Machine Drawing

MACHINE DRAWING & INDUSTRIAL DRAFTING (MH402)

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MACHINE DRAWING & INDUSTRIAL DRAFTING Teaching Scheme (Hours/Week)

Examination Scheme (Marks)

Lectures

Tutorial

Practical

Theory

Sessional

Practical

T.W.

Total

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2+3

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50

50

100

1

2

3

4

5

PART A (MACHINE DRAWING) PRINCIPLES OF DRAWING: Drawing sheet (sizes and designations, title block, borders and frames, grid reference system), Scales (Designation, recommended scales, specifications), lines, lettering, sectioning, conventional representations, dimensioning, standard abbreviations DETACHABLE FASTNERS: Screw threads, approximate and conventional representations, specifications, Threaded fasteners (Types, forms, standard and specifications), Foundation bolts, locking devices (Classification, principles of operation, standard types and their proportions PERMANENT FASTNERS: Rivets (Standard forms and proportions), Riveted joints (Common types of joints, terminology, proportions and representations), Types of welds and welded joints, edge preparation, specifications and representation of welds on drawings, IS designation of weld symbols ASSEMBLY DRAWING: Review of sheet preparation, boundary lines, zones, title block, revision panel, parts list, numbering of components and associated detail drawing, bill of materials, assembly drawings of various machine sub-assemblies and assemblies from detail drawings, sketches and actual machine components PRODUCTION DRAWING: Limits, fits and tolerances of size and form, types and grade, use of tolerance tables and specification of tolerances, form and cumulative tolerances, tolerance dimensioning, general tolerances, surface quality symbols, terminology and representation on drawings, correlation 2 of tolerances and surface quality with manufacturing techniques.

MACHINE DRAWING & INDUSTRIAL DRAFTING PART B (COMPUTER AIDED DRAFTING) 1 2 3

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INTRODUCTION TO AutoCAD: Starting with AutoCAD, AutoCAD dialog boxes, Co-ordinate Systems, drawing lines, circle, arcs, rectangle, ellipse, polygons, etc EDITING SKETCHED OBJECTS: Editing sketches, moving, copying, pasting, offsetting, scaling, chamfering, trimming, mirroring. Filleting, sketched objects BASIC DIMENSIONING: Geometric dimensioning and Tolerance: Dimensioning AutoCAD, Creating linear, rotated, angular aligned base line Dimensions, Modifying dimensions PLOTTING: Plotting the drawings in AutoCAD, plotting drawing using the plot dialog box, adding plotters and using plot styles, plotting sheets BASIC 3D MODELLING

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MACHINE DRAWING & INDUSTRIAL DRAFTING Text Books: •Machine Drawing – K. L. Narayana, P. Kannaiah, K. Venkata Reddy, 3rd edition, New age international (P) Ltd. •Machine Drawing – N. Sidheswar, P. Kannaiah, V.V.S. Sastry, Tata McGraw Hill

•Machine Drawing – N. D. Junnarkar, Pearson Education Pvt. Ltd Reference Books: •P.S. Gill, Machine Drawing by S.K. Kataria, New Delhi •Sham Tickoo, AutoCAD 2012 CENGAGE learning

•Technical Drawing byGiesecke, F.E., Mitchel, A., Spencer, H.C., Hill, I.L.,”, 13th Ed., Prentice-Hall • SP 46: 1988 Engineering Drawing Practice for Schools and Colleges, Bureau of Indian standards 1988 •PSG Design data book

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PRINCIPLES OF DRAWING  Drawing sheet  Scales  Title block  Borders and Frames  Grid reference system (zoning)  Lines  Lettering  Sections

 Conventional representation  Dimensioning  Standard Abbreviations

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DRAWING SHEET  Use of standard size sheet saves paper and facilitates convenient storage of drawing  For sheet sizes the basic principles are; (a) X:Y 1: 2 (b) XY=1  For A0 size, surface area is 1m2, X=841mm and Y=1189mm  Preferred drawing sheet sizes as per ISOA series is given in Table 1.1

Table 1.1

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DRAWING SHEET  The special elongated sizes are obtained by multiplying the shorter sides of the chosen basic format as shown in Table 1.2

Table 1.2

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DRAWING SHEET  Different drawing shown in Figure 1.1

sheet

formats

Figure 1.1 Drawing sheet formats

are

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DRAWING SCALE  The proportion by which we either reduce or increase the actual size of an object on a drawing is known as drawing to scale or simply Scale.  Scale is the ratio of linear dimension of an element of an object as represented in the drawing to the real linear dimension of the same element of the object  Where ever possible, full scale is desirable  Enlarged scales are used for drawing very small objects  Reduced scales are used for drawing very 10 large objects

DRAWING SCALE SIZES OF THE SCALE  Full scale :

