV.3.4 WIRING AND ELECTRONICS The Arduino board and power supply were housed inside a compartment below the print area, with all the wiring running along the Perspex frame to the Arduino. All soldered connections to the motors were covered in heat-shrink tubing to ensure positive electrical connections while the motors move. All wiring was secured to the Perspex frame via adhesive wire clamps to prevent the wires from interfering with the print job.

Print area kept clear of wiring

Electronics Compartment

Adhesive wire clamps Figure 50: Wiring scheme and Electronics Compartment

Finally, the power supply unit was secured to the Perspex with machine screws and a Velcro patch was added to the bottom of the Arduino board to secure it in place while still maintaining the ability of rapid retrieval in the event that physical trouble shooting was necessary.

Figure 51: Arduino on Velcro attachment

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IV.3.5 ASSEMBLED PROTOTYPE

Figure 52: Picture of the assembled printer

36


Depar

V.4 Calibration After the printer had been assembled, the stepper motors were calibrated. The purpose of this operation was to ensure that displacements of the print head in the X, Y and Z directions corresponded to the commands sent as G-Code. This was implemented by defining the “steps per unit”: the number of steps done by each motor in response to a command to move by 1 millimetre. An estimate of this value was calculated for the X and Z axis motors using design data for the transmission such as the belt module, and threaded rod pitch. This value was refined by measuring the displacement of the print head in response to a GCode command. This was done with a Vernier calliper over large distances to reduce the impact of measurement errors. The values found using this iterative process were then written into the Arduino firmware, as shown in figure 53. Steps per mm

PC-Printer communication rate Figure 53: Excerpt of calibration settings in Marlin Firmware

A different approach was used for the Y axis, which corresponds to the rotation of the print bed. In a conventional 3D printer, the angular position of the Y axis motor corresponds to a certain linear displacement of the print bed. This is not the case with a cylindrical printer, where the linear displacement at the surface of the printed part increases as each layer is deposited. The calibration forces a single value to be chose for the “steps per unit”. While this does not incur an error in the angular position of the print bed, there is an error in the amount of material deposited. Indeed, no matter what the layer is, the printer still acts as if the linear distance it needs to cover with fused plastic is the same. Y-rotation

Y-direction

78.8 steps per mm

72.6 steps per mm 66.3 steps per mm 60 steps per mm Three layers on a cylindrical print bed

Linear Representation

Ideal Calibration

Figure 54: Diagram of printed layer lengths and corresponding calibration

For the purpose of calibration, the steps per unit were determined using the radius of the print bed. Ideally, the calibration would need to be updated at each new layer, as shown in figure 54 above. While this is too time consuming to be done manually by printing each layer separately, the printing firmware could be rewritten to increment the calibration factor as each layer is completed.

37



V. TESTING The testing element of the projects is divided into two sections. The first deals with testing and assessing the performance of the printer. This is executed to compare the prototype to the technical requirements set in the PDS at the start of the project. A second section is dedicated to the testing of the printed parts produced by the printer. This encompasses the different methods used to generate G-Code for these parts, as well as an assessment of the quality of the resulting printed components. In particular, the parts obtained in this way are compared with identical parts obtained with a traditional 3D printer.

V.1 Testing the Printer Prototype The design of the printer had been rigorously assessed with the help of a design review before the prototype was constructed. As a result, the team had some assurance that the completed prototype would meet the requirements set in the Product Design Specification (PDS). The results of this design review are presented in the progress report [5]. Aspects of the design lacking before the design review, such as the electrical insulation of some components, were corrected before the prototype was manufactured. Many of the testing results presented in this section were obtained simply by using the printer over a long period of time. The DMT team accumulated over 50 hours troubleshooting and using the printer. A peer review session was organised to complement these results. Three members from other DMT groups were invited to use the printer for two hours. The feedback from this session was the basis for the evaluation of requirements such as ergonomics and user appeal. Some other results necessary to assess the prototype were obtained through specifically designed tests. One such test was designed to compare the time taken to print an identical cylinder on a traditional 3D printer and on our cylindrical printer. The same motor speed and acceleration settings were used on both printers. The cylinder was printed in 15 minutes and 43 seconds by the Cartesian printer and in 11 minutes and 39 seconds by the cylindrical printer. This corresponds to a time gain of 35%. This time gain can be attributed to the number of layers. Indeed, in the case of Cartesian printing, the cylinder is divided into 50 layers, and substantial amounts of time are wasted as the print head is raised to each new layer. Conversely, there are effectively only three layers in the other part, which is printed much faster. The mechanical properties of the cylinders are outside of the scope of the PDS, and are explored in section V.2 Cylindrical

3 Layers

Cartesian

50 Layers

Figure 55: Layer layout of Cartesian and cylindrically printed cylinders

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Each objective of the PDS was given a score from 0 to 10, with 0 indicating a feature is entirely lacking from our prototype, and 10 showing that the criteria is completely satisfied. Sections where the product fails to meet specifications are shown in green. The resulting table is shown in table 6. Table 6: Performance and Safety Assessment

Aspect

Criteria

Objective

4

<0.5mm

5

Smooth and even

3

At least 200x200x150mm

Can print features with accuracy of <0.3mm Parts have smooth features and good finish Printing volume is 210x80x60mm

Use mains power

6

220V Standard

Plugged into mains

No large vibrations

3

<3mm displacement

Easy STL to GCode translation

3

Less than 5min

Close to no vibration (<1m at peak) Maximum recorded 69 seconds for a complex part (598 triangles)

Seldom breaks down

3

-

Long life

2

At least 10 hours

4

At least 20min

3

Up to 100N

3

10 consecutively printed parts

3

0.1cm3/s

1

Less than 50

40 excluding fasteners

8

Heat protection

4

Heat insulated

Temperature lower than 30°C except at nozzle

10

Electrical Protection

5

All wires insulated

10

Safe disposal

1

Adequate Materials

10

Use of safe materials

1


10

No sharp edges

2

Only on Nozzle

10

High precision printing Homogeneous deposition Large printing volume

Performance

Quality

Reliability

Robustness

Safety

Efficiency

Low risk to user

Can be used for lengthy jobs Must withstand light loads Must resist regular use Prints parts quickly Minimal number of parts

