Chapter I: The Detached Lever Escapement (5)

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 at _B'''_, 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 out _all_ the 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.

Suppose, for illustration, we should make such a change in the pallet stone of the entrance pallet; we have increased the angle between the lines _k l_ by (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 line _m_, Fig. 99.

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.

QUIZ PROBLEMS IN THE DETACHED 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.

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 at _g_. 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.

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 slot _g_ move 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 pin _b_, as indicated by the dotted outline _b'_ in Fig. 103, said figure being a side view of Fig. 102 seen in the direction of the arrow _a_. 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 line _m_. We can see that if the prong of the fork was extended to about the length indicated by the outline at _c_, 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 jaws _B''_ are intended to grasp the pallet staff by the notches _e_, and hold by friction. The prongs _l l_ are only to guard the staff so it will readily enter the notch _e_. The circle _d_ is only to enable us to better hold the hand _B_ flat.

HOW TO MEASURE ESCAPEMENT ANGLES.

From the center of the notches _e_ to the tip of the index hand _B'_ the length is 2". This distance is also the radius of the index arc _C_. 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 arc _C_, Fig. 105, can be made of brass and is about 1½" long by ¼" wide; said arc is mounted on a brass wire about 1/8" diameter, as shown at _k_, Fig. 106, which is a view of Fig. 105 seen in the direction of the arrow _i_. This wire _k_ enters a base shown at _D E_, Fig. 106, which is provided with a set-screw at _j_ for holding the index arc at the proper height to coincide with the hand _B_.

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 ¼" diameter and 3/8" long, through which drill axially a hole to receive the wire _k_. After the jaws _B''_ are clamped on the pallet staff, we set the index arc _C_ so the hand _B'_ will indicate the angular motion of the pallet staff. By placing the index hand _B_ on the balance staff we can get at the exact angular duration of the engagement of the jewel pin in the fork.

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 arc _C_ so that the hand _B'_ 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 arc _C_ how 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.

DETERMINATION OF "RIGHT" METHODS.

"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 it is 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.

ESCAPEMENTS COMPARED.

(_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 objection is 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.

HOW TO SET PALLET STONES.

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.

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, where _A A'_ shows a lever fork as if in contact with both banks, and the jewel pin, represented at _B B''_, just passes the angle _a c'_ of the fork. The circle described by the jewel pin _B_ is indicated by the arc _e_. 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 the fork and roller action sound. For all ordinary lever escapements the angular motion of the lever banked in as just described should be _about_ ten 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.

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 of parting of the tooth with the pallet. The idea will be seen by inspecting Fig. 108, where we show the tooth _D_ and pallet _C_ as 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 tooth _D_, after dropping from the pallet _C_, 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 lines _i f_ and _i 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 fork _A'_ is banked a little close and the jewel pin as shown would, in some portions, rub on _C'_, making a scraping sound.

HOW TO MAKE AN ESCAPEMENT MATCHING TOOL.

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 this _B_ represents the bed plate, which supports three swing jaws, shown at _C_, Figs. 109 and 110. The watch plate is indicated by the parallel dotted lines _A_, Fig. 109. The seat _a_ of the swing jaws _C_ must hold the watch plate _A_ exactly parallel with the bed plate _B_. In the cheap movement holders these seats (_a_) are apt to be of irregular heights, and must be corrected for our purpose. We will take it for granted that all the seats _a_ are of precisely the same height, measured from _B_, and that a watch plate placed in the jaws _C_ will be held exactly parallel with the said bed _B_. We must next provide two pillars, shown at _D 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 pillars _D E_ are at right angles to the plane of the bed _B_, in order that the slides like _G N_ on the pillars _D E_ move 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 plate _A_. Suppose, to illustrate, that we place the plate _A_ in position as shown, and insert the cone point _n_, Figs. 109 and 112, in the pivot hole for the pallet staff, adjusting the slide _G N_ so that the cone point rests accurately in said pivot hole. It is further demanded that the parts _I H F G N D_ be so constructed and adjusted that the sliding center _I_ moves truly vertical, and that we can change ends with said center _I_ and place the hollow cone end _m_, Fig. 112, so it will receive the top pivot of the pallet staff and hold it exactly upright.

The idea of the sliding center _I_ is 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 pillar _D_ has a flange attached, as shown at _f_, which aids in holding it perfectly upright. It is well to cut a screw on _D_ at _D'_, and screw the flange _f_ on such screw and then turn the lower face of _f_ flat to aid in having the pillar _D_ perfectly upright.

DETAILS OF FITTING UP ESCAPEMENT MATCHER.

