The Project Gutenberg eBook ofWatch and Clock EscapementsThis ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online atwww.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.Title: Watch and Clock EscapementsAuthor: AnonymousRelease date: November 6, 2005 [eBook #17021]Most recently updated: December 12, 2020Language: EnglishCredits: E-text prepared by Robert Cicconetti, Janet Blenkinship, and the Project Gutenberg Online Distributed Proofreading Team*** START OF THE PROJECT GUTENBERG EBOOK WATCH AND CLOCK ESCAPEMENTS ***
This ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online atwww.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.
Title: Watch and Clock EscapementsAuthor: AnonymousRelease date: November 6, 2005 [eBook #17021]Most recently updated: December 12, 2020Language: EnglishCredits: E-text prepared by Robert Cicconetti, Janet Blenkinship, and the Project Gutenberg Online Distributed Proofreading Team
Title: Watch and Clock Escapements
Author: Anonymous
Author: Anonymous
Release date: November 6, 2005 [eBook #17021]Most recently updated: December 12, 2020
Language: English
Credits: E-text prepared by Robert Cicconetti, Janet Blenkinship, and the Project Gutenberg Online Distributed Proofreading Team
*** START OF THE PROJECT GUTENBERG EBOOK WATCH AND CLOCK ESCAPEMENTS ***
E-text prepared by Robert Cicconetti, Janet Blenkinship,and the Project Gutenberg Online Distributed Proofreading Team(https://www.pgdp.net/).Book provided by the New York University Library.
A Complete Study In Theory and Practice of the Lever, Cylinder and Chronometer Escapements, Together with a Brief Account of the Origin and Evolution of the Escapement in Horology
Compiled from the well-known Escapement Serials published in The Keystone
PUBLISHED BYTHE KEYSTONETHE ORGAN OF THE JEWELRY AND OPTICAL TRADES19th & Brown Sts., Philadelphia, U.S.A.
All Rights Reserved
Copyright, 1904, BY B. Thorpe, Publisher of The Keystone.
Especially notable among the achievements of The Keystone in the field of horology were the three serials devoted to the lever, cylinder and chronometer escapements. So highly valued were these serials when published that on the completion of each we were importuned to republish it in book form, but we deemed it advisable to postpone such publication until the completion of all three, in order that the volume should be a complete treatise on the several escapements in use in horology. The recent completion of the third serial gave us the opportunity to republish in book form, and the present volume is the result. We present it to the trade and students of horology happy in the knowledge that its contents have already received their approval. An interesting addition to the book is the illustrated story of the escapements, from the first crude conceptions to their present perfection.
In this treatise we do not propose to go into the history of this escapement and give a long dissertation on its origin and evolution, but shall confine ourselves strictly to the designing and construction as employed in our best watches. By designing, we mean giving full instructions for drawing an escapement of this kind to the best proportions. The workman will need but few drawing instruments, and a drawing-board about 15" by 18" will be quite large enough. The necessary drawing-instruments are a T-square with 15" blade; a scale of inches divided into decimal parts; two pairs dividers with pen and pencil points—one pair of these dividers to be 5" and the other 6"; one ruling pen. Other instruments can be added as the workman finds he needs them. Those enumerated above, however, will be all that are absolutely necessary.
Fig. 001
We shall, in addition, need an arc of degrees, which we can best make for ourselves. To construct one, we procure a piece of No. 24 brass, about 5-1/2" long by 1-1/4" wide. We show such a piece of brass atA, Fig. 1. On this piece of brass we sweep two arcs with a pair of dividers set at precisely 5", as shown (reduced) ata aandb b. On these arcs we set off the space held in our dividers—that is 5"—as shown at the short radial lines at each end of the two arcs. Now it is a well-known fact that the space embraced by our dividers contains exactly sixty degrees of the arcsa aandb b, or one-sixth of the entire circle; consequently, we divide the arcsa aandb binto sixty equal parts, to representdegrees, and at one end of these arcs we halve five spaces so we can get at half degrees.
