Fig. 152
Fig. 153
A careful study of Fig. 150 will discover a simple transposition which it became necessary to make in the clocks, for the effectual adaptation of the pendulum to their regulation. The vergeVwas set up horizontally and the pendulumB, suspended freely from a flexible cord, received the impulses through the intermediation of the forked armF, which formed a part of the verge. At first this forked arm was not thought of, for the pendulum itself formed a part of the verge. A far-reaching step had been taken, but it soon became apparent that perfection was still a long way off. The crown-wheel escapement forcibly incited the pendulum to wider oscillations; these oscillations not being as Galileo had believed, of unvaried durations, but they varied sensibly with the intensity of the motive power.
Fig. 154
Huygens rendered his pendulumisochronous; that is, compelled it to make its oscillations of equal duration, whatever might be the arc described, by suspending the pendulum between two metallic curvesc c', each one formed by an arc of a cycloid and against which the suspending cord must lie upon each forward orbackward oscillation. We show this device in Fig. 151. In great oscillations, and by that we mean oscillations under a greater impulse, the pendulum would thus be shortened and the shortening would correct the time of the oscillation. However, the application of an exact cycloidal arc was a matter of no little difficulty, if not an impossibility in practice, and practical men began to grope about in search of an escapement which would permit the use of shorter arcs of oscillation. At London the horologist, G. Clement, solved the problem in 1675 with his rack escapement and recoil anchor. In the interval other means were invented, especially the addition of a second pendulum to correct the irregularities of the first. Such an escapement is pictured in Fig. 152. The verge is again vertical and carries near its upper end two armsD D, which are each connected by a cord with a pendulum. The two pendulums oscillate constantly in the inverse sense the one to the other.
Fig. 155
We show another escapement with two pendulums in Fig. 153. These are fixed directly upon two axes, each one carrying a palletP P'and a segment of a toothed wheelD D, which produces the effect of solidarity between them. The two pendulums oscillate inversely one to the other, and one after the other receives an impulse. This escapement was constructed by Jean Baptiste Dutertre, of Paris.
Fig. 154 shows another disposition of a double pendulum. While the pendulum here is double, it has but one bob; it receives the impulse by means of a double forkF.C Crepresents the cycloidal curves and are placed with a view of correcting theinequality in the duration of the oscillations. In watches the circular balances did not afford any better results than the regulating rods or rules of the clocks, and the pendulum, of course, was out of the question altogether; it therefore became imperative to invent some other regulating system.
Fig. 156
Fig. 157
It occured to the Abbé d'Hautefeuille to form a sort of resilient mechanism by attaching one end of a hog's bristle to the plate and the other to the balance near the axis. Though imperfect in results, this was nevertheless a brilliant idea, and it was but a short step to replace the bristle with a straight and very flexible spring, which later was supplanted by one coiled up like a serpent; but in spite of this advancement, the watches did not keep much better time. Harrison, the celebrated English horologist, had recourse to two artifices, of which the one consisted in giving to the pallets of the escapement such a curvature that the balance could be led back with a velocity corresponding to the extension of the oscillation; the second consisted of an accessory piece, the resultant action of which was analogous to that of the cycloidal curves in connection with the pendulum.
Fig. 158
Huygens attempted to correct these irregularities in the verge escapement in watches by amplifying the arc of oscillation of the balance itself. He constructed for that purpose a pirouette escapement shown in Fig. 155, in which a toothed wheelAadjusted uponthe vergeVserves as an intermediary between that and the balanceB, upon the axis of which was fixed a pinionD. By this method he obtained extended arcs of vibration, but the vibrations were, as a consequence, very slow, and they still remained subject to all the irregularities arising from the variation in the motive power as well as from shocks. A little later, but about the same epoch, a certain Dr. Hook, of the Royal Society of London, contrived another arrangement by means of which he succeeded, so it appeared to him at least, in greatly diminishing the influence of shock upon the escapement; but many other, perhaps greater, inconveniences caused his invention to be speedily rejected. We shall give our readers an idea of what Dr. Hook's escapement was like.
