Fig. 19
The fault we previously pointed out, of the generally accepted method of delineating a detached lever escapement, is not as conspicuous here as it is where the pallets are drawn with equidistant locking faces; that is, the inner angle of the entrance pallet (shown ats) does not have to be carried down on the arcd'as far to insure a continuous pallet action of ten degrees, as with the pallets with equidistant locking faces. Still, even here we have carried the anglesdown about half a degree on the arcd', to secure a safe lock on the exit pallet.
If we study the large drawing, where we delineate the escape wheel ten inches in diameter, it will readily be seen that although we claim one and a half degrees lock, we really have only about one degree, inasmuch as the curve of the peripheral linemdiverges from the lineB f, and, as a consequence, the absolute lock of the toothCon the locking face of the entrance palletEis but aboutone degree. Under these conditions, if we did not extend the outer angle of the exit pallet attdown to the peripheral linem, we would scarcely secure one-half a degree of lock. This is true of both pallets. We must carry the pallet angles atr s n tdown on the circlesc'' d'if we would secure the lock and impulse we claim; that is, one and a half degrees lock and eight and a half degrees impulse.
Now, while the writer is willing to admit that a one-degree lock in a sound, well-made escapement is ample, still he is not willing to allow of a looseness of drawing to incorporate to the extent of one degree in any mechanical matter demanding such extreme accuracy as the parts of a watch. It has been claimed that such defects can, to a great extent, be remedied by setting the escapement closer; that is, by bringing the centers of the pallet staff and escape wheel nearer together. We hold that such a course is not mechanical and, further, that there is not the slightest necessity for such a policy.
By making the drawings large, as we have already suggested and insisted upon, we can secure an accuracy closely approximating perfection. As, for instance, if we wish to get a lock of one and a half degrees on the locking face of the entrance palletE, we measure down on the arcc''from its intersection with the peripheral linemone and a half degrees, and establish the pointrand thus locate the outer angle of the entrance palletE, so there will really be one and a half degrees of lock; and by measuring down on the arcd'ten degrees from its intersection with the peripheral linem, we locate the points, which determines the position of the inner angle of the entrance pallet, and we know for a certainty that when this inner angle is freed from the tooth it will be after the pallet (and, of course, the lever) has passed through exactly ten degrees of angular motion.
For locating the inner angle of the exit pallet, we measure on the arcd', from its intersection with the peripheral linem, eight and a half degrees, and establish the pointn, which locates the position of this inner angle; and, of course, one and a half degrees added on the arcd'indicates the extent of the lock on this pallet. Such drawings not only enable us to theorize to extreme exactness, but also give us proportionate measurements, which can be carried into actual construction.
We will now take up the club-tooth form of the lever escapement. This form of tooth has in the United States and in Switzerland almost entirely superceded the ratchet tooth. The principal reason for its finding so much favor is, we think, chiefly owing to the fact that this form of tooth is better able to stand the manipulations of the able-bodied watchmaker, who possesses more strength than skill. We will not pause now, however, to consider the comparative merits of the ratchet and club-tooth forms of the lever escapement, but leave this part of the theme for discussion after we have given full instructions for delineating both forms.
With the ratchet-tooth lever escapement all of the impulse must be derived from the pallets, but in the club-tooth escapement we can divide the impulse planes between the pallets and the teeth to suit our fancy; or perhaps it would be better to say carry out theories, because we have it in our power, in this form of the lever escapement, to indulge ourselves in many changes of the relations of the several parts. With the ratchet tooth the principal changes we could make would be from pallets with equidistant lockings to circular pallets. The club-tooth escape wheel not only allows of circular pallets and equidistant lockings, but we can divide the impulse between the pallets and the teeth in such a way as will carry out many theoretical advantages which, after a full knowledge of the escapement action is acquired, will naturally suggest themselves. In the escapement shown at Fig. 20 we have selected, as a very excellent example of this form of tooth, circular pallets of ten degrees fork action and ten and a half degrees of escape-wheel action.