Fig. 2
Before we take up the details of drawing an escapement we will say a few words about "degrees," as this seems to be something difficult to understand by most pupils in horology when learning to draw parts of watches to scale. At Fig. 2 we show several short arcs of fifteen degrees, all having the common centerg. Most learners seem to have an idea that a degree must be a specific space, like an inch or a foot. Now the first thing in learning to draw an escapement is to fix in our minds the fact that the extent of a degree depends entirely on the radius of the arc we employ. To aid in this explanation we refer to Fig. 2. Here the arcsc,d,eandfare all fifteen degrees, although the linear extent of the degree on the arccis twice that of the degree on the arcf. When we speak of a degree in connection with a circle we mean the one-three-hundred-and-sixtieth part of the periphery of such a circle. In dividing the arcsa aandb bwe first divide them into six spaces, as shown, and each of these spaces into ten minor spaces, as is also shown. We halve five of the degree spaces, as shown ath. We should be very careful about making the degree arcs shown at Fig. 1, as the accuracy of our drawings depends a great deal on the perfection of the division on the scaleA. In connection with such a fixed scale of degrees as is shown at Fig. 1, a pair of small dividers, constantly set to a degree space, is very convenient.
Fig. 3
To make such a pair of small dividers, take a piece of hard sheet brass about 1/20" thick, 1/4" wide, 1-1/2" long, and shape it as shown at Fig. 3. It should be explained, the part cut from the sheet brass is shown below the dotted linek, the portion above (C) being a round handle turned from hard wood or ivory. The slotlis sawn in, and two holes drilled in the end to insert the needle pointsi i. In making the slotlwe arrange to have the needle points come a little too close together to agree with the degree spaces on the arcsa aandb b. We then put the small screwjthrough one of the legsD'',and by turningj, set the needle pointsi ito exactly agree with the degree spaces. As soon as the pointsi iare set correctly,jshould be soft soldered fast.
The degree spaces onAare set off with these dividers and the spaces onAvery carefully marked. The upper and outer arca ashould have the spaces cut with a graver line, while the lower one,b bis best permanently marked with a carefully-made prick punch. After the arca ais divided, the brass plateAis cut back to this arc so the divisions we have just made are on the edge. The object of having two arcs on the plateAis, if we desire to get at the number of degrees contained in any arc of a 5" radius we lay the scaleAso the edge agrees with the arca a, and read off the number of degrees from the scale. In setting dividers we employ the dotted spaces on the arcb b.
Fig. 4
We will now proceed to delineate an escape wheel for a detached lever. We place a piece of good drawing-paper on our drawing-board and provide ourselves with a very hard (HHH) drawing-pencil and a bottle of liquid India ink. After placing our paper on the board, we draw, with the aid of our T-square, a line through the center of the paper, as shown atm m, Fig. 4. At 5-1/2" from the lower margin of the paper we establish the pointpand sweep the circlen nwith a radius of 5". We have said nothing about stretching our paper on the drawing-board; still, carefully-stretched paper is an important part of nice and correct drawing. We shall subsequently give directions for properly stretching paper, but for the present we will suppose the paper we are using is nicely tacked to the face of the drawing-board with the smallest tacks we can procure. The paper should not come quite to the edge of the drawing-board, so as to interfere with the head of the T-square. We are now ready to commence delineating our escape wheel and a set of pallets to match.
The simplest form of the detached lever escapement in use is the one known as the "ratchet-tooth lever escapement," and generally found in English lever watches. This form of escapement gives excellent results when well made; and we can only account for it not being in more general use from the fact that theescape-wheel teeth are not so strong and capable of resisting careless usage as the club-tooth escape wheel.
It will be our aim to convey broad ideas and inculcate general principles, rather than to give specific instructions for doing "one thing one way." The ratchet-tooth lever escapements of later dates have almost invariably been constructed on the ten-degree lever-and-pallet-action plan; that is, the fork and pallets were intended to act through this arc. Some of the other specimens of this escapement have larger arcs—some as high as twelve degrees.
Fig. 5
We illustrate at Fig. 5 what we mean by ten degrees of pallet-and-fork action. If we draw a line through the center of the pallet staff, and also through the center of the fork slot, as shown ata b, Fig. 5, and allow the fork to vibrate five degrees each side of said linesa b, to the linesa canda c', the fork has what we term ten-degree pallet action. If the fork and pallets vibrate six degrees on each side of the linea b—that is, to the linesa danda d'—we have twelve degrees pallet action. If we cut the arc down so the oscillation is only four and one-quarter degrees on each side ofa b, as indicated by the linesa sanda s', we have a pallet-and-fork action of eight and one-half degrees; which, by the way, is a very desirable arc for a carefully-constructed escapement.