Fig. 159
On looking at Fig. 156 we see the escape wheelR, which was flat and in the form of a ratchet; it was provided with two balances.B Bengaging each other in teeth, each one carrying a palletP P'upon its axis; the axes of the three wheels being parallel. Now, in our drawing, the toothaof the escape wheel exerts its lift upon the palletP'; when this tooth escapes the toothbwill fall upon the palletP'on the opposite side, a recoil will be produced upon the action of the two united balances, then the toothbwill give its impulse in the contrary direction. Considerable analogy exists between this form of escapement and that shown in Fig. 153 and intended for clocks. This was the busy era in the watchmaker's line. All the great heads were pondering upon the subject and everyone was on thequi vivefor the newest thing in the art.
In 1674 Huygens brought out the first watch having a regulating spring in the form of a spiral; the merit of this invention was disputed by the English savant, Dr. Hook, who pretended, asdid Galileo, in the application of the pendulum, to have priority in the idea. Huygens, who had discovered and corrected the irregularities in the oscillations of the pendulum, did not think of those of the balance with the spiral spring. And it was not until the close of the year 1750 that Pierre Le Roy and Ferdinand Berthoud studied the conditions of isochronism pertaining to the spiral.
However that may be, this magnificent invention, like the adaptation of the pendulum, was welcomed with general enthusiasm throughout the scientific world: without spiral and without pendulum, no other escapement but the recoil escapement was possible; a new highway was thus opened to the searchers. The water clocks (clepsydræ) and the hour glasses disappeared completely, and the timepieces which had till then only marked the hours, having been perfected up to the point of keeping more exact time, were graced with the addition of another hand to tell off the minutes.
Fig. 160
Fig. 161
It was not until 1695 that the firstdead-beat escapementappeared upon the scene; during the interval of over twenty years all thought had been directed toward the one goal, viz.: the perfecting of theverge escapement; but practice demonstrated that no other arrangement of the parts was superior to the original idea. For the benefit of our readers we shall give a few of these attempts at betterment, and you may see for yourselves wherein the trials failed.
Fig. 157 represents averge escapementwith a ratchet wheel, the palletsP P'being carried upon separate axes. The two axes are rigidly connected, the one to the other, by means of the armso o'. One of the axes carries besides the forkF, which transmits theimpulse to the pendulumB. In the front view, at the right of the plate, for the sake of clearness the fork and the pendulum are not shown, but one may easily see the jointure of the armso o'and their mode of operation.
Another very peculiar arrangement of theverge escapementwe show at Fig. 158. In this there are two wheels, one,R', a small one in the form of a ratchet; the other,R, somewhat larger, called the balance wheel, but being supplied with straight and slender teeth. The vergeVcarrying the two pallets is pivoted in the vertical diameter of the larger wheel. The front view shows themodus operandiof this combination, which is practically the same as the others. The toothaof the large wheel exerts its force upon the palletP, and the toothbof the ratchet will encounter the palletP'. This pallet, after suffering its recoil, will receive the impulse communicated by the toothb. This escapement surely could not have given much satisfaction, for it offers no advantage over the others, besides it is of very difficult construction.
Fig. 162
Fig. 163
Much ingenuity to a worthy end, but of little practical value, is displayed in these various attempts at the solution of a very difficult problem. In Fig. 159 we have a mechanism combining two escape wheels engaging each other in gear; of the two wheels,R R', one alone is driven directly by the train, the other being turned in the opposite direction by its comrade. Both are furnished with pinsc c', which act alternately upon the palletsP P'disposed in the same plane upon the vergeVand pivoted between the wheels. Our drawing represents the escapement at the moment when the pinC'delivers its impulse, and this having been accomplished, the lockingtakes place upon the pinCof the other wheel upon the palletP'. Another system of two escape wheels is shown in Fig. 160, but in this case the two wheelsR Rare driven in a like direction by the last wheelAof the train. The operation of the escapement is the same as in Fig. 159.
