Fig. 13. (A) Dog that is too Short for Faceplate.
(B) Straight Driving Dog
Application of Drivers or Dogs.—Work that is turned between centers is sometimes driven by a dog which is so short for the faceplate that the bent driving end bears against the bottom a of the faceplate slot, as shown at A, [Fig. 13]. If the dog is nearly the right length, it may allow the headstock center to enter the center in the work part way, with the result that the turned surface is not true with the centers. When a driving dog of this type is used, care should be taken to see that it moves freely in the faceplate slot and does not bind against the bottom. By using a straight dog (B), which is driven by a pin b bolted to the faceplate, all danger from this source is eliminated. The straight dog, however, is used more particularly to do away with the leverage l of a bent dog, as this leverage tends to spring a flexible part when a cut is being taken.
Straight dogs are also made with two driving ends which engage pins on opposite sides of the faceplate. This type is preferable because it applies the power required for turning, evenly to the work, which still further reduces the tendency to spring it out of shape. The principal objection to the double-ended type lies in the difficulty of adjusting the driving pins so that each bears with equal pressure against the dog. The double-ended driver is often used for large work especially if deep roughing cuts are necessary.
Fig. 14. Bushing mounted on Arbor for Turning