The controlling idea which would seem to rule in constructing a detached lever escapement, would be to make it so the balance is free of the fork; that is, detached, during as much of the arc of the vibration of the balance as possible, and yet have the action thoroughly sound and secure. Where a ratchet-tooth escapement is thoroughly well-made of eight and one-half degrees of pallet-and-fork action, ten and one-half degrees of escape-wheel action can be utilized, as will be explained later on.
Fig. 6
We will now resume the drawing of our escape wheel, as illustrated at Fig. 4. In the drawing at Fig. 6 we show the circlen n, which represents the periphery of our escape wheel; and in the drawing we are supposed to be drawing it ten inches in diameter.
We produce the vertical linempassing through the centerpof the circlen. From the intersection of the circlenwith the linematiwe lay off thirty degrees on each side, and establish the pointse f; and from the centerp, through these points, draw the radial linesp e'andp f'. The pointsf e, Fig. 6, are, of course, just sixty degrees apart and represent the extent of two and one-half teeth of the escape wheel. There are two systems on which pallets for lever escapements are made, viz., equidistant lockings and circular pallets. The advantages claimed for each system will be discussed subsequently. For the first and present illustration we will assume we are to employ circular pallets and one of the teeth of the escape wheel resting on the pallet at the pointf; and the escape wheel turning in the direction of the arrowj. If we imagine a tooth as indicated at the dotted outline atD, Fig. 6, pressing against a surface which coincides with the radial linep f, the action would be in the direction of the linef hand at right angles top f. If we reason on the action of the toothD, as it presses against a pallet placed atf, we see the action is neutral.
Fig. 7
With a fifteen-tooth escape wheel each tooth occupies twenty-four degrees, and from the pointftoewould be two and one-half tooth-spaces. We show the dotted points of four teeth atD D' D'' D'''. To establish the center of the pallet staff we draw a line at right angles to the linep e'from the pointeso it intersects the linef hatk. For drawing a line at right angles to another line, as we have just done, a hard-rubber triangle, shaped as shown atC, Fig. 7, can be employed. To use such a triangle, we place it so the right, or ninety-degrees angle, rests ate, as shown at the dotted triangleC, Fig. 6, and the long side coincides with the radial linep e'. If the short side of the hard-rubber triangle is too short, as indicated, we place a short ruler so it rests against the edge, as shown at the dotted lineg e, Fig. 7, and while holding it securely down on the drawing weremove the triangle, and with a fine-pointed pencil draw the linee g, Fig. 6, by the short rule. Let us imagine a flat surface placed ateso its face was at right angles to the lineg e, which would arrest the toothD''after the toothDresting onfhad been released and passed through an arc of twelve degrees. A tooth resting on a flat surface, as imagined above, would also rest dead. As stated previously, the pallets we are considering have equidistant locking faces and correspond to the arcl l, Fig. 6.
In order to realize any power from our escape-wheel tooth, we must provide an impulse face to the pallets faced atf e; and the problem before us is to delineate these pallets so that the lever will be propelled through an arc of eight and one-half degrees, while the escape wheel is moving through an arc of ten and one-half degrees. We make the arc of fork action eight and one-half degrees for two reasons—(1) because most text-books have selected ten degrees of fork-and-pallet action; (2) because most of the finer lever escapements of recent construction have a lever action of less than ten degrees.
To "lay out" or delineate our escape-wheel teeth, we continue our drawing shown at Fig. 6, and reproduce this cut very nearly at Fig. 8. With our dividers set at five inches, we sweep the short arca a'fromfas a center. It is to be borne in mind that at the pointfis located the extreme point of an escape-wheel tooth. On the arca awe lay off fromptwenty-four degrees, and establish the pointb; at twelve degrees beyondbwe establish the pointc. Fromfwe draw the linesf bandf c; these lines establishing the form and thickness of the toothD. To get the length of the tooth, we take in our dividers one-half a tooth space, and on the radial linep festablish the pointdand draw circled' d'.
To facilitate the drawing of the other teeth, we draw the circlesd' c', to which the linesf bandf care tangent, as shown. We divide the circlen n, representing the periphery of our escape wheel, into fifteen spaces, to represent teeth, commencing atfand continued as shown ato ountil the entire wheel is divided. We only show four teeth complete, but the same methods as produced these will produce them all. To briefly recapitulate the instructions for drawing the teeth for the ratchet-tooth lever escapement: We draw the face of the teeth at an angle of twenty-four degrees to aradial line; the back of the tooth at an angle of thirty-six degrees to the same radial line; and make teeth half a tooth-space deep or long.