Fig. 164
Fig. 165
In Fig. 161 we have a departure from the road ordinarily pursued. Here we see an escapement combining two levers, invented by the Chevalier de Béthune and applied by M. Thiout, master-horologist, at Paris in 1727.P P'are the two levers or pallets separately pivoted. Upon the axisV, of the leverP, is fixed a fork which communicates the motion to the pendulum. The two levers are intimately connected by the two armsB B', of which the former carries an adjusting screw, a well-conceived addition for regulating the opening between the pallets. The counter-weightCcompels constant contact between the armsB B'. The function is always the same, the recoil and the impulsion operate upon the two pallets simultaneously. This escapement enjoyed a certain degree of success, having been employed by a number of horologists who modified it in various ways.
Some of these modifications we shall show. For the first example, then, let Fig. 162 illustrate. In this arrangement the fork is carried upon the axis of the palletP', which effectually does away with the counter-weightC, as shown. Somewhat more complicated, but of the same intrinsic nature, is the arrangement displayed in Fig. 163. We should not imagine that it enjoyed a very extensive application. Here the two levers are completely independent of each other; they act upon the pieceB Bupon the axisVof the fork. The counter-weightsC C'maintain the armscarrying the rollersD D'in contact with the pieceB B'which thus receives the impulse from the wheelR. Two adjusting screws serve to place the escapement upon the center. By degrees these fantastic constructions were abandoned to make way for the anchor recoil escapement, which was invented, as we have said, in 1675, by G. Clement, a horologist, of London. In Fig. 164 we have the disposition of the parts as first arranged by this artist. Here the pallets are replaced by the inclinesAandBof the anchor, which is pivoted atVupon an axis to which is fixed also the fork. The toothaescapes from the incline or leverA, and the toothbimmediately rests upon the leverB; by the action of the pendulum the escape wheel suffers a recoil as in the pallet escapement, and on the return of the pendulum the toothcgives out its impulse in the contrary direction. With this new system it became possible to increase the weight of the bob and at the same time lessen the effective motor power. The travel of the pendulum, or arc of oscillation, being reduced in a marked degree, an accuracy of rate was obtained far superior to that of the crown-wheel escapement. However, this new application of the recoil escapement was not adopted in France until 1695.
Fig. 166
Fig. 167
The travel of the pendulum, though greatly reduced, still surpassed in breadth the arc in which it is isochronous, and repeated efforts were made to give such shape to the levers as would compel its oscillation within the arc of equal time; a motion which is, as was recognized even at that epoch, the prime requisite to a precise rating. Thus, in 1720, Julien Leroy occupied himself working out the proper shapes for the inclines to produce this desired isochronism. Searching along the same path, Ferd. Berthoud constructed anescapement represented by the Fig. 165. In it we see the same inclinesA Bof the former construction, but the locking is effected against the slidesCandD, the curved faces of which produce isochronous oscillations of the pendulum. The toothbimparts its lift and the toothcwill lock against the faceC; after having passed through its recoil motion this toothcwill butt against the inclineAand work out its lift or impulse upon it.
Fig. 168
Fig. 169
Thegable escapement, shown in Fig. 166, allows the use of a heavier pendulum, at the same time the anchor embraces within its jaws a greater number of the escape-wheel teeth; an arrangement after this manner leads to the conclusion that with these long levers of the anchor the friction will be considerably increased and the recoil faces will, as a consequence, be quickly worn away. Without doubt, this was invented to permit of opening and closing the contact points of the anchor more easily. Under the name of theEnglish recoil anchorthere came into use an escapement with areduced gable, which embraced fewer teeth between the pallets or inclines; we give a representation of this in Fig. 167. This system seems to have been moderately successful. The anchor recoil escapement in use in Germany to-day is demonstrated in Fig. 168; this arrangement is also found in the American clocks. As we see, the anchor is composed of a single piece of curved steel bent to the desired curves. Clocks provided with this escapement keep reasonably good time; the resistance of the recoils compensate in a measure for the want of isochronism in the oscillations of the pendulum. Ordinary clocks require considerably more power to drive them than finer clocks and, as a consequence, their tickingis very noisy. Several means have been employed to dampen this noise, one of which we show in Fig. 169.
