Fig. 90
We have now come to the point where we must exercise our reasoning powers a little. We know the locking angle of the escape-wheel tooth passes on the arca, and if we utilize the impulse face of the tooth for five degrees of pallet or lever motion we must shape it to this end. We draw the short arckthrough the pointn, knowing that the inner angle of the pallet stone must rest on this arc wherever it is situated. As, for instance, when the locking face of the pallet is engaged, the inner angle of the pallet stone must rest somewhere on this arc (k) inside ofa, and the extremeouter angle of the impulse face of the tooth must part with the pallet on this arck.
With the parts related to each other as shown in the cut, to establish where the inner angle of the pallet stone is located in the drawing, we measure down on the arckfive degrees from its intersection witha, and establish the points. The lineB b, Fig. 90, as the reader will see, does not coincide with the intersection of the arcsaandk, and to conveniently get at the proper location for the inner angle of our pallet stone, we draw the lineB b', which passes through the pointnlocated at the intersection of the arcawith the arck. FromBas a center we sweep the short arcjwith any convenient radius of which we have a sixty-degree scale, and from the intersection ofB b'withjwe lay off five degrees and draw the lineB s', which establishes the pointson the arck. As stated above, we allow one degree for lock, which we establish on the arcoby laying off one degree on the arcjbelow its intersection with the lineB b. We do not show this line in the drawing, from the fact that it comes so near toB b'that it would confuse the reader. Above the arcaon the arckat five degrees from the pointnwe establish the pointl, by laying off five degrees on the arcjabove the intersection of the lineB bwithj.
The pointl, Fig. 90, establishes where the outer angle of the tooth will pass the arckto give five degrees of angular motion to the lever. FromAas a center we sweep the arcm, passing through the pointl. The intersection of the arcmwith the lineA hwe call the pointr, and by drawing the right liner fwe delineate the impulse face of the tooth. On the arcoand one degree below its intersection with the lineB bwe establish the pointt, and by drawing a right line fromttoswe delineate the impulse face of our entrance pallet.
One great fault with most of our text books on horology lies in the fact that when dealing with the detached lever escapement the drawings show only the position of the pallets when locked, and many of the conditions assumed are arrived at by mental processes, without making the proper drawings to show the actual relation of the parts at the time such conditions exist. For illustration, it is often urged that there is a time in the action of the club-tooth leverescapement action when the incline on the tooth and the incline on the pallet present parallel surfaces, and consequently endure excessive friction, especially if the oil is a little thickened.
We propose to make drawings to show the exact position and relation of the entrance pallet and tooth at three intervals viz: (1) Locked; (2) the position of the parts when the lever has performed one-half of its angular motion; (3) when half of the impulse face of the tooth has passed the pallet. The position of the entrance pallet when locked is sufficiently well shown in Fig. 90 to give a correct idea of the relations with the entrance pallet; and to conform to statement (2), as above. We will now delineate the entrance pallet, not in actual contact, however, with the pallet, because if we did so the lines we employed would become confused. The methods we use are such thatwe can delineate with absolute correctness either a pallet or tooth at any point in its angular motion.
We have previously given instructions for drawing the pallet locked; and to delineate the pallet after five degrees of angular motion, we have only to conceive that we substitute the lines'for the lineb'. All angular motions and measurements for pallet actions are from the center of the pallet staff atB. As we desire to now delineate the entrance pallet, it has passed through five degrees of angular motion and the inner anglesnow lies on the pitch circle of the escape wheel, the angular space between the linesb' s'being five degrees, the lineb''[**note: check this against the diagram-most other lines nave a two-letter identification] reducing the impulse face to four degrees.