Fig. 8
We now come to the consideration of the pallets and how to delineate them. To this we shall add a careful analysis of their action. Let us, before proceeding further, "think a little" over some of the factors involved. To aid in this thinking or reasoning on the matter, let us draw the heavy arclextending from a little inside of the circlenatfto the circlenate. If now we imagine our escape wheel to be pressed forward in the direction of the arrowj, the toothDwould press on the arcland be held. If, however, we should revolve the arclon the centerkin the direction of the arrowi, the toothDwouldescapefrom the edge ofland the toothD''would pass through an arc (reckoning from the centerp) of twelve degrees, and be arrested by the inside of the arclate. If we now should reverse the motion and turn the arclbackward, the tooth atewould, in turn, be released and the tooth following afterD(but not shown) would engagelatf. By supplying motive to revolve the escape wheel (E) represented by the circlen, and causing the arclto oscillate back and forth in exactintervals of time, we should have, in effect, a perfect escapement. To accomplish automatically such oscillations is the problem we have now on hand.
In clocks, the back-and-forth movement, or oscillating motion, is obtained by employing a pendulum; in a movable timepiece we make use of an equally-poised wheel of some weight on a pivoted axle, which device we term a balance; the vibrations or oscillations being obtained by applying a coiled spring, which was first called a "pendulum spring," then a "balance spring," and finally, from its diminutive size and coil form, a "hairspring." We are all aware that for the motive power for keeping up the oscillations of the escaping circlelwe must contrive to employ power derived from the teethDof the escape wheel. About the most available means of conveying power from the escape wheel to the oscillating arclis to provide the lip of said arc with an inclined plane, along which the tooth which is disengaged fromlatfto slide and move said arclthrough—in the present instance an arc of eight and one-half degrees, during the time the toothDis passing through ten and one-half degrees. This angular motion of the arclis represented by the radial linesk f'andk r, Fig. 8. We desire to impress on the reader's mind the idea that each of these angular motions is not only required to be made, but the motion of one mobile must convey power to another mobile.
In this case the power conveyed from the mainspring to the escape wheel is to be conveyed to the lever, and by the lever transmitted to the balance. We know it is the usual plan adopted by text-books to lay down a certain formula for drawing an escapement, leaving the pupil to work and reason out the principles involved in the action. In the plan we have adopted we propose to induct the reader into the why and how, and point out to him the rules and methods of analysis of the problem, so that he can, if required, calculate mathematically exactly how many grains of force the fork exerts on the jewel pin, and also how much (or, rather, what percentage) of the motive power is lost in various "power leaks," like "drop" and lost motion. In the present case the mechanical result we desire to obtain is to cause our lever pivoted atkto vibrate back and forth through an arc of eight and one-half degrees; this lever not only to vibrate back and forth, but also to lock and hold theescape wheel during a certain period of time; that is, through the period of time the balance is performing its excursion and the jewel pin free and detached from the fork.
We have spoken of paper being employed for drawings, but for very accurate delineations we would recommend the horological student to make drawings on a flat metal plate, after perfectly smoothing the surface and blackening it by oxidizing.
By adopting eight and one-half degrees pallet-and-fork action we can utilize ten and one-half degrees of escape-wheel action. We show atA A', Fig. 9, two teeth of a ratchet-tooth escape wheel reduced one-half; that is, the original drawing was made for an escape wheel ten inches in diameter. We shall make a radical departure from the usual practice in making cuts on an enlarged scale, for only such parts as we are talking about. To explain, we show at Fig. 10 about one-half of an escape wheel one eighth the size of our large drawing; and when we wish to show some portion of such drawing on a larger scale we will designate such enlargement by saying one-fourth, one-half or full size.
Fig. 9
At Fig. 9 we show at half size that portion of our escapement embraced by the dotted linesd, Fig. 10. This plan enables us to show very minutely such parts as we have under consideration, and yet occupy but little space. The arca, Fig. 9, represents the periphery of the escape wheel. On this line, ten and one-half degrees from the point of the toothA, we establish the pointcand draw the radial linec c'. It is to be borne in mind that the arcembraced between the pointsbandcrepresents the duration of contact between the toothAand the entrance pallet of the lever. The space or short arcc nrepresents the "drop" of the tooth.