Fig. 170
Here the anchor is composed of two pieces,A B, screwed upon a plateHpivoting atV. In their arrangement the two pieces represent, as to distance and curvature, the counterpart of Fig. 168. At the moment of impact their extreme ends recoil or spring back from the shock of the escape teeth, but the resiliency of the metal is calculated to be strong enough to return them immediately to the contact studse e.
As a termination to this chapter, we shall mention the use made at the present day of the recoil lever escapement in repeating watches. We give a diagram of this construction in Fig. 170. The lever here is intended to restrain and regulate the motion of the small striking work. It is pivoted atVand is capable of a very rapid oscillatory motion, the arc of which may, however, be fixed by the stud or stopD, which limits the swing of the flyC. This fly is of one piece with the lever and, together with the studD, determines the angular motion of the lever. If the angle be large that means the path of the fly be long, then the striking train will move slowly; but if the teeth of the escape wheelRcan just pass by without causing the lever to describe a supplementary or extended arc, the striking work will run off rapidly.
Putting in a new cylinder is something most watchmakers fancy they can do, and do well; but still it is a job very few workmen can do and fulfill all the requirements a job of this kind demands under the ever-varying conditions and circumstances presented in repairs of this kind. It is well to explain somewhat at this point: Suppose we have five watches taken in with broken cylinders. Out of this number probably two could be pivoted to advantage and make the watches as good as ever. As to the pivoting of a cylinder, we will deal with this later on. The first thing to do is to make an examination of the cylinder, not only to see if it is broken, but also to determine if pivoting is going to bring it out all right. Let us imagine that some workman has, at some previous time, put in a new cylinder, and instead of putting in one of the proper size he has put one in too large or too small. Now, in either case he would have to remove a portion of the escape-wheel tooth, that is, shorten the tooth: because, if the cylinder was too large it would not go in between the teeth, and consequently the teeth would have to be cut or stoned away. If the cylinder was too small, again the teeth would have to be cut away to allow them to enter the cylinder. All workmen have traditions, rules some call them, that they go by in relation to the right way to dress a cylinder tooth; some insisting that the toe or point of the tooth is the only place which should be tampered with. Other workmen insist that the heel of the tooth is the proper place. Now, with all due consideration, we would say that in ninety-nine cases out of a hundred the proper thing to do is to let the escape-wheel teeth entirely alone. As we can understand, after a moment's thought, that it is impossible to have the teeth of the escape wheel too long and have the watch run at all; hence, the idea of stoning a cylinder escape-wheel tooth should not be tolerated.
It will not do, however, to accept, and take it for granted that the escape-wheel teeth are all right, because in many instances they have been stoned away and made too short; but if we accept thiscondition as being the case, that is, that the escape-wheel teeth are too short, what is the workman going to do about it? The owner of the watch will not pay for a new escape wheel as well as a new cylinder. The situation can be summed up about in this way, that we will have to make the best we can out of a bad job, and pick out and fit a cylinder on a compromise idea.
In regard to picking out a new cylinder, it may not do to select one of the same size as the old one, from the fact that the old one may not have been of the proper size for the escape wheel, because, even in new, cheap watches, the workmen who "run in" the escapement knew very well the cylinder and escape wheel were not adapted for each other, but they were the best he had. Chapter II, on the cylinder escapement, will enable our readers to master the subject and hence be better able to judge of allowances to be made in order to permit imperfect material to be used.
