THE task of making an engine crank is by no means beyond the abilities of the average amateur mechanic. The following directions will be found comparatively simple: Take a piece of steel 2 inches thick, 5 inches wide and of a length to suit the purpose. A thin paste made of chalk dust and water may be spread over the metal and when dry it will provide an excellent surface for taking the lines of a sharp lead pencil. The crank may be laid out on this surface to the exact size required. The lines indicated in the accompanying Fig. I.-Cutting out a crank shaft. drawing at A (Fig. 1) can be cut with a power sa I. The cuts running lengthwise of the piece can be made to better advantage by drilling, although the two long cuts might be made by the power band saw. To facilitate the operation of drillJng, a jig should be made of cold rolled steel, 1/16 inch thick, 2 inches wide and about a foot in length. Drill holes in this piece in a perfectly straight line. spacing the ho:es as close together as possible without letting one cut into the other. This jig need not be hardened unless a large number of cranks are to be drilled. The piece should be attached to the surface of the steel plate by means of three machine screws. Now, the workman can proceed with his drilling and if the holes have been laid out nicely in the jig, the steel can be separated without much trouble after drilling. After thn crank has been cut out roughly in this manner it may be centered on the ends and turned in the lathe. The tool should be sharpened with can· Fig. 2.-Machining the crank pin. siderable bevel and made to cut deep but thin chips, taking off nearly the whole corner at the first cut. This procedure will do away with a great deal of knocking. The cranked shaft should be roughed out at first, leaving plenty of stock for the finishing cut. For turning the crank pin, make a flange of the form indicated at B (Fig. 2) with two ears at the outer end, as shown at D. The machining on this casting is simple. It consists in facing the flange and boring it out to receive the crankshaft. The flange is clamped +' the face plate and a bolt at C acts as a pivot, so that adjustment up or down can be secured by tapping the piece lightly with a hammer. The straps are then bolted securely. Lateral adjustment is attained with two set screws indicated at E. Two more set screws will serve to hold the shaft firmly in the neck of the flange. A counterbalance F may be strapped or bolted to the face plate.
This article was originally published with the title "How to Make an Engine Crank" in Scientific American 105, 13, 276 (September 1911)