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Watch Repair - Balances And Hairsprings, Adjusting And Timing

( Originally Published 1918 )

A Balance is a fly-wheel, and may be circular or any other shape; it may run true or not. The one essential is that it must be in perfect poise; that is, it must have no- heavy part, and when rested on the straight edges of a poising tool it must have no tendency to settle in any one position. It is an advantage to have as much of the weight of a balance as possible in its outer rim. It is also an advantage, principally for the sake of appearance and for convenience, that a balance should be circular and should run fairly true.

Balances may be plain or compensated. Plain balances are made of gold (so as to be non-corrosive and keep clean), brass, or steel. They generally have three light arms and a true circular rim.

Temperature Error.—A balance is controlled by its attached hairspring, and the time of its vibrations depends upon the strength of the hairspring. A strong spring will cause rapid vibration, and a weak spring a slow motion. Both hairspring and balance are affected by changes in the temperature. The balance expands as it is warmed, and contracts as it is cooled. When it expands the arms lengthen and the rim increases in size, removing the weight further from its centre and causing it to move more slowly. When a spring is warmed it loses some of its force, also causing the balance to move more slowly. The combined effect of a change of temperature of 45°Fahr. (from the cold of a bedroom dressing-table to a warm waistcoat pocket, say from 40 to 85°) is to cause an uncompensated watch to lose several minutes per day. Temperature also affects the depths a little by causing the wheels to expand; it alters the strength of the mainspring, and affects the fluidity of the oil. The combined effect of all these is the "temperature error" of the particular watch in question, and varies in each individual watch. Therefore machine-made watches cannot be turned out " compensated," but each one must be finally adjusted by itself.

Compensation Balance.—The net result of a change of temperature is to cause a serious loss in heat and a gain in cold. To counteract this the compensation balance is used. Fig. 147 shows the construction of an ordinary compensation balance. It is a circular rim with a steel crossbar. The rim is bi-metallic, being steel inside and brass outside, and cut through at two opposite points. Brass is more affected by heat than steel, and in a rise of the temperature the outer brass will lengthen more than the inside steel. The effect of this is to curve each half of the rim inwards and bring the weight of the balance as a whole nearer to its centre. This causes the watch to go faster, and, if the amount of the inward movement of the rim is exactly sufficient, will compensate the tendency of the watch to lose. These balances are weighted by screws fitted in a series of tapped holes all round the rim. By moving the screws nearer to the free ends of the two segments of the rim the effect of the balance is increased ; by moving them towards the fixed portions the effect is diminished. Therefore adjusting for temperature consists in trying the watch in cold, then in heat, and moving the screws according to the performance of the watch, until its rate in cold (40 to 50°) is equal to its rate in heat (80 to 90 degrees).

In Fig. 147 there will be noticed four screws at equal distances from each other, with long taps. These are the "quarter screws." They are never moved for temperature adjustment, but are for poising the balance or for small timing alterations. Drawing one out a little makes that part of the rim heavier. Drawing out an opposite pair will slow the watch. Turning a pair in will make it go faster. In the best balances " quarter nuts" are fitted instead of screws. Fig. 148 shows a quarter nut. It is a gold nut, turning on a fixed steel screw, and is not so liable to work loose as a plain quarter screw from frequent turnings. A quarter nut is split, and slightly sprung on to its screw to move firmly and not get loose. To turn these nuts a split screwdriver blade like A (Fig. 148) is used.

In making a compensation balance, a steel disc is turned up true, with a central hole. It is then covered with molten brass, which adheres to it all over. The brass is filed off the flat sides of the disc and the central hole cleared ; then the surplus brass is turned off the edge, leaving the thickness required. It is hammer-hardened and turned smooth. The interior of the balance is cut out by turning and filing, leaving the crossbar; the rim is drilled and tapped in a dividing engine, and finally cut through at two opposite points, after being mounted upon its staff by the escapement maker.