In illustration, let us imagine that we have to put in a new cylinder, and we have none of precisely the proper size, but we have them both a mere trifle too large and too small, and the question is which to use. Our advice is to use the smaller one if it does not require the escape-wheel teeth to be "dressed," that is, made smaller. Why we make this choice is based on the fact that the smaller cylinder shell gives less friction, and the loss from "drop"—that is, side play between the escape-wheel teeth and the cylinder—will be the same in both instances except to change the lost motion from inside to outside drop.
In devising a system to be applied to selecting a new cylinder, we meet the same troubles encountered throughout all watchmakers' repair work, and chief among these are good and convenient measuring tools. But even with perfect measuring tools we would have to exercise good judgment, as just explained. In Chapter II we gave a rule for determining the outside diameter of a cylinder from the diameter of the escape wheel; but such rules and tables will, in nine instances out of ten, have to be modified by attendant circumstances—as, for instance, the thickness of the shell of the cylinder, which should be one-tenth of the outer diameter of the shell, but the shell is usually thicker. A tolerably safe practical rule and one also depending very much on the workman's good judgment is, when the escape-wheel teeth have been shortened, to select a cylinder giving ample clearance inside the shell to the tooth, but by no means large enough to fill the space between the teeth.After studying carefully the instructions just given we think the workman will have no difficulty in selecting a cylinder of the right diameter.
Fig. 171
The next thing is to get the proper heights. This is much more easily arrived at: the main measurement being to have the teeth of the escape wheel clear the upper face of the lower plug. In order to talk intelligently we will make a drawing of a cylinder and agree on the proper names for the several parts to be used in this chapter. Such drawing is shown at Fig. 171. The names are: The hollow cylinder, made up of the partsA A' A'' A''', called the shell—Ais the great shell,A'the half shell,A''the banking slot, andA'''the small shell. The brass partDis called the collet and consists of three parts—the hairspring seatD, the balance seatD'and the shoulderD'', against which the balance is riveted.
The first measurement for fitting a new cylinder is to determine the height of the lower plug face, which corresponds to the linexx, Fig. 171. The height of this face is such as to permit the escape wheel to pass freely over it. In selecting a new cylinder it is well to choose one which is as wide at the banking slotA''as is consistent with safety. The width of the banking slot is represented by the dotted linesx u. The dotted linevrepresents the length to which the lower pivotyis to be cut.
Fig. 172
Fig. 173
There are several little tools on the market used for making the necessary measurements, but we will describe a very simple one which can readily be made. To do so, take about a No. 5 sewing needle and, after annealing, cut a screw thread on it, as shown at Fig, 172, whereErepresents the needle andt tthe screw cut upon it. After the screw is cut, the needle is again hardened and tempered to a spring temper and a long, thin pivot turned upon it. The needle is now shaped as shown at Fig. 173. The pivot atsshould be small enough to go easily through the smallest hole jewel to be found in cylinder watches, and should be about 1/16" long. The part atrshould be about 3/16" long andonly reduced in size enough to fully remove the screw threads shown att.
Fig. 174
Fig. 175
Fig. 176
Fig. 177
We next provide a sleeve or guard for our gage. To do this we take a piece of hard brass bushing wire about 1/2" long and, placing it in a wire chuck, center and drill it nearly the entire length, leaving, say, 1/10" at one end to be carried through with a small drill. We show atF, Fig. 174, a magnified longitudinal section of such a sleeve. The pieceFis drilled from the endlup to the lineqwith a drill of such a size that a female screw can be cut in it to fit the screw on the needle, andFis tapped out to fit such a screw fromlup to the dotted linep. The sleeveFis run on the screwtand now appears as shown at Fig. 175, with the addition of a handle shown atG G'. It is evident that we can allow the pivotsto protrude from the sleeveFany portion of its length, and regulate such protrusion by the screwt. To employ this tool for getting the proper length to which to cut the pivoty, Fig. 171, we remove the lower cap jewel to the cylinder pivot and, holding, the movement in the left hand, pass the pivots, Fig. 175, up through the hole jewel, regulate the length by turning the sleeveFuntil the arm of the escape wheelI, Fig. 176, will just turn free over it. Now the length of the pivots, which protrudes beyond the sleeveF, coincides with the length to which we must cut the pivoty, Fig. 171. To hold a cylinder for reducing the length of the pivoty, we hold said pivot in a pair of thin-edged cutting pliers, as shown at Fig. 177, whereN N'represent the jaws of a pair of cutting pliers andythe pivot to be cut. The measurement is made by putting the pivotsbetween the jawsN N'as they hold the pivot. The cutting is done by simply filing back the pivot until of the right length.
