Fig. 476. Fig. 477.
Hubs are sometimes fastened to their shafts by pins passing through both the hub and the shaft. These pieces may be made parallel or taper, but the latter obviously secures the most firmly. If the pin is located as in [Fig. 476], its resisting strength is that due to its cross sectional area at a and b. But if the pin be located as in [Fig. 477] it secures the hub more firmly, because it draws the bore (on the side opposite to the pin) against the shaft, causing a certain amount of friction, and, furthermore, the area resisting the pressure of the hub is increased, and that pressure is to a certain degree in a crushing as well as a shearing direction.
Fig. 478.
If unturned pins are used and the holes are rough or drilled but not reamed, it is better that two sides of the pin should be eased off with a file or on the emery wheel, so that all the locking pressure of the pin shall fall where it is the most important that it should—that is, where it performs locking duty. This is shown in [Fig. 478], the hole being round and the pin being very slightly oval (not, of course, so much as shown in the drawing), so that it will bind at a b, and just escape touching at c, d, so that all the pressure of contact is in the direction to bind the hub to the shaft.