56

Electrically insulated Relevant Standards Relevant standards -

Result

Score

Weight

No sign of wear Has been used for over 22 hours (04/06/13) Has completed a 43min job with no errors Structure supports 10kg load with no sign of strain. 10 small parts were printed in 2 hours Tested up to 0.4cm/s with satisfactory finish

Weighted Total

10 10 8 10 10 10 10 10 10 10 10 10

552/560

One of the features identified as lacking was the overall printing volume, which is lower than was originally planned. This was a voluntary choice made during the design. Given the prototype is intended to be a proof of concept, the current printing volume is more than sufficient to showcase relatively large and complex parts. An increased printing volume would have escalated costs without creating any real value for the project overall. These parts would also take several hours to print. Members of the supervising team agreed the current printing volume was sufficient for the purpose of the project.

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Table 7 shows the assessment of the printer in terms of ergonomics and user appeal. Table 7: Ergonomics and User Appeal Assessment

Aspect

Criteria

Size and Weight

Reasonably compact Moderate weight Compact addons and tools

Ergonomics

Easy to set up

Usability

Accessible controls and features Good visibility of printing process Minimal effort to operate Low noise

Maintenance

User Appeal

Manufacturing

Easily serviceable parts Use cheap processes Use FDM printer for parts Easy to manufacture Within budget

Cost

Proof of Concept

Low operating costs Features interweaving Faster printing of some shapes Accurate GCode and path

Weight

Target

Result

Score

1

Less than 500x500x500mm

500x210x340mm

10

1

Less than 15kg

12kg with power supply

10

2

User testing

3

User testing

4

Clear and concise

2

-

Perspex sheets allow excellent visibility

10

3

No physical strain

No physical strain

10

2

Less than 60dB

Estimated below 50dB

10

2

Design Review

2 1

Within costing budget For standard components

Print beds and chuck key stored inside printer Printing can be started in less than 90 seconds Mechanical components easily accessible, G-Code command log available

Components are standard or readily printable with FDM printer. Material costs estimated as 19p per printed part. 16 components 3D printed Perspex tolerances tight but achievable

10 10 10

10 10

10

2

Design Review

6

Less than £600

Total Cost £527

10

1

Less than £30/kg

PLA cost £25/kg

10

4

Prototype testing

3

20% Reduction

3

No construction errors

42

Print cylindrical part with interweaving Simple cylinder printed 24% faster Minor errors with Slic3r, no error with MATLAB

Weighted Total

8

10 10 8 414/420

The ergonomics score has been improved by the design review that suggested adding wire clamps. The score for the overall prototype is 98.6%, which shows that the main objectives of the project have been achieved. The shortcomings of the printer, such as limited printing volume and manufacturability are minor given that they are not central to the aims of the project.

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V.2 G-Code Generation This section explores the two methods that are used to generate G-Code for the lathe-type 3D printer. The first method consists in using Cartesian slicing software to generate the G-Code. A custom MATLAB was written to overcome the limitations of this method. V.2.1 SLIC3R GCODE GENERATION The current platform used to create print files for the standard Mendel max 3D printer can be made use of in cylindrical coordinate printing by “unwrapping” the part to be printed, the only difference being the replacement of the Y-axis with the Ɵ-axis. The unwrapped part does not resemble the final printout, but takes on its proper form as it is printed onto the cylindrical surface.

Figure 56: An unwrapped model and the resulting printout

The software treats the cylindrical printer as it would the standard Cartesian printer, with the X, Y and Z axis mapping onto the Z, Ɵ and R respectively. The part to be sent to the printer is modelled as if it were flat, ensuring the Y-axis base measurement corresponds to the circumference of the print bed being used. This method has an advantage of being fairly simple and quick, requiring no further programming or coding to achieve cylindrically printed parts. However, the disadvantages include limited complexity and dimensional accuracy as the part has to be unwrapped manually, leading to small geometrical discrepancies. This method also introduces a weakness in the form of a weld line that runs down the length of the printed part due to the discontinuity of the unwrapped part. The edge where the two opposite ends of the unwrapped part meet usually becomes the weakest part of the structure, overriding the advantage of cylindrical printing having interweaving filaments. Helical Unwrapping

Flat Unwrapping

Weld Line

Figure 57: Helical and Flat Unwrapping

This can be overcome by unwrapping the part helically, but as a result requires much more complex modelling. At this point, writing automatic slicing software becomes more practical.

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V.2.2 MATLAB GCODE GENERATION A custom MATLAB program was created as an alternative method to create G-Code. The main aim of this initiative was to see whether some of the errors caused by using the SLic3r method outlined above could be mitigated. The main appeal of the MATLAB method is that the angular velocity of the print bed can be updated at each layer. Unlike the Slic3r method, this can be used to ensure that as the number of layers increases, enough material is deposited to match the increasingly large surface which must be covered. Another important benefit of the MATLAB code is that it can be used to produce interweaving. Instead of depositing material as a series of adjacent rings, each layer can be printed helically as one continuous filament, as shown in figure 58. If the direction of the helix is reversed at each layer, the tensile properties in the axial direction and the surface finish could be enhanced.

Figure 58: A single layer printed as adjacent rings (left) and as a continuous helix (right)

The program is constructed as three functional blocks, represented in figure 59. The output is a list of GCode commands which is displayed in the MATLAB window.

Figure 59: Main building blocks of the MATLAB GCode Generator

The first step is initialisation, in which user-defined parameters such as print bed diameter and filament thickness are defined. The second step consists of the generation of setup instructions which must be sent before the part can start printing. Once these steps have been completed, the actual G-Code printing instructions are generated from the parameters set in section 1. Steps 1 and 3 are then repeated for every layer to generate the GCode.