We have now the pivotyof the proper length, and what remains to be done is to turn it to the right size. We do not think it advisable to try to use a split chuck, although we have seen workmen drive the shellA A'''out of the colletDand then turn up the pivotsy zin said wire chuck. To our judgment there isbut one chuck for turning pivots, and this is the cement chuck provided with all American lathes. Many workmen object to a cement chuck, but we think no man should lay claim to the name of watchmaker until he masters the mystery of the cement chuck. It is not such a very difficult matter, and the skill once acquired would not be parted with cheaply. One thing has served to put the wax or cement chuck into disfavor, and that is the abominable stuff sold by some material houses for lathe cement. The original cement, made and patented by James Bottum for his cement chuck, was made up of a rather complicated mixture; but all the substances really demanded in such cement are ultramarine blue and a good quality of shellac. These ingredients are compounded in the proportion of 8 parts of shellac and 1 part of ultramarine—all by weight.
The shellac is melted in an iron vessel, and the ultramarine added and stirred to incorporate the parts. Care should be observed not to burn the shellac. While warm, the melted mass is poured on to a cold slab of iron or stone, and while plastic made into sticks about 1/2" in diameter.
Fig. 178
Fig. 179
We show at Fig. 178 a side view of the outer end of a cement chuck with a cylinder in position. We commence to turn the lower pivot of a cylinder, allowing the pivotzto rest at the apex of the hollow conea, as shown. There is something of a trick in turning such a hollow cone and leaving no "tit" or protuberance in the center, but it is important it should be done. A little practice will soon enable one to master the job. A graver for this purpose should be cut to rather an oblique point, as shown atL, Fig. 179. The slope of the sides to the recessa, Fig. 178, should be to about forty-five degrees, making the angle ataabout ninety degrees. The only way to insure perfect accuracy of centering of a cylinder in a cement chuck is center by the shell, which is done by cutting a piece of pegwood to a wedge shape and letting it rest on the T-rest; then hold the edge of the pegwood to the cylinder as the lathe revolves and the cement soft and plastic. A cylinder so centered will be absolutely true. The outline curve atc, Fig. 178, represents the surface of the cement.
The next operation is turning the pivot to the proper size to fit the jewel. This is usually done by trial, that is, trying the pivot into the hole in the jewel. A quicker way is to gage the hole jewel and then turn the pivot to the right size, as measured by micrometer calipers. In some cylinder watches the end stone stands at some distance from the outer surface of the hole jewel; consequently, if the measurement for the length of the pivot is taken by the tool shown at Fig. 175, the pivot will apparently be too short. When the lower end stone is removed we should take note if any allowance is to be made for such extra space. The trouble which would ensue from not providing for such extra end shake would be that the lower edge of the half shell, shown ate, Fig. 171, would strike the projection on which the "stalk" of the tooth is planted. After the lower pivot is turned to fit the jewel the cylinder is to be removed from the cement chuck and the upper part turned. The measurements to be looked to now are, first, the entire length of the cylinder, which is understood to be the entire distance between the inner faces of the two end stones, and corresponds to the distance between the linesv d, Fig. 171. This measurement can be got by removing both end stones and taking the distance with a Boley gage or a douzieme caliper.
