Studies in the Lever Escapement

From The American Horologist magazine, March 1938

Studies in the Lever Escapement
By HAROLD C. KELLY
Member National Technical Board, U. H. A. of A.
(Continued)

Shifting Pallet Stones - The shifting of pallet stones has a greater effect on the entire escapement than many horologists realize. We have already learned that when one pallet stone is drawn out the lock is increased on both pallets but much more than that takes place. In fact the draw, the lift, the lock and the drop are altered by merely moving one pallet stone.

For example let us draw out the receiving stone. This is what occurs:

1. The draw is increased on both pallets.
2. The lift is increased on the receiving pallet.
3. The lock (although increased on both pallets) is made deeper on the discharging stone than on the receiving stone.
4. The drop is increased.
Now supposing that instead of drawing out the receiving stone we draw out only the discharging stone. This is what occurs:
1. The draw is decreased on both pallets.
2. The lift is decreased on the discharging stone.
3. The lock (although increased on both pallets) is made less on the receiving stone than on the discharging stone.
4. The drop remains practically the same. 

Discharging stone has the opposite effect as compared with the drawing out of the receiving stone. Likewise if we push in the receiving stone the draw and lift are lessened and if we push in the discharging stone the draw and lift are increased.

Why is this true? It may be explained in this way: Let us assume that the discharging stone has been drawn out. (See Figure 10). We now find it necessary to turn the banking so as to let the escape wheel tooth pass the discharging stone and another tooth lock on the receiving stone. Having opened the banking we find that the receiving stone has dipped further into the escape wheel. 

Of course the lever is now out of angle but if we bend the lever so as to make the angular motion from the line of centers equal and re-bank to the drop, we have actually created a new and reduced angle of draw on both pallets.

For the same reason the lift is also altered but it is observed that the lift is changed only on the stone that is moved and not on both stones as it is in the case of the draw. The reason for this is because draw functions thru the entire distance that a stone is locked while the lift occurs only along the path traversed by the escape wheel tooth.

In reversing the alteration the opposite effect takes place is already stated.
Let us now give our attention regarding the statement relative to the drop. It was stated that by drawing out the receiving pallet the drop is increased. Referring to Figure 11 note that the dotted line A is longer than the solid line B. The drawing is self explanatory therefore further comment is not required.

Thus it is evident that a thorough understanding of the effect of shifting pallet stones should be acquired if one is to be efficient in escapement work.

Many practical examples actually experienced at the bench in escapement adjusting are given in the writer's book.