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Step 1: Initialisation The first functional block of the MATLAB program is shown in figure 60. Two parameters required to initialise the print are the filament width and the print bed diameter (lines 4 and 5). The number of full rotations of the print bed necessary to print a layer is denoted as ‘NL’ (line 9). This number is obtained by dividing the length of the current layer by the filament width. The starting position for the print head is initialised in the axial, rotational and vertical directions with variables ‘x’, ‘y’ and ‘z’ respectively (lines 10-15). Vertical position ‘z’ is initially set as the filament width so that the extruded material can be deposited. Finally, the extrusion coordinates (line 15) and the iteration counter ‘i’ (line 11) are initialised.

Figure 60: Step 1 of the code: setting the relevant parameters

Step 2: Setup The function of this part of the program is to setup the printer before the printing can start. Unlike the other functional blocks which are iterated, this step is carried out only once. Comments are inserted in the G-Code commands preceded by a semicolon. The print head’s position is sent to the origin for the X and Z axes (line 19) and verified using the endstops. The Y axis (rotation) does not need to be homed, as the initial angle of the print bed is irrelevant. The nozzle temperature is set to 190°C and is maintained throughout the printing process (line 20). The commands G90 and G21 (line 21) imposes the use of absolute coordinates throughout the entire printing process, and sets the units to millimetres.

Figure 61: Step 2 of the code: sending the setup up commands to the printer

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Step 3: Generating printing instructions Once the printer is ready, the printing instructions can be loaded. The first command in step 3 is to set the feed rate (line 30). The value “50*p” was determined from trial and error. The continuous printing instructions are generated through a while loop (lines 31 to 38). As long as the counter ‘i’ is inferior to or equal to the number of lines required to print the layer, the while loop is enabled. The counter ‘i’ is updated in the loop by adding 1 every time the loop is repeated (line 36). The counter ‘i’ represents the number of rotations the print bed has undergone on the current layer. It is compared to the total number of rotations that are necessary for the layer. The printing instructions are generated through a long string (lines 32 and 33). The values of x, y, z and e are updated every loop in the required GCode format. The “strcat” function concatenates the elements into a unique string. G1 is the GCode function for a controlled move from the current location to the defined location. The translation is done in a straight line while the nozzle extrudes.

Figure 62: Step 3 of the code: generating the printing instructions

Once the layer is finished, the above steps are repeated for each subsequent layer. Output Once run, the MATLAB program generates the code displayed in figure 63. The code is very long, so only the beginning of it is shown. The structure of the remaining part of the code is identical to what is displayed in the figure.

Setup commands (step 2)

Printing commands (step 3)

Figure 63: The generated G-Code by the MATLAB program. Only the beginning of the code is shown

44



The printed part A picture of the printed part using the GCode produced with MATLAB is shown in figure 64.

Continuous filament

Figure 64: Part Printed with MATLAB

V.3 Testing the Printed Parts Identical cylinders were printed using the standard Cartesian printer and the cylindrical 3D printer in order to asses and compare their strengths and weaknesses. These include printing time, structural integrity and filament usage. The filament usage and printing time were both measured during printing, while structural integrity was compared using two comparative tests. In order to ensure a fair comparison between the two processes, all the infill, filament and printing speed settings were set to the same values. Part printed with a Cartesian printer. The filament is perpendicular to the cylinder axis

Part printed with the additive lathe. The filament interweaving is visible

Figure 65: Printed Test Parts

The total printing time is displayed by the interface software automatically after every print job. These values are recorded. To measure filament consumption, a mark is made on the incoming filament and the length of the consumed filament is measured. After the printing is complete, the difference in the distance mentioned corresponds to the amount of filament used up by the printer.

Figure 66: Measuring Filament usage

45



To compare the structural strength of both parts, two simple tests were planned. The first test consisted in inserting a rubber tube inside the printed cylinders and pressuring the tube using a gauged pump. The pressure at failure of each cylinder is recorded. However, the maximum rated pressure of the pump was exceeded and the pump failed before reaching the failure pressure of both cylinders, rendering the test inconclusive. The second test was a simple compressive test where an arm was used to apply a compressive force onto the cylinders using a fixed weight. An arm was used to apply the force due to the limited availability of weights. Graduating the arm and moving the weight further from the pivot point simulated the addition of force gradually. The distance between the weight and the pivot point was measured for each cylinder, indicating the force at failure. A Schematic drawing of the test is shown in figure 67 below.

Figure 67: Compressive Force test

The results are shown in table 8 below. Table 8: Printed part mechanical properties comparison test results

Printed Part Cartesian Cylindrical

Test 1: Failure pressure /Bar Apparatus Failure Apparatus Failure

Test 2: Failure force / Newton 147.15 168.73

Printing time /seconds 943 699

Filament usage /mm 55 84

The tests indicate that, as mentioned earlier, the cylindrical printer produced the parts faster due to significantly decreased layer count. However, due to the more complex interweaving infill pattern, more filament was consequently used up. This is justified by the enhanced mechanical properties exhibited by the cylindrically printed cylinder, as it was able to withstand a greater compressive load before failure. A further observation made during the compressive load test was the failure method of each type of cylinder. The Cartesian cylinder failed in a brittle manner, shattering into several pieces, while the cylindrically printed cylinder failed mainly by yielding slowly. Shown below is the Cartesian printed cylinder before (right) and after (left) failure.

