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Watch Repair - The Use Of Tools

( Originally Published 1918 )

Flat Filing.--Filing is the first operation to be learned by an apprentice. To file flat and true is an art difficult to acquire, but very necessary to a good workman. Novices attempting to file often seem to imagine that a file is to be used as an emery stick, or rubbed backwards and forwards over the work with as much pressure as can be applied, until the metal is removed by abrasion.

This is fat from the truth. A file is a cutting tool, resembling very much in action a carpenter's saw. Its teeth are of the same general shape. Consequently the file only cuts one way, and that is on the outward stroke, just like the saw. Suppose a piece of brass of uneven surface to be screwed in the vice. The potance file is taken in the right hand, and the forefinger of the left is placed upon its tip to help to keep an even pressure from end to end of the stroke. The file is first carefully held level, and a forward stroke is made, with just sufficient pressure to cut freely. All the attention should be directed to keeping the file level from the commencement to the end of the stroke. When the end of the stroke is reached, the file may be lifted off the brass and drawn back for another cut, seeing that it is level before commencing again; or it may be drawn back lightly just in contact with the brass and another stroke given. This" latter method is the one generally adopted when continuous filing has to be done to reduce a piece of metal, as it has the advantage of not disturbing the level of the file so much at each stroke as lifting the file off the work does. Two or three such strokes with a sharp file should make the uneven surface of the brass flat.

The tendency of a beginner is to round the surface of the work, leaving it high in the centre. This is caused by not regulating the pressure at each end of the file. If too much pressure is applied to the file handle at the commencement of the cut, the handle will be depressed. The secret is to use hardly any downward pressure on the handle at first, tut merely to use the handle to push the file forward, exerting all the pressure needed to cut (not a great deal) by means of the finger on the file tip. At about mid stroke the pressure on file handle and file tip must be more nearly equal, and at the end of the stroke all the needful pressure is put on the handle and none on the tip. Thus, the pressure upon the file handle begins at nothing and finishes at a maximum, while the pressure of the finger on the file tip begins at a maximum and finishes at nothing. The art of automatically regulating these pressures to a nicety is the art of filing flat, and it is only to be acquired by much careful practice, taking slow and de-liberate strokes.

A good way to practise filing flat and true is to take a 1-in. length of 1/4 in. brass or steel rod and file it square throughout its length, just leaving the original surface of the round rod visible as a thin line down each corner.

Strictly speaking, a surface is either flat or it is not. There are no degrees of flatness. Judged by this standard, the man who can file flat does not live. By flat filing is meant producing a surface not visibly convex, one that will bear the application of a straightedge without the latter rocking on its centre. When a piece of metal, of the size usually operated upon by a watchmaker, has been thus filed " flat," there are several methods of making it still flatter. The metal may be laid upon a piece of cork screwed in the vice, and filed again with a file of finer cut, allowing the file to rest flat on the metal and never leave perfect contact with it. Or the metal may be laid upon the tip of the forefinger of the left hand and filed as on the cork. If too large for that, it may he held in the finger and thumb against the file. In any of these cases the principle is that the metal operated upon is made to follow the unequal motion of the file and is not rounded by it. Surfaces filed in this way are very nearly flat.

Pin Filing: Flat filing is not all that is required, as the watchmaker has also to file round pins and rods. Round is here used in the same relative sense as "flat " has been, and means passably round, not visibly oval or having flats upon it. For this purpose a pin vice is used. Into this the wire or rod is screwed, taking care that it is central and straight. In the bench vice a block of boxwood is screwed, having several grooves of various depths in it. In one of these grooves of about half its depth the wire is laid, the pin vice being held level between the thumb and forefinger of the left hand. The file is taken in the right, and as the outward or cutting stroke is made the pin vice is revolved between the thumb and finger by a twirling motion in the direction to meet the file, being given at least a complete revolution during the stroke of the file. On the back or non-cutting stroke the file is just pressed sufficiently on the pin to keep it in its groove, and the pin vice is revolved in the contrary direction. The process is repeated until the pin has been evenly tapered down from its full diamater to almost a needle point. If the revolution of the pin vice is stopped during the stroke of the file a flat will be made upon the pin. If the pin vice is not revolved sufficiently the pin will become oval. Fig. 27 shows how the pin should lie in its groove on the boxwood.

The Use of Files.—Watchmakers' files generally have one if not two " safe edges." A safe edge is plain, having no teeth cut upon it.