When a balance is cut the unequal hardness of the brass and steel composing its rim generally causes the two segments to go out of truth. They are trued by removing all the screws and putting in the turns to note where they depart from the circle, and bending with the fingers as far as possible or with brass pliers, Absolute truth looks very nice, but is not essential.

Compensation balances that have been running some time generally go a little out, and, so long as they can be poised by means of the quarter screws, are best left alone. The only way to true them is to remove all the screws. Before doing this it is best to make a sketch of the balance rim, noting the position of the screws, so as to replace them as before.

A watch with an uncut compensation balance is no better than one with a plain balance; but if the balance be cut and trued as described it will be greatly improved. A watch with a cut compensation balance, not specially adjusted, like the great majority of ordinary watches, is cured of most of its temperature error, and may generally be depended upon not to vary more than 30) secs. from its rate in one day between 40 and 85°. An adjusted watch is one with a compensation balance cut, and the screws arranged by trial to reduce the error to about 2 secs. per day or less.

Its outer end is pinned into a fixed stud and its inner end into a collet.

The stud may be a small square of brass fixed in the watch plate, as in some English full plates, a small square of brass pushed friction tight into the balance cock, as in many Genevas, or a steel stud screwed to the plate or the balance cock, as in the best English levers, American and Swiss watches, The collet is in most watches a small brass circle turned to fit the balance staff friction tight, and split to give it a certain amount of spring, as in Fig. 149. A better form of collet, used in the best English levers, is that shown in Fig. 150). It is a circle of steel, hardened and tempered, made to accurately fit the staff. It has two flats filed upon it, making it nearly oblong. Such a collet goes on more truly, and is not liable to become damaged; it also allows the hairspring to be trued in the centre more easily.

The spring itself is of steel wire, ribbon-shaped, drawn hard, and coiled up into a close spiral. The closeness of the coils depends upon how many are coiled up together. Thus, if three lengths of wire are coiled up together, when released the resulting spirals will be rather open. If two are treated together the coils will be closer. If only one is coiled up on itself the coils will be very close and nearly touch. The closer a spring is coiled the longer it is for a given diameter.

The strength of a spring depends on its thickness and width —that is, its stiffness—and its length. Hairsprings are sold in small packets, numbered according to their strength in a series of numbers which differ with each maker, and are only useful to compare one spring with another of the same make. It is, therefore, best in hairsprings to keep to one make only for ordinary quality springs, and to send specially for one of extra good quality when required.

To select a new hairspring, the number of beats required in an hour must first be known. This is termed the "train" of the watch. Most watches have 18,000, 16,200, or 14,400 trains; that is, they make that number of beats in one hour. All Genevas and American watches have 18,000 trains. Old English watches often have 14,400 trains, and many more recent ones 16,200, or 15,400. But it is probable that all watches in the future will be made 18,000.

The train of a watch can be ascertained by multiplying the numbers of teeth in the centre, third, fourth, and scape wheels, and dividing the result by the third, fourth, and scape pinions. Twice this number is the train.

It will be noticed that in all these trains the fourth wheel makes one revolution per minute ; and when the fourth wheel has ten times as many teeth as the scape pinion, the train is 18,000; when nine times, the train is 16,200; and when eight times, the train is 14,400.

In counting vibrations when fitting hairsprings, double vibrations only are counted, thus each time the balance comes to the left is counted one. In this way an 18,000 train counts 75 in half a minute; a 16,200, 67 ; and a 14,400, 60); or in proportion for twenty seconds or a full minute.

Pick out a spring that is a little too large in diameter to lie in the curb pins of the index. Lay the spring on the balance and press the collet down upon it to temporarily hold it in place. Hold the end in tweezers and let the balance hang down with its lower pivot resting on a watch glass. With a turn of the fingers and tweezers, set the balance vibrating about half a turn each way, or more. Then hold it perfectly still and steady and it will continue to vibrate for a full minute. The vibrations can be counted for twenty seconds to see if it is anywhere near what is required. Fig. 151 shows how the spring and balance are held. If the balance moves too slowly, select a stronger spring, if too fast, a weaker one, and try again. The spring should be held in the tweezers at the exact point at which it will have to be pinned in its stud ; thus, if the spring is two coils too large to go in the curb pins, it must be counted while held two coils from the end.

