To regulate the exact distance to which the work shall be placed within the chuck, a piece of wire rod may be placed within the hollow spindle n being detained in its adjusted position by the set screw s.

The construction whereby the nut is permitted to revolve with spindle l, and be operated by hand to move spindle l when the lathe is at rest, is as follows.

The cylindrical rim t of the nut is provided with a series of notches arranged around its circumference. r is a lever whose hub envelops nut m, but has journal bearing on v. r receives the pin s, which rests upon a spiral spring t. When, therefore, s is pushed down it depresses the spring t and its end w enters some one of the notches in the rim t, and operates the nut after the manner of a ratchet. But so soon as the end pressure on r is released, the spiral spring lifts it and m is free to revolve with l as before. The inner spindle is driven by means of the feather g.

Pulley p has two steps y for the belt, and a friction step z, around which passes a friction band operated by the operator’s foot to stop the lathe quickly. This performs two functions, as follows. The thread of m is a left-hand one so that the inertia of the nut will not, when the lathe is started, operate to screw the nut back, and release the chuck jaws from the work, by moving spindle l endwise. Per contra, however, in stopping the lathe suddenly by means of the brake, there is a tendency of nut m to stop less quickly than spindle l, and this operates to unscrew nut n and release the work. To assist this r is sometimes in lathes for watch manufactories provided with a hand wheel whose weight is made sufficient for the purpose.

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Fig. 667.