Fig. 180
A pair of common pinion calipers slightly modified makes as good a pair of calipers for length measurement as one can desire. This instrument is made by inserting a small screw in one of the blades—the head on the inner side, as shown atf, Fig. 180. The idea of the tool is, the screw headfrests in the sink of the cap jewel or end stone, while the other blade rests on the cock over the balance. After the adjusting screw to the caliper is set, the spring of the blades allows of their removal. The top pivotzof the cylinder is next cut to the proper length, as indicated by the space between the screwheadfand the other blade of the pinion caliper. The upper pinionzis held in the jaws of the cutting pliers, as shown in Fig. 177, the same as the lower one was held, until the proper length between the linesd v, Fig. 171, is secured, after which the cylinder is put back into the cement chuck, as shown at Fig. 178, except this time the top portion of the cylinder is allowed to protrude so that we can turn the top pivot and the balance colletD, Fig. 171.
The sizes we have now to look to is to fit the pivotzto the top hole jewel in the cock, also the hairspring seatDand balance seatD'. These are turned to diameters, and are the most readily secured by the use of the micrometer calipers to be had of any large watchmakers' tool and supply house. In addition to the diameters named, we must get the proper height for the balance, which is represented by the dotted lineb. The measurement for this can usually be obtained from the old cylinder by simply comparing it with the new one as it rests in the cement chuck. The true tool for such measurements is a height gage. We have made no mention of finishing and polishing the pivots, as these points are generally well understood by the trade.
One point perhaps we might well say a few words on, and this is in regard to removing the lathe cement. Such cement is usually removed by boiling in a copper dish with alcohol. But there are several objections to the practice. In the first place, it wastes a good deal of alcohol, and also leaves the work stained. We can accomplish this operation quicker, and save alcohol, by putting the cylinder with the wax on it in a very small homeopathic bottle and corking it tight. The bottle is then boiled in water, and in a few seconds the shellac is dissolved away. The balance to most cylinder watches is of red brass, and in some instances of low karat gold; in either case the balance should be repolished. To do this dip in a strong solution of cyanide of potassium dissolved in water; one-fourth ounce of cyanide in half pint of water is about the proper strength. Dip and rinse, then polish with a chamois buff and rouge.
Fig. 181
In staking on the balance, care should be observed to set the banking pin in the rim so it will come right; this is usually secured by setting said pin so it stands opposite to the opening in the half shell. The seat of the balance on the colletDshould be undercut so that there is only an edge to rivet down on the balance. This will be better understood by inspecting Fig. 181, where we show a vertical section of the colletDand cylinderA. Atg gis shown the undercut edge of the balance seat, which is folded over as the balance is rivetted fast.
About all that remains now to be done is to true up the balance and bring it to poise. The practice frequently adopted to poise aplain balance is to file it with a half-round file on the inside, in order not to show any detraction when looking at the outer edge of the rim. A better and quicker plan is to place the balance in a split chuck, and with a diamond or round-pointed tool scoop out a little piece of metal as the balance revolves. In doing this, the spindle of the lathe is turned by the hand grasping the pulley between the finger and thumb. The so-called diamond and round-pointed tools are shown ato o', Fig. 182. The idea of this plan of reducing the weight of a balance is, one of the toolsois rested on the T-rest and pressed forward until a chip is started and allowed to enter until sufficient metal is engaged, then, by swinging down on the handle of the tool, the chip is taken out.
Fig. 182
Fig. 183
In placing a balance in a step chuck, the banking pin is caused to enter one of the three slots in the chuck, so as not to be bent down on to the rim of the balance. It is seldom the depth between the cylinder and escape wheel will need be changed after putting in a new cylinder; if such is the case, however, move the chariot—we mean the cock attached to the lower plate. Do not attempt to change the depth by manipulating the balance cock. Fig. 183 shows, ath h, the form of chip taken out by the toolo o', Fig. 182.