Figure 68: Failure of the Cartesian printed cylinder (left) and cylindrically printed (right)

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VI. COSTING AND PURCHASING The team was allocated a budget of £600 to acquire all the necessary components for the project. It was important to remain within budget as the overall cost is a contributing factor to the overall success of the product. Initially, an estimation of the cost of parts was made and expenditures were tracked. Table 9 shows the quantity of parts purchased, their estimated and actual cost. Table 9: Parts purchased from external suppliers

Subsystem Structure

Control

Mechanical

Item Perspex Sheet

Quantity 1

Expected Cost £ 60

Final Cost £ 98.39

Bumper Feet Stops

4

2

2.18

NEMA 17 Motor

4

100

44.80

NEMA 23 Motor

1

60

58.58

60 Teeth HTD3 Pulley

1

10

15 Teeth HTD3 Pulley

1

5

3mm HTD Timing Belt

1

7

Z-Axis MOD 2.5 Timing Belt

1

15

16 Teeth MOD 2.5 Pinion

1

7

End Stops

6

10

3.96

Extruder Assembly

1

40

17.53

Nozzle

1

30

44.64

Hobbed bolt for extruder

1

5

4.48

Spool and PLA filament

1

25

32.00

Printed parts - ICRS

14

50

10.00

6mm Threaded Rod

2

5

2.27

608-ZZ Roller Bearing

2

4

2.99

LM8UU Linear Bearing

7

12

7.99

Deep Groove 10mm Bearing

2

5

11.46

Deep Groove 12mm Bearing

1

5

2.71

Live Centre

1

15

21.00

Chuck key

1

4

4.50

Thermistors

2

2

RAMPS and wiring

1

50

5

15

Power Supply

1

25

17.40

Arduino Board

1

25

18.69

Electronics Stepper Motor Drivers

27.06

28.56

66.38

Total

£527.57

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The costing in table 9 includes parts that were obtained from external suppliers. Further parts, such as bolts, washers, nuts, guide rails, material, and the chuck were obtained from the Mechanical Engineering Stores, were manufactured or came from individual group members. These supplementary parts were provided free of charge to the group and are therefore not taken into account in the costing as they were not directly billed to the group.

£160.00 £140.00 £120.00 £100.00 £80.00 £60.00 £40.00 £20.00 £0.00

£600.00 £500.00 £400.00 £300.00 £200.00 £100.00

Cumulative Spending

Monthly Spending

The expenditures are classified into subsystems. The relative financial importance of each subsystem is shown in figure 69. The histogram shows the monthly expenses throughout the project. Purchasing peaked at the beginning of the project. In October, most of the electronic components were purchased so that they could be tested on the existing RepRap printer in the Mechanical Engineering Department. The high spending in November can be explained principally by the purchasing of the motors. These early purchases allowed one part of the group to test, troubleshoot and calibrate the electronics section while work was carried out in parallel finalising the printer design. From December onwards, purchasing was lower, the peak in January can be explained by the procuring of the acrylic sheet. The cumulative spending is shown in blue.

£0.00

Figure 69: Budget allocation per section (left) and monthly (bar chart) and cumulative (line graph) purchasing (right)

The largest expenditures were the motors, the electronics and the acrylic sheet. The high precision NEMA 23 was necessary for the rotational axis; however savings were made by purchasing smaller and less accurate NEMA 17 motors for the other axes. In regards the electronic hardware, efforts were made to reduce the total price. The cost of the Perspex sheet exceeded the expected cost by more than 60%. This is mainly due to the high price of acrylic, the 10mm thickness of the sheet and a significant delivery charge due to the size of the sheet. None of the budget was spent on programs as all the software used was open source. Thanks to the team’s efficient purchasing strategy, the project was completed under budget, with £72.43 to spare. Purchasing was done early to allow time for delivery delays or parts to be reordered in case of flaws. This early purchasing strategy permitted the team to have the printer functioning by March 2013.

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VII DISCUSSION The project was carried out with success as demonstrated by the functioning prototype that was constructed, meeting quality, time and cost requirements that were set in the initial stages of the project. Despite this success, supplementary features can be added or improved to incorporate novel functionalities. This section also outlines the societal or industrial utility of the project, such as applications and advantages or drawbacks relative to Cartesian printers. Finally project management and progress will also be discussed.

VII.1 Shortcomings and potential improvements A key characteristic that required testing was determining the benefits of interweaving. Interweaving consists in inverting the direction of the material fibres on every layer. An interlaced sample is shown (left) next to a normal sample (right). It can be seen on the interwoven part that the filaments on the top layer are at a 90° angle to those on the layer beneath it. The results from the testing, although not entirely reliable, suggest that this method does make stronger parts.

Figure 70: Left: Identical parts printed on the additive lathe with interweaving (left) and on a Mendel Max Cartesian printer without interweaving (right)

The full benefits of interlacing could not be properly determined as the group did not possess sufficient testing apparatus. A tensile test along the axial direction was envisaged to test the increase in strength due to this technique. Stress analysis suggests that the maximum shear angles coincide with the angle of the filament (45 degrees). This angle can be varied and adapted to the loading conditions. However, a tensile test required precise equipment and holding elements that weren’t available to the group. For this reason, a tensile test was not carried out, but could be undertaken in the future. Similarly, the team considered doing a Charpy impact test and torsion test, but lacked the equipment to conduct these reliably. The additive lathe successfully printed parts as initially required. The project served more as a proof of concept rather than having a precise application. Therefore additional features could be added if this prototype was to be further developed. The team ensured the design was fully upgradable by selecting electronic equipment which could power and control additional components. The first area where improvements can be made is the print bed. Having a print bed that could have a changing diameter would allow for any sized parts to be made. Ideas were generated

49



during the design process, however solutions were either too difficult to manufacture or did not guarantee concentricity with the rotating axis. Although the team acknowledged this as an issue, a solution appeared too complicated. To limit warping of the parts, the team also envisaged a heated print bed, however this also was also judged too complex to implement due to the rotating nature of the print bed. Given the large capacity of the power supply, this could easily be implemented using a small blow heater or simply by adding a resistive heating element inside the print bed, connected via a brush and commutator connection to the supply. Improvements could also be made by writing cylindrical slicing software. Although it goes beyond the scope of this project, having a specifically designed program would allow for complex and thicker parts to be constructed. As explained in the report, components with high thicknesses tend to be deformed as an insufficient amount of material is extruded as the surface area which needs to be covered increases. Writing a custom slicing method would solve this problem. A MATLAB code was designed in order to solve this issue, but the code is limited to simple geometries and is not capable of generating a GCode directly from a CAD model. Having a specific program would also prevent the formation of a weld line when slicing with a Cartesian program. This would in turn improve the overall strength of the printed parts. Another way to address this problem would be to modify the calibration of the printer for each layer, as explained in section V.4. Equivalently, the extrusion rate could be increased to keep up with the increasing surface area. This could be done either by modifying the Arduino firmware, or by modifying the GCode using a MATLAB code.