To delineate our locking face we draw a line at right angles to the lineB b''from the pointt, said point being located at the intersection of the arcowith the lineB b''. To draw a line perpendicular toB b''from the pointt, we take a convenient space in our dividers and establish on the lineB b''the pointsx x'at equal distances from the pointt. We open the dividers a little (no special distance) and sweep the short arcsx'' x''', as shown at Fig. 91. Through the intersection of the short arcsx'' x'''and to the pointtwe draw the linet y. The reader will see from our former explanations that the linet yrepresents the neutral plane of the locking face, and that to have the proper draw we must delineate the locking face of our pallet at twelve degrees. To do this we draw the linet x'at twelve degrees to the linet y,and proceed to outline our pallet faces as shown. We can now understand, after a moment's thought, that we can delineate the impulse face of a tooth at any point or place we choose by laying off six degrees on the arcm, and drawing radial lines fromAto embrace such arc. To illustrate, suppose we draw the radial linesw' w''to embrace six degrees on the arca. We make these lines contiguous to the entrance palletCfor convenience only. To delineate the impulse face of the tooth, we draw a line extending from the intersection of the radial lineA' w'with the arcmto the intersection of the arcawith the radial lineA w''.
Fig. 91
We next desire to know where contact will take place between the wheel-toothDand palletC. To determine this we sweep, with our dividers set so one leg rests at the escape-wheel centerAand the other at the outer angletof the entrance pallet, the short arct' w. Where this arc intersects the linew(which represents the impulse face of the tooth) is where the outer angletof the entrance palletCwill touch the impulse face of the tooth. To prove this we draw the radial lineA vthrough the point where the short arct t'passes through the impulse facewof the toothD. Then we continue the linewton, to represent the impulse face of the tooth, and then measure the angleA w nbetween the linesw nandv A, and find it to be approximately sixty-four degrees. We then, by a similar process, measure the angleA t s'and find it to be approximately sixty-six degrees. When contact ensues between the toothDand palletCthe toothDwill attack the pallet at the point where the radial lineA vcrosses the tooth face. We have now explainedhow we can delineate a tooth or pallet at any point of its angular motion, and will next explain how to apply this knowledge in actual practice.
To delineate our entrance pallet after one-half of the engaged tooth has passed the inner angle of the entrance pallet, we proceed, as in former illustrations, to establish the escape-wheel center atA, and from it sweep the arcb, to represent the pitch circle. We next sweep the short arcsp s, to represent the arcs through which the inner and outer angles of the entrance pallet move. Now, to comply with our statement as above, we must draw the tooth as if half of it has passed the arcs.
To do this we draw fromAas a center the radial lineA j, passing through the points, said pointsbeing located at the intersection of the arcssandb. The toothDis to be shown as if one half of it has passed the points; and, consequently, if we lay off three degrees on each side of the pointsand establish the pointsd m, we have located on the arcbthe angular extent of the tooth to be drawn. To aid in our delineations we draw from the centerAthe radial linesA d'andA m', passing through the pointsd m. The arcais next drawn as in former instructions and establishes the length of the addendum of the escape-wheel teeth, the outer angle of our escape-wheel tooth being located at the intersection of the arcawith the radial lineA d'.
As shown in Fig. 92, the impulse planes of the toothDand palletCare in contact and, consequently, in parallel planes, as mentioned on page 91. It is not an easy matter to determine at exactly what degree of angular motion of the escape wheel such condition takes place; because to determine such relation mathematically requires a knowledge of higher mathematics, which would require more study than most practical men would care to bestow, especially as they would have but very little use for such knowledge except for this problem and a few others in dealing with epicycloidal curves for the teeth of wheels.
For all practical purposes it will make no difference whether such parallelism takes place after eight or nine degrees of angular motion of the escape wheel subsequent to the locking action. The great point, as far as practical results go, is to determine if it takes place at or near the time the escape wheel meets the greatestresistance from the hairspring. We find by analysis of our drawing that parallelism takes place about the time when the tooth has three degrees of angular motion to make, and the pallet lacks about two degrees of angular movement for the tooth to escape. It is thus evident that the relations, as shown in our drawing, are in favor of the train or mainspring power over hairspring resistance as three is to two, while the average is only as eleven to ten; that is, the escape wheel in its entire effort passes through eleven degrees of angular motion, while the pallets and fork move through ten degrees. The student will thus see we have arranged to give the train-power an advantage where it is most needed to overcome the opposing influence of the hairspring.
