Modern Machine-Shop Practice Part 88

[Ill.u.s.tration: Fig. 1266.]

[Ill.u.s.tration: Fig. 1267.]

The half bearing B, Fig. 1266, is chucked upon a half-round mandrel, C being the spherical surface to be turned, a sectional view of C being shown in Fig. 1267.

[Ill.u.s.tration: Fig. 1268.]

In Fig. 1268 is a plan view of the chuck, work, and lathe rest; D is a former attachment bolted to the slider of the rest, and E a rod pa.s.sing through the lathe block. The weight W, Fig. 1269, is suspended by a cord attached to the slide rest so as to keep the former D firmly against the end of E.

As the slider is operated, the rest is caused by E to slide upon the lathe bed, and the cutting tool forms a spherical curve corresponding to the curve on the former D. The weight W of course lifts or falls according to the direction of motion of the slider.

The cut is put on by operating handle G, thus causing E to advance.

The weight W causes any play between the slider and the cross slide to be taken up in the same direction as the tool pressure would take it up, hence the cut taken is a very smooth one. The half-round mandrel being fixed to the lathe face plate will remain true, obviating the liability of the centre of the spherical surface being out of line with the axis of the bearing-bore.

A method of producing cams without a lathe especially adopted for the purpose is shown in Figs. 1270 and 1272, which are extracted from _Mechanics_. The apparatus consists of a frame E, which fits on the cross ways of an ordinary lathe. The cross-feed screw is removed, so that E may slide backwards and forthwards freely. The frame E carries the worm-wheel A and the worm-gear B, which is operated by the crank F.

The cam C to be cut is bolted on to the face of the worm-wheel, which faces the headstock of the lathe. The form for the cam, which may be made of sheet steel, or thicker material, according to the wear it is to have, is fastened to the face of the cam.

[Ill.u.s.tration: Fig. 1269.]

[Ill.u.s.tration: Fig. 1270.]

[Ill.u.s.tration: Fig. 1271.]

[Ill.u.s.tration: Fig. 1272.]

A cutter, like a fluted reamer, such as is shown in Fig. 1271, is then put in the live centre of the lathe. Care must be taken that the shank is the same size as the fluted part, and that the flutes are not cut up farther than the thickness that the cam grooves are to be cut in the blank. Having attached a cord to the back of E, pa.s.s it over a pulley H, fastened on the rear of the lathe, and hang on a weight G. Fig. 1272 is an edge view of the device, looking from the back of the lathe. It shows the worm A, blank C, and former D all bolted together, while the cutter I is ready in its place on a line with the centre of the worm, and just at back of the former. The machine is operated by turning the crank F, which causes the worm A, also C and D, to revolve slowly, while the cutter I has a rather rapid rotation. The weight causes the cutter to be held firmly against the form F, and to follow its curves in and out.

[Ill.u.s.tration: Fig. 1273.]

[Ill.u.s.tration: Fig. 1274.]

[Ill.u.s.tration: Fig. 1275.]

KNURLING OR MILLING TOOLS.--In Fig. 1273 is shown the method of using the knurling tool in the slide rest of a lathe. It represents the tool at work producing the indentations which are employed to increase the hand grip of screw heads, or of cylindrical bodies, as shown in the figure by the crossed lines. Fig. 1274 is an end view of the tool, which consists of a holder to go in the slide rest tool post, and carrying two small hardened steel wheels, each of which is serrated all round its circ.u.mference, the serrations of one being in an opposite direction to those of the other. The method of using the tool is shown in Fig. 1275, where it is represented operating upon a cylindrical piece of work. If the knurling is to be carried along the work to a greater length than the thickness of the knurl wheels, the lathe slide rest is slowly traversed the same as for a cutting tool.

As the knurling tool requires to be forced against the work with considerable pressure, there is induced a strain tending to force the tool directly away from the work, as denoted by the arrow in Fig. 1276, and this, in a weighted lathe, acts to raise the lathe carriage and weight. This is avoided by setting the tool at an angle, as in Fig.

1277, so that the direction of strain is below and not above the pivot on which the cross slide rests. This is accomplished by pivoting the piece carrying the wheels to the main body of the stem, as shown in Fig.

1277.

For use by hand the knurling or milling tool is fitted to a holder and handle, as in Fig. 1278, and the hand tool rest is placed some little distance from the work so that the knurl can pa.s.s over it, and below the centre of the work.

Knurls for screw heads are made convex, concave, or parallel, to fit the heads of the screws, and may be indented with various patterns.

[Ill.u.s.tration: Fig. 1276.]

