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Watch Repair - Turning

( Originally Published 1918 )



Using the Turns.—Turning with a bow and "turns" will be first described. Fig. 32 shows a pair of Swiss turns. They are provided with "runners," which are lengths of steel or brass rod, having centres, between which the objects to be turned are placed. The work is rotated by means of a bow, as in drilling, the same bows being used. An adjustable ferrule is attached to the work. Fig. 33 shows such a ferrule. Or the work, if it has a central hole, like a watch hand or a roller, is placed upon a turning arbor like Fig. 34. The various ways of turning work and fitting up the turns for different jobs will be described later on. In this chapter the method of turning only will be considered.

Adjustable ferrules, like that shown in Fig. 33, and of other patterns also, can be bought in sets from very small sizes upwards. Also sets of turning arbors, like Fig. 34, made of hardened steel with brass ferrules attached, are sold in running sizes to take anything from a roller to a clock wheel.

The hand rest of a pair of Swiss turns, as bought, is too wide for most purposes, and is in the way. It will be best to at once cut it off at each end, as shown in Fig. 35 by the dotted lines.

The turning is done by gravers. Gravers are of hardened steel, square in section, or diamond-shaped. The diamond-shaped gravers are known as " lozenge " gravers, and are useful where a long narrow point is desired. The graver is sharpened to an angle, as shown in Fig. 36. It will be seen to have two bright sides and two black ones. The black ones should come on the top and the bright ones underneath. A graver is pre-pared for turning by first grinding its face down to the angle shown in Fig. 36. Then it is rubbed smooth and flat on an oilstone, upon the ground diamond-shaped face. When sharp up to the edges, the two bright undersides are just given two or three rubs on the stone to make the edges quite smooth. Gravers should be held in handles.

Suppose a piece of brass rod 4 in. in diameter and 4 in. long be drilled from end to end and the hole broached out tapered and smooth. This is pushed tight upon an arbor, like Fig. 34, and placed in the turns between the plain centred runners. The medium bow is used, and the turns are held in the bench vice as in Fig. 32, which shows all in position for turning. The bow is held in the left hand and the graver in the, right, resting upon the hand rest, as shown in Fig. 32. The lest should be adjusted as close to the work as possible. Fig. 38 is a view from above, showing graver point and work in position for turning the face A true. It will be noticed that the point of the graver is used for cutting, not the flat edge. Cutting is done on the down stroke of the bow. During the up stroke the graver point is eased off from the work, so as to be just free from it, by an almost imperceptible movement of the hand and wrist. The graver is not slid backwards and forwards upon the rest to free it, but is turned aside an almost immeasurable amount without actually shifting it on the hand rest.

To begin with, the face A will be out of truth and the first few cuts will be uneven and jerky, the graver point only touching the projecting parts; but after a while it will be turned true, when the graver point should take off a clean shaving, like Fig. 39. The face A being turned true and smooth, the face B, Fig. 38, is commenced, holding the graver as in Fig. 40.

To turn C, the arbor may be reversed as in Fig. 41, or the brass may be taken off the arbor and reversed. The latter method will not make the work so true as the former, as, the hole being tapered the wrong way to fit the arbor, the brass will not go on exactly as before. In reversing the arbor, as shown in Fig. 41, the bow is still held in the left hand and graver in the right. Care should be taken that oil is applied to the centres, or the arbors and turn runners will be spoiled.

Brass requires a sharp graver to cut clean and smooth, and a fairly high speed of revolution. To attain this, use a long bow, and use its entire length at each stroke.

Steel should not be turned so fast, especially tempered steel, or it will glaze and refuse to cut at all.

The graver should be applied level with the centres, that is, the graver must point to the centre of the work. If below, it will tend to spring the work up and roll it upon the graver point. This would be certain to either break the point or spring the work out of truth if it is slender. If above the centre, it will not cut. Fig. 42 shows what is meant. The graver in this figure is shown held as in Fig. 40.

Brass is the best metal to practise upon at first. When able to turn a brass cylinder smooth and true on all faces as just described, a length of soft steel may be taken in hand. A piece of steel rod 3/16 in. diameter and 1 1/2 in. long may be centred and a ferrule affixed to it. It may then be turned down to a shoulder, as in Fig. 43, A, smooth and true. Then a second shoulder may be turned, as B ; then a third and a fourth, as C. When this can be done, a similar or a smaller piece of steel may be centred, hardened and tempered blue, and treated in the same manner, continuing the shouldering and reducing process until the steel is as fine as a watch pivot. This is the best practise possible for turning, and many hours may be profitably spent in attaining proficiency in it.

The Watch Lathe.—Until about twenty years ago the turns as here described were used by all watchmakers, but since that time watch lathes have been perfected, and have made quite a revolution in the watch repairing shop.

The great disadvantage of the turns is the alternate motion and consequent break of the "cut" of the graver each time the bow is raised. The continuous motion of the lathe renders turning easier, more rapid, and more certain. Another disadvantage of the turns is that only work can be turned in them that can be placed between centres or upon an arbor. Work that required chucks to hold it, or a face plate, could not be done; hence a mandrel was required as well as turns for such work. A mandrel is a lathe having a fixed face plate for holding work and a slide rest and hand rest.

The watch lathe combines in one tool the turns and the mandrel, as well as having a multitude of chucks to hold nearly all parts of a watch. And it turns all with a continuous motion. For a young watchmaker buying his tools, it will be as cheap, and very much better, to begin by purchasing a lathe and leave the mandrel out. The many chucks with the lathe will also enable him to dispense with the pivot centring tool, the Jacot tool, and the screw-head tool. But the turns themselves cannot be altogether discarded. For many small jobs they save a great deal of time, and really cannot very well be done without. In the workshop of the up-to-date watchmaker the watch lathe and the turns should be found side by side.