VII.2 Utility of the cylindrical printer and potential applications Although the project served as a proof of concept, it is interesting to evaluate a target market for the product and unique applications that cannot be achieved by a classic 3D printer. One advantage of the cylindrical printer is the use of interweaving. This is not possible on standard 3D printers. For cylindrical shapes, the additive lathe can produce stronger parts in the axial direction which can be made 30% faster. The interweaving angle can be varied along the length of the cylinder to suit specific loading conditions. Unique geometries can only be made by the additive lathe. This includes springs, propellers, cylindrical shapes with axial overhangs and screws. These are the applications where the cylindrical printer has a significant added value. An interesting application would be to make a spring with a non-constant cross sectional area, this would make its stiffness non uniform along its length. Large overhangs

Complex radial features

Figure 71: Examples of printed parts unique to cylindrical printers

50



The utility of the printer could be further increased if a changing diameter print bed was made and a second nozzle added printing filler material. This would allow for parts to be printed with overhangs in the vertical direction. The printed parts are also air-tight and so applications could include low pressure vessels or piping. Controlling the surface finish of printed parts is another major potential application of the cylindrical printer due to greater control over the filament layout. Cartesian printers are limited to produce only one kind of surface finish with filament being laid out in perpendicular layers. Controlling the infill angle of each layer can create coarse or fine filament lines, with very smooth surfaces achievable.

VII.3 Planning and Conduct of Task Overall, the project was run successfully and all deadlines were respected. The design of the printer was finished early and was functioning by mid-March. Allocation of work was well distributed. However, the work for programming was initially over-estimated. This was because it was believed that the program Slic3r could have been adapted to cylindrical printing. This was however judged too complex so team members in charge of programming were given supplementary tasks in design to better distribute tasks. The idea generation process at the beginning of the project was relatively successful. Some ambitious ideas were put forward and may have been the reason the design stage lasted longer than expected. Once this was realised, it was decided to keep the printer as simple as possible and this allowed for the final design to be established. Although the printer was finished and was working by March, better manufacturing planning could have made it possible to have it completed a few weeks earlier. By mid-February, most parts had been manufactured apart from the Perspex sheets, delaying the assembly. Acrylic test parts could have been made earlier, in January in parallel with other projects. The final assembly was also delayed when the laser cutter broke down and a new lens had to be installed. This made a third test part necessary, delaying the project by a week. In hindsight, acrylic testing should have started before the final design of the printer was completed, therefore reducing the impact of the breakdown.

51



VIII. CONCLUSION Overall, the project was a success, and all major objectives were met. The team successfully designed, manufactured and assembled a working lathe-type 3D printer. The prototype met or exceeded the criteria set in the Product Design Specification and showcases the viability of cylindrical 3D printing as a manufacturing method. The project plan was respected, and all key deadlines were adhered to. The final cost of the project is £527.57. Parts have been printed that effectively demonstrate the unique features of the printer. In particular, the printer enables the production of complex geometries and overhangs not achievable with standard 3D printers. For example, propellers, springs and external threads can be easily produced. Testing suggests that components printed using this method can be significantly stronger than those printed in Cartesian coordinates. Indeed, interweaving can be effectively implemented and tailored to specific loading conditions. The project could benefit from some additions to explore the concept further. Notably, a custom slicing procedure could be written in order to produce G-Code to print complex parts more efficiently. Additionally, a heated print bed could be designed to reduce warping and provide better adherence. The prototype presented in this report provides an excellent platform to implement these changes.

Figure 72: The Team and the completed prototype

52



IX. REFERENCES [1]

Elsey, J. 3D Printing on a Rotating Cylindrical Surface, Zydex Pty Ltd. EP2459361 A1, 2012.

[2]

Pham, D. T. and S. Dimov. Rapid manufacturing, 2001.

[3] Rolland, E., Y. Ibrahim, M. Burnand-Galpin, and A. Kenich. Progress Report: Lathe-Type 3D Printer. 2013. [4] Rolland, E., Y. Ibrahim, M. Burnand-Galpin, and A. Kenich. Project Plan Report: Lathe-type 3D Printer, 2012. [5] Sen, D. and T. K. Srikanth. Efficient computation of volume fractions for multi-material cell complexes in a grid by slicing. Journal of Computing and Geoscience. 34, 754-782, 2008 [6] Sterman, Y. Additive Lathe Project, [Online] Available from: http://fab.cba.mit.edu/classes/4.140/people/yoav.shterman/secondUpdate.html, 2012

X. ACKNOWLEDGEMENTS The group is very grateful for the guidance and help from the following people: Dr Shaun Crofton, for his helpful and friendly support as supervisor. Shaun also supplied us with non-standard parts such as the M14 bolt and a large Aluminium rod for which we are very grateful. Dr Paul Hooper, for his advice and guidance in programming and the overall conduct of the task. Dr Daniel Plant, for his ideas regarding cylindrical printing and guidance as associate supervisor. Mr Suresh Viswanathan Chettiar, for his assistance and supervision in the Polymer Technology Laboratory. Paul Woodward and the workshop team, for their responsiveness and help, particularly during the manufacturing of the acrylic sheet. Miss Sam Tolhurst, for her help processing expenses. Alessandro Ranellucci and all the other open source contributors, for developing and sharing open source software such as Slic3r.

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APPENDICES Appendix A1: Structural and Control Calculations LASER CUTTING TESTS To ensure that the laser cut acrylic sheets met their required dimensions, test parts were manufactured. Their nominal dimensions were compared to their actual measured dimension. Measurements were performed with a micrometre and the results are presented in the following four tables. In red, the average laser width is computed.

