Watch and Clock Escapements

Although the marine chronometer is in a sense a portable timepiece, still it is not, like a pocket watch, capable of being adjusted to positions

escapements when the detent is broken, and the fact that the spring detent could not be adjusted to positio

OF THE CH

early escapements were all frictional escapements, i.e., the balance staff was never free from the influence of the train. The verge escapement, which was undoubtedly the first employed, was constantly in contact with the escape wheel, and was what is known as a "recoiling beat," that is, the contact of the pallets actually caused the escape wheel to recoil or turn back. Such escapements were too much influenced by the train, and any increase in power

SCAPEMENTS I

iction of the tooth acted as a corrective, and led no doubt to the introduction of going-barrel watches. To illustrate, suppose in a cylinder watch we increase the motive power, such increase of power would not, as in the verge escapement, increase the

perfectly detached escapement, these two frictional escapements also differing, the duplex requiring other properties from what would isochronize a spring for a cylinder escapement. Although pocket watches with duplex and cylinder escapements having balances compensated for heat and cold and balance

THE DETENT

h surround the detent escapement in a marine chronometer and take account of the causes which are combined to make it an accurate time measurer, and also take cognizance of other interfering causes which have a tendency to prevent desired results. First, we will imagine a balance with its s

he quickest or to synchronize them. We can readily comprehend we have now established a very perfect measure of short intervals of time. We can also see if we provide the means of maintaining these vibrations and counting them we should possess the means of counting the flights of time with great accuracy. The conditions which surround our balance are very con

STIC INF

mply to afford these two forces perfect facilities to act on each other and compel each to realize its full effect. We must also devise mechanical means to record the duration of each conflict, that is, the time length of each vibration. Many years have been spent in exper

the tooth. By thickness we mean the measurement of extent of the tooth in the direction of the axis of the escape wheel. An escape-wheel tooth might be of the best form to act in conveying power to the b

AT MUST BE

; also, if we should decrease the motive power and increase the arc of impulse. Or, if we should diminish the extent of the impulse arc and add to the motive force, every change would have a controlling influence. In the designs we shall employ, it is our purpose to follow such proportions as have been adopted by our best makers, in all respects, in

s are made up of sub-parts: thus, the escape wheel is composed of arms, teeth, recess and collet, the recess being the portion of the escape wheel sunk, to enable us to get wide teeth actions on the impulse pallet. The collet is a brass bush on which the wheel is set to afford better support to the escape wheel than could be obtained by the thinned wheel if driven directly on the pinion arbor. The impulse roller is composed of a cylindrical steel collet B, the impulse pallet d (some call it the impulse ston

itional security has a pipe or short socket e which embraces the balance staff at g. The pipe e is usually flattened on opposite sides to admit of employing a special wrench for turning the discharging roller in adjusting the jewel for opening the escapement at the proper instant to permit the escape wheel to act on the impulse jewel a. The parts wh

ven from the hands of our best makers, are as light as they might be. We should in such construction have very lit

an escapement and give empirical rules for the length of this or the diameter of that. As, for instance, in finishing the detent spring h, suppose we read in text books the spring should be reduced in thickness, so that a weight of one pennyweight suspended from the pipe j will deflect the deten

S OF THE

e thrust of the escape wheel, represented by the arrows p o. Now we can readily understand that the lighter we make the parts i j k m, the weaker the spring h can be. You say, perhaps, if we make it too weak it will be liable to buckle under the pressure of the escape wheel; this, in turn, will depend in a great measure on the condition of the spring h. Suppose we have it straight when we put it in position, it will then have no stress to keep it pressed to the holding,

THE BEST C

top screw, which regulates the lock, and still be perfectly straight. This matter is of so much importance that we will give further explanation. Suppose we bend the detent spring h so it is curved to the dotted line t, Fig. 136, and then the

make the length of the detent from the foot F to the center of the locking jewel pipe j equal to the diameter of the escape wheel, and the length of the detent spring h two-sevenths of this distance. The length of the horn k is determined by the graphic plan and can be taken from the plotted plan. The end, however, should approach as near to the discharging jewel as

T CONSID

cker than k and at the same time deeper; or, to make a comparison to a clumsy article, y is like the head of a nail, which is all on one side. Some makers bend the horn k to a curve and allow the end of the horn to arrest or stop the gold spring; but as it is important the entire detent should be as light as possible, the square end best answers this purpose. The banking placed at j should arrest the detent as thrown back by

RRIVED AT B

t these proportions and conditions as best, from the fact that they are now almost universally adopted by our best chronometer makers. Although it would seem as if these proportions should have established themselves earlier among practical men, we shall in these drawings confine ourselves

the peripheries of these two mobiles, and the problem in hand is to locate and define the position of the two centers a c. These, of course, are not separated, the sum of the two radii, i.e., 5" + 2-1/2" (in the large drawing), as these circl

CENTER OF THE

ing off twelve degrees, one-half of the impulse arc on each side of the line of centers a f on this circle and establishing the points e e2. These points e e2 being located at the intersection of the circles A and B, must be at the respective distances of 5" and 2-1/2" distance from the center of the circles A B; consequently,

balance staff, we measure carefully on our drawing the distance from a to c (the latter we having just established) and make our statement in the rule of three, as follows:

e of perfection to which measuring tools have arrived in this day. It will be found on measurement of the arc of the circle B, embraced between the intersections

l periphery, in order that the attacking tooth shall act with certainty and its full effect. A good deal of thought and study can be bestowed to great advantage on the "action" of a chronometer escapement. Let us examine the conditions involved. We show in Fig. 140 the impulse jewel D just passing inside the circle of the periphery of the escape wheel. Now the attendant conditions are these: The escape wheel is locked fast and perfectly dead, and in

d, the escape wheel is not only dead but actually moving back at the time the release takes place. Now, it is evident that the escape wheel requires an appreciable time to move forward and attack the impulse jewel, and during this appreciable time the impulse jewel has been