There are two principal patterns of watch lathe, the American and the German. The American pattern is the larger of the two. It stands upon a pedestal foot and has a broad solid bed. Its centres are about 2 in. high, taking a 4-in. mandrel face plate, large enough for any watchwork. Where board space is available, such a lathe is the best, and it can always be erected ready for work, and be protected when not in use by a wood box-cover.

The German pattern more resembles an overgrown pair of turns, and is smaller and lighter. It is fixed in a pedestal foot, or screwed in the vice like a pair of turns. Its bed is a bar, and its centres only about 1 5/8 in. high, taking a face plate 3 1/16 in. in diameter. This is large enough for most jobs, but occasionally it is not large enough, and causes trouble. Each pattern is provided with the same kind of chucks, etc., and, except in point of size, there is not much between them.

The principal accessories to these lathes are as follows:---

A mandrel plate (Fig. 46). This is a face plate having three slots and three dogs to hold flat plates, etc., for turning on the face. In some lathes it is a separate headstock, as in Fig. 46, to ensure absolute truth; in others it is in the form of a chuck. It is provided with a "pump centre." This is a loose centre runner, by which work upon it is accurately centred from the back.

A slide rest (Fig. 47) to use in conjunction with the mandrel or any other chuck. This is provided with two slides. The lower cross slide is fixed ; the upper longitudinal slide swivels, and can be set to any angle required. A set of cutters to fit it may be bought ready made.

A wheel-cutting apparatus is made to suit most lathes. It is rather elaborate and expensive ; but a simple cutter frame that can be fixed in the tool holder of the slide rest, devised by the writer, is shown in Fig. 48. The frame is filled up from a brass casting. The arbor is tempered steel, and put in from the top, being held by the upper cock, which is adjustable and presses on the top centre only. The cutters are shaped as shown at A, and may be single-bladed "fly" cutters, filed up and hardened, shaped up when hard by polishing with oil-stone dust and oil on a steel polisher, to fit a tooth space accurately. The cutter is held by a nut screwed against it, and may be itself also screwed on, the nut being a lock nut. It is driven by a thread band from a 6-in. wood pulley on the distributing pulley axis, to get as much speed as possible. These cutters cannot be driven too fast.

A hand rest like that provided with turns, and for the same purpose.

Loose pulley runners or chucks for turning between dead centres, like Fig. 49. The centre upon which the work turns is stationary. The loose pulley and carrying arm only revolve, driving the work by a carrier affixed to it. Fig. 5o shows one of a set of such carriers.

A set of turning centres to fit the back runner.

A set of five wheel or step chucks, like Fig. 5 r, for holding wheels, barrels, covers, or other circular articles. A (Fig. 51) shows a step or wheel-chuck that has been turned down to half size. It is time well spent to buy a second set of these chucks and turn them down to the size shown at A. They can be done with the slide rest without any softening or other treatment, being about blue temper. Their special use is for holding small wheels when the pivots require turning or polishing, etc. If such wheels are placed in the full-sized wheel chucks they are buried in the chuck, and the pivot cannot be seen or got at to turn properly.

A set of split chucks (Fig. 52) for holding wire, pinions, arbors, etc. These are sized in tenths of a millimetre, from No. 4 = mm., upwards, a useful assortment being 4 to 40.

An adapter chuck and shellac chucks to fit it, for attaching parts by shellac which cannot otherwise be held conveniently.

A drill holder to fit the tail stock, with clips for standard sized watch drills.

Besides these, many other chucks and appliances are provided, some of which will be described later on as the use of them becomes apparent.

The chucks are of a peculiar pattern. They do not screw into the mandrel noze like an ordinary lathe, but fit in a plain turned seating, held by a key or feather from turning round, and drawn in by a drawing-in spindle from the back. This method answers the double purpose of ensuring absolute truth and automatically closing the chucks upon whatever work is placed in them.

A watch lathe may be driven direct by a hand wheel fixed under the board, or by a foot wheel fastened to the floor; or a foot wheel may be inverted and fastened to the underside of the board, the treadle driving by a cord on to the crank. The treadle in this case can rest upon the floor or be hooked upon the cross rail of the stool. The latter is a very nice way of working, leaving the workman seated upon his stool as usual, with both hands free and the poise of his body undisturbed.

Generally, when a foot wheel is used, the lathe is not driven direct, but through a distributing pulley placed at the back of the board. The arrangements in use are outlined in Fig. 53.

For a driving band from foot wheel to distributing pulley, grandfather clock gut does very well. From distributing pulley to lathe, vienna clock gut or cotton cord; or, when turning fine pivots by means of a small loose pulley runner, cotton does well.

A hand wheel, like that used by some for a watch lathe, can be used to drive a pair of turns, and so get a continuous motion. For this purpose Swiss turns are now often provided with a loose pulley runner. This will be found a great improvement upon the bow for many purposes; but, however the turns are improved, they will never equal the watch lathe in capacity for rapid work. No watchmaker worthy of the name should be without one.

The work in a watch lathe is held more solidly and rotated at an even speed. This enables a heavier cut to be taken, and on all work, except pivots, the back edges of the graver can be used for cutting in the same way as an engineer uses a hand tool. A graver held thus (Fig. 40) rests firmer upon its bed, and takes off a good continuous shaving.



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