It will be noticed that the pallets here are comparatively thin to those in general use; this condition is accomplished by deriving the principal part of the impulse from driving planes placed on the teeth. As relates to the escape-wheel action of the ten and one-half degrees, which gives impulse to the escapement, five and one-half degrees are utilized by the driving planes on the teeth and five by the impulse face of the pallet. Of the ten degrees of fork action, four and a half degrees relate to the impulse face of the teeth, one and a half degrees to lock, and four degrees to the driving plane of the pallets.
In delineating such a club-tooth escapement, we commence, as in former examples, by first assuming the center of the escape wheelatA, and with the dividers set at five inches sweeping the arca a. ThroughAwe draw the vertical lineA B'. On the arca a, and each side of its intersection with the lineA B', we lay off thirty degrees, as in former drawings, and through the points so established on the arca awe draw the radial linesA bandA c. From the intersection of the radial lineA bwith the arcawe draw the lineh hat right angles toA b. Where the linehintersects the radial linesA B'is located the center of the pallet staff, as shown atB. Inasmuch as we decided to let the pallet utilize five degrees of escape-wheel action, we take a space of two and a half degrees in the dividers, and on the arca alay off the said two and a half degrees to the left of this intersection, and through the point so established draw the radial lineA g. FromBas a center we sweep the arcd dso it passes through the point of intersection of the arcawith the lineA g.
Fig. 20
We again lay off two and a half degrees from the intersection of the lineA bwith the arca, but this time to the right of said intersection, and through the point so established, and fromBas a center, we sweep the arce. From the intersection of the radial lineA gwith the arcawe lay off to the left five and a half degrees on said arc, and through the point so established draw the radial lineA f. With the dividers set at five inches we sweep the short arcmfromBas a center. From the intersection of the lineh B h'with the arcmwe lay off on said arc and above the lineh'four and a half degrees, and through the point so established draw the lineB j.
We next set the dividers so they embrace the space on the radial lineA bbetween its intersection with the lineB jand the centerA, and fromAas a center sweep the arci, said arc defining theaddendumof the escape-wheel teeth. We draw a line from the intersection of the radial lineA fwith the arcito the intersection of the radial lineA gwith the arca, and thus define the impulse face of the escape-wheel toothD. For defining the locking face of the tooth we draw a line at an angle of twenty-four degrees to the lineA g, as previously described. The back of the tooth is defined with a curve swept from some point on the addendum circlei, such as our judgment will dictate.
In the drawing shown at Fig. 20 the radius of this curve was obtained by taking eleven and a half degrees from the degree arc of 5" radius in the dividers, and setting one leg at the intersection of the radial lineA fwith the arci, and placing the other on the linei, and allowing the point so established to serve as a center, the arc was swept for the back of the tooth, the small circle atndenoting one of the centers just described. The length for the face of the tooth was obtained by taking eleven degrees from the degree arc just referred to and laying that space off on the linep, which defined the face of the tooth. The lineB kis laid off one and a half degrees belowB hon the arcm. The extent of this arc on the arcddefines the locking face of the entrance pallet. We set off four degrees on the arcmbelow the lineB k, and through the point so established draw the lineB l. We draw a line from the intersection of the lineA gwith the linec hto the intersection of the arcewith the linec l, and define the impulse face of the entrance pallet.
Before we proceed to delineate the exit pallet of our escapement, let us reason on the relations of the several parts.
The club-tooth lever escapement is really the most complicated escapement made. We mean by this that there are more factors involved in the problem of designing it correctly than in any other known escapement. Most—we had better say all, for there are no exceptions which occur to us—writers on the lever escapement lay down certain empirical rules for delineating the several parts,without giving reasons for this or that course. For illustration, it is an established practice among escapement makers to employ tangential lockings, as we explained and illustrated in Fig. 16.
Now, when we adopt circular pallets and carry the locking face of the entrance pallet around to the left two and a half degrees, the true center for the pallet staff, if we employ tangent lockings, would be located on a line drawn tangent to the circlea afrom its intersection with the radial lineA k, Fig. 21. Such a tangent is depicted at the lines l'. If we reason on the situation, we will see that the lineA kis not at right angles to the lines l; and, consequently, the locking face of the entrance palletEhas not really the twelve-degree lock we are taught to believe it has.
