Part 14 (1/2)

As an illustration, let us consider the subject of depth between the cylinder and the escape wheel As previously stated, 196 degrees of cylinder shell should be employed; but suppose we find a watch in which the half shell has had toothe half shell after parting with the entrance lip does not strike dead on the inside of the shell, but encounters the edge of the exit lip In this case the irade and the watch would go but would lack a good ht advance of the chariot would remedy the fault--not perfectly remedy it, but patch up, so to speak--and the watch would run

[Illustration: Fig 135]

In this day, fine cylinder watches are not made, and only the common kind are met with, and for this reason the student should fainary faults which could occur from bad construction The best way to do this is to delineate what he (the student) knows to be a faulty escapement, as, for instance, a cylinder in which too much of the half shell is cut away; but in every instance let the tooth be of the correct form Then delineate an escapement in which the cylinder is correct but the teeth faulty; also change the thickness of the cylinder shell, so as to make the teeth too short This sort of practice e which will never be forgotten, but always be present to aid him in the puzzles to which the practical watchmaker is every day subject

The ability to solve these perplexing probleree the worth of ahis reputation as a skilled workman The question is frequently asked, ”How can I profitably employ myself in spare time?” It would seem that a watchmaker could do no better than to carefully study reater degree of perfection, for by so doing his earning capacity will undoubtedly be increased

CHAPTER III

THE CHRONOMETER ESCAPEMENT

Undoubtedly ”the detent,” or, as it is usually termed, ”the chronometer escapement,” is the most perfect of any of our portable tih the marine chronometer is in a sense a portable timepiece, still it is not, like a pocket watch, capable of being adjusted to positions As we are all aware, the detent escape ofno doubt is owing to thethe chronometer escape detent could not be adjusted to position We shall have occasion to speak of position adjustments as relate to the chronometer escapement later on

ADVANTAGES OF THE CHRONOMETER

We will proceed now to consider briefly the advantages the detent escapement has over all others It was soon discovered in constructing portable timepieces, that to obtain the best results the vibrations of the balance should be as free as possible from any control or influence except at such times as it received the necessary impulse to maintain the vibrations at a constant arc This want undoubtedly led to the invention of the detent escapement The early escapements were all frictional escapements, ie, the balance staff was never free froe escapement, which was undoubtedly the first employed, was constantly in contact with the escape wheel, and hat 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 caused the tiain The first attempt to correct this imperfection led to the invention and introduction of the fusee, which enabled the watch the entire period of action The next step in advance was the ”dead-beat escapement,” which included the cylinder and duplex In these frictional escapements the balance staff locked the train while the balance performed its arc of vibration

FRICTIONAL ESCAPEMENTS IN HIGH FAVOR

These frictional escapements held favor with many eminent watchmakers even after the introduction of the detached escapements It is no more than natural we should inquire, why? The idea with the advocates of the frictional rest escapements was, the friction 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 e escapeht, in fact, cause the timepiece to run slower from the increased friction of the escape-wheel tooth on the cylinder; also, in the duplex escape tooth on the staff retards the vibrations

Dr Hooke, the inventor of the balance spring, soon discovered it could be manipulated to isochronism, ie, so arcs of different extent would be formed in equal ti to possess different properties from one which would be isochronal with a perfectly detached escape, the duplex requiring other properties fro for a cylinder escapeh pocket watches with duplex and cylinder escape balances cos adjusted to isochronisood results, careful makers were satisfied that an escape the greater proportion of the arc of vibration and uncontrolled by any cause, would do still better, and this led to the detent escapement

FAULTS IN THE DETENT ESCAPEMENT

As stated previously, the detent escape pronounced faults in positions which held it back, it is probable it would never have been employed in pocket watches to any extent if it had not acquired such a high reputation in marine chronometers Let us now analyze the influences which surround the detent escapement in a marine chronometer and take account of the causes which are conizance of other interfering causes which have a tendency to prevent desired results First, ill i such as we find in fine hly-polished jewels; such pivots are perfectly cylindrical, and no larger than are absolutely necessary to endure the task iht of the balance and endure careful handling

To afford the necessary vibrations a spring is fitted, usually of a helical form, so disposed as to cause the balance to vibrate in arcs back and forth in equal time, _provided these arcs are of equal extent_

It is now to be taken note of that we have it at our disposal and option toor short arcs the quickest or to synchronize them We can readily comprehend we have now established a very perfect measure of short intervals of ti these vibrations and counting thehts of tireat accuracy The conditions which surround our balance are very constant, the s in fine hard jewels lubricated with an oil on which exposure to the action of the air has little effect, leaves but few influences which can interfere with the regular action of our balance

We add to the influences an adjustable correction for the disturbances of heat and cold, and we are convinced that but little could be added

ANTAGONISTIC INFLUENCES

In this coainst each other, viz, the elasticity of the spring and the weight and inertia of the balance; both forces are theoretically constant and should produce constant results The mechanical part of the problem is simply 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 tith of each vibration Many years have been spent in experi to arrive at the best propositions to employ for the several parts to obtain the best practical results Consequently, in designing a chronometer escapement we must not only draw the parts to a certain forht of material to employ

To illustrate e have just said, suppose, in drawing an escape wheel, weface of the tooth, but nizance of the thickness of 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 toothpower to the balance and yet by being too thin soon wear or produce excessive friction How thick an escape wheel should be to produce best results, is one of the many matters settled only by actual workshop experience

FACTORS THAT MUST BE CONSIDERED

Even this experience is in every instance modified by other influences

To illustrate: Let us suppose in the ordinary to-day iven average force, which we set down as so rains Now, if we should employ other material than hammer-hardened brass for an escape wheel it would modify the thickness; also, if we should decrease the motive power and increase the arc of impulse Or, if we should diminish the extent of the ie 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 bestform, size and material We would say, however, there has been but little deviation with our principal manufacturers of eneral principle on which they were constructed, the chief ai to excel in the perfection of the several parts and the care taken in the several adjustments