Fig. 92
As regards the exalted adhesion of the parallel surfaces, we fancy there is more harm feared than really exists, because, to take the worst view of the situation, such parallelism only exists for the briefest duration, in a practical sense, because theoretically these surfaces never slide on each other as parallel planes. Mathematicallyconsidered, the theoretical plane represented by the impulse face of the tooth approaches parallelism with the plane represented by the impulse face of the pallet, arrives at parallelism and instantly passes away from such parallelism.
As delineated in Fig. 92, the impulse planes of the tooth and pallet are in contact; but we have it in our power to delineate the pallet at any point we choose between the arcsp s. To describe and illustrate the above remark, we say the linesB eandB fembrace five degrees of angular motion of the pallet. Now, the impulse plane of the pallet occupies four of these five degrees. We do not draw a radial line fromBinside of the lineB eto show where the outer angle of the impulse plane commences, but the reader will see that the impulse plane is drawn one degree on the arcpbelow the lineB e. We continue the lineh hto represent the impulse face of the tooth, and measure the angleB n hand find it to be twenty-seven degrees. Now suppose we wish to delineate the entrance pallet as if not in contact with the escape-wheel tooth—for illustration, say, we wish the inner angle of the pallet to be at the pointvon the arcs. We draw the radial lineB lthroughv; and if we draw another line so it passes through the pointvat an angle of twenty-seven degrees toB l, and continue said line so it crosses the arcp, we delineate the impulse face of our pallet.
We measure the anglei n B, Fig. 92, and find it to be seventy-four degrees; we draw the linev tto the same angle withv B, and we define the inner face of our pallet in the new position. We draw a line parallel withv tfrom the intersection of the linev ywith the arcp, and we define our locking face. If now we revolve the lines we have just drawn on the centerBuntil the linel Bcoincides with the linef B, we will find the liney yto coincide withh h, and the linev v'withn i.
We have now instructed the reader how to delineate either tooth or pallet in any conceivable position in which they can be related to each other. Probably nothing has afforded more efficient aid to practical mechanics than has been afforded by the graphic solution of abstruce mathematical problems; and if we add to this the means of correction by mathematical calculations which do notinvolve the highest mathematical acquirements, we have approached pretty close to the actual requirements of the practical watchmaker.
Fig. 93
To better explain what we mean, we refer the reader to Fig. 93, where we show preliminary drawings for delineating a lever escapement. We wish to ascertain by the graphic method the distance between the centers of action of the escape wheel and the pallet staff. We make our drawing very carefully to a given scale, as, for instance, the radius of the arcais 5". After the drawing is in the condition shown at Fig. 93 we measure the distance on the linebbetween the points (centers)A B, and we thus by graphic means obtain a measure of the distance betweenA B. Now, by the use of trigonometry, we have the length of the lineA f(radius of the arca) and all the angles given, to find the length off B, orA B, or bothf BandA B. By adopting this policy we can verify the measurements taken from our drawings. Suppose we find by the graphic method that the distance between the pointsA Bis 5.78", and by trigonometrical computation find the distance to be 5.7762". We know from this that there is .0038" to be accounted for somewhere; but for all practical purposes either measurement should be satisfactory, because our drawing is about thirty-eight times the actual size of the escape wheel of an eighteen-size movement.
Let us further suppose the diameter of our actual escape wheel to be .26", and we were constructing a watch after the lines of our drawing. By "lines," in this case, we mean in the same general form and ratio of parts; as, for illustration, if the distance from the intersection of the arcawith the linebto the pointBwas one-fifteenth of the diameter of the escape wheel, this ratio would hold good in the actual watch, that is, it would be the one-fifteenth part of .26". Again, suppose the diameter of the escape wheel in the large drawing is 10" and the distance between the centersA Bis 5.78"; to obtain the actual distance for the watch with the escapewheel .26" diameter, we make a statement in proportion, thus: 10 : 5.78 :: .26 to the actual distance between the pivot holes of the watch. By computation we find the distance to be .15". These proportions will hold good in every part of actual construction.