Fig. 21
We will not discuss these minor points further at present, but leave them for subsequent consideration. We will say, however, that we could locate the center of the pallet action at the small circleB'above the centerB, which we have selected as our fork-and-pallet action, and secure a perfectly sound escapement, with several claimed advantages.
Let us now take up the delineation of the exit pallet. It is very easy to locate the outer angle of this pallet, as this must be situated at the intersection of the addendum circleiand the arcg, and located ato. It is also self-evident that the inner or lockingangle must be situated at some point on the arch. To determine this location we draw the lineB cfromB(the pallet center) through the intersection of the archwith the pitch circlea.
Again, it follows as a self-evident fact, if the pallet we are dealing with was locked, that is, engaged with the toothD'', the inner anglenof the exit pallet would be one and a half degrees inside the pitch circlea. With the dividers set at 5", we sweep the short arcb b, and from the intersection of this arc with the lineB cwe lay off ten degrees, and through the point so established, fromB, we draw the lineB d. Below the point of intersection of the lineB dwith the short arcb bwe lay off one and a half degrees, and through the point thus established we draw the lineB e.
The intersection of the lineB ewith the arch, which we will term the pointn, represents the location of the inner angle of the exit pallet. We have already explained how we located the position of the outer angle ato. We draw the linen oand define the impulse face of the exit pallet. If we mentally analyze the problem in hand, we will see that as the exit pallet vibrates through its ten degrees of arc the lineB dandB cchange places, and the toothD''locks one and a half degrees. To delineate the locking face of the exit pallet, we erect a perpendicular to the lineB efrom the pointn, as shown by the linen p.
Fromnas a center we sweep the short arct t, and from its intersection with the linen pwe lay off twelve degrees, and through the point so established we draw the linen u, which defines the locking face of the exit pallet. We draw the lineo o'parallel withn uand define the outer face of said pallet. In Fig. 21 we have not made any attempt to show the full outline of the pallets, as they are delineated in precisely the same manner as those previously shown.
We shall next describe the delineation of a club-tooth escapement with pallets having equidistant locking faces; and in Fig. 22 we shall show pallets with much wider arms, because, in this instance, we shall derive more of the impulse from the pallets than from the teeth. We do this to show the horological student the facility with which the club-tooth lever escapement can be manipulated. We wish also to impress on his mind the facts that the employment of thick pallet arms and thin pallet arms depends onthe teeth of the escape wheel for its efficiency, and that he must have knowledge enough of the principles of action to tell at a glance on what lines the escapement was constructed.
Suppose, for illustration, we get hold of a watch which has thin pallet arms, or stones, if they are exposed pallets, and the escape was designed for pallets with thick arms. There is no sort of tinkering we can do to give such a watch a good motion, except to change either the escape wheel or the pallets. If we know enough of the lever escapement to set about it with skill and judgment, the matter is soon put to rights; but otherwise we can look and squint, open and close the bankings, and tinker about till doomsday, and the watch be none the better.
In drawing a club-tooth lever escapement with equidistant locking, we commence, as on former occasions, by producing the vertical lineA k, Fig. 22, and establishing the center of the escape wheel atA, and with the dividers set at 5" sweep the pitch circlea. On each side of the intersection of the vertical lineA kwith the arcawe set off thirty degrees on said arc, and through the points so established draw the radial linesA bandA c.
From the intersection of the radial lineA bwith the arcalay off three and a half degrees to the left of said intersection on the arca, and through the point so established draw the radial lineA e. From the intersection of the radial lineA bwith the arcaerect the perpendicular linef, and at the crossing or intersection of said line with the vertical lineA kestablish the center of the pallet staff, as indicated by the small circleB. FromBas a center sweep the short arclwith a 5" radius; and from the intersection of the radial lineA bwith the arcacontinue the linefuntil it crosses the short arcl, as shown atf'. Lay off one and a half degrees on the arclbelow its intersection with the linef', and fromBas a center draw the lineBithrough said intersection. FromBas a center, through the intersection of the radial lineA band the arca, sweep the arcg.
