*Project Gutenberg*. Public domain.

HOW TO DELINEATE A FORK AND ROLLER.

To arrive at the proper proportions of the several
parts, we divide the space *A B* into four equal
parts, as previously directed, and draw the circle
*a* and short arc *b*. With our dividers
set at 5”, from *B* as a center we sweep
the short arc *c*. From our arc of sixty
degrees, with a 5” radius, we take five degrees,
and from the intersection of the right line *A B*
with the arc *c* we lay off on each side five
degrees and establish the points *d e*; and from
*B* as a center, through these points draw the
lines *B d’* and *B e’*.
Now the arc embraced between these lines represents
the angular extent of our fork action.

From *A* as a center and with our dividers set
at 5”, we sweep the arc *f*. From
the scale of degrees we just used we lay off fifteen
degrees on each side of the line *A B* on the
arc *f*, and establish the points *g h*.
From *A* as a center, through the points just
established we draw the radial lines *A g’*
and *A h’*. The angular extent between
these lines defines the limit of our roller action.

Now if we lay off on the arc *f* six degrees
each side of its intersection with the line *A B*,
we define the extent of the jewel pin; that is, on
the arc *f* we establish the points *l m*
at six degrees from the line *A B*, and through
the points *l m* draw, from *A* as a center,
the radial lines *A l’* and *A m’*.
The extent of the space between the lines *A l’*
and *A m’* on the circle *a* defines
the size of our jewel pin.

TO DETERMINE THE SIZE OF A JEWEL PIN.

[Illustration: Fig. 56]

To make the situation better understood, we make an
enlarged drawing of the lines defining the jewel pin
at Fig. 56. At the intersection of the line *A
B* with the arc *a* we locate the point *k*,
and from it as a center we sweep the circle *i*
so it passes through the intersection of the lines
*A l’* and *A m’* with the arc
*a*. We divide the radius of the circle
*i* on the line *A B* into five equal parts,
as shown by the vertical lines *j*. Of these
five spaces we assume three as the extent of the jewel
pin, cutting away that portion to the right of the
heavy vertical line at *k*.

[Illustration: Fig. 57]

We will now proceed to delineate a fork and roller
as the parts are related on first contact of jewel
pin with fork and initial with the commencing of the
act of unlocking a pallet. The position and relations
are also the same as at the close of the act of impulse.
We commence the drawing at Fig. 57, as before, by
drawing the line *A B* and the arcs *a*
and *b* to represent the pitch circles. We