All parts—thickness of the pallet stones, length of pallet arms, etc.—bear the same ratio of proportion. We measure the thickness of the entrance pallet stone on the large drawing and find it to be .47"; we make a similar statement to the one above, thus: 10 : .47 :: .26 to the actual thickness of the real pallet stone. By computation we find it to be .0122". All angular relations are alike, whether in the large drawing or the small pallets to match the actual escape wheel .26" in diameter. Thus, in the palletD, Fig. 93, the impulse face, as reckoned fromBas a center, would occupy four degrees.
Reason would suggest the idea of having the theoretical keep pace and touch with the practical. It has been a grave fault with many writers on horological matters that they did not make and measure the abstractions which they delineated on paper. We do not mean by this to endorse the cavil we so often hear—"Oh, that is all right in theory, but it will not work in practice." If theory is right, practice must conform to it. The trouble with many theories is, they do not contain all the elements or factors of the problem.
Fig. 94
Near the beginning of this treatise we advised our readers to make a large model, and described in detail the complete parts for such a model. What we propose now is to make adjustable the pallets and fork to such a model, in order that we can set them both right and wrong, and thus practically demonstrate a perfect action and also the various faults to which the lever escapement is subject. The pallet arms are shaped as shown atA, Fig. 94. The palletsB B'can be made of steel or stone, and for all practical purposes those made of steel answer quite as well, and have the advantage of being cheaper. A plate of sheet brass should be obtained, shaped as shown atC, Fig. 95. This plate is of thin brass, about No. 18, and on it are outlined the pallet arms shown at Fig. 94.
Fig. 95
Fig. 96
Fig. 97
To make the pallets adjustable, they are set in thick disks of sheet brass, as shown atD, Figs. 95, 96 and 97. At the center of the plateCis placed a brass diskE, Fig. 98, which serves to support the lever shown at Fig. 99. This diskEis permanently attached to the plateC. The lever shown at Fig. 99 is attached to the diskEby two screws, which pass through the holesh h. If we now place the brass piecesD D'on the plateCin such a way that the pallets set in them correspond exactly to the pallets as outlined on the plateC, we will find the action of the pallets to be precisely the same as if the pallet armsA A', Fig. 94, were employed.
Fig. 98
Fig. 99
To enable us to practically experiment with and to fully demonstrate all the problems of lock, draw, drop, etc., we make quite a large hole inCwhere the screwsbcome. To explain, if the screwsb bwere tapped directly intoC, as they are shown at Fig. 95, we could only turn the diskDon the screwb; but if we enlarge the screw hole inCto three or four times the natural diameter, and then place the nuteunderCto receive the screwb, we can then set the disksD D'and palletsB B'in almost any relation we choose to the escape wheel, and clamp the pallets fast and try the action. We show at Fig. 97 a view of the palletB', diskD'and plateC(seen in the direction of the arrowc) as shown in Fig. 95.
It will be noticed in Fig. 99 that the holegfor the pallet staff in the lever is oblong; this is to allow the lever to be shifted back and forth as relates to roller and fork action. We will not bother about this now, and only call attention to the capabilities of such adjustments when required. At the outset we will conceive the forkFattached to the pieceEby two screws passing through the holesh h, Fig. 99. Such an arrangement will insure the fork androller action keeping right if they are put right at first. Fig. 100 will do much to aid in conveying a clear impression to the reader.
The idea of the adjustable features of our escapement model is to show the effects of setting the pallets wrong or having them of bad form. For illustration, we make use of a pallet with the angle too acute, as shown atB''', Fig. 101. The problem in hand is to find out by mechanical experiments and tests the consequences of such a change. It is evident that the angular motion of the pallet staff will be increased, and that we shall have to open one of the banking pins to allow the engaging tooth to escape. To trace outallthe consequences of this one little change would require a considerable amount of study, and many drawings would have to be made to illustrate the effects which would naturally follow only one such slight change.
Fig. 100
Suppose, for illustration, we should make such a change in the pallet stone of the entrance pallet; we have increased the angle between the linesk lby (say) one and a half degrees; by so doing we would increase the lock on the exit pallet to three degrees, provided we were working on a basis of one and a half degrees lock; and if we pushed back the exit pallet so as to have the proper degree of lock (one and a half) on it, the tooth which would next engage the entrance pallet would not lock at all, but would strike the pallet on the impulse instead of on the locking face. Again, such a change might cause the jewel pin to strike the horn of the fork, as indicated at the dotted linem, Fig. 99.
