Fig. 194 illustrates a finished cast-iron disk crank for an engine, of 12-inch stroke. This crank is finished on the face, on the outer edge, and on the end of the hub. It is bored out 3 1/4 inches to fit on the engine shaft, and 2 1/4 inches to receive the wrist pin. An addition of 1/8 inch must be allowed on the pattern for finish of the face, and the same on the end of the hub; 3/16 inch will be sufficient to add for finish on the outer rim, making the diameter of the pattern 16 3/8 inches, and the thickness of the disk 3/4 inch. A sectional view of the pattern is shown in Fig, 195.
The disk or web for this pattern is to be made of six sectors, Fig. 196. The finished thickness of the web will be 5/8 inch, and, allowing 1/8 inch for metal finish, the web of the pattern will be 3/4 inch thick. Each section after being fitted should have the edges glue sized, and be grooved for a spline. The grain of the stock used in these splines should be at right angles to the joint, as mentioned in the consideration of the hand-wheel pattern, Fig. 171. Band saw this web to a diameter 1/4 inch greater than required for the completed pattern, bore a 1-inch hole through the web at the center, and fasten to a wood faceplate having a 1-inch pin at its center, with six 1 1/2-inch wood screws, as shown in Fig. 196. Turn the rabbet in the web at d and chuck the center at e, as shown in Fig. 195.
Fig. 194. Dick Crank.
The first layer of segments for the rim or flange are to have the inner edge fitted into the rabbet, and are made wide enough to make the wood fillet c. The other layers of the flange will not be required to be as wide, but make all segments of the same thickness, which should he about 5/8 inch, six segments to the layer, and put the work into the lathe before gluing on a layer of segment, and turn the face of the preceding layer true and concentric with the center of the pattern. Fit the segments carefully and use three hand screws to hold each segment while the glue is drying. A wait of about two hours should be allowed between gluing a layer of segments and turning; so take advantage of the noon hour, and overnight.
The work on the hub, wrist-pin boss, and counterweight should be proceeding while building the stock for the web and flange. The hub shall be turned from a solid piece of stock or from glued stock if the dimensions of the hub are too great. The grain of the stock used in the hub and wrist-pin boss should be parallel to the length of the hub.
If positive that the diameter of the cored holes will not be changed, the nowel core prints may be turned as a part of the hub and boss. The cope core prints x and y, Fig. 195, shall be loose on the pattern so that when the nowel mold is rammed these core prints can be removed when the pattern is laid on its back on the mold board. The core prints should be shellacked a different color from the body of the pattern.
The fillet at the base of the hub should be turned from the hub stock, as shown in Fig. 195. The hub is to be turned before it is glued to the web; the fillet, however, should be turned after the hub is in place so as to be tangent to the face of the web.
The counterweight b is next shaped from a single piece, or it may be glued up of 2 thicknesses of l 1/8-inch stock. In sawing this block to shape, the band-saw table should be tilted so as to give it a draft of § inch in 12 inches. Give the inside of the rim, the hub, and the boss a, the same draft as the counterweight, but the outside of the rim should not have a draft of more than 1/8 inch in 12 inches.
When turning on the inside of the rim, a fillet or curve of 3/8-inch radius, as shown at c, Fig. 195, must be made where the rim joins the disk. Around the counterweight block, and also around the wrist-pin boss, a 3/8-inch leather fillet can be used.