When filing a shoulder, as in Fig. 28, if it is desired to cut deeper and not further along the steel, the safe edge is used next the surface A; while if it is deep enough, but wants backing more at A, the file is used up on edge, the safe edge resting on the surface B.

Brass and other soft metals require a sharp new file to cut freely. A worn file will only slip over the surface and burnish the metal. On the other hand, steel, and especially tempered steel, cuts best with a worn file, one in which the extreme sharpness has been taken off the teeth. Therefore a new file should first be used for brass only, until too worn for that purpose, then it is passed on for steel use, and a new one started for brass. A rough potance file, which is only occasionally used to rapidly reduce a large piece of metal, may be chalked on one side to distinguish it, and the chalked side kept for use on brass, the other being used for steel. This insures having one sharp side for use on brass.

Steel that has been hardened and tempered requires care in filing to see that the file really cuts and does not slip. Considerable pressure is required and very slow strokes. By allowing a file to slip upon blue tempered steel, it is quite possible to so burnish and harden its surface that the file cannot be persuaded to start cutting again. Also it ruins the file to let it slip.

Drilling.—Drills are used in two ways by watchmakers. They may be held in a stock with a ferrule attached and rotated by a bow, or be placed in a lathe. The first method revolves the drill alternately in both directions ; the second gives a continuous motion in one direction only. Fig. 29 shows the arrangement used in drilling with a bow. A is the drill, fastened by a clamping screw, B, into the stock C. D is the ferrule for the bow to encircle. The centre at the ferrule end works in a centre hole in the vice jaws. The work to be drilled, E, is held up to the drill by hand only. The bow varies according to the size of drill in use. For pivot drills, the smallest, a bow of thin whalebone about 9 in. long, strung with a stout horsehair, is strong enough. A larger whale-bone bow, strung with strong thread, is used for medium drills, and for the largest clock drills a cane bow, strung with twine or gut. The bow string is given one turn around the ferrule.

This method of drilling is handy for odd jobs in which no particular truth is required ; but if anything has to be drilled straight and true, the lathe is to be preferred. Drills for use with a bow are generally sharpened on both sides, as in Fig. 30. A cutting edge of this wedge shape does not really cut; it scrapes. It simply has the advantage of cutting, or scraping, equally in both directions. Since lathes have come more into use, drills sharpened to cut only in one direction, as in Fig. 31, are common, and do for both bow and lathe. When used with a bow, these drills cut on the forward stroke and run back, not cutting at all on the back stroke. On the whole, even with a bow, they will be found to cut better than those shown in Fig. 30.

As seen in Fig. 31, the "point" of a drill is not a point, but a chisel edge; and it requires a centre to start in, or else it will wander and not start where required. This centre may be made with a centre punch, or by a pointed chamfering tool. Drills, like all pure cutting tools, require plenty of oil for lubrication when drilling ordinary metals. For drilling cast iron they may be run dry, except in the smallest sizes. For drilling tempered steel, turps is the best lubricant. Pressure greatly assists drills to cut, and as much should be applied as the drill or the work can safely stand. The moment a drill ceases to cut by reason of its edge becoming dulled it should be re-sharpened on a smooth-cut oilstone. In drilling a deep hole the drill should be constantly drawn out and cleared of cuttings, or it may choke and break in the hole. This is especially true of drilling soft metals, such as zinc, copper, soft gold, and silver, etc., also for substances like vulcanite, ivory, jet, etc.

Broaching.—Broaching requires good lubrication and constant clearing of cuttings. A broach should not be forced, but just worked with sufficient pressure to continue cutting. The smaller sizes of broaches are best held in holders or a small pin vice. The larger ones may be driven into wood handles.

Cutting Screw Threads.— Taps for cutting screw threads should not be forced, and require plenty of oil. In using a - tap, a great deal depends upon the hole being of the correct size to begin with. A hole a little too small will break the tap if much pressure is applied. A tap should be worked in very gradually. A half turn forward, then eased back to clear cuttings and allow the oil to flow; then forward another half turn, and so on. If a tap squeaks, it is a sure sign it is not cutting, and that if pressed it will break. The same remarks apply to cutting threads with a screw plate. Small screws or pins can be threaded by holding them in a pin vice. The plate is held in one hand and the pin vice in the other, and with care no strain is put upon the thread. Larger work is best fixed upright in the bench vice, while the plate is worked on with both hands to balance the strain as much as possible.

Watchmakers' screw plates, that is, sizes up to 1/16 in. diameter, generally have no cutting edges ; they only burr or force a thread upon the screw. Small screws made thus have harder and smoother threads than when cut by a true cutting plate.

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