When pieces of lathe work are to be made from rod or bar iron, they should be cut off to the proper length in a cutting-off machine, such as described in [special forms of the lathe], and for the reasons set forth in describing that machine.
Fig. 1207.
An excellent tool, however, for cutting up rods of not more than 1⁄2 inch in diameter, is Elliott’s cutting-off tool shown in [Fig. 1207]. It consists of a jaw carrying steadying pieces for the rod to be cut up, these pieces being adjusted to fit the rod by the screw and nut shown. On the same jaw is pivoted a tool-holder, carrying a cutting-off tool, which is fed to its cut by the upper handle being pressed towards the lower one.
An adjustable stop or gauge is attached, by means of a small rod, to the swinging arm which carries the cutting tool, and can be removed when its use is not desirable.
The operation of this tool is as follows:—The rod to be cut up is held in the lathe chuck, projecting beyond any desired distance, and arranged to revolve at the same speed as for turning. The tool is placed upon the rod, and the movable jaw of the rest adjusted to a bearing. If several pieces are to be cut to a length, the gauge is adjusted, the tool moved along the rod till the gauge-stop comes in contact with the end, the handles pressed together, which moves the cutting tool up to the work in such a way that it will come exactly to the centre, thus cutting the piece entirely off, no adjustment of the tool ever being necessary to provide for its cutting to the centre, except keeping the cutting edge (which is not in this respect changed by grinding) at a distance specified in the directions from the part in which it is clamped. As the tool is moved up to cut, by the same operation the gauge is moved back out of contact with the end. When the pressure on the handles is removed, a spring returns the cutting tool to its original position, and also brings the gauge in position for determining the length of the next piece to be cut. The operation is repeated by simply moving the tool along the rod, the cutting up being done with great rapidity and accuracy. It will be noticed that all the appliances for cutting, gauging, &c., being a part of the tool itself, if the rod runs out of truth—in other words, wabbles—it will have no effect on the cutting, the rod to be cut forming the gauge for all the operations required; also that comparatively no time is lost in adjustment between the several pieces to be cut from a rod.
The cutting tool is a piece of steel of the proper thickness, cleared on the sides by concave grinding. It is held in place by a clamp and two small screws, and requires grinding on the end only.
When the work is centred, it should, for reasons already explained, have its end faces trued up.
In doing this, however, it is desirable in some cases to cut off the work to its exact finished length. This possesses the advantage, that when the work is finished, the work centres will be left intact, and the work may be put into the lathe at any time, and it will run true to the original centres. But this is not always the best plan; suppose, for example, that there are a number of collars or flanges on the work, then it is better to leave a little extra length to the work when truing up the ends, so that if any of the collars are scant of metal, or if it be desirable to turn off more on one side of a collar than on another, as may be necessary to turn out a faulty place in the material, the end measurements on the work may be conformed to accommodate this requirement, and not confined to an exact measurement from the end of the work.