Tid-Bit 10 - Adjusting Pallets
The Graham deadbeat escapement is found in a wide variety of clocks, including most of the Vienna Regulators and Precision Regulators seen in my shop. With time the escapements pallet faces become grooved from sliding across the tip of the escape-wheel teeth. Over the centuries this grooving can convert a deadbeat escapement to a recoil escapement. Interestingly, when this happens the clock often continues to run, perhaps a tad fast, but run none the less.
While hardened pallets wear at a slower rate than softer pallets, eventually they all develop grooves, unless of course one is lucky enough to own a clock with jeweled pallets. My methods for dressing grooved pallets are discussed in a previous Technical Tid Bit (see the April 2010 Bulletin, page 191 for Tech Tid-Bit 4).
Figure 5 – Tip of Escape-Wheel Tooth Resting on Deadbeat Pallet Face
The Graham deadbeat escapement is designed such that the tip of an escape wheel tooth falls onto a pallets dead beat face when the other pallet “releases” the escape wheel. Typically the anchor will then continue to follow the motion of the pendulum, slightly increasing the “lock” (the distance between where the tip of the escape-wheel tooth rests on the dead beat face and the break point between the deadbeat and the impulse pallet faces – Dimension “L” in Figure 5). The pendulum then reverses its motion, and the tip of the escape wheel tooth slides off of the deadbeat face and onto the impulse face. The pendulum is pushed (or impulsed) during the time that the escape-wheel tooth tip slides down the impulse face (Dimension “I” in Figure 5). When the tip of the tooth falls off the end of the impulse face a tooth on the other side of the escape wheel falls onto the deadbeat face of the opposite pallet.
There are two criteria that I check to make sure the escapement is set up correctly – drop and lock. Drop is the distance between the tip of an escape-wheel tooth and the deadbeat face of the pallet just as the opposite pallet releases the escape wheel. It is important that the drop be equal for both pallets – this assures that a deadbeat escapement can be set up with sufficient lock. As mentioned above, a future Tid-Bit will discuss adjusting drop.
Which brings us to “lock”. A pallets initial lock is the distance between the initial contact point of an escape-wheel tooth and the break point between the two faces – Distance “L” in Figure 5.
When setting up an escapement I set the initial lock such that it is roughly 60% of the length of the impulse face. This is shown in Figure 6.
