Crankpin Turning Device Some time ago we had a crankpin to true up on a double 20 x 40-inch Corliss engine that was worn so out of round that the engine pounded like a steam hammer. As there was no crankpin-turning device available, and as all machinists know it is a heart-breaking job to attempt to file a crankpin 6 3/4 inches in diameter and 7 1/4 inches long, round and square with the face of the crank, the writer proceeded to design the device illustrated. It is a cheap and simple rig, and answered the purpose as well as a $5 crankpin turner. It consists of two rings A and A', fastened together with three bars B set at 120 deg. apart, cap screwed to the inner finished faces of the bars. There are three bearing blocks C, which fit the diameter at the outer and enlarged end of the crankpin. The inner ring A' is bored to fit the shoulder E of the pin. A piece of finished square key steel is fitted and fastened with set screws to the rings A and A'. It acts as a guide or way for the tool carriage G. The tool carriage, or the movable block to which the turning tool is fastened or clamped, has a square hole through it to fit the guide-bar F, and is free to move along it without wabbling. A hole is bored and tapped through the end of the carriage for the feed screw H. Attached to the end of the t he feed screw is a small rope sheave which is belted to the sheave part of the handle with a 1/2-inch rope, giving an automatic feed as the handle turns on its axis, while the machine is in operation.
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Fig. 151 - An improvised crankpin turner. In making a device of this kind, the hole in ring A', preliminary to the final finishing, should be left small, and the three bearing blocks should be cap-screwed to the spacers, the backs of the bearing blocks only being finished. When the spacers have been cap-screwed securely to the rings A and A', the partly assembled machine should be chucked in a lathe, and the bearing blocks C bored and faced to fit the end of the crankpin. The hole in the ring A' should then be bored to fit that part of the enlarged pin nearest the crank. This being done, the square rail F, tool carriage, and feed screw can be put in place. On attaching the machine to the crankpin, the three bearing blocks are removed, the machine slid over the crankpin until the ring A fits over and against the enlarged end E of the pin and against the face of the crank. The bearing blocks C are then fastened in place, ready to do the work. A ring I is counterbored to fit ring A', as shown, and is then clamped against the arm of the crank with two bolts, one on each side. The necessary clearance is allowed in ring /. so as to allow ring A' to revolve when ring I is clamped securely agains the arm of the crankpin.