It is well to fit the screw _D'_ loosely, so that the flange _f_ will come perfectly flat with the upper surface of the base plate _B_. The slide _G N_ on the pillar _D_ can be made of two pieces of small brass tube, one fitting the pillar _D_ and the other the bar _F_. The slide _G N_ is held in position by the set screw _g_, and the rod _F_ by the set screw _h_.

The piece _H_ can be permanently attached to the rod _F_. We show separate at Figs. 113 and 114 the slide _G N_ on an enlarged scale from Fig. 109. Fig. 114 is a view of Fig. 113 seen in the direction of the arrow _e_. All joints and movable parts should work free, in order that the center _I_ may be readily and accurately set. The parts _H F_ are shown separate and enlarged at Figs. 115 and 116. The piece _H_ can be made of thick sheet brass securely attached to _F_ in such a way as to bring the V-shaped groove at right angles to the axis of the rod _F_. It is well to make the rod _F_ about 1/8" in diameter, while the sliding center _I_ need not be more than 1/16" in diameter. The cone point _n_ should be hardened to a spring temper and turned to a true cone in an accurately running wire chuck.

The hollow cone end _m_ of _I_ should 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 center _I_ can be held in the V-shaped groove by two light friction springs, as indicated at the dotted lines _s s_, Fig. 115, or a flat plate of No. 24 or 25 sheet brass of the size of _H_ can be employed, as shown at Figs. 116 and 117, where _o_ represents the plate of No. 24 brass, _p p_ the small screws attaching the plate _o_ to _H_, and _k_ a clamping screw to fasten _I_ in position. It will be found that the two light springs _s s_, Fig. 115 will be the most satisfactory. The wire legs, shown at _L_, will aid in making the device set steady. The pillar _E_ is provided with the same slides and other parts as described and illustrated as attached to _D_. The position of the pillars _D_ and _E_ are indicated at Fig. 110.

We will next tell how to flatten _F_ to keep _H_ exactly vertical. To aid in explanation, we will show (enlarged) at Fig. 118 the bar _F_ shown in Fig. 109. In flattening such pieces to prevent turning, we should cut away about two-fifths, as shown at Fig. 119, which is an end view of Fig. 118 seen in the direction of the arrow _c_. In such flattening we should not only cut away two-fifths at one end, but we must preserve this proportion from end to end. To aid in this operation we make a fixed gage of sheet metal, shaped as shown at _I_, Fig. 120.

ESCAPEMENT MATCHING DEVICE DESCRIBED.

In practical construction we first file away about two-fifths of _F_ and then grind the flat side on a glass slab to a flat, even surface and, of course, equal thickness from end to end. We reproduce the sleeve _G_ as shown at Fig. 113 as if seen from the left and in the direction of the axis of the bar _F_. To prevent the bar _F_ turning on its axis, we insert in the sleeve _G_ a piece of wire of the same size as _F_ but with three-fifths cut away, as shown at _y_, Fig. 121. This piece _y_ is soldered in the sleeve _G_ so its flat face stands vertical. To give service and efficiency to the screw _h_, we thicken the side of the sleeve _F_ by adding the stud _w_, through which the screw _h_ works. A soft metal plug goes between the screw _h_ and the bar _F_, to prevent _F_ being cut up and marred. It will be seen that we can place the top plate of a full-plate movement in the device shown at Fig. 109 and set the vertical centers _I_ so the cone points _n_ will rest in the pivot holes of the escape wheel and pallets. It is to be understood that the lower side of the top plate is placed uppermost in the movement holder.

If we now reverse the ends of the centers _I_ and let the pivots of the escape wheel and pallet staff rest in the hollow cones of these centers _I_, we have the escape wheel and pallets in precisely the same position and relation to each other as if the lower plate was in position. It is further to be supposed that the balance is in place and the cock screwed down, although the presence of the balance is not absolutely necessary if the banking screws are set as directed, that is, so the jewel pin will just freely pass in and out of the fork.

HOW TO SET PALLET STONES.

We have now come to setting or manipulating the pallet stones so they will act in exact conjunction with the fork and roller. To do this we need to have the shellac which holds the pallet stones heated enough to make it plastic. The usual way is to heat a piece of metal and place it in close proximity to the pallets, or to heat a pair of pliers and clamp the pallet arms to soften the cement.

Of course, it is understood that the movement holder cannot be moved about while the stones are being manipulated. The better way is to set the movement holder on a rather heavy plate of glass or metal, so that the holder will not jostle about; then set the lamp so it will do its duty, and after a little practice the setting of a pair of pallet stones to perfectly perform their functions will take but a few minutes. In fact, if the stones will answer at all, three to five minutes is as much time as one could well devote to the adjustment. The reader will see that if the lever is properly banked all he has to do is to set the stones so the lock, draw and drop are right, when the entire escapement is as it should be, and will need no further trial or manipulating.