Fig. 101
Dealing with such and similar abstractions by mental process requires the closest kind of reasoning; and if we attempt to delineate all the complications which follow even such a small change, we will find the job a lengthy one. But with a large model having adjustable parts we provide ourselves with the means for the very best practical solution, and the workman who makes and manipulates such a model will soon master the lever escapement.
Some years ago a young watchmaker friend of the writer made, at his suggestion, a model of the lever escapement similar to the one described, which he used to "play with," as he termed it—that is,he would set the fork and pallets (which were adjustable) in all sorts of ways, right ways and wrong ways, so he could watch the results. A favorite pastime was to set every part for the best results, which was determined by the arc of vibration of the balance. By this sort of training he soon reached that degree of proficiency where one could no more puzzle him with a bad lever escapement than you could spoil a meal for him by disarranging his knife, fork and spoon.
Fig. 102
Let us, as a practical example, take up the consideration of a short fork. To represent this in our model we take a lever as shown at Fig. 99, with the elongated slot for the pallet staff atg. To facilitate the description we reproduce at Fig. 102 the figure just mentioned, and also employ the same letters of reference. We fancy everybody who has any knowledge of the lever escapement has an idea of exactly what a "short fork" is, and at the same time it would perhaps puzzle them a good deal to explain the difference between a short fork and a roller too small.
Fig. 103
In our practical problems, as solved on a large escapement model, say we first fit our fork of the proper length, and then by the slotgmove the lever back a little, leaving the bankings precisely as they were. What are the consequences of this slight change? One of the first results which would display itself would be discovered by the guard pin failing to perform its proper functions. For instance, the guard pin pushed inward against the roller would cause the engaged tooth to pass off the locking face of the pallet, and the fork, instead of returning against the banking, would cause the guard pin to "ride the roller" during the entire excursion of the jewel pin. This fault produces a scraping sound in a watch. Suppose we attempt to remedy the fault by bending forward the guard pinb, as indicated by the dotted outlineb'in Fig. 103, said figure being a side view of Fig. 102 seen in the direction of the arrowa. This policy would prevent the engaged pallet from passing off of the locking face of the pallet, but would be followed by the jewel pin not passing fully into the fork, but striking the inside face of the prong of the fork at about the point indicated by the dotted linem. We can see that if theprong of the fork was extended to about the length indicated by the outline atc, the action would be as it should be.
To practically investigate this matter to the best advantage, we need some arrangement by which we can determine the angular motion of the lever and also of the roller and escape wheel. To do this, we provide ourselves with a device which has already been described, but of smaller size, for measuring fork and pallet action. The device to which we allude is shown at Figs. 104, 105 and 106. Fig. 104 shows only the index hand, which is made of steel about 1/20" thick and shaped as shown. The jawsB''are intended to grasp the pallet staff by the notchese, and hold by friction. The prongsl lare only to guard the staff so it will readily enter the notche. The circledis only to enable us to better hold the handBflat.
Fig. 104
From the center of the notcheseto the tip of the index handB'the length is 2". This distance is also the radius of the index arcC. This index arc is divided into thirty degrees, with three or four supplementary degrees on each side, as shown. For measuring pallet action we only require ten degrees, and for roller action thirty degrees. The arcC, Fig. 105, can be made of brass and is about 1-1/2" long by 1/4" wide; said arc is mounted on a brass wire about 1/8" diameter, as shown atk, Fig. 106, which is a view of Fig. 105 seen in the direction of the arrowi. This wirekenters a base shown atD E, Fig. 106, which is provided with a set-screw atjfor holding the index arc at the proper height to coincide with the handB.
Fig. 105
A good way to get up the parts shown in Fig. 106 is to take a disk of thick sheet brass about 1" in diameter and insert in it a piece of brass wire about 1/4" diameter and 3/8" long, through which drill axially a hole to receive the wirek. After the jawsB''are clamped on the pallet staff, we set the index arcCso the handB'will indicatethe angular motion of the pallet staff. By placing the index handBon the balance staff we can get at the exact angular duration of the engagement of the jewel pin in the fork.