1:1

 Reduced scales The standard reducing proportions are; 1:2, 1:5, 1:10, 1:20, 1:50 and 1:100  Enlarged scales The standard enlarging proportions are;

2:1, 5:1, 10:1, 20:1 and 50:1 11

DRAWING SCALE  Complete designation of scale consists of the word scale followed by the indication of its ratio as: SCALE 1:1 for full size SCALE X:1 for enlarged size SCALE 1:X for reduced size  Standard scales are shown in Table 1.2

Table 1.2

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TITLE BLOCK  Important feature of the drawing  It

gives

all

the

information

of

the

prepared drawing  It is drawn at the bottom right corner  The recommended size of the title block

by Bureau of Indian Standards (B.I.S.) SP-46:1998 is 185mm x 65mm for all designations of drawing sheets 13

TITLE BLOCK  The title block should contain - Title of the drawing - Drawing/sheet number

- Scale - Symbol, denoting the method of projection - Name of the company/firm

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TITLE BLOCK NAME :

DHARMSINH DESAI UNIVERSITY, NADIAD

CLASS :

FACULTY OF TECHNOLOGY

COMP.:

TITLE OF THE DRAWING

YEAR: 2011-12 50 150

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START:

MECHANICAL ENGINEERING DEPARTMENT

DRAWING NO.: CHECKED BY:

15

50

ROLL NO :

50

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BORDERS AND FRAMES  Border should be provided with all sheet sizes  Borders have a minimum width of 20mm for

the sizes A0 and A1  Borders have a minimum width of 10mm for the sizes A2, A3 and A4  A filling margin may be provided on far left edge

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BORDERS AND FRAMES The drawing sheet layout is shown in Figure 1.3

Figure 1.3

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CENTRING MARKS  Provided to facilitate positioning of the drawing when reproduced  Four centring marks may be provided

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ORIENTATION MARKS  Provided to indicate the drawing sheet on the board

orientation

of

the

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METRIC REFERENCE GRADUATION  Provide figure-less metric reference  Provided with minimum length 100mm and divided into 10 intervals  Drawn symmetrically about the centring mark with width 5mm

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TRIMMING MARKS  Provided at four corners of the sheet in order to facilitate trimming  These marks are in the form of right angled isosceles triangles

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GRID REFERENCE SYSTEM  Recommended in order to permit easy location on the drawing of details, additions or modifications  Number of divisions should be divisible by two  Chosen in relation to the complexity of the drawing  Length of any side of grid should not be less than 25mm and should not be more than 75mm  The rectangles of the grid should be referenced by means of capital letters along one edge and numerals along the other edge  The numbering may start at the sheet corner opposite to the title block as shown in Figure 1.5 22

LINES

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LINES

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LINES THICK LINE / OBJECT OUTLINES  Represented by thick line (0.7mm thickness) and is used to show the outer visible feature of the object in the drawing

LINES HIDDEN LINES  Represented by short dashes closely and evenly spaced  Used to show the invisible or hidden parts on the drawing

LINES CHAIN THIN DOUBLE DASHED (PHANTOM LINES)  These Lines are used to represent the outline of an adjacent part, show alternate position of a moving part or replace repetitive details such as gear teeth and threads

LINES LONG BREAK LINES  Represented by thin ruled line provided with free hand zig-zags at suitable intervals and is used to show the break for a considerable length of the object

LINES SHORT BREAK LINES  Represented by thin free-hand and is used to show the break of an object for a short length

LINES CUTTING PLANE LINE  Represented by thick long line at the ends with thin long and short lines at the centre  Used to show the edge of the cutting plane

LINES CONTINUOUS THIN LINE  Used for showing dimension lines, extension lines, construction lines, hatching lines or section lines

LINES CENTRE LINE  Represented by long and short dashed in proportion ranging from 6:1 to 4:1, closely and evenly spaced in any drawing  Used to show the centre line location of cylindrical, conical and spherical objects

LETTERING  Lettering

on

a

drawing

enables

engineer,

architect or designer to communicate a complete description of an object  Standard lettering for technical drawing are called Gothic lettering

 All letters in words are capitalized and squared

LETTERING  The height (h) of capital letters is taken as the base of dimensioning  Two standard ratios for d/h, 1/14 and 1/10 are used  The lettering may be vertical or inclined at 150 to the right  The proportions of different dimensions are shown below

LETTERING  For standard ratios for d/h, 1/14 different dimensions are shown below

LETTERING  For standard ratios for d/h, 1/10 different dimensions are shown below

LETTERING RULES FOR LETTERING  Use the single-stroke, vertical, gothic style of lettering  Use upper case (capital) letters only!  Always skip a space between rows of letters