The space between the linesB f'andB ion the arcgdefines the extent of the locking face of the entrance palletC. The intersection of the lineB f'with the arcgwe denominate the pointo, and from this point as a center sweep the short arcpwith a 5" radius; and on this arc, from its intersection with the radial lineA b, lay off twelve degrees, and through the point so established,fromoas a center, draw the radial lineo m, said line defining the locking face of the entrance palletC.
Fig. 22
It will be seen that this gives a positive "draw" of twelve degrees to the entrance pallet; that is, counting to the lineB f'. In this escapement as delineated there is perfect tangential locking. If the locking face of the entrance-pallet stone atCwas made to conform to the radial lineA b, the lock of the toothDatowould be "dead"; that is, absolutely neutral. The toothDwould press the palletCin the direction of the arrowx, toward the center of the pallet staffB, with no tendency on the part of the pallet to turn on its axisB. Theoretically, the pallet with the locking face cut to coincide with the lineA bwould resist movement on the centerBin either direction indicated by the double-headed arrowy.
A pallet atCwith a circular locking face made to conform to the arcg, would permit movement in the direction of the double-headed arrowywith only mechanical effort enough to overcome friction. But it is evident on inspection that a locking face on the lineA bwould cause a retrograde motion of the escape wheel, and consequent resistance, if said pallet was moved in either direction indicated by the double-headed arrowy. Precisely the same conditions obtain at the pointu, which holds the same relations to the exit pallet as the pointodoes to the entrance palletC.
The arc (three and a half degrees) of the circleaembraced between the radial linesA bandA edetermines the angular motion of the escape wheel utilized by the escape-wheel tooth. To establish and define the extent of angular motion of the escape wheel utilized by the pallet, we lay off seven degrees on the arcafrom the pointoand establish the pointn, and through the pointn, fromBas a center, we sweep the short arcn'. Now somewhere on this arcn'will be located the inner angle of the entrance pallet. With a carefully-made drawing, having the escape wheel 10" in diameter, it will be seen that the arcaseparates considerably from the line,B f'where it crosses the arcn'.
It will be remembered that when drawing the ratchet-tooth lever escapement a measurement of eight and a half degrees was made on the arcn'down from its intersection with the pitch circle, and thus the inner angle of the pallet was located. In the present instance the addendum linewbecomes the controlling arc, and it will be further noticed on the large drawing that the lineB hat its intersection with the arcn'approaches nearer to the arcwthan does the lineB f'to the pitch circlea; consequently, the inner angle of the pallet should not in this instance be carried down on the arcn'so far to correct the error as in the ratchet tooth.
Reason tells us that if we measure ten degrees down on the arcn'from its intersection with the addendum circlewwe must define the position of the inner angle of the entrance pallet. We name the point so established the pointr. The outer angle of this pallet is located at the intersection of the radial lineA bwith the lineB i; said intersection we name the pointv. Draw a line from the pointvto the pointr, and we define the impulse face of the entrance pallet; and the angular motion obtained from it as relates to the pallet staff embraces six degrees.
Measured on the arcl, the entire ten degrees of angular motion is as follows: Two and a half degrees from the impulse face of the tooth, and indicated between the linesB handB f; one and a half degrees lock between the linesB f'andB i; six degrees impulse from pallet face, entrance between the linesB iandB j.
Grossmann and Britten, in all their delineations of the club-tooth escapement, show the exit pallet as disengaged. To vary from thisbeaten track we will draw our exit pallet as locked. There are other reasons which prompt us to do this, one of which is, pupils are apt to fall into a rut and only learn to do things a certain way, and that way just as they are instructed.
To illustrate, the writer has met several students of the lever escapement who could make drawings of either club or ratchet-tooth escapement with the lock on the entrance pallet; but when required to draw a pallet as illustrated at Fig. 23, could not do it correctly. Occasionally one could do it, but the instances were rare. A still greater poser was to request them to delineate a pallet and tooth when the action of escaping was one-half or one-third performed; and it is easy to understand that only by such studies the master workman can thoroughly comprehend the complications involved in the club-tooth lever escapement.
