Application of Steadyrest when Boring.—Another example illustrating the use of the steadyrest is shown in [Fig. 22]. The rod R is turned on the outside and a hole is to be bored in the end (as shown by dotted lines) true with the outer surface. If the centers used for turning the rod are still in the ends, as they would be ordinarily, this work could be done very accurately by the following method: The rod is first placed between the centers as for turning, with a driving dog D attached, and the steadyrest jaws J are set against it near the outer end, as shown.
Fig. 23. Hold-back used when Outer End of Work is held in Steadyrest
Before any machine work is done, means must be provided for holding the rod back against the headstock center h, because, for an operation of this kind, the outer end cannot be supported by the tailstock center; consequently the work tends to shift to the right. One method of accomplishing this is shown in the illustration. A hardwood piece w, having a hole somewhat larger than the work, is clamped against the dog, in a crosswise position, by the swinging bolts and thumb-screws shown. If the dog is not square with the work, the wood piece should be canted so that the bearing will not be all on one side. For large heavy parts a similar “bridle” or “hold-back”—as this is commonly called—is made by using steel instead of wood for the part w. Another very common method which requires no special equipment is illustrated in [Fig. 23]. An ordinary leather belt lacing L is attached to the work and faceplate while the latter is screwed off a few turns as shown. Then the lacing is drawn up by hand and tied, and the faceplate is screwed onto the spindle, thus tightening the lacing and drawing the work against the headstock center. The method of applying the lacing is quite clearly indicated in the illustration. If a small driving faceplate is used, it may be necessary to drill holes for the belt lacing, as shown.
Fig. 24. Testing Work with Dial Indicator
A hole is next drilled in the end of the rod by using a twist drill in the tailstock. If the hole is finished by boring, a depth mark should be made on the tool shank that will warn the workman of the cutting end's approach to the bottom. A chuck can also be used in connection with a steadyrest for doing work of this kind, as shown in [Fig. 24], the end of the rod being held and driven by the chuck C. If the piece is centered, it can be held on these centers while setting the steadyrest and adjusting the chuck, but if the ends are without centers, a very good way is to make light centers in the ends with a punch; after these are properly located they are used for holding the work until the steadyrest and chuck jaws have been adjusted. In case it is necessary to have the end hole very accurate with the outside of the finished rod, a test indicator I should be applied to the shaft as shown. This is an instrument which shows with great accuracy whether a rotating part runs true and it is also used for many other purposes in machine shops. The indicator is held in the lathe toolpost and the contact point beneath the dial is brought against the work. If the latter does not run true, the hand of the indicator vibrates and the graduations on the dial show how much the work is out in thousandths of an inch.