Finally, select one that counts one double beat slow in a full minute. Lay this on a convex watch glass on white paper, and with tweezers and a needle point, or two pairs of tweezers, break out short pieces (about 1/4 turn) at a time from the "eye" or inner coil, gradually enlarging the central opening until it will go easily over the collet with a little A room to spare. Then bend a short piece sharply inwards to pin in the collet, as in Fig. 152. For breaking out and bending springs, a needle set in a handle, filed up, and slotted as shown at A (Fig. 152) is useful.

To pin the spring in its collet, put the collet on a broach, pass the spring over the broach, and insert the end with tweezers. File up a fine burnished brass pin, and file a flat upon it, making it D-shaped. Insert this pin to see if it fits, with the flat against the spring. Cut off any that projects, and try again. Cut off the end until the pin goes in half-way through the hole. Then lay the pin on the filing block (still in the pin vice), and half cut it through with a knife ; insert it finally, and break it off in the hole. With very strong tweezers press the pin well home. A hairspring must be pinned tight in its collet, or nothing can be done with it. When pinned in, put the collet and spring on a turning arbor in the turns and revolve with a light bow. Set it flat with tweezers so that it runs true. Note if it is true and concentric in the "eye," and in which direction it is out. Take it out and lay on the watch glass to bend true as required, try in the turns again, and so on until it is both flat and true. Put it on the balance and count for a full minute. If correct, break off the outer waste coils and pin it in the stud with a flatted pin. To set the spring central and flat on the balance cock or plate, pin it in as in Fig. 153, and bend it until the outer coil lies between the curb pins without strain, the spring stands level, and the collet is central with the jewel hole. If all these points are attended to before the spring is put in the watch at all, there will be no bending or cramping needed afterwards, and the balance and spring will go straight in, lie true and flat, be central, and free of everything.

The watch can be started and set by the seconds hand with the regulator clock. A loss or gain will be quickly seen.

If too slow, take the spring up a little and re-pin in the stud ; if too fast, let it out. It is here that the advantage of counting the spring one beat slow is found. If the balance is a compensation, or a sham one with screws, to make it go faster, a pair of screws can be reduced by filing or drawn out altogether. If too fast, a pair of screws can be added, or for a small alteration, " timing washers " can be added under the screw-heads. These are small washers stamped from thin brass sheet, and can be bought by the gross.

Balance screws can be reduced by holding in a small pin vice of the pattern shown in Fig. 154, and revolving it in the fingers as the file is passed across the screw-head. Smooth them with a 3/0 emery buff and polish with a rouge-on-leather buff. Always be careful to leave the balance in perfect poise after any alteration.

The hairspring and its collet can be removed from the balance staff by levering up with a sharp pocket-knife alternately from either side. A collet can be turned round by inserting the thin blade of an oiler into its slit and using it as a lever.

A flat hairspring should be pinned in at equal turns, as shown in Fig. 149 ; that is, it should consist of so many complete turns, finishing_ against the point where it starts from the collet. Such springs time better in good watches.

Sometimes when a flat hairspring is pinned in its collet and in its stud it will not lie flat. It is dome-shaped or cup-shaped, owing to the stud hole not being drilled level with the collet hole. In such a case the innermost coil of the spring, just where it leaves the collet, must be bent up or down as required to get the spring flat, as shown at A (Fig. 155), and the spring then set flat and true in the turns.

In some very flat Geneva watches and undersprung English levers there is very little room for a hairspring without it touching the plate, the balance arms, the stud, or the index. For these watches a spring made from specially narrow wire must be got from the hairspring makers.

To lower a collet and spring bodily, or to lower the top of a collet to prevent it fouling the balance cock, the collet, together with the spring, may be placed on an arbor and turned down. A very sharp graver must be used and light cuts.