This arc of one and one-half degrees of escape-wheel movement is a complete loss of six and one-fourth per cent. of the entire power of the mainspring, as brought down to the escapement; still, up to the present time, no remedy has been devised to overcome it. All the other escapements, including the chronometer, duplex and cylinder, are quite as wasteful of power, if not more so. It is usual to construct ratchet-tooth pallets so as to utilize but ten degrees of escape-wheel action; but we shall show that half a degree more can be utilized by adopting the eight and one-half degree fork action and employing a double-roller safety action to prevent over-banking.
Fig. 10
From the pointe, which represents the center of the pallet staff, we draw throughbthe linee f. At one degree belowe fwe draw the linee g, and seven and one-half degrees below the linee gwe draw the linee h. For delineating the linese g, etc., correctly, we employ a degree-arc; that is, on the large drawing we are making we first draw the linee b f, Fig. 10, and then, with our dividers set at five inches, sweep the short arci, and on this lay off first one degree from the intersection off ewith the arci, and through this point draw the linee g.
From the intersection of the linef ewith the arciwe lay off eight and one-half degrees, and through this point draw the linee h. Bear in mind that we are drawing the pallet atBto represent one with eight and one-half degrees fork-and-pallet action, and with equidistant lockings. If we reason on the matter under consideration, we will see the toothAand the palletB, against which it acts, part or separate when the tooth arrives at the pointc; that is, after the escape wheel has moved through ten and one-half degrees of angular motion, the tooth drops from the impulse face of the pallet and falls through one and one-half degrees of arc, when the toothA'', Fig. 10, is arrested by the exit pallet.
To locate the position of the inner angle of the palletB, sweep the short arclby setting the dividers so one point or leg rests at the centereand the other at the pointc. Somewhere on this arclisto be located the inner angle of our pallet. In delineating this angle, Moritz Grossman, in his "Prize Essay on the Detached Lever Escapement," makes an error, in Plate III of large English edition, of more than his entire lock, or about two degrees. We make no apologies for calling attention to this mistake on the part of an authority holding so high a position on such matters as Mr. Grossman, because a mistake is a mistake, no matter who makes it.
We will say no more of this error at present, but will farther on show drawings of Mr. Grossman's faulty method, and also the correct method of drawing such a pallet. To delineate the locking face of our pallet, from the point formed by the intersection of the linese g b b', Fig. 9, as a center, we draw the linejat an angle of twelve degrees tob b''. In doing this we employ the same method of establishing the angle as we made use of in drawing the linese gande h, Fig. 10. The linejestablishes the locking face of the palletB. Setting the locking face of the pallet at twelve degrees has been found in practice to give a safe "draw" to the pallet and keep the lever secure against the bank. It will be remembered the face of the escape-wheel tooth was drawn at twenty-four degrees to a radial line of the escape wheel, which, in this instance, is the lineb b', Fig. 9. It will now be seen that the angle of the pallet just halves this angle, and consequently the toothAonly rests with its point on the locking face of the pallet. We do not show the outlines of the palletB, because we have not so far pointed out the correct method of delineating it.
Fig. 11
Fig. 12
Perhaps we cannot do our readers a greater favor than to digress from the study of the detached lever escapement long enough to say a few words about drawing instruments and tablets or surfaces on which to delineate, with due precision, mechanical designs or drawings. Ordinary drawing instruments, even of the higher grades, and costing a good deal of money, are far from being satisfactory to a man who has the proper idea of accuracy to be rated as a first-class mechanic. Ordinary compasses are obstinate when we try to set them to the hundredth of an inch; usually the points are dull and ill-shapen; if they make a puncture in the paper it is unsightly.
Fig. 13
Watchmakers have one advantage, however, because they can very easily work over a cheap set of drawing instruments and make them even superior to anything they can buy at the art stores. To illustrate, let us take a cheap pair of brass or German-silver five-inch dividers and make them over into needle points and "spring set." To do this the points are cut off at the linea a, Fig 11, and a steel tube is gold-soldered on each leg. The steel tube is made by taking a piece of steel wire which will fit a No. 16 chuck of a Whitcomb lathe, and drilling a hole in the end about one-fourth of an inch deep and about the size of a No. 3 sewing needle. We Show at Fig. 12 a view of the pointA', Fig. 11, enlarged, and the steel tube we have just drilled out attached atC. About the best way to attachCis to solder. After the tubeCis attached a hole is drilled throughA'atd, and the thumb-screwdinserted. This thumb-screw should be of steel, and hardened and tempered. The use of this screw is to clamp the needle point. With such a device as the tubeCand set-screwd, a No. 3 needle is used for a point; but for drawings on paper a turned point, as shown at Fig 13, is to be preferred. Such points can be made from a No. 3 needle after softening enough to be turned so as to form the pointc. This point at the shoulderfshould be about 12/1000 of an inch, or the size of a fourth-wheel pivot to an eighteen size movement.
