roller, or roller table, as it is frequently called.

[Illustration: Fig. 61]

[Illustration: Fig. 62]

For deciding the angular extent of the passing hollow we have no fixed
rule, but if we make it to occupy about half more angular extent on the
circle _y_ than will coincide with the angular extent of the jewel pin,
it will be perfectly safe and effectual. We previously stated that the
jewel pin should occupy about twelve degrees of angular extent on the
circle _c_, and if we make the passing hollow occupy eighteen degrees
(which is one and a half the angular extent of the jewel pin) it will do
nicely. But if we should extend the width of the passing hollow to
twenty-four degrees it would do no harm, as the jewel pin would be well
inside the horn of the fork before the guard pin could enter the passing
hollow.

[Illustration: Fig. 63]

We show in Fig. 61 the fork as separated from the roller, but in Fig.
62, which is a side view, we show the fork and jewel pin as engaged.
When drawing a fork and roller action it is safe to show the guard pin
as if in actual contact with the roller. Then in actual construction, if
the parts are made to measure and agree with the drawing in the gray,
that is, before polishing, the process of polishing will reduce the
convex edge of the roller enough to free it.

It is evident if thought is given to the matter, that if the guard pin
is entirely free and does not touch the roller in any position, a