Breguet Springs.—Fig. 153 shows a breguet or overcoil spring at A. This is perhaps the best form of hairspring for any watch. Sometimes a double overcoil is made, as at B, but apparently has no advantage. Helical or cylindrical springs, as at C, are used in marine chronometers and some pocket watches, but do not seem to perform any better than a single overcoil breguet.

Breguet springs are made from flat springs by the workman who springs the watch. For this purpose hardened and tempered hairsprings are best. These can be obtained by sending the balance to the spring maker and telling him the train. Sometimes springs of palladium wire are used, especially in non-magnetic " watches. This metal does not rust, and cannot be magnetized. Balances also are made with palladium in place of steel for the same purpose.

Having procured or selected a spring, preferably a close coiled one, with a diameter equal to half that of the balance rim, proceed to put it on like a flat spring, getting it perfectly true in the eye and flat. Count it exactly to time, and break off all surplus coils.

Unless a breguet spring is quite true in the eye it looks very bad and will not time well. When a spring is true there will be seen one coil, about midway between the outer coil and the eye, that apparently stands still. This is, of course, only an optical illusion. If a spiral be revolved in one direction, the coils all appear to run outwards; in the other direction they will all seem to go in. The " stationary coil" is merely that point at which this optical effect is exactly neutralized by the mechanical opening and closing of the spring caused by the vibration of the balance and which takes place in the opposite direction to the optical effect. How-ever, this coil should be seen in a true spring, and should apparently lie motionless. If it jumps or shakes, the eye of the spring is not quite true.

When broken down to size, take two pairs of tweezers and bend up the outer coil like Fig. 157, A. Hold the spring firmly with one pair and twist the outer coil upwards with the other pair, in a gradually ascending slant. Halfway round the raised coil it will want another twist up, to make the raised part level, as at B. Take a curved pair of tweezers, like Fig. 158, and proceed to curve the raised coil inwards by nipping it up tight. Complete the overcoil with two pairs of ordinary tweezers, to the form shown in Fig. 156, at A. See that the overcoil is quite free from the second coil at the point where it commences to curve inwards. To judge the height required for the over-coil, put the balance in the watch and see how far up the balance staff the level of the pin hole in the stud comes, by sighting it across. Raise the overcoil to this point. If the watch has an index, the last quarter turn of the overcoil must be circular, and of the same radius as the curb pins.

This can be measured with the millimetre gauge. All manipulation of the spring should be done while on a watch glass over white paper. Finally, pin the spring in its stud with a flatted pin, and drive it home hard. With a breguet spring, all timing is done by means of the balance screws, and the spring itself is not disturbed. Set it flat and true as it lies on the cock, so that it stands level and with the collet central over the jewel hole. Sight this across in two directions, as in Fig. 159. Then put it in the watch with the balance and see if it is flat and correct. If the spring is hollow the overcoil is not high enough, and must be raised a little; if domed it is too high.

A great deal has been said and written about breguet springs being pinned in at equal turns, like Fig. 160), so that the spring starts at the eye at the same point or in the same direction as it is pinned in the stud. There appears to be no real advantage in this, as breguet springs, unlike flat ones, may be pinned in anywhere, simply at haphazard, and act just as truly and nicely as at equal turns. Watches so sprung by the writer have many times obtained 80) marks and over at Kew, and taken high positions in Greenwich Admiralty trials.

Time the watch by altering the weight of the screws. Additional weight can sometimes be given by changing a pair of brass screws for a pair of gold ones, by changing common gold for good gold, or gold for platinum.

If the watch in hand is a good one, with a compensation balance, it may be desired to adjust it for temperature and positions. At all events, one thing is quite certain ; if the watch ever had been so adjusted, by the very fact of re-springing it all adjustment is gone. A new hairspring will require a fresh adjustment for temperature to suit itself, and disturbing the balance screws altogether upsets the position rates.