Table 10: Results from the first laser cut test part

Reference A B C D E F G H

Part 1 Part 2 Nominal Max error Average Laser width dimension Meast 1 Meast 2 Meast 1 Meast 2 5.00 5.30 5.32 5.32 5.32 0.02 5.32 0.32 20.00 20.21 20.22 20.23 20.21 0.02 20.22 0.22 10.00 10.27 10.28 10.31 10.28 0.04 10.29 0.30 15.00 15.26 15.25 15.24 15.26 0.02 15.25 0.25 5.00 5.29 5.28 5.34 5.33 0.06 5.31 0.34 10.00 10.27 10.26 10.27 10.27 0.01 10.27 0.27 10.00 10.30 10.29 10.22 10.29 0.08 10.28 0.25 20.00 20.25 20.24 20.26 20.23 0.03 20.25 0.25

Average

0.04

0.27

Table 11: Results from the second laser cut: inner dimensions

Reference A B C D E F G I J K L M N

Inner Meast 1 Meast 2 Max error Average Laser width dimensions 6.80 7.48 7.48 0.68 4.00 4.48 4.48 0.48 9.73 10.14 10.16 0.02 10.15 0.42 4.73 5.08 5.08 0.35 19.73 20.09 20.09 0.36 20.00 20.33 20.33 0.33 5.00 5.37 5.37 0.37 10.00 10.45 10.45 0.45 10.00 10.34 10.45 0.11 10.395 0.40 10.00 10.49 10.49 0.49 8.00 8.48 8.48 0.48 6.10 6.48 6.49 0.01 6.485 0.39 59.90 60.23 60.23 0.33

Average

0.42

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Table 12: Results from the second laser cut: outer dimensions

Meast 1 Meast 2 Average Laser width

Outer dimensions a b c d e f g h i Average

30.00 90.00 65.00 86.00 60.00 10.00 10.27 10.27 10.00

29.55 89.52 64.6 85.64 59.53 9.65 9.86 9.67 9.49

29.55 89.52

9.63 9.87

29.55 89.52 64.6 85.64 59.53 9.64 9.865 9.67 9.49

0.45 0.48 0.40 0.36 0.47 0.36 0.41 0.60 0.51 0.44

Table 13: Results from the third laser cut test part

Meast 1 Meast 2 Average Laser width

Ref a b c d e f g h i Average

9.08 69.60 29.40 100.00 60.00 10.00 10.27 10.27 10.00

9.2 69.65 29.3 99.8 59.53 9.65 9.86 9.67 9.49

9.15 69.62 29.25 99.85 9.63 9.87

9.175 69.64 29.3 99.8 59.53 9.64 9.87 9.67 9.49

0.10 0.04 0.10 0.20 0.47 0.36 0.41 0.60 0.51 0.28

MOTOR DYNAMIC TORQUE CALCULATIONS To calculate the dynamic torque it is necessary to measure the mass moment of inertia Ig of the main components coupled to the print bed. It can be calculated using the following formula:

Where M is the total mass of the component, r its radius, ρ the density of the material and L its length. The mass moment inertia calculations are summarized in table 14.

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Table 14: Mass moment of inertia calculations

M (kg)

r (m)

ρ (kg.m-3)

L (m)

Ig (kg.m2)

1240

0,25

2

0,05 0,035

3.04×10-3 1.23×10-3

Shaft

0,006

7850

0,18

2.88×10-6

Gear on print bed

0,055

2720

0.012

4.69×10-4

Live centre

0.006

7850

0.02

3.20×10-7

Part Print bed Chuck

Bearings Gear on motor Motor

0,1

3.13×10-5

0.025 0.012

2720

0.02

1.77×10-6 1.35×10-5 4.79×10-3

Total

TRANSMISSION BELT LENGTH Evaluating the length of the pulley was essential as the pulley had to be of the exact length to limit backlash.

Figure 73: Schematic representation of the gear pulley system to measure the required pulley length

The length of the pulley depends on the angle alpha, which is defined in figure 72. By geometry, the angle can be determined:

Furthermore, from the right angled triangle: (

) (

√

)

The length l of the belt can be obtained by summing its length on the small pulley, its length on the big pulley and twice the length h.

(

)

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(


(

)

)

(

(

)

)

√

(

√

)

(

)

From the above calculations, a belt of length 276mm was used (92 teeth with a 3mm pitch). MAXIMUM PRINT BED DEFLECTION The rails are the major cause for the deflection of the print bed. Calculations are carried out to determine the maximum deflection if the rail slider is halfway along the rails. ( )

The maximum deflection, assuming a 2kg print bed (there are two rails) is of 0.249mm. This is a conservative estimate as most print beds are lighter than 1kg and the rail slider is not usually in the middle of the rails. Therefore, this is a maximum value and in practice the deflection will be much lower.

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Appendix A2: Detailed Bill of Materials Table 15: Detailed Bill of Materials

NO. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

DRAWING NO. DMT-27-001 DMT-27-003 DMT-27-004 DMT-27-002 -

PART NAME BASE PLATE TOP PLATE SIDE PLATE LEFT SIDE PLATE RIGHT SHEAR PLATE BOTTOM BASE PLATE NEMA 23 MOTOR NEMA 17 MOTOR Z-AXIS 8MM RAIL Z-AXIS RAIL CLAMP 8MM RAIL ROD BEARING SUPPORT BEARING BRACKET LINEAR LM8UU BEARING X-AXIS 8MM RAIL X-AXIS FIXTURE 1 X-AXIS FIXTURE 2 X-AXIS 22MM OD RAIL BEARING X-AXIS MOD 2.5 PULLEY X-AXIS MOD 2.5x1000MM BELT 6MM THREADED ROD SHAFT COUPLER EXTRUDER ASSEMBLY CHUCK SHAFT 60 TEETH HTD3 TIMING PULLEY 15 TEETH HTD3 TIMING PINION 3MM GEAR SQUARE KEY HTD3 273MM TIMING BELT SPOOL SHAFT SPOOL 32MM OD BALL BEARING ARDUINO MEGA RAMPS 360W POWER PACK RUBBER FOOT MOUNT MOBILE SUPPORT PRINT BED RBB 19MM OD RBB 27MM OD LIVE CENTRE BEARING HOUSING M3 SOCKET CAP M4 SOCKET CAP M5 SOCKET CAP M14 SOCKET CAP M3 NUT M4 NUT M5 NUT M3 WASHER M4 WASHER M5 WASHER