The idea is, when drawing on paper the pointcenters the paper. For drawing on metal the form of the point is changed to a simple cone, as shown atB'c, Fig. 13. such cones can be turned carefully, then hardened and tempered to a straw color; and when they become dull, can be ground by placing the points in a wire chuck and dressing them up with an emery buff or an Arkansas slip. The opposite leg of the dividers is the one to which is attached the spring for close setting of the points.
Fig. 14
In making this spring, we take a piece of steel about two and one-fourth inches long and of the same width as the leg of the divider, and attach it to the inside of the leg as shown at Fig. 14, whereDrepresents the spring andAthe leg of the dividers. The springDhas a short steel tubeC''and set-screwd''for a fine point likeBorB'. In the lower end of the legA, Fig. 14, is placed the milled-head screwg, which serves to adjust the two points of the dividers to very close distances. The springDis, of course, set so it would press close to the legAif the screwgdid not force it away.
It will be seen that we can apply a springDand adjusting screw opposite to the leg which carries the pen or pencil point of all our dividers if we choose to do so; but it is for metal drawing that such points are of the greatest advantage, as we can secure an accuracy very gratifying to a workman who believes in precision. For drawing circles on metal, "bar compasses" are much the best, as they are almost entirely free from spring, which attends the jointed compass. To make (because they cannot be bought) such an instrument, take a piece of flat steel, one-eighth by three-eighths of an inch and seven inches long, and after turning and smoothing it carefully, make a slide half an inch wide, as shown at Fig. 15, with a set-screwhon top to secure it at any point on the barE. In the lower part of the slideFis placed a steel tube likeC, shown in Figs. 12 and 14, with set-screw for holding points likeB B', Fig. 13. At the opposite end of the barEis placed a looped springG, which carries a steel tube and point like the springD, Fig. 14. Above this tube and point, shown atj, Fig. 15, is placed an adjustment screwkfor fine adjustment. The inner end of the screwkrests against the end of the barE. The tendency of the springGis to close upon the end ofE; consequently if we make use of the screwkto force away the lower end ofG, we can set the fine point injto the greatest exactness.
Fig. 15
The springGis made of a piece of steel one-eighth of an inch square, and secured to the barEwith a screw and steady pins atm. A pen and pencil point attachment can be added to the springG; but in case this is done it would be better to make another spring likeGwithout the pointj, and with the adjusting screw placed atl. In fitting pen and pencil points to a spring likeGit would probably be economical to make them outright; that is, make the blades and screw for the ruling pen and a spring or clamping tube for the pencil point.
We will now, with our improved drawing instruments, resume the consideration of the ratchet-tooth lever escapement. We reproduce at Fig. 16 a portion of diagram III, from Moritz Grossmann's "Prize Essay on the Detached Lever Escapement," in order to point out the error in delineating the entrance pallet to which we previously called attention. The cut, as we give it, is not quite one-half the size of Mr. Grossmann's original plate.
In the cut we give the letters of reference employed the same as on the original engraving, except where we use others in explanation. The angular motion of the lever and pallet action as shown in the cut is ten degrees; but in our drawing, where we only use eight and one-half degrees, the same mistake would give proportionate error if we did not take the means to correct it. The error to which we refer lies in drawing the impulse face of the entrance pallet. The impulse face of this pallet as drawn by Mr. Grossmann would not, from the action of the engaging tooth, carry this pallet through more than eight degrees of angular motion; consequently, the tooth which should lock on the exit pallet would fail to do so, and strike the impulse face.
We would here beg to add that nothing will so much instruct a person desiring to acquire sound ideas on escapements as making a large model. The writer calls to mind a wood model of a lever escapement made by one of the "boys" in the Elgin factory about a year or two after Mr. Grossmann's prize essay was published. It went from hand to hand and did much toward establishing sound ideas as regards the correct action of the lever escapement in that notable concern.
