In the double-roller action which we shall
consider, we shall adopt three-fifths of the pitch diameter of the
jewel-pin action as the proper size. Not but what the proportions given
by Grossmann will do good service; but we adopt the proportions named
because it enables us to use a light fork, and still the friction of the
guard point on the roller is but little more than where a guard roller
of half the diameter of the acting roller is employed.
The fork action we shall consider at present is ten degrees, but
subsequently we shall consider a double-roller action in which the fork
and pallet action is reduced to eight degrees. We shall conceive the
play between the guard point and the safety roller as one degree, which
will leave half a degree of lock remaining in action on the engaged
pallet.
THEORETICAL ACTION OF DOUBLE ROLLER CONSIDERED.
In the drawing at Fig. 81 we show a diagram of the action of the
double-roller escapement. The small circle at _A_ represents the center
of the pallet staff, and the one at _B_ the center of the balance staff.
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