MATERIAL PERSPEX PERSPEX PERSPEX PERSPEX PERSPEX PERSPEX

STEEL PLA STEEL ALUMINIUM PLA STEEL STEEL ABS ABS STEEL ALUMINIUM RUBBER STEEL STEEL STEEL ALUMINIUM ALUMINIUM STEEL RUBBER STEEL PP STEEL

RUBBER ALUMINIUM ALUMINIUM STEEL STEEL STEEL STEEL STEEL STEEL STEEL STEEL STEEL STEEL STEEL STEEL STEEL STEEL

QTY 1 1 1 1 1 1 1 4 2 4 2 1 1 7 2 1 1 2 1 1 2 2 1 1 1 1 1 1 1 1 1 1 1 1 4 1 1 1 1 1 1 10 14 8 1 10 14 8 10 14 8

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Appendix A4: Detailed Drawings

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Appendix A5: Individual Critiques ERWAN ROLLAND The project proved to be a tremendous learning experience from both an engineering and a team building perspective. The project was organised effectively, and all key objectives were met within deadlines and budget. I suspect our performance was enhanced by our relative lack of prior knowledge concerning 3D printing, as the motivation of discovering a new technology carried us through the task Being elected project manager, I was in charge of the organisational and planning of the project. I feel this aspect of the assignment was particularly successful, and I devoted much of my time to it. Early on, I ensured that all team members had a common set of objectives and expectations for the project, in order to make certain that no misunderstandings would delay our conduct of the task. As such, I decided to discard some ideas which were not entirely in line with the initial brief. While this led to some ambitious ideas being cast aside, I am confident these choices were necessary for the project to be completed on time. I believe one of the key initiatives which led our team to success was the implementation of shared leadership. Each team member was given an area of the design in which they could contribute in a significant manner. While all decisions were shared, this prevented team members from feeling alienated or neglected. Regular meetings were implemented to ensure all members were aware of the other aspects of the design. As project manager, I had a good overview of the design process, and took care to ensure the design was being steered in the right direction. Unfortunately, this led to some decisions being taken without the direct involvement of certain team members. However, I encouraged disagreements to be voiced in the open order to avoid frustrations from building up, and I believe everyone was satisfied with our final design. One of the things I have learnt from this is the importance of self-evaluation and frequent feedback from other team members, particularly being in a leadership position. Indeed, this allowed me to realise I may have been too demanding from other group members at times. While I believe this attention to detail brought the overall quality of our prototype upwards, perhaps I should have been more diplomatic when suggesting large changes to be implemented. Thankfully, the team got on very well together and no one felt like their contributions were not being taken into account. As project manager, I was also responsible for generating content for the report and putting it together. Perhaps I took a too involved approach, which caused the elaboration of the reports to last a long time. However, this time allocation was planned beforehand, and scrutiny of the report allowed us to highlight which aspects of the project could still be improved upon. During the design process I took on the tasks related to Electronics and Programming, and was accountable for the key decisions shaping this aspect of the project. Given this side of the project was the least akin to mechanical engineering I found it difficult to communicate some of my ideas to the group. In hindsight, I should have encouraged other team members to take a more active role in this task, but this would have taken up time vital to the other parts of the design. Finally, I should have sought more help from the supervising team, who always provided valuable advice and experience when asked. Taking their suggestions on board more frequently could have resulted in an even more refined design.

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MATTHIEU BURNAND-GALPIN The success of a project is often quantified by three criteria: cost, quality and time. Judging by these criteria, I feel the project was an outright success as it was completed on time, met the quality requirements set out in the PDS in the Project Plan Report and was completed under budget. However I believe the impact of the project is more profound than these simple three criteria. The human relationships, the transferrable and technical skills as well as the experience that I developed through this project are what really added value to the project. As Head of Control and Structure, my engineering knowledge was put to the test. Parts had to be designed in a coherent way, to ensure they were manufacturable and minimised backlash. I learnt much about precise transmission design and how to select motors. Automation and mechatronic systems are of ever increasing importance for engineering and this project opened my eyes to the importance of robotics. I learnt about G-Code, embedded systems such as the Arduino and Ramps which are essential functionalities used in many engineering domains. What I particularly enjoyed about this project is that it was multidisciplinary and developed my skills in many areas: design, manufacture, mechatronics, mechanics, materials science and project management. This made me aware of the importance of being well rounded which is a key quality for working in industry. This project taught me much about team work. I applied knowledge I had gained from previous group projects and further improved them. There was great cohesion in the team and I think this was mainly due to the effort we put on communication. Our regular meetings, three times a week, ensured everyone was up to date on the most recent developments. This was a strong contributing factor to the success of the team as it created an emulating group spirit which increased overall motivation. In hindsight, the team building exercises at the beginning of the DMT were very useful as it enabled us to reach the “performing” stage much quicker. The additive lathe project allowed me to put into practice the concepts that I learned during the Integrated Design and Manufacture course. I applied the concept of “kaizen” (continuous improvement) to the group and I feel this was particularly valuable to the group as it allowed us to learn from each other. By continually discussing ideas and proposing alternate solutions to problems we progressed as a team. This was particularly true as our skills were complimentary: I learnt much from Youssef’s manufacturing knowledge, Alex’s skills in the C language and Erwan’s different approach to management. The group was very open to criticism and I believe this increased our overall learning. Voicing concerns through constructive criticism allowed me to learn and teach much from the others in the group. By having an external view, I think we all developed our self-evaluation skills. An important lesson that I learnt in this project is the importance of planning. At times we excelled in this domain, for example when we finished the printer early, in March. However we could have improved planning when it came to report writing. When writing the final report, I lacked structure before writing parts. This resulted in sometimes confused sections which I had to rewrite. Learning from this will allow me to write better structured reports in a more time efficient manner in the future. A piece of advice that marked me during the project came from Dr Shaun Crofton who at one occasion told us to “keep it simple”. I understood the full significance of this when we were finding ideas for a changing diameter print bed. Although this could have been an interesting feature, this