If a horological student should construct a large model on the lines laid down in Mr. Grossmann's work, the entrance pallet wouldbe faulty in form and would not properly perform its functions. Why? perhaps says our reader. In reply let us analyze the action of the toothBas it rests on the palletA. Now, if we move this pallet through an angular motion of one and one-half degrees on the centerg(which also represents the center of the pallet staff), the toothBis disengaged from the locking face and commences to slide along the impulse face of the pallet and "drops," that is, falls from the pallet, when the inner angle of the pallet is reached.
Fig. 16
This inner angle, as located by Mr. Grossmann, is at the intersection of the short arciwith the lineg n, which limits the ten-degree angular motion of the pallets. If we carefully study the drawing, we will see the pallet has only to move through eight degrees of angular motion of the pallet staff for the tooth to escape,because the tooth certainly must be disengaged when the inner angle of the pallet reaches the peripheral line a. The true way to locate the position of the inner angle of the pallet, is to measure down on the arciten degrees from its intersection with the peripheral lineaand locate a point to which a line is drawn from the intersection of the lineg mwith the radial linea c, thus defining the inner angle of the entrance pallet. We will name this point the pointx.
It may not be amiss to say the arciis swept from the centergthrough the pointu, said point being located ten degrees from the intersection of the radiala cwith the peripheral linea. It will be noticed that the inner angle of the entrance palletAseems to extendinward, beyond the radial linea j, that is, toward the pallet centerg, and gives the appearance of being much thicker than the exit palletA'; but we will see on examination that the extreme anglexof the entrance pallet must move on the arciand, consequently, cross the peripheral lineaat the pointu. If we measure the impulse faces of the two palletsA A', we will find them nearly alike in linear extent.
Fig. 17
Mr. Grossmann, in delineating his exit pallet, brings the extreme angle (shown at4) down to the periphery of the escape, as shown in the drawing, where it extends beyond the intersection of the lineg fwith the radial linea 3. The correct form for the entrance pallet should be to the dotted linez x y.
We have spoken of engaging and disengaging frictions; we do not know how we can better explain this term than by illustrating the idea with a grindstone. Suppose two men are grinding on the same stone; each has, say, a cold chisel to grind, as shown at Fig. 17, whereGrepresents the grindstone andN N'the cold chisels. The grindstone is supposed to be revolving in the direction of the arrow. The chiselsNandN'are both being ground, but the chiselN'is being cut much the more rapidly, as each particle of grit of the stone as it catches on the steel causes the chisel to hug the stone and bite in deeper and deeper; while the chisel shown atNis thrust away by the action of the grit. Now, friction of any kind is only a sort of grinding operation, and the same principles hold good.
It is to be hoped the reader who intends to profit by this treatise has fitted up such a pair of dividers as those we have described, because it is only with accurate instruments he can hope to produce drawings on which any reliance can be placed. The drawing of a ratchet-tooth lever escapement of eight and one-half degrees pallet action will now be resumed. In the drawing at Fig. 18 is shown a complete delineation of such an escapement with eight and one-half degrees of pallet action and equidistant locking faces. It is, of course, understood the escape wheel is to be drawn ten inches in diameter, and that the degree arcs shown in Fig. 1 will be used.
We commence by carefully placing on the drawing-board a sheet of paper about fifteen inches square, and then verticallythrough the center draw the linea' a''. At some convenient position on this line is established the pointa, which represents the center of the escape wheel. In this drawing it is not important that the entire escape wheel be shown, inasmuch as we have really to do with but a little over sixty degrees of the periphery of the escape wheel. With the dividers carefully set at five inches, froma, as a center, we sweep the arcn n, and from the intersection of the perpendicular linea' a''with the arcnwe lay off on each side thirty degrees from the brass degree arc, and through the points thus established are drawn the radial linesa b'anda d'.
Fig. 18
The point on the arcnwhere it intersects with the lineb'is termed the pointb. At the intersection of the radial linea d'is established the pointd. We take ten and one-half degrees in the dividers, and from the pointbestablish the pointc, which embraces the arc of the escape wheel which is utilized by the pallet action. Through the pointbthe lineh' his drawn at right angles to the linea b'. The linej j'is also drawn at right angles to the linea d'through the pointd. We now have an intersection of the lines just drawn in common with the linea a'at the pointg, said point indicating the center of the pallet action.