As an illustration: Two draughtsmen, employed by two competing watch factories, each designs a club-tooth escapement. We will further suppose the trains and mainspring power used by each concern to be precisely alike. But in practice the escapement of the watches made by one factory would "set," that is, if you stopped the balance dead still, with the pin in the fork, the watch would not start of itself; while the escapement designed by the other draughtsman would not "set"—stop the balance dead as often as you choose, the watch would start of itself. Yet even to experienced workmen the escape wheels and palletslookedexactly alike. Of course, there was a difference, and still none of the text-books make mention of it.
For the present we will go on with delineating our exit pallet. The preliminaries are the same as with former drawings, the instructions for which we need not repeat. Previous to drawing the exit pallet, let us reason on the matter. The pointrin Fig. 23 is located at the intersection of pitch circleaand the radial lineA c; and this will also be the point at which the toothCwill engage the locking face of the exit pallet.
This point likewise represents the advance angle of the engaging tooth. Now if we measure on the arck(which represents the locking faces of both pallets) downward one and a half degrees, we establish the lock of the palletE. To get this one and a half degrees defined on the arck, we set the dividers at 5", and fromBas a center sweep the short arci, and from the intersection of the arciwith the lineB ewe lay off on said arcione and a half degrees, and through the point so established draw the lineB f.
Now the space on the arckbetween the linesB eandB fdefines the angular extent of the locking face. With the dividers set at 5" and one leg resting at the pointr, we sweep the short arct, and from the intersection of said arc with the lineA cwe draw the linen p; but in doing so we extend it (the line) so that it intersects the lineB f, and at said intersection is located the inner angle of the exit pallet. This intersection we will name the pointn.
Fig. 23
From the intersection of the lineB ewith the arciwe lay off two and a half degrees on said arc, and through the point so established we draw the lineB g. The intersection of this line with the arckwe name the pointz. With one leg of our dividers set atAwe sweep the arclso it passes through the pointz. This last arc defines the addendum of the escape-wheel teeth. From the pointron the arcawe lay off three and a half degrees, and through the point so established draw the lineA j.
The intersection of this line with the addendum arcllocates the outer angle of the impulse planes of the teeth, and we name it the pointx. From the pointrwe lay off on the arcaseven degreesand establish the pointv, which defines the extent of the angular motion of the escape wheel utilized by pallet. Through the pointv, fromBas a center, we sweep the short arcm. It will be evident on a moment's reflection that this arcmmust represent the path of movement of the outer angle of the exit pallet, and if we measure down ten degrees from the intersection of the arclwith the arcm, the point so established (which we name the points) must be the exact position of the outer angle of the pallet during locking. We have a measure of ten degrees on the arcm, between the linesB gandB h, and by taking this space in the dividers and setting one leg at the intersection of the arclwith the arcm, and measuring down onm, we establish the points. Drawing a line from pointnto pointswe define the impulse face of the pallet.
Fig. 24
It is next proposed we apply the theories we have been considering and make an enlarged model of an escapement, as shown at Figs. 24 and 25. This model is supposed to have an escape wheel one-fifth the size of the 10" one we have been drawing. In the accompanying cuts are shown only the main plate and bridgesin full lines, while the positions of the escape wheel and balance are indicated by the dotted circlesI B. The cuts are to no precise scale, but were reduced from a full-size drawing for convenience in printing. We shall give exact dimensions, however, so there will be no difficulty in carrying out our instructions in construction.
Fig. 25
Perhaps it would be as well to give a general description of the model before taking up the details. A reduced side view of the complete model is given at Fig. 26. In this cut the escapement model shown at Figs. 24 and 25 is sketched in a rough way atR, whileNshows a glass cover, andMa wooden base of polished oak or walnut. This base is recessed on the lower side to receive an eight-day spring clock movement, which supplies the motive power for the model. This base is recessed on top to receive the main plateA, Fig. 24, and also to hold the glass shadeNin position. The baseMis 2½" high and 8" diameter. The glass coverNcan have either a high and spherical top, as shown, or, as most people prefer, a flattened oval.