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was not central to the project and added unnecessary complexity. Simple systems are often the most efficient and I do think in the end this contributed to the success of the project. Working on this project also developed my general awareness of the additive manufacturing industry. 3D printing is a growing sector and is one that has the potential of revolutionising manufacturing processes. I learnt much in this project and developed a strong interest in this industry which allows me to have my own opinion on this matter. The project had such a profound impact on me that I am planning on making my own Cartesian printer. I am glad we decided to take on this project. Before this project I also believed that developing innovative ideas in Mechanical Engineering was limited to those with expert knowledge in a specific field. However this project proved me the opposite. I was in charge of designing the print bed assembly and this was one of the main innovations of the project. This taught me that being audacious and focusing on the problem is the key to innovation. All in all, the collaboration with the team was mutually beneficial. I learnt that trust and compromise are key to the project success. Criticism has to be taken in a constructive way to allow for continuous improvement. By effectively working as a team, we managed to develop a novel and successful additive lathe.

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ALEXANDROS KENICH Before starting this project, 3D printing was a technique which I had only heard about a few times and in each instance, it was presented as a complex process far beyond the capability and means of students. It was therefore enlightening to witness the gradual realisation of our own printer. Of all the knowledge and skills I have gained while working on this project, I would say that the most significant was how it expanded my notion of what is possible with limited resources and concerted efforts. Our group was versatile and this trait proved especially useful given the unpredictable nature of such proof of concept projects. Indeed, the finished printer has several effective fixes for issues that came up suddenly during the project, such as when we printed a clamp on a Cartesian 3D printer in order to fix a bearing whose housing had failed unexpectedly, or the use of rubber mounts to reduce the excessive vibration exhibited while printing certain parts. Issues such as these tested our resourcefulness and helped me develop my lateral thinking as well as providing valuable experience of working with these materials and systems. Furthermore, as this project was more demanding than the one from last year, it required that I improve my time management and organisational skills in order to keep up to date with the project as well as my other courses or risk being overwhelmed with work towards the deadlines. Additionally, the importance of effective communication became very clear as a result of working on this project. Our regular meetings during the week were vital for progressing with tasks and resolving issues in the project while also keeping each other aware of any subtle changes or events which would otherwise have not been known, such as a small dimensional change in a model to incorporate a new component or availability of a member to attend on certain days. As head of programming, my efforts were focused on the development of the Arduino code mainly in order to accommodate a rotational axis for cylindrical printing. The code used for Cartesian printers is open source so that was used as a foundation to build upon. I used skills that I had gained from the Embedded C course which I completed this year. This greatly aided my understanding of the existing code because the Arduino board uses a language which is very similar to C. One problem which came up once we started printing was the low quality of the infill of printed parts. These initial parts had thin and erratic infills which severely reduced their structural integrity. To rectify this, I altered the code to increase the nozzle diameter. This meant that the extruder would draw more filament in order to satisfy the increased calculated mass flow implied by a larger diameter nozzle. Once the optimal nozzle diameter was found, the infill became consistent and completely free of voids. This made the parts we printed thereafter much stronger as shown by their performance in the loading tests we carried out. In hindsight, I would have given myself more time in the earlier stages of the project to understand and prepare for my assigned tasks fully so that I could complete them in a shorter period of time and also be able to assist the other group members with their tasks in order to spread the workload. I would also take up more of the CAD tasks rather than split them evenly between members because I believe this area is one of my strengths and this would also eliminate issues with cross-referencing when producing drawings due to different component versions and inconsistencies due to different authors. In all other regards, the project went smoothly and it was a fun and fulfilling journey together with an excellent group.

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YOUSSEF IBRAHIM The project was a success. Progress was smooth and steady, leading to very satisfying results. All the goals were met, and all deliverables were achieved in accordance with the original plan set at the beginning of the project. In my opinion, this was due to realistic and accurate organisation, as well as excellent delegation of tasks which conformed with the strengths of each group member. Another, perhaps more important, influential aspect on the group’s performance was the excitement associated with 3D printers. Demystifying the concept and seeing it at work was one of my main motivational drivers, and I am sure my group members shared the same sentiment. I was particularly impressed by the group dynamics during the project. The project was broken down into separate sections; each member being allocated responsibility for the section in which they exhibited the strongest understanding. Communication was effective and plentiful leading to great ideas being generated readily. The diverse range of skills and interests held by each member contributed to a well-balanced performance without excessive emphasis being placed on any one aspect. I was able to witness first-hand the benefits of mutual respect and admiration, as well as punctuality as compared to my previous experience with group work. An efficient group formation phase lead to more time being spent focusing on the project at hand and less time spent on group relations. This emphasised the importance of establishing firm foundations with group members before any real progress can be made. My role in the project was rooted in design and manufacturing, being the head of mechanical design. I took an active position in producing conceptual overall design solutions to the main problems the project had to face. I found that most of my initial ideas were very ambitious, and so eventually had to be abandoned as the extent of our capabilities became clearer. The influence of costing and availability of components also began to place unexpected restrictions on design, as I had previously not realised their effect. Once the final design was agreed upon and all the relevant purchase orders were placed, manufacturing considerations became my main focus. Owing to my great interest in manufacturing, I played the lead role in producing most of the machined parts, as well as keeping track of and organising all the components as they arrived. Many alterations had to be made to the final design in order to ease manufacturing and assembly. Making the most of the available material also imposed some design changes as to minimise wastage. I also played a key role in assembly and fitting once all the components were available. It was during this phase that quick adaptive thinking became important in order to deal with unforeseen setbacks. Finally, I found myself concerned with aesthetics and convenience, for example spawning the addition of the filament spool to the design post assembly. In conclusion, I realised that my view has perhaps been too narrow. My contributions to the programming and software side of the project were very limited, and I found myself unable to reproduce the printer alone had I had the desire to make one for personal use. This brought to light the importance of keeping a general idea of the task as a whole, preventing the loss of touch with the main objectives of the project. Otherwise, it was an extremely rewarding experience with a brilliant group and a pleasure to have undergone.

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Lathe-Type 3D Printer

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