 Always use very light guide  Fraction bars are always drawn horizontal  Use a medium (B, HB, H) lead for normal

lettering  Use a hard (4H to 9H) lead for drawing guide lines

LETTERING STEPS FOR LETTERING  Draw 2 lines parallel and write letters in it  The lines can be drawn using 2H pencil  The line must be very soft enough for our own eyes to be seen

 Line can be drawn horizontally using T Square  Firstly, determine the height (h) of the letter to be drawn

h

 The length between 2 line must be h mm

LETTERING VERTICAL LETTERING

LETTERING VERTICAL LETTERING

LETTERING INCLINED LETTERING

LETTERING  Don't mix capital letters with small letters (a)  Write in a form of same type of letter (b)

LETTERING  Don’t mix letters which written straight with leaning letters

LETTERING  Letter

must

have

uniform

blackness

INCORRECT

CORRECT

thickness

and

SECTIONS  A section drawing shows the inside details of an object by cutting away part of the object

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SECTIONS

Normal multiview drawing Normal section view Section view drawing with convention

SECTIONS CUTTING PLANE LINES  Cutting plane lines mark the point at which the object is to be cut apart (with dashed line)  Sight lines point to the part of the object that is to be kept CUTTING PLANE LINE

SIGHT LINE

SECTIONS HATCHING  Used to show where the object has been cut  If the part was cut with a saw, the hatching would represent where the saw actually touched the object as it was being cut  Hatch lines should match the color of the cutting plane line  The pattern of the hatching used represents different types of materials

Hatch lines

SECTIONS FULL SECTION  The cutting plane line cuts through the entire length, height, or width

SECTIONS HALF SECTION  The cutting plane line cuts through only “Half” the length, height, or width of the object

This line divides the object so the sectioned portion and the non-sectioned portion can be defined.

SECTIONS OFFSET SECTION  Offset sections allow one cutting plane line to transect multiple areas of a part  This reduces the amount of work needed to complete a drawing

SECTIONS PARTIAL OR LOCAL SECTION  Local section is drawn if half or full section is not convenient  Local break may be shown by continuous thin free hand line

SECTIONS REVOLVED SECTION  Cross sections may be revolved in relevant view  The outline of the section should be shown with thin continuous line inside the object as shown

SECTIONS REVOLVED AND REMOVED SECTION  The removed section may be placed near to and connected with the view by a chain thin line (a) or in a different position and identified in the conventional manner (b)

SECTIONS SECTIONS NOT TO BE HATCHED

INVISIBLE LINE TECHNIQUE

INVISIBLE LINE TECHNIQUE

AXIS REPRESENTATION

CONVENTIONAL REPRESENTATION OF MATERIALS

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CONVENTIONAL REPRESENTATION OF M/C COMPONENTS

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62


63


64


Title

65


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DIMENSIONING  Dimension is a numerical value expressed in appropriate units of measurement and indicated on drawing using lines, symbols, notes etc…  As far as possible, dimensions should be placed outside the view  Dimensions should be taken from visible outlines rather than from hidden lines  Each feature should be dimensioned once on a drawing  Dimensions should be placed on the view or section that relates most clearly to the corresponding features  Each drawing should use the same unit for all dimensions but without unit symbol

DIMENSIONING METHODS  Dimensions should be indicated on a drawing according to any one of the following methods; (a) Aligned system (b) Uni-directional system

(a)

(b)

DIMENSIONING BASIC TYPES

Angular dimensions are placed so that they show the angle of an inclined feature on a drawing


 Arrowless dimensions are used in confined areas where other dimensioning methods would confuse the reader  Also arrowless dimensioning is very accurate since all features are dimensioned from an origin point or datum point


Chain dimensions are placed end to end This practice is not as accurate as datum dimensioning because the location of the each feature is dependent upon neighboring features


Datum dimensions are placed so that all dimensions originate at the same coordinate This practice is accurate than chain dimensioning because the location of each feature is independent of the other feature


Chart dimensioning is used when part sizes change to fit an application. In the above example part #ADD120 may be needed: therefore a note is placed on the drawing to indicate that the part is to be fabricated according to these specifications. This type of method eliminates the need to create a separate drawing for each suitable change in design. If new part is needed with a larger hole, that instance is added to the table with its own part number


Tabular dimensioning is used to locate features on a (X,Y) coordinate system. In the above example a hole is identifying by a letter, and its location is identified by a coordinate This method saves space and avoids confusing and error If a new hole is needed or the location is changed another hole number may be added or the coordinate may be quickly changed


Radius/Diameter dimensioning is used to dimension fillets, rounds and circles Fillets are small inside arcs and rounds are small outside arcs


To avoid repetitious dimensions on a drawing the abbreviation TYP (meaning typical) is used. When TYP appears after a size dimension, such as a diameter, un-dimensioned circles are intended to be the same dimension.

MEANING OF NOTES

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DRAFTING ABBREVIATIONS

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MATERIAL ABBREVIATIONS

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Machine Drawing

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