Good watches often require re-springing. Sometimes a little rust appears on the coils. This is fatal, as it eats further and further in, causing the watch to lose at a gradually increasing rate. Sometimes they get damaged by a careless workman or wearer. From one cause and another a repairer often is called upon to re-spring a good watch, and there is no reason why he should not re-adjust it and turn it out a credit to himself, if he will take the trouble.

Adjusting for Temperature.—When this is to be done, some sort of oven is necessary to keep the watch at about 80 to 90°. The cold can generally be managed in England. In the winter 400 to 50° is easily obtained in a workshop, too easily in fact; while our summers are not so sultry that a few days cannot be found when 55° or 60)° can be got without waiting long. With care these temperatures will serve. The oven may be a tin box set on an iron plate, and warmed underneath by being placed on brackets against a wall, about a foot, or less, over a small gas-jet. Or there are many ways that suggest themselves and are suitable to the special conditions of the workshop. A thermometer should be in the oven with the watch.

The watch, when running on time for about two days in the cold, is set by the shop regulator, and its rate noted in a rate book. It is then put in the oven for 24 hours and a comparison made. If 20 seconds slow in heat, it is under-compensated, and one or more screws should be moved several holes nearer to the free ends of the segments. If fast in heat, it is over-compensated, and screws must be moved back. Proceed thus until the watch shows an equal rate, even when tried three days in succession in cold and in the oven. It will be found that moving a pair of screws one hole will make a difference of about z seconds per day.

Timing in Positions.—When correct, poise the balance, and again bring to time within about 20 seconds per day. The next thing to do is to get the long and short arcs equal. When a watch is lying down, the balance spins on one pivot and makes a large vibration, say 1 1/2 turns. When it is placed vertically, with 12, 9, or 3 up, the balance runs on the sides of two pivots, and there is more friction. It therefore makes, say, only r f turns.

These are, therefore, the long and short arcs, and in all probability the short arcs are slower than the long ones. This is a fault of the hairspring, and the overcoil can be so shaped that the spring will cause the long and short arcs to be made in equal times.

To test the watch, note its rate lying for 24 hours (do not be tempted to make trials shorter than this, as they are misleading). Then 9 up and 3 up for 24 hours each. These two opposite quarters are tried so as to eliminate the errors caused by want of perfect poise.

Here the rate 9 up is 8 seconds faster than lying, and 3 up 8 seconds slower. The mean of the two is equal to the lying rate, showing that the long and short arcs are equal, and the difference between the two quarter positions is only a question of poising the balance by a touch of a quarter screw.

This is a more likely rate, and shows that 9 up the watch is 5 seconds slow, and 3 up 16 seconds slow. The mean is ro- seconds, which is the amount the short arcs are slow.

To correct this, the form of the overcoil is slightly altered to make it more flexible. Therefore bend the overcoil to make the curve more symmetrical, an easy flow from start to finish, with no angles or straights, is the most flexible, and will quicken the short arcs. Fig. 161 shows the overcoils of two watches that have taken Kew "A" certificates with over 80) marks, and may serve as a guide. If this does not do it sufficiently, cause the spring to open or develop more in the direction opposite to that in which it is pinned in its collet. This can be easily done by a trifling bend, quite unnoticeable, in the overcoil.

It is at this point that there is sometimes a slight advantage in having the spring pinned in at equal turns. When the overcoil is a short one, it is not so easy to cause the spring to develop in the required direction unless it is so pinned in.

With a longer overcoil or a double overcoil, this difficulty disappears.

When the mean of the short arcs equals the lying rate, correct the positions by trying 12 up, 9 up, and 3 up. A loss in any position shows that the upper part of the balance in that position is heavy. Put that quarter screw in a trifle, or draw the opposite one out. In this way the position rates can be got equal all round, unless there are escapement faults which cause errors of their own.

Such faults are, an imperfectly poised lever, worn or bent pivots, unequal endshakes of scape wheel and pallets, oval jewel holes, wide pivot holes, unequal banking shake of the lever, or sloping bent banking pins and guard pin.