Fig. 106
Of course, it is understood that this instrument will also measure the angles of impulse and lock. Thus, suppose the entire angular motion of the lever from bank to bank is ten degrees; to determine how much of this is lock and how much impulse, we set the index arcCso that the handB'marks ten degrees for the entire motion of the fork, and when the escapement is locked we move the fork from its bank and notice by the arcChow many degrees the hand indicated before it passed of its own accord to the opposite bank. If we have more than one and a half degrees of lock we have too much and should seek to remedy it. How? It is just the answers to such questions we propose to give by the aid of our big model.
"Be sure you are right, then go ahead," was the advice of the celebrated Davie Crockett. The only trouble in applying this motto to watchmaking is to know when you are right. We have also often heard the remark that there was only one right way, but any number of wrong ways. Now we are inclined to think that most of the people who hold to but one right way are chiefly those who believe all ways but their own ways are wrong. Iron-bound rules are seldom sound even in ethics, and are utterly impracticable in mechanics.
We have seen many workmen who had learned to draw a lever escapement of a given type, and lived firm in the belief that all lever escapements were wrong which were not made so as to conform to this certain method. One workman believes in equidistant lockings, another in circular pallets; each strong in the idea that their particular and peculiar method of designing a lever escapement was the only one to be tolerated. The writer is free to confess that he has seen lever escapements of both types, that is, circular pallets and equidistant lockings, which gave excellent results.
Another mooted point in the lever escapement is, to decide between the merits of the ratchet and the club-tooth escape wheel. English makers, as a rule, hold to the ratchet tooth, while Continental and American manufacturers favor the club tooth. The chief arguments in favor of the ratchet tooth are: (a) It will run without oiling the pallets; (b) in case the escape wheel is lost or broken itis more readily replaced, as all ratchet-tooth escape wheels are alike, either for circular pallets or equidistant lockings. The objections urged against it are: (a) Excessive drop; (b) the escape wheel, being frail, is liable to be injured by incompetent persons handling it; (c) this escapement in many instances does require to have the pallets oiled.
(a) That a ratchet-tooth escape wheel requires more drop than a club tooth must be admitted without argument, as this form of tooth requires from one-half to three-fourths of a degree more drop than a club tooth; (b) as regards the frailty of the teeth we hold this as of small import, as any workman who is competent to repair watches would never injure the delicate teeth of an escape wheel; (c) ratchet-tooth lever escapements will occasionally need to have the pallets oiled. The writer is inclined to think that this defect could be remedied by proper care in selecting the stone (ruby or sapphire) and grinding the pallets in such a way that the escape-wheel teeth will not act against the foliations with which all crystalline stones are built up.
All workmen who have had an extended experience in repair work are well aware that there are some lever escapements in which the pallets absolutely require oil; others will seem to get along very nicely without. This applies also to American brass club-tooth escapements; hence, we have so much contention about oiling pallets. The writer does not claim to know positively that the pallet stones are at fault because some escapements need oiling, but the fact must admit of explanation some way, and is this not at least a rational solution? All persons who have paid attention to crystallography are aware that crystals are built up, and have lines of cleavage. In the manufacture of hole jewels, care must be taken to work with the axis of crystallization, or a smooth hole cannot be obtained.
The advantages claimed for the club-tooth escapement are many; among them may be cited (a) the fact that it utilizes a greater arc of impulse of the escape wheel; (b) the impulse being divided between the tooth and the pallet, permits greater power to be utilized at the close of the impulse. This feature we have already explained. It is no doubt true that it is more difficult to match a set of pallets with an escape wheel of the club-tooth order than with a ratchet tooth; still the writer thinks that this objectionis of but little consequence where a workman knows exactly what to do and how to do it; in other words, is sure he is right, and can then go ahead intelligently.
