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.
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.
HOW TO MAKE AN ESCAPEMENT MATCHING TOOL.
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 all the seats a are of precisely the same height, measured from B, and that a watch plate placed in the jaws C will be held exactly parallel with the said bed B. We must next provide two pillars, shown at D E, Figs. 109 and 111. These pillars furnish support for sliding centers which hold the top pivots of the escape wheel and pallet staff while we are testing the depths and adjusting the pallet stones. It will be understood that these pillars D E are at right angles to the plane of the bed B, in order that the slides like G N on the pillars D E move exactly vertical. In fact, all the parts moving up and down should be accurately made, so as not to destroy the depths taken from the watch plate A. Suppose, to illustrate, that we place the plate A in position as shown, and insert the cone point n, Figs. 109 and 112, in the pivot hole for the pallet staff, adjusting the slide G N so that the cone point rests accurately in said pivot hole. It is further demanded that the parts I H F G N D be so constructed and adjusted that the sliding center I moves truly vertical, and that we can change ends with said center I and place the hollow cone end m, Fig. 112, so it will receive the top pivot of the pallet staff and hold it exactly upright.
The idea of the sliding center I is to perfectly supply the place of the opposite plate of the watch and give us exactly the same practical depths as if the parts were in their place between the plates of the movement. The foot of the pillar D has a flange attached, as shown at f, which aids in holding it perfectly upright. It is well to cut a screw on D at D', and screw the flange f on such screw and then turn the lower face of f flat to aid in having the pillar D perfectly upright.