Fig. 1283.
If it is not essential that the coils be exactly true, take a plain mandrel, such as shown in [Fig. 1283], and a hook, such as shown at a, fasten the end of the wire either round the lathe dog, or in a hole in the mandrel as before, and wind one full coil of the spring upon the mandrel, then force this coil open until the hook end of a can be inserted between it and over the mandrel, the other end hanging down between the lathe shears, which will prevent it from rotating, starting the lathe while holding the unwound end of the wire against the hook with a slight pressure, and the winding will proceed as shown in the figure, the thickness of a regulating the width apart of the coils. It is obvious that if the coil is to be a right-handed one and is started at the carrier end, the lathe must revolve backwards.
Spiral springs for railroad cars are wound while red-hot in special spring-winding lathes and with special appliances.
Tools for Hand Turning.—Many of the tools formerly used in hand turning have become entirely obsolete, because they were suitable for larger work than any to which hand turning is now applied; hence, reference to such tools will be omitted, and only such hand tools will be treated of as are applicable to foot lathes and wood turning, their purposes being those for which hand tools are now used.
To the learner, practice with hand tools is especially advantageous, inasmuch as the strain due to the cut is felt by the operator; hence, the effects of alterations in the shape of the tools, its height or position with relation to the work, and also the resistance of the metal to severance, are more readily understood and appreciated than is the case where the tool is held in a slide rest or other mechanical device. If under certain conditions the hand tool does not operate to advantage, these conditions may be varied by a simple movement of the hands, altering the height of the tool to the work, the angle of the cutting edges to the work, or the rate of feed, as the case may be, and instantly perceiving the effects; whereas with tools held by mechanical means, such alterations would involve the expenditure of considerable time in loosening, packing, and fastening the tool, and adjusting it to position.
Small work that is turned by hand may, under exceptionally expert manipulation, be made as interchangeable and more accurate in dimensions than it could be turned by tools operated in special machines. That is to say, it is possible to turn by hand a number of similar small pieces that will be when finished as true, more nearly corresponding in dimensions, and have a finer finish, than it is practicable to obtain with tools operated or guided by parts of a machine. This occurs because of the wear of the cutting tools, which upon small work may be compensated for in the hand manipulation in cases where it could not be in machine manipulation. But with ordinary skill, and under ordinary conditions, the liability to error in hand work induces greater variation in the work than is due to the wear of the tool cutting edges in special machine work; hence, the practical result is that work made by special machinery is more uniform and true to size and shape than that made by hand, while also the quantity turned out by special machines is very much greater.
Fig. 1284.
The most desirable form of tool for taking a heavy hand cut is the heel tool shown in [Fig. 1284], which, it may be remarked, is at present but little used on account of the greater expedition of tools held in slide rests. It consists of a steel bar, about 3⁄8 or 1⁄2 inch square, forged with a heel at f, so that it may firmly grip the hand rest, and having a cutting edge at e. This bar is about 8 inches long, and is held in a groove in a wooden stock by a strap passing over it, and having a stem which passes down through the handle d, in which is fixed a nut, so that by screwing up or unscrewing d the bar is gripped or released, as the case may be, in a groove in the stock. In use, the end h of the stock is held firmly against the operator’s shoulder, the left hand grasps the stock and presses the tool firmly down upon the face of the hand rest, while with the right the handle d is moved laterally, causing the tool to move to its cut. The depth of the cut is put on and regulated by elevating the end h of the stock. The heel f is placed close enough to the work to keep e f nearly vertical, for if it inclines too much in any direction the tool gets beyond the operator’s control. The position of the heel f is moved from time to time along the hand rest to carry the cut along.