A Lever Escapement Fault

American Watchmaker and Jeweler (1892)

This is what is called mismatched pallets and escape wheel. In the club tooth this error is very fatal to good rate and is about as represented in Fig. 230. With the escapement at its best the friction is very little, but to maintain it constant is of the greatest importance. Now, to thoroughly explain the fault above mentioned it is necessary to first state it and then call attention to the illustrations. This error is the relative pitch or slant of the impulse plane of the tooth and the pallet. When in a perfect relation, as in Fig. 229, the tooth gets onto the impulse plane of the pallet, with its front corner touching the pallet's plane and so moves about two-thirds of the way across, with only the corner touching, then as it proceeds, the whole face of the tooth touches the plane, shortly after the front corner has left the plane, and thus the escapement is made. With the faulty escapement, as in Fig. 230, the pallet's front corner gets onto the impulse plane of the tooth and thus proceeds a part of the way before the correct relation begins. Now when, as in the first case, the tooth rides over pallet with its corner, the corner of the tooth cannot cut the plane of the pallet, as the metal will not act on the stone; but as in the second case, when the pallet's corner gets onto the plane of the tooth and so proceeds, the pallet corner will wear the face of the tooth, as the stone will cut the soft metal. This fault is present in a more or less degree in many escapements with the club tooth, and when a watch gives trouble by failing to keep its rate after cleaning, as soon as the oil is the least dry on pallets, it argues that this fault may be looked for. The illustrations of the two actions are purposely exaggerated to clearly illustrate the points under treatment.