Watch and Clock Escapements | Page 3

and we can only account for it not being in more
general use from the fact that the escape-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.
PALLET-AND-FORK ACTION.
[Illustration: 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 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 what we term ten-degree 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 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.
We will now resume the drawing of our escape wheel, as illustrated at
Fig. 4. In the drawing at Fig. 6 we show the circle n 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 line m passing through the center p of the
circle n. From the intersection of the circle n with the line m at i we lay
off thirty degrees on each side, and establish the points _e f_; and from
the center p, through 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 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
point _f_; and the escape wheel turning in the direction of the arrow j.
If we imagine a tooth as indicated at the dotted outline at D, Fig. 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]
ESTABLISHING 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 employed.
To use such a triangle, we place it so the right, 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