Fig. 34. Drawing escape wheel to fit a tracing from a pallet fork.
Can we work the rule backwards? Suppose we get a clock in which we have the pallet arbor adjustable as before, and we have the pallet fork all in good shape, but we have lost the escape wheel, or it has been butchered by somebody before coming to us, so that a new one is required.
Take off the pallet fork; lay it on a sheet of brass and trace around it carefully with a needle point. [Fig. 34]. Mark the center carefully at the pallet arbor hole and measure carefully the distance between the pallets and mark that center. Draw a center line cutting these centers and extending beyond. Now draw the tangent from the beginning of the entering pallet (as shown by the tracing on our brass) to the pallet center; do the same with the exit pallet. Now take a metal square and place it on one of the tangents exactly, with the end at the beginning of the entering pallet; trace a line cutting the line of centers and we have the radius of our escape wheel. Trace a circle from the intersection of the radius and the center line and we have the circumference of our escape wheel. This circle should also cut the intersection of the tangent and radius on the other side if it is drawn correctly; if it does not do this an error has been made in the drawing.
