For building the rim, a wooden chuck 20 1/2 inches in diameter will be necessary. A board 7/8 inch in thickness and having a bar 8 inches wide and of the same thickness, well screwed to the back with wood screws, is all that is necessary for a pulley of this size. To the 8-inch bar, the iron faceplate of the lathe is screwed, and the whole turned off true in the lathe, especially the face of the chuck to which the first layer of segments is to be glued.
Strips of paper will be glued between the first layer of segments and the face of the faceplate so that the completed rim may be easily removed - repeating the process used for similar work in making the 12-inch hand wheel.
Prepare stock 5/8 inch thick for rim segments, cutting the stock long enough to make 6 segments for each layer, and 11 layers, making 66 segments. Stack the stock and band saw at least 4 segments at one time. Have the layout and process carried out the same as suggested for the 12-inch hand wheel.
The segments should have an outside diameter of 20 1/2 inches, and inside diameter of 19 inches, making a width of 3/4 inch, and a length 1/16 inch longer than the outside radius. The grain of the stock should be parallel to the chord of the segment.
The first layer is fitted and glued to the faceplate with paper between, and securely clamped with small hand screws through to each segment. Do not use any nail this time, as the rim is only 5/16 inch thick at the edge next to the faceplate. When the glue is dry - one hour being sufficient - place the faceplate in the lathe and carefully turn off the face of the segments true, and also turn the inside edge of the segments to the proper diameter and draft.
Before turning the face of the second layer of segments, glue to the faceplate - six pieces of stock 1/4-inch thick - using no paper - so that they will bear firmly against the inner edge of the segments in the first layer, to prevent the work from becoming loose. Do not glue these blocks to the rim segments. No nails should be used in any work of this description. Fit and glue the second layer, and when the glue is sufficiently dry, turn the face and also the inside edge as before. Do not turn the outside edge of the segments at this time, but it is best to mark an oversize diameter with a pencil or the point of a chisel to keep the layers concentric. This layer, in turn, is turned off in the lathe, and the third layer is glued on, hand screws being used on each layer as on the first, and the joints of the segments so broken that no two will be directly opposite each other, all joints being carried to right or left of all preceding joints, thus securing the greatest possible strength to the rim.
Having glued on a sufficient number of layers to build the rim up to the edge of the arms - five in this case - fasten the arms temporarily in their correct location, and glue the segments between the ends of the arms. Remove the arms - as noted while considering the 12-inch hand wheel - and turn out the inside of the rim to the finished diameter and draft, and smooth with sandpaper. Glue the arms back into place, first seeing that the fillets which have been used at the outer end of the arms are trimmed to fit the the inside of the rim.
The next five layers of the rim are built on the same way, except that the inside edges need not be turned until all layers are in place. The outside of the rim should be turned straight, with its largest diameter next to the faceplate. This diameter should be 20 1/4 inches, and, as the outer edge of the rim is to be made 20 1/8 inches in diameter to allow facing, this gives 1/16 inch for draft.
The parting of the mold should be flush with one edge of the rim, and coped down to the center of the arms on the inside of the rim. This allows more than the usual amount of metal finish on one edge of the rim, but, if the face of the rim were crowned or drafted both ways from the center of the arms, a perfect lift would be difficult when the cope mold is lifted to get at the pattern.
To permit a satisfactory lift, the cope hub should be made loose so that it will lift with the cope mold. In constructing any pattern it is best to so arrange its parts that change may be made in order to adapt the pattern to as many requirements as possible. Even if this pulley is designed as a standard part of some equipment, there are times when it might be used for other purposes that would likely require a larger shaft, a longer, or an offset hub. To meet these conditions, make all hubs and core prints loose.
The pulley being intended for a 13/4-inch shaft, the core prints x and y, Fig. 177, should be 1 1/2 inches in diameter, which will give 1/8 inch of metal for boring out to fit the shaft. The hubs should be turned from solid stock, having the grain run parallel to the length of the hub. Select stock 4 inches by 4 inches and saw two pieces 2 1/2 inches long. Band saw to a circle 3 3/4 inches in diameter and bore a 1-inch hole through each at the center. Mount these pieces on an arbor; turn to a diameter of 3 1/2 inches at one end, and a draft of about 1/4 inch per foot should be allowed on the outside diameter. The length of the hubs should be 2\ inches each.
No fillet should be turned on the large end of the hubs, as it is easily broken and it will be easier to lengthen the hub by the addition of a thin piece of stock, should occasion demand, if the hub is made straight. The molder can produce the fillet by slicking the corner of the mold with a fillet tool.
Core-print usage is discussed in the next section, in the paragraph on "Standard Core Prints".