It is claimed by some that all American escape wheels of a given grade are exact duplicates; but, as we have previously stated, this is not exactly the case, as they vary a trifle. So do the pallet jewels vary a little in thickness and in the angles. Suppose we put in a new escape wheel and find we have on the entrance pallet too much drop, that is, the tooth which engaged this pallet made a decided movement forward before the tooth which engaged the exit pallet encountered the locking face of said pallet. If we thoroughly understand the lever escapement we can see in an instant if putting in a thicker pallet stone for entrance pallet will remedy the defect. Here again we can study the effects of a change in our large model better than in an escapement no larger than is in an ordinary watch.
There have been many devices brought forward to aid the workman in adjusting the pallet stones to lever watches. Before going into the details of any such device we should thoroughly understand exactly what we desire to accomplish. In setting pallet stones we must take into consideration the relation of the roller and fork action. As has already been explained, the first thing to do is to set the roller and fork action as it should be, without regard in a great degree to pallet action.
Fig. 107
To explain, suppose we have a pallet stone to set in a full-plate movement. The first thing to do is to close the bankings so that the jewel pin will not pass out of the slot in the fork on either side; then gradually open the bankings until the jewel pin will pass out. This will be understood by inspecting Fig. 107, whereA A'shows a lever fork as if in contact with both banks, and the jewel pin, represented atB B'', just passes the anglea c'of the fork. The circle described by the jewel pinBis indicated by the arce. It is well to put a slight friction under the balance rim, in order that we can try the freedom of the guard pin. As a rule, all the guard pin needs is to be free and not touch the roller. The entire point, as far as setting the fork and bankings is concerned, is to have thefork and roller action sound. For all ordinary lever escapements the angular motion of the lever banked in as just described should beaboutten degrees. As explained in former examples, if the fork action is entirely sound and the lever only vibrates through an arc of nine degrees, it is quite as well to make the pallets conform to this arc as to make the jewel pin carry the fork through full ten degrees. Again, if the lever vibrates through eleven degrees, it is as well to make the pallets conform to this arc.
The writer is well aware that many readers will cavil at this idea and insist that the workman should bring all the parts right on the basis of ten degrees fork and lever action. In reply we would say that no escapement is perfect, and it is the duty of the workman to get the best results he can for the money he gets for the job. In the instance given above, of the escapement with nine degrees of lever action, when the fork worked all right, if we undertook to give the fork the ten degrees demanded by the stickler for accuracy we would have to set out the jewel pin or lengthen the fork, and to do either would require more time than it would to bring the pallets to conform to the fork and roller action. It is just this knowing how and the decision to act that makes the difference in the workman who is worth to his employer twelve or twenty-five dollars per week.
We have described instruments for measuring the angle of fork and pallet action, but after one has had experience he can judge pretty nearly and then it is seldom necessary to measure the angle of fork action as long as it is near the proper thing, and then bring the pallets to match the escape wheel after the fork and roller action is as it should be—that is, the jewel pin and fork work free, the guard pin has proper freedom, and the fork vibrates through an arc of about ten degrees.
Usually the workman can manipulate the pallets to match the escape wheel so that the teeth will have the proper lock and drop at the right instant, and again have the correct lock on the next succeeding pallet. The tooth should fall but a slight distance before the tooth next in action locks it, because all the angular motion the escape wheel makes except when in contact with the pallets is just so much lost power, which should go toward giving motion to the balance.
Fig. 108
There seems to be a little confusion in the use of the word "drop" in horological phrase, as it is used to express the act ofparting of the tooth with the pallet. The idea will be seen by inspecting Fig. 108, where we show the toothDand palletCas about parting or dropping. When we speak of "banking up to the drop" we mean we set the banking screws so that the teeth will just escape from each pallet. By the term "fall" we mean the arc the tooth passes through before the next pallet is engaged. This action is also illustrated at Fig. 108, where the toothD, after dropping from the palletC, is arrested at the position shown by the dotted outline. We designate this arc by the term "fall," and we measure this motion by its angular extent, as shown by the dotted radial linesi fandi g. As we have explained, this fall should only extend through an arc of one and a half degrees, but by close escapement matching this arc can be reduced to one degree, or even a trifle less.
We shall next describe an instrument for holding the escape wheel and pallets while adjusting them. As shown at Fig. 107, the forkA'is banked a little close and the jewel pin as shown would, in some portions, rub onC', making a scraping sound.