Also a breguet hairspring should have no play between the curb pins. It should touch each pin, but not be nipped between them or strained by them. Watches with no index, "free sprung," time much better than those with curb pins. One troublesome source of errors is absent in them ; but a free-sprung watch that is not perfectly adjusted for temperature and in positions is a nuisance.

The method of position timing just explained is condemned by some writers as bad. They say that alterations of the quarter screws upset the poise of the balance. This is not so. The poising tool at its best is imperfect. There is a small error always present. Also the balance as poised on the tool has not the hairspring and collet on. This disturbs the poise in itself, seeing that a part of the weight of the hairspring is borne by the stud and a part by the balance, and there is no means of ascertaining how much or in what manner. The balance is poised as nearly as possible and then put in the watch. There its poising is perfected by the only possible means, viz. noting its rates in the various positions and touching the quarter screws accordingly. It has been recommended that the collet be put on the balance when poising, with its pin and a small piece of hairspring inserted as a refinement. This is absurd, as when subsequently sprung the poise is altogether upset many times by altering the balance screws to bring it to time and adjust for temperature.

A theoretical balance is one having all its weight in its rim, no friction at its pivots, and not connected in any way with an escapement. For such a balance, a mathematician can plan an overcoil for the hairspring that will make the long and short arcs equal. A number of these curves have been planned and published, and many watchmakers have copied them in the belief that they solve the difficulty. But as the theoretical balance is impossible in practice, so the theoretical curve is inapplicable. Just as friction at the pivots varies, balances have long and short staffs, and escapements differ, so the curve to obtain isochronism differs in each watch, and must be made to suit each individual case by trial.

Variations between the positions of dial up and dial down are caused by some parts of the escapement having unequal endshakes, unequal sized pivots, bent banking pins or guard pin, or it maybe a little dirt in a jewel hole.

Fig. 156, at A and B, and Fig. 160 show overcoils made for an index in which the first part of the curve is a portion of a circle. Fig. 161 shows two overcoils for watches with no index—" free sprung," as they are termed. In these no portion of the curve is necessarily circular.

If a very exact temperature adjustment is wanted, the watch should be first adjusted in heat and cold until within three or four seconds per day; then the isochronism—equal times of long and short arcs—got correct. It may then be run several-months to settle. All balances go off their temperature adjustment a little as the two metals composing the rim settle to one another. It is then readjusted for temperature, the balance finally poised, and the positions got right last of all.

It is a help to a new balance to settle quickly to warm a brass plate and lay the balance on it, to close up the rim; then to cool it by laying on very cold steel. Repeat the process half a dozen times.

Non-magnetic springs are soft and heavy. They are not so nice to handle, being liable to damage and to being bent out of shape. Their weight makes them shake about in the watch during pocket wear and foul the balance arms, the cock, the curb pins, or the stud. This affects the timekeeping. But they are very necessary in electricians' watches. Non-magnetic balances also are soft and easily bent out of truth. They often go out of truth with the mere lapse of time, and altogether upset the rate of the watch. Like the springs, they are a necessary evil.

Some Swiss watches have latterly been made with balances and springs of an alloy of nickel steel, that is claimed to be hardly affected at all by changes in temperature ; but for exact compensation they cannot yet touch the steel spring and compensation balance.

Very cheap watches with plain balances and springs of this alloy have been made, and in their class are a great advance on the same watch with a plain balance of brass and a steel spring. One use to which this alloy has been put in watch-work is to make hairsprings that require very little compensating. It is found that an ordinary balance compensates too much for them if cut as usual; but if cut at the centres of the rim, leaving four short bi-metallic arms, a stronger and stiffer balance is produced, that at the same time compensates quite enough to correct all the errors. This pattern of balance is found now on many Swiss levers.

"Invar" at one time seemed likely to effect a revolution in both watches and clocks. Pendulum rods for clocks made of it have been tested at Kew, and found to expand only 1/20 in. per mile per degree Centigrade, which is, of course, quite an inappreciable quantity; but in watches the applications of invar are still in an experimental stage, and that they will be equally far-reaching in the near future seems doubtful. Compensation balances made of invar and brass instead of steel and brass have not proved so satisfactory as was anticipated. Possibly the difference between the expansion of the two metals is too great to be stable.