Fig. 26
The main plateAis of hard spring brass, 1/10" thick and 6" in diameter; in fact, a simple disk of the size named, with slightly rounded edges. The top plate, shown atC, Figs. 24 and 25, is 1/8" thick and shaped as shown. This plate (C) is supported on two pillars 1/2" in diameter and 1-1/4" high. Fig. 25 is a side view of Fig. 24 seen in the direction of the arrowp. The cockDis also of 1/8" spring brass shaped as shown, and attached by the screwfand steady pinss sto the top plateC. The bridgeF Gcarries the top pivots of escape wheel and pallet staff, and is shaped as shown at the full outline. This bridge is supported on two pillars 1/2" high and 1/2" in diameter, one of which is shown atE, Fig. 25, and both at the dotted circlesE E', Fig. 24.
To lay out the lower plate we draw the linea aso it passes through the center ofAatm. At 1.3" from one edge ofAweestablish on the lineathe pointd, which locates the center of the escape wheel. On the same lineaat 1.15" fromdwe establish the pointb, which represents the center of the pallet staff. At the distance of 1.16" frombwe establish the pointc, which represents the center of the balance staff. To locate the pillarsH, which support the top plateC, we set the dividers at 2.58", and from the centermsweep the arcn.
From the intersection of this arc with the linea(atr) we lay off on said arcn2.1" and establish the pointsg g', which locate the center of the pillarsH H. With the dividers set so one leg rests at the centermand the other leg at the pointd, we sweep the arct. With the dividers set at 1.33" we establish on the arct, from the pointd, the pointse e', which locate the position of the pillarsE E'. The outside diameter of the balanceBis 3-5/8" with the rim 3/16" wide and 5/16" deep, with screws in the rim in imitation of the ordinary compensation balance.
Speaking of a balance of this kind suggests to the writer the trouble he experienced in procuring material for a model of this kind—for the balance, a pattern had to be made, then a casting made, then a machinist turned the casting up, as it was too large for an American lathe. A hairspring had to be specially made, inasmuch as a mainspring was too short, the coils too open and, more particularly, did not look well. Pallet jewels had to be made, and lapidists have usually poor ideas of close measurements. Present-day conditions, however, will, no doubt, enable the workman to follow our instructions much more readily.
In case the reader makes the bridgesCandF, as shown in Fig. 27, he should locate small circles on them to indicate the position of the screws for securing these bridges to the pillars which support them, and also other small circles to indicate the position of the pivot holesd bfor the escape wheel and pallet staff. In practice it will be well to draw the linea athrough the center of the main plateA, as previously directed, and also establish the pointdas therein directed.
Fig. 27
The pivot holed'for the escape wheel, and also the holes ate eandb, are now drilled in the bridgeF. These holes should be about 1/16" in diameter. The same sized hole is also drilled in the main plateAatd. We now place a nicely-fitting steel pin in theholed'in the bridgeFand let it extend into the holedin the main plate. We clamp the bridgeFtoAso the holebcomes central on the linea, and using the holese einFas guides, drill or mark the corresponding holese' e'andbin the main plate for the pillarsE E'and the pallet staff.
This plan will insure the escape wheel and pallet staff being perfectly upright. The same course pursued with the plateCwill insure the balance being upright. The pillars which support the bridges are shaped as shown at Fig. 28, which shows a side view of one of the pillars which support the top plate or bridgeC. The ends are turned to 1/4" in diameter and extend half through the plate, where they are held by screws, the same as in American movements.
Fig. 28
Fig. 29
The pillars (likeH) can be riveted in the lower plateA, but we think most workmen will find it more satisfactory to employ screws, as shown at Fig. 29. The heads of such screws should be about 3/8" in diameter and nicely rounded, polished and blued. We would not advise jeweling the pivot holes, because there is but slight friction, except to the foot of the balance pivot, which should be jeweled with a plano-convex garnet.
The top pivots to the escape wheel should be capped with imitation rubies for appearance sake only, letting the cap settings be red gold, or brass red gilded. If real twelve-karat gold is employed the cost will not be much, as the settings are only about 3/8" across and can be turned very thin, so they will really contain but very little gold. The reason why we recommend imitation ruby cap jewels for the upper holes, is that such jewels are much more brilliant than any real stone we can get for a moderate cost. Besides, there is no wear on them.
