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Fig. 802.

When the work is sufficiently long or slender to cause it to sag and bend from its own weight, or bend from the pressure of the cut, it is supported by means of special guides or rests. [Fig. 802] represents a steady rest of the ordinary pattern; its construction being as follows:—f is a base fitting to the Vs of the lathe shears at f, and capable of being fastened thereto by the bolt c, nut n, and clamp a. f′ is the top half of the frame, being pivoted at p to f, the bolt p′ forming the pivot for both halves (f and f′), of the frame, which may be secured together by the nut of p′. On the other side of the frame the bolt is pivoted at b to f. This bolt passes through an open slot in f′, so that its nut being loose, it may swing out of the way as denoted by the arrow e, and the top half frame f′ may be swung over in the direction of arrow g, the centre of motion or pivot being on the bolt p′. With f′ out of the way the work may be placed within the frame, the nut of b and also that of p′ may be tightened up so as to lock the two halves of the frame firmly together.

On this frame and forming a part of it are the three ways, g g′ g′′, which contain cavities or slide ways to which are fitted and in which may slide the respective jaws j, and to operate these jaws are the respective square-headed screws s, which are threaded through the tops of the respective ways g, g′, and g′. The screws are operated until the ends of the jaws j have contact with the work w, and hold it axially true with the line of centres of the lathe, or otherwise, as the nature of the work may require. When adjusted the jaws are locked to the frame by means of the bolts d, which are squared to fit in the rectangular openings, shown at h in the respective jaws, so as to prevent the bolts from rotating when their locking nuts d are screwed home.

As an example of the use of this device as a steadying rest, suppose a long shaft to require turning from end to end and to be so slight as to require steadying, then a short piece of the shaft situated somewhat nearer the live centre than the middle of the length of the work is turned upon the work, so that this place shall be round and true to receive the jaws, or plates p, and revolve smoothly in them. The jaws are then adjusted to fit the turned part a close sliding fit, but not a tight fit, as that would cause the jaws to score the work. To prevent this even under a light pressure of contact, oil should be occasionally supplied. This steadies the work at its middle, preventing it from springing or trembling when under the pressure of the cut.

By placing the steady rest to one side of the middle of the work length, at least one half of that length may be turned before reversing the work in the lathe centres. After reversing the work end for end in the lathe centres, the jaws, or plates p, are adjusted to the turned part, and the turning may be completed.

In adjusting the plates p to the work, great care is necessary or they will spring the work out of its normal line of straightness, and cause it to be out of parallel, or to run out of true in the middle of its length, as explained in the remarks referring to the cat head shown in [Fig. 809].

The plates p should be gripped to the frame by the nuts with sufficient force to permit them to be moved by the set-screw s under a slight pressure, which will help their proper adjustment. They should also be adjusted to just touch the work, without springing it, the two lower ones being set up to the work first, so that their contact shall serve to relieve the work of its spring or deflection, due to its own weight. This is especially necessary in long slender spindles, in which the deflection may occur to a sensible degree.