Watches in which the balance comes at or about the centre of length of the balance staff have been noticed to time better and go more steadily than those in which the balance is at one end of the staff. The reason of this is not very apparent, but it is none the less true. A peculiarity the writer has found in Karrusel watches (in which the balance comes in the centre of the staff and the staff is extremely short) is that, when first sprung and tested for isochronism, the short arcs are found fast, whereas in most watches they are invariably more or less slow to begin with. An explanation of this is also wanting.

A good watch wanting a breguet spring is worth fitting with one fire hardened and tempered, although these are rather expensive, and cost from 1s. 6d. to 3s. 6d. each. For ordinary fair quality work, the usual hard drawn springs, costing about 4d, are good enough.

Repairing Hairsprings.—Geneva watches are often badly treated by their wearers. If they stop from any cause, ladies often stir them up with a pin ; the inevitable result being a bent or tangled up hairspring. To get such a spring fairly straight again is a task requiring some skill and patience. Take such a spring off the balance and lay it on a glass. Begin at the centre and follow it round, coil by coil, until the first bend or departure from truth is detected. With tweezers and needle-point correct this. Follow round further and correct, until the end is reached. Then proceed to get it flat. Do this in the same way. Begin at the centre ; hold the spring up edgeways to the light, and note where it first departs from the flat. With two pairs of tweezers, correct it as in Fig. 157, and proceed to the next point, and so on. Generally speaking, springs that look all tangled up and done for will, on close inspection, be found to have one or two sharp bends, which, when corrected, bring the spring right again as if by magic. Finally, place the collet on a turning arbor and set the spring flat in the turns; affix the stud to the cock or plate, and set it flat in the watch (without the balance), as in Figs. 153 and 159, and see that it passes between the curb pins properly, and that the collet is central with the balance holes.

A spring that has been pulled up like A, Fig. 162, may be flattened by putting the collet on a broach and pulling the stud down with tweezers in the reverse direction, as at B. One that is partly pulled up, as at A, Fig. 163, maybe treated with two pairs of tweezers, as at B, and sprung flat.

Occasionally in brushing a balance the hairspring gets tangled up, it may be round the balance rim or round its stud. If round the balance rim, lever up the collet and get it off; then turn the spring round and round until it screws off the balance rim. If round its own stud, unpin from the stud, and with a needle-point begin at the centre coil and run the needle round the spiral until the outer end is reached. This will disentangle it safely.

In many watches a shake during wear will frequently jolt the hairspring out of the curb pins, or shake the second coil over or into them. To avoid this, the curb pins should be as long as possible; or in some cases they may be bridged over by arching them at the points and bending towards each other till they touch, making a complete loop enclosing the outer coil. To replace curb pins, file the old ones off flush with the under side of the index, and lay it over a hole in a steel stake, punch them through with a needle, the point of which has been flatted on an oilstone. New curb pins should be filed up nearly straight and well burnished.

In common watches the hairspring usually has some play between the curb pins. This is a source of error, and makes the watch go slower in the hanging position than when lying down. A good watch should be allowed no play here. Each curb pin should just touch the outer coil of the spring lightly without nipping it between them.

Many old watches had plain uncompensated balances and " compensation curbs." A compensation curb was a bimetallic strip of metal, made so that its movements caused by heat and cold opened and closed the curb pins, thus keeping the watch to time. This was the earliest application of the bi-metallic principle to the compensation of watches, and has been completely superseded by the compensation balance.

From the foregoing, it will be readily understood that an "adjusted " watch takes a long time to get perfect ; and its good performance depends upon the fine adjustments of the balance spring and the poise of the balance. When such a watch has an accident and requires a new balance staff, its position rates are at once gone. Several weeks' careful rating are required to re-adjust the poise of the balance.

Careless handling of the balance or hairspring will destroy all the adjustment the watch ever had. Such watches should therefore always receive the greatest care.

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