Part 1 (2/2)

PALLET-AND-FORK ACTION

[Illustration: Fig 5]

We illustrate at Fig 5 e rees 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 at _a b_, Fig 5, and allow the fork to vibrate five degrees each side of said lines _a b_, to the lines _a c_ and _a c'_, the fork has e terree pallet action If the fork and pallets vibrate six degrees on each side of the line _a b_--that is, to the lines _a d_ and _a 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 of _a b_, as indicated by the lines _a s_ and _a 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 escape idea which would see 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 escaperees of pallet-and-fork action, ten and one-half degrees of escape-wheel action can be utilized, as will be explained later on

We will now resu 4 In the drawing at Fig 6 we show the circle _n n_, which represents the periphery of our escape wheel; and in the drae are supposed to be drawing it ten inches in diah the center _p_ of the circle _n_ From the intersection of the circle _n_ with the line _rees on each side, and establish the points _e f_; and froh these points, draw the radial lines _p e'_ and _p f'_ The points _f 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 escapes and circular pallets

The advantages claimed for each system will be discussed subsequently

For the first and present illustration ill assume we are to employ circular pallets and one of the teeth of the escape wheel resting on the pallet at the point _f_; and the escape wheel turning in the direction of the arrow _j_ If we i 6, pressing against a surface which coincides with the radial line _p f_, the action would be in the direction of the line _f h_ and at right angles to _p f_ If we reason on the action of the tooth _D_, as it presses against a pallet placed at _f_, we see the action is neutral

[Illustration: Fig 6]

ESTABLIshi+NG THE CENTER OF PALLET STAFF

[Illustration: Fig 7]

With a fifteen-tooth escape wheel each tooth occupies twenty-four degrees, and from the point _f_ to _e_ would be two and one-half tooth-spaces We show the dotted points of four teeth at _D D' D''D'''_

To establish the center of the pallet staff we draw a line at right angles to the line _p e'_ from the point _e_ so it intersects the line _f h_ at _k_ For drawing a line at right angles to another line, as we have just done, a hard-rubber triangle, shaped as shown at _C_, Fig 7, can be eht, or ninety-degrees angle, rests at _e_, as shown at the dotted triangle _C_, Fig 6, and the long side coincides with the radial line _p 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 line _g e_, Fig 7, and while holding it securely down on the drae rele, and with a fine-pointed pencil draw the line _e g_, Fig 6, by the short rule Let us iht angles to the line _g e_, which would arrest the tooth _D''_ after the tooth _D_ resting on _f_ had been released and passed through an arc of twelve degrees A tooth resting on a flat surface, as iined above, would also rest dead As stated previously, the pallets we are considering have equidistant locking faces and correspond to the arc _l l_, Fig 6

In order to realize any power from our escape-wheel tooth, we must provide an impulse face to the pallets faced at _f 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 rees We rees for two reasons--(1) because rees 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

LAYING OUT ESCAPE-WHEEL TEETH

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, eep the short arc _a a'_ from _f_ as a center It is to be borne in mind that at the point _f_ is located the extreme point of an escape-wheel tooth On the arc _a a_ we lay off frorees, and establish the point _b_; at twelve degrees beyond _b_ we establish the point _c_ From _f_ we draw the lines _f b_ and _f c_; these lines establishi+ng the forth of the tooth, we take in our dividers one-half a tooth space, and on the radial line _p f_ establish the point _d_ and draw circle _d' d'_

To facilitate the drawing of the other teeth, we draw the circles _d' c'_, to which the lines _f b_ and _f c_ are tangent, as shown We divide the circle _n n_, representing the periphery of our escape wheel, into fifteen spaces, to represent teeth, co at _f_ and continued as shown at _o o_ until the entire wheel is divided We only show four teeth complete, but the same methods as produced these will produce the the teeth for the ratchet-tooth lever escapele of twenty-four degrees to a radial line; the back of the tooth at an angle of thirty-six degrees to the same radial line; and

[Illustration: 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 so or reasoning on thefrom a little inside of the circle _n_ at _f_ to the circle _n_ at _e_ If noe iine our escape wheel to be pressed forward in the direction of the arrow _j_, the tooth _D_ would press on the arc _l_ and be held If, however, we should revolve the arc _l_ on the center _k_ in the direction of the arrow _i_, the tooth _D_ would _escape_ froh an arc (reckoning frorees, and be arrested by the inside of the arc _l_ at _e_ Ifshould reverse the motion and turn the arc _l_ backward, the tooth at _e_ would, in turn, be released and the tooth following after _D_ (but not shoould engage _l_ at _f_ By supplying motive to revolve the escape wheel (_E_) represented by the circle _n_, and causing the arc _l_ to oscillate back and forth in exact intervals of time, we should have, in effect, a perfect escapement To accomplish automatically such oscillations is the problem we have now on hand

HOW MOTION IS OBTAINED

In clocks, the back-and-fortha pendulum; in a movable tiht on a pivoted axle, which device we ter obtained by applying a coiled spring, which was first called a ”pendulu,” and finally, fro” We are all aware that for thecircle _l_ we must contrive to employ power derived from the teeth _D_ of the escape wheel About thepower fro arc _l_ is to provide the lip of said arc with an inclined plane, along which the tooth which is disengaged froh--in the present instance an arc of eight and one-half degrees, during the tirees This angular motion of the arc _l_ is represented by the radial lines _k f'_ and _k r_, Fig 8 We desire to iular 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 fro 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 for 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 rains of force the fork exerts on the jewel pin, and also how e) 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 at _k_ to 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 the escape wheel during a certain period of tih the period of ti its excursion and the jewel pin free and detached from the fork