Watch and Clock Escapements | Page 9

periphery of the escape, as shown in the
drawing, where it extends beyond the intersection of the line g f with
the radial line _a 3_. The correct form for the entrance pallet should be
to the dotted line z x y.
[Illustration: Fig. 17]
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, where G
represents the grindstone and _N N'_ the cold chisels. The grindstone is
supposed to be revolving in the direction of the arrow. The chisels N
and _N'_ are both being ground, but the chisel _N'_ 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 at N is 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.
THE NECESSITY FOR GOOD INSTRUMENTS.
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 vertically through the center
draw the line _a' a''_. At some convenient position on this line is
established the point a, 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, from a, as a center, we sweep the arc n n,
and from the intersection of the perpendicular line _a' a''_ with the arc n
we lay off on each side thirty degrees from the brass degree arc, and
through the points thus established are drawn the radial lines _a b'_ and
_a d'_.
[Illustration: Fig. 18]
The point on the arc n where it intersects with the line _b'_ is termed
the point b. At the intersection of the radial line _a d'_ is established the
point d. We take ten and one-half degrees in the dividers, and from the
point b establish the point c, which embraces the arc of the escape

wheel which is utilized by the pallet action. Through the point b the
line _h' h_ is drawn at right angles to the line _a b'_. The line _j j'_ is
also drawn at right angles to the line _a d'_ through the point d. We
now have an intersection of the lines just drawn in common with the
line _a a'_ at the point g, said point indicating the center of the pallet
action.
The dividers are now set to embrace the space between the points b and
g on the line _h' h_, and the arc f f is swept; which, in proof of the
accuracy of the work, intersects the arc n at the point d. This arc
coincides with the locking faces of both pallets. To lay out the entrance
pallet, the dividers are set to five inches, and from g as a center the
short arc o o is swept. On this arc one degree is laid off below the line
_h' h_, and the line g i drawn. The space embraced between the lines h
and i on the arc f represents the locking face of the entrance pallet, and
the point formed at the intersection of the line g i with the arc f is called
the point p. To give the proper lock to the face of the pallet, from the
point p as a center is swept the short arc r r, and from its intersection
with the line _a b'_ twelve degrees are laid off and the line b s drawn,
which defines the locking face of the entrance pallet. From g as a center