The dividers are now set to embrace the space between the pointsbandgon the lineh' h, and the arcf fis swept; which, inproof of the accuracy of the work, intersects the arcnat the pointd. This arc coincides with the locking faces of both pallets. To lay out the entrance pallet, the dividers are set to five inches, and fromgas a center the short arco ois swept. On this arc one degree is laid off below the lineh' h, and the lineg idrawn. The space embraced between the lineshandion the arcfrepresents the locking face of the entrance pallet, and the point formed at the intersection of the lineg iwith the arcfis called the pointp. To give the proper lock to the face of the pallet, from the pointpas a center is swept the short arcr r, and from its intersection with the linea b'twelve degrees are laid off and the lineb sdrawn, which defines the locking face of the entrance pallet. Fromgas a center is swept the arcc' c', intersecting the arcn natc. On this arc (c) is located the inner angle of the entrance pallet. The dividers are set to embrace the space on the arcc'between the linesg h'andg k. With this space in the dividers one leg is set at the pointc, measuring down on the arcc'and establishing the pointt. The pointspandtare then connected, and thus the impulse face of the entrance palletBis defined. From the pointtis drawn the linet t', parallel to the lineb s, thus defining the inner face of the entrance pallet.
To delineate the exit pallet, sweep the short arcu u(fromgas a center) with the dividers set at five inches, and from the intersection of this arc with the lineg j'set off eight and one-half degrees and draw the lineg l. At one degree below this line is drawn the lineg m. The space on the arcfbetween these lines defines the locking face of the exit pallet. The point where the lineg mintersects the arcfis named the pointx. From the pointxis erected the linex w, perpendicular to the lineg m. Fromxas a center, and with the dividers set at five inches, the short arcy yis swept, and on this arc are laid off twelve degrees, and the linex zis drawn, which line defines the locking face of the exit pallet.
Next is taken ten and one-half degrees from the brass degree-scale, and from the pointdon the arcnthe space named is laid off, and thus is established the pointv; and fromgas a center is swept the arcv' v'through the pointv. It will be evident on a little thought, that if the toothA'impelled the exit pallet to the position shown, the outer angle of the pallet must extend down tothe pointv, on the arcv' v'; consequently, we define the impulse face of this pallet by drawing a line from pointxtov. To define the outer face of the exit pallet, we draw the linev eparallel to the linex z.
There are no set rules for drawing the general form of the pallet arms, only to be governed by and conforming to about what we would deem appropriate, and to accord with a sense of proportion and mechanical elegance. Ratchet-tooth pallets are usually made in what is termed "close pallets"; that is, the pallet jewel is set in a slot sawed in the steel pallet arm, which is undoubtedly the strongest and most serviceable form of pallet made. We shall next consider the ratchet-tooth lever escapement with circular pallets and ten degrees of pallet action.
To delineate "circular pallets" for a ratchet-tooth lever escapement, we proceed very much as in the former drawing, by locating the pointA, which represents the center of the escape wheel, at some convenient point, and with the dividers set at five inches, sweep the arcm, to represent the periphery of the escape wheel, and then draw the vertical lineA B', Fig. 19. We (as before) lay off thirty degrees on the arcmeach side of the intersection of said arc with the lineA B', and thus establish on the arcmthe pointsa b, and fromAas a center draw through the points so established the radial linesA a'andA b'.
We erect from the pointaa perpendicular to the lineA a, and, as previously explained, establish the pallet center atB. Inasmuch as we are to employ circular pallets, we lay off to the left on the arcm, from the pointa, five degrees, said five degrees being half of the angular motion of the escape wheel utilized in the present drawing, and thus establish the pointc, and fromAas a center draw through this point the radial lineA c'. To the right of the pointawe lay off five degrees and establish the pointd. To illustrate the underlying principle of our circular pallets: with one leg of the dividers set atBwe sweep through the pointsc a dthe arcsc'' a'' d''.
FromBas a center, we continue the lineB atof, and with the dividers set at five inches, sweep the short arce e. From the intersection of this arc with the lineB fwe lay off one and a half degrees and draw the lineB g, which establishes the extent of thelock on the entrance pallet. It will be noticed the linear extent of the locking face of the entrance pallet is greater than that of the exit, although both represent an angle of one and a half degrees. Really, in practice, this discrepancy is of little importance, as the same side-shake in banking would secure safety in either case.