Usually the workman can manipulate the pallets to match the escape wheel so that the teeth will have the proper lock and drop at the right instant, and again have the correct lock on the next succeeding pallet. The tooth should fall but a slight distance before the tooth next in action locks it, because all the angular motion the escape wheel makes except when in contact with the pallets is just so much lost power, which should go toward giving motion to the balance.
There seems to be a little confusion in the use of the word “drop” in horological phrase, as it is used to express the act of parting of the tooth with the pallet. The idea will be seen by inspecting Fig. 108, where we show the tooth D and pallet C as about parting or dropping. When we speak of “banking up to the drop” we mean we set the banking screws so that the teeth will just escape from each pallet. By the term “fall” we mean the arc the tooth passes through before the next pallet is engaged. This action is also illustrated at Fig. 108, where the tooth D, after dropping from the pallet C, is arrested at the position shown by the dotted outline. We designate this arc by the term “fall,” and we measure this motion by its angular extent, as shown by the dotted radial lines i f and i g. As we have explained, this fall should only extend through an arc of one and a half degrees, but by close escapement matching this arc can be reduced to one degree, or even a trifle less.
[Illustration: Fig. 108]
We shall next describe an instrument for holding the escape wheel and pallets while adjusting them. As shown at Fig. 107, the fork A’ is banked a little close and the jewel pin as shown would, in some portions, rub on C’, making a scraping sound.
[Illustration: Fig. 109]
A point has now been reached where we can use an escapement matcher to advantage. There are several good ones on the market, but we can make one very cheaply and also add our own improvements. In making one, the first thing to be provided is a movement holder. Any of the three-jaw types of such holders will answer, provided the jaws hold a movement plate perfectly parallel with the bed of the holder. This will be better understood by inspecting Fig. 109, which is a side view of a device of this kind seen edgewise in elevation. In this B represents the bed plate, which supports three swing jaws, shown at C, Figs. 109 and 110. The watch plate is indicated by the parallel dotted lines A, Fig. 109. The seat a of the swing jaws C must hold the watch plate A exactly parallel with the bed plate B. In the cheap movement holders these seats (a) are apt to be of irregular heights, and must be corrected for our purpose. We will take it for granted that