Fig. 30
Fig. 31
The pallet jewels are also best made of glass, as garnet or any red stone will look almost black in such large pieces. Red carnelian has a sort of brick-red color, which has a cheap appearance. Thereis a new phosphorus glass used by optical instrument makers which is intensely hard, and if colored ruby-red makes a beautiful pallet jewel, which will afford as much service as if real stones were used; they are no cheaper than carnelian pallets, but much richer looking. The prettiest cap for the balance is one of those foilback stones in imitation of a rose-cut diamond.
Fig. 32
Fig. 33
In turning the staffs it is the best plan to use double centers, but a piece of Stubs steel wire that will go into a No. 40 wire chuck, will answer; in case such wire is used, a brass collet must be provided. This will be understood by inspecting Fig. 30, whereLrepresents the Stubs wire andB Nthe brass collet, with the balance seat shown atk. The escape-wheel arbor and pallet staff can be made in the same way. The lower end of the escape wheel pivot is made about 1/4" long, so that a short piece of brass wire can be screwed upon it, as shown in Fig. 31, wherehrepresents the pivot,Athe lower plate, and the dotted line atpthe brass piece screwed on the end of the pivot. This piecepis simply a short bit of brass wire with a female screw tapped into the end, which screws on to the pivot. An arm is attached top, as shown atT. The idea is, the piecesT pact like a lathe dog to convey the power from one of the pivots of an old eight-day spring clock movement, which is secured by screws to the lower side of the main plateA. The plan is illustrated at Fig. 32, wherelrepresents pivot of the eight-day clock employed to run the model. Counting the escape-wheel pivot of the clock as one, we take the third pivot from this in the clock train, placing the movement so this point comes opposite the escape-wheel pivot of the model, and screw the clock movement fast to the lower side of the plateA. The partsT, Fig. 33, are alike on both pivots.
To fully appreciate such a large escapement model as we have been describing, a person must see it with its great balance, nearly 4" across, flashing and sparkling in the show window in the evening, and the brilliant imitation ruby pallets dipping in and out of the escape wheel. A model of this kind is far more attractive than if the entire train were shown, the mystery of "What makes it go?"being one of the attractions. Such a model is, further, of great value in explaining to a customer what you mean when you say the escapement of his watch is out of order. Any practical workman can easily make an even $100 extra in a year by making use of such a model.
For explaining to customers an extra balance cock can be used to show how the jewels (hole and cap) are arranged. Where the parts are as large as they are in the model, the customer can see and understand for himself what is necessary to be done.
It is not to be understood that our advice to purchase the jewels for an extra balance cock conflicts with our recommending the reader not to jewel the holes of his model. The extra cock is to be shown, not for use, and is employed solely for explaining to a customer what is required when a pivot or jewel is found to be broken.
Fig. 34
Fig. 35
The screws which hold the plates in place should have heads about 3/8" in diameter, to be in proportion to the scale on which the balance and escape wheel are gotten up. There is much in the manner in which the screw heads are finished as regards the elegance of such a model. A perfectly flat head, no matter how highly polished, does not look well, neither does a flattened conehead, like Fig. 35. The best head for this purpose is a cupped head with chamfered edges, as shown at Fig. 34 in vertical section. The centerbis ground and polished into a perfect concave by means of a metal ball. The face, between the linesa a, is polished dead flat, and the chamfered edgea cfinished a trifle convex. The flat surface atais bright, but the concaveband chamfer atcare beautifully blued. For a gilt-edged, double extra head, the chamfer atccan be "snailed," that is, ground with a suitable lap before bluing, like the stem-wind wheels on some watches.
Fig. 36
There are two easy methods of removing the blue from the flat part of the screwhead ata. (1) Make a special holder for the screw in the end of a cement brass, as shown atE, Fig. 36, and while it is slowly revolving in the lathe touch the flat surfaceawith a sharpened pegwood wet with muriatic acid, which dissolves theblue coating of oxide of iron. (2) The surface of the screwhead is coated with a very thin coating of shellac dissolved in alcohol and thoroughly dried, or a thin coating of collodion, which is also dried. The screw is placed in the ordinary polishing triangle and the flat face atapolished on a tin lap with diamantine and oil. In polishing such surfaces the thinnest possible coating of diamantine and oil is smeared on the lap—in fact, only enough to dim the surface of the tin. It is, of course, understood that it is necessary to move only next to nothing of the material to restore the polish of the steel. The polishing of the other steel parts is done precisely like any other steel work.