[Ill.u.s.tration: Fig. 1277.]

[Ill.u.s.tration: Fig. 1278.]

WINDING SPIRAL SPRINGS IN THE LATHE.--Spiral springs whose coils are close, and which therefore act on distension only, may be wound by simply starting the first coil true, and keeping the wire as it winds on the mandrel close to that already wound thereon.

[Ill.u.s.tration: Fig. 1279.]

Spiral springs with open coils may be best wound as shown in Fig. 1279, in which is shown a mandrel held between the lathe centres and driven by a dog that also grips one end of the wire W, of which the spring is to be made. The wire is pa.s.sed through two blocks B, which, by means of the set-screw in the lathe tool post, place a friction on it sufficient to place it under a slight tension which keeps it straight. The change gears of the lathe are arranged as they would be to cut a screw of a pitch equal to the thickness of the wire added to the s.p.a.ce there is to be between the coils of the spring. The first turn of the lathe should wind a coil straight round the mandrel when the self-acting feed motion is put in operation and the winding proceeds, and when the spring is sufficiently long, the feed motion is disconnected, and the last coil is allowed to wind straight round the mandrel, thus giving each end of the spring a flat or level end.

If the wire is of bra.s.s it will be necessary to close it upon the mandrel with blows from a lead mallet to prevent it from uncoiling on the mandrel when the end is released, which it will do to some extent in any event.

[Ill.u.s.tration: Fig. 1280.]

If it is of steel it may be necessary to heat the coil red-hot to prevent its uncoiling, and in the coiling it will, if of stout wire, require to be bent against the mandrel during winding with a piece of steel placed in the tool post, as in Fig. 1280, in which A represents the mandrel, B the spring wire, and D the lathe tool post.

[Ill.u.s.tration: Fig. 1281.]

[Ill.u.s.tration: Fig. 1282.]

In the absence of a lathe with a self-acting feed motion, the mandrel may have a spiral groove in it and the piece of steel or other hard metal shown in figure must be used, the feed screw of the slide rest being removed so that the wire can feed itself along as the mandrel rotates. Near one end of the mandrel a small hole is drilled through, there being sufficient s.p.a.ce between the hole and the end of the mandrel to admit of a loose washer being placed thereon; the bore of this washer requires to be rather larger in diameter than the outside diameter of the spring, when wound upon the mandrel, and also requires to be provided with a keyway and key. The washer D (Fig. 1281), is slipped over the mandrel, the end of the wire C is inserted in the hole B and the spring being wound, the washer is pa.s.sed up to the end, and the key driven home as in Fig. 1282; when the wire is cut off and the mandrel may be taken from the lathe with the spring closely wound round it to be hammered if of bra.s.s, and heated if of steel. The hammering should be done over the whole circ.u.mference, not promiscuously, but beginning at one end and following along the wire with the blows delivered not more than 1/4 of an inch apart; for unless we do this we cannot maintain any definite relation between the size of the mandrel and the size of the spring.

When a grooved mandrel is used, its diameter should be slightly less than the required diameter of spring, as when released the coils expand in diameter.

[Ill.u.s.tration: 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 quant.i.ty turned out by special machines is very much greater.

[Ill.u.s.tration: 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 pa.s.sing over it, and having a stem which pa.s.ses down through the handle D, in which is fixed a nut, so that by s.c.r.e.w.i.n.g up or uns.c.r.e.w.i.n.g 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.

A cut of 1/8 inch deep, that is, reducing the work diameter 1/4 inch, may readily be taken with this tool, which, however, requires skilful handling to prevent it from digging into the work.

The shorter the distance from the face E to the heel F the more easily the tool can be controlled; hence, as F serves simply as a sharp and gripping fulcrum it need not project much from the body of the steel; indeed, in many cases it is omitted altogether, the bottom of the steel bar being slightly hollowed out instead. No oil or water is required with the heel tool.

The hand rest should be so adjusted for height that the cutting edge of the tool stands slightly above the horizontal level of the work, a rule which obtains with all hand tools used upon wrought iron and steel.

[Ill.u.s.tration: Fig. 1285.]

The graver is the most useful of all hand turning tools, since it is applicable to all metals, and for finis.h.i.+ng as well as roughing out the work. It is formed by a square piece of steel whose end is ground at an angle, as shown in the top and the bottom view, Fig. 1285, A A being the cutting edges, C C the points, and D D the heels.

It is held in a wooden handle, which should be long enough to grasp in both hands, so that the tool may be held firmly. For cutting off a maximum of metal in roughing out the work the graver is held as in Fig.