Fig. 109
A point has now been reached where we can use an escapement matcher to advantage. There are several good ones on the market, but we can make one very cheaply and also add our own improvements. In making one, the first thing to be provided is a movement holder. Any of the three-jaw types of such holders will answer, provided the jaws hold a movement plate perfectly parallel with the bed of the holder. This will be better understood by inspecting Fig. 109, which is a side view of a device of this kind seen edgewise in elevation. In thisBrepresents the bed plate, which supports three swing jaws, shown atC, Figs. 109 and 110. The watch plate is indicated by the parallel dotted linesA, Fig. 109. The seataof the swing jawsCmust hold the watch plateAexactly parallel with the bed plateB. In the cheap movement holders these seats (a) are apt to be of irregular heights, andmust be corrected for our purpose. We will take it for granted that all the seatsaare of precisely the same height, measured fromB, and that a watch plate placed in the jawsCwill be held exactly parallel with the said bedB. We must next provide two pillars, shown atD E, Figs. 109 and 111. These pillars furnish support for sliding centers which hold the top pivots of the escape wheel and pallet staff while we are testing the depths and adjusting the pallet stones. It will be understood that these pillarsD Eare at right angles to the plane of the bedB, in order that the slides likeG Non the pillarsD Emove exactly vertical. In fact, all the parts moving up and down should be accurately made, so as not to destroy the depths taken from the watch plateA. Suppose, to illustrate, that we place the plateAin position as shown, and insert the cone pointn, Figs. 109 and 112, in the pivot hole for the pallet staff, adjusting the slideG Nso that the cone point rests accurately in said pivot hole. It is further demanded that the partsI H F G N Dbe so constructed and adjusted that the sliding centerImoves truly vertical, and that we can change ends with said centerIand place the hollow cone endm, Fig. 112, so it will receive the top pivot of the pallet staff and hold it exactly upright.
Fig. 110
Fig. 111
Fig. 112
The idea of the sliding centerIis to perfectly supply the place of the opposite plate of the watch and give us exactly the same practical depths as if the parts were in their place between the plates of the movement. The foot of the pillarDhas a flange attached, as shown atf, which aids in holding it perfectly upright. It is well to cut a screw onDatD', and screw the flangefon such screw and then turn the lower face offflat to aid in having the pillarDperfectly upright.
Fig. 113
Fig. 114
It is well to fit the screwD'loosely, so that the flangefwill come perfectly flat with the upper surface of the base plateB. The slideG Non the pillarDcan be made of two pieces of small brass tube, one fitting the pillarDand the other the barF. The slideG Nis held in position by the set screwg, and the rodFby the set screwh.
The pieceHcan be permanently attached to the rodF. We show separate at Figs. 113 and 114 the slideG Non an enlarged scale from Fig. 109. Fig. 114 is a view of Fig. 113 seen in the direction of the arrowe. All joints and movable parts should work free, in order that the centerImay be readily and accurately set. The partsH Fare shown separate and enlarged at Figs. 115 and 116. The pieceHcan be made of thick sheet brass securely attached toFin such a way as to bring the V-shaped groove at right angles to the axis of the rodF. It is well to make the rodFabout 1/8" in diameter, while the sliding centerIneed not be more than 1/16" in diameter. The cone pointnshould be hardened to a spring temper and turned to a true cone in an accurately running wire chuck.
Fig. 115
Fig. 116
The hollow cone endmofIshould also be hardened, but this is best done after the hollow cone is turned in. The hardening of both ends should only be at the tips. The sliding centerIcan be held in the V-shaped groove by two light friction springs, as indicated at the dotted liness s, Fig. 115, or a flat plate of No. 24 or 25 sheet brass of the size ofHcan be employed, as shown at Figs. 116 and 117, whereorepresents the plate of No. 24 brass,p pthe small screws attaching the plateotoH, andka clamping screw to fastenIin position. It will be found that the two light springss s, Fig. 115 will be the most satisfactory. The wire legs, shown atL, will aid in making the device set steady. The pillarEis provided with the same slides and other parts as described and illustrated as attached toD. The position of the pillarsDandEare indicated at Fig. 110.
Fig. 118