THE DISCHAR

e to turn rapidly in one direction and with increasing velocity until, in fact, the escape wheel has but very little effect on the impulse jewel; in fact, we could, by applying some outside source of power-like blowing with a blow pipe on the balance-cause the impulse jewel to pass in advance of the escape wheel; that is, the escape-wheel tooth would not be able to catch the impulse jewel during the entire impulse arc. Let us suppose, now, we set our unlocking or discharging jewel in advance, that is, so the escapement is really unlocked a little before the setting parts are in the positions and relations shown in Fig. 141. Under the new conditions the escape wheel would commence to move and get sufficient velocity on it

hand; i.e., explaining the action of the chronometer escapement, as the chariot relates entirely to the convenience of setting and adjusting the relation of the second parts. The size, or better, say, the inside diameter of the pipe at C, Fig. 143, w

RM OF LOC

he cylinder, as shown at I, Fig. 143. Here the line m represents the locking face of the jewel and the line o the clearance to free the escaping tooth, the angle at n being about fifty-four degrees. This angle (n) should leave the rounding of the stone intact, that is, the rounding of the angle should be left and

is acted upon by the discharging jewel h. We have previously mentioned the importance of avoiding wide, flat contacts between all acting surfaces, like where the gold spring rests on the horn of the detent at p; also where the detent banks on the banking screw, shown at G, Fig. 142. Under this principle the impact of the face of the discharging jewel with the end of the gold spring should be confined to as small a surface as is consistent with what will not produce

the gold spring H is opposite the arrow y, Fig. 141, it will readily be understood the contact of the discharging stone h would continue longer than if the point of greatest (or easiest) flexure was nearer to the pipe C. If the end D2 of the horn of the detent is as near as it should be to the discharging stone there need be no fear but the escapement will be unlocked. The horn D2 of the detent should be bent until five degrees of angular motion of the balance will unlock the escape, and the contact of discharging jewel h should be made without engaging friction.

TENT S

of the wide surfaces which we assert are important. We guarantee that with a detent and spring made as we show, there will be no tendency to cockle, or if there is, it will be too feeble to even display itself. Those who have had extended experience with chronometers cannot fail to have noticed a gummy secretion which accumulates on the impulse and discharging stones of a chronometer, althou

OF CONST

ight as possible, should have sufficient strength to perform its functions properly. The thickness or, more properly, the face extent of the tooth, measured in the direction of the axis of the escape wheel, should be about 1/20". The recessing should extend half way up the radial back of the tooth at t. The curvature of the back of the teeth is produced with the same radii as the impulse roller. To locate the center from which the arc which defines the back of the teeth is swept, we halve the space

IGNING OF TH

ts. An escapement of any kind is only a machine, and merely requires in its construction a combination of sound mechanical principles. Neither Saunier nor Britten, in their works, give instru

TIAL L

the point of the escape-wheel tooth resting on the locking jewel. In escapements not set tangential, the detent is pushed forward in the direction of the arrow x about half a tooth space. Britten, in his "Hand-Book," gives a drawing of such an escapement. We claim the chief advantage of tangential locking to lie in the action of

angle of an escape-wheel tooth we draw the line C d, from the point of the escape-wheel tooth resting on the locking stone shown at C a

ing allowed for the impulse jewel to pass inside of the arc of periphery of the escape wheel before the locking jewel releases the tooth of the escape wheel resting upon it. At this point it is supposed the escape wheel attacks the impulse jewel, because, as we just explained, the locking jewel has released the tooth engaging it. Now, if the train had no weight, no inertia to

radial lines c e and c g, Fig. 141, and yet have the tooth attack the jewel after the five degrees of arc. In practice it is safe to set the discharging jewel h so the release of the held tooth A1 will take place as soon as the tooth A2 is inside the p

ce, but the tooth would strike the impulse jewel on its outer angle. A continued inspection will also reveal the fact that in order to have the point of the tooth engage the flat surface of the impulse pallet the impulse jewel must coincide with the radial line c g. If we seek to remedy this condition by setting the impulse jewel so the face is not radial, but inclined backward, we encounter a bad engaging friction, because, during the first part of the impulse action, the tooth has to slide up the face of the impulse jewel. All

AND DRAW

f workmanship, but should in no instance be more than what is absolutely required to make the escapement safe. The amount of draw given to the locking stone c is usually about twelve degre

matter for hand and eye, but should never exceed 2/1000". After the locking jewel c is set, we can set the foot F of the detent D forward or back, to perfect and correct

equal radial extent of each tooth should be only limited by our powers toward perfection. It is usual to give the detent a locking of about two

UP OF

t way of fitting up the foot F seems to be to provide it with two soft iron steady pins (shown at j) with corresponding holes in the chariot, said holes being conically enlarged so they (the pins) can be bent and manipulated so the detent not o

ause the pins j to take the correct positions as determined by the adjuster and set the screw l up to hold the foot F when all the other relations a

orkman should be familiar with the subject from a historical point of view. To aid in such an understanding of the matte