Fig. 37
The regulator is of the Howard pattern. The hairspring stud is set in the cock like the Elgin three-quarter-plate movement. The richest finish for such a model is frosted plates and bridges. The frosting should not be a fine mat, like a watch movement, but coarse-grained—in fact, the grain of the frosting should be proportionate to the size of the movement. The edges of the bridges and balance cock can be left smooth. The best process for frosting is by acid. Details for doing the work will now be given.
Fig. 38
To do this frosting by acid nicely, make a sieve by tacking and gluing four pieces of thin wood together, to make a rectangular box without a bottom. Four pieces of cigar-box wood, 8" long by 1-1/2" wide, answer first rate. We show atA A A A, Fig. 37, such a box as if seen from above; with a side view, as if seen in the direction of the arrowa, at Fig. 38. A piece of India muslin is glued across the bottom, as shown at the dotted linesb b. By turning up the edges on the outside of the box, the muslin bottom can be drawn as tight as a drum head.
Fig. 39
To do acid frosting, we procure two ounces of gum mastic and place in the square sieve, shown at Fig. 37. Usually more than half the weight of gum mastic is in fine dust, and if not, that is, if the gum is in the shape of small round pellets called "mastic tears," crush these into dust and place the dust inA. Let us nextsuppose we wish to frost the cock on the balance, shown at Fig. 39. Before we commence to frost, the cock should be perfectly finished, with all the holes made, the regulator cap in position, the screw hole made for the Howard regulator and the index arc engraved with the letters S and F.
It is not necessary the brass should be polished, but every file mark and scratch should be stoned out with a Scotch stone; in fact, be in the condition known as "in the gray." It is not necessary to frost any portion of the cockC, except the upper surface. To protect the portion of the cock not to be frosted, like the edges and the back, we "stop out" by painting over with shellac dissolved in alcohol, to which a little lampblack is added. It is not necessary the coating of shellac should be very thick, but it is important it should be well dried.
For illustration, let us suppose the back and edges of the cock at Fig. 39 are coated with shellac and it is laid flat on a piece of paper about a foot square to catch the excess of mastic. Holes should be made in this paper and also in the board on which the paper rests to receive the steady pins of the cock. We hold the sieve containing the mastic over the cock and, gently tapping the boxAwith a piece of wood like a medium-sized file handle, shake down a little snowstorm of mastic dust over the face of the cockC.
Exactly how much mastic dust is required to produce a nice frosting is only to be determined by practice. The way to obtain the knack is to frost a few scraps to "get your hand in." Nitric acid of full strength is used, dipping the piece into a shallow dish for a few seconds. A good-sized soup plate would answer very nicely for frosting the bottom plate, which, it will be remembered, is 6" in diameter.
After the mastic is sifted on, the cock should be heated up to about 250° F., to cause the particles of mastic to adhere to the surface. The philosophy of the process is, the nitric acid eats or dissolves the brass, leaving a little brass island the size of the particle of mastic which was attached to the surface. After heating to attach the particles of mastic, the dipping in nitric acid isdone as just described. Common commercial nitric acid is used, it not being necessary to employ chemically pure acid. For that matter, for such purposes the commercial acid is the best.
After the acid has acted for fifteen or twenty seconds the brass is rinsed in pure water to remove the acid, and dried by patting with an old soft towel, and further dried by waving through the air. A little turpentine on a rag will remove the mastic, but turpentine will not touch the shellac coating. The surface of the brass will be found irregularly acted upon, producing a sort of mottled look. To obtain a nice frosting the process of applying the mastic and etching must be repeated three or four times, when a beautiful coarse-grain mat or frosting will be produced.
The shellac protection will not need much patching up during the three or four bitings of acid, as the turpentine used to wash off the mastic does not much affect the shellac coating. All the screw holes likes sandd, also the steady pins on the back, are protected by varnishing with shellac. The edges of the cocks and bridges should be polished by rubbing lengthwise with willow charcoal or a bit of chamois skin saturated with oil and a little hard rouge scattered upon it. The frosting needs thorough scratch-brushing.