The Escapement is the area of the movement that regulates the timekeeping so it must be setup correctly in order for a watch to keep accurate time. The rest of the movement could be setup perfectly but if the Escapement isn’t right, you can forget achieving excellent timekeeping. There are a number of components that make up the Escapement including- the pallets, the roller, the balance wheel, the balance staff, the hairspring and of course the escape wheel.
(6) Entry Arm
(7) Exit Arm
(8) Entry pallet jewel
(9) Exit pallet jewel
(11) Entry Horn
(12) Exit Horn
(13) Guard pin
(14) Entry banking pin
(15) Exit banking pin
(16) Roller table
(17) Safety roller
(18) Impulse pin (jewel)
(19) Passing Crescent
There are multiple things that need to be set correctly in order for the Escapement to function efficiently or even at all. I will go through each area in more detail but for now I will just list these main areas. The end shakes on the escape wheel, pallets and balance. The division between the escape wheel and pallets. The division between the pallets and balance wheel. There are also another couple of things that need to be checked, horn shake and guard pin shake. And something I’ve covered previously, the depth of lock of the pallets.
The first thing to check is the end shakes which should be set at a maximum of 1/100th of a millimetre on the escape wheel, pallet fork and balance wheel. This reflects the size of the pivots which are tiny when compared to a centre wheel for example. The purpose of end shake to allow the pivots to move freely in there bearing surfaces (jewels). Too much end shake can cause two components to line up incorrectly when the movement is rotated in different positions. The end shakes are adjusted using a Horia jeweling tool that accurately pushes the jewel in the plate/bridge up or down.
The next thing to check is the division between the pallets and the balance, the horns on the pallet fork must sit in the middle of the impulse jewel on the roller and the guard pin must sit in the middle of the safety roller. The guard pin must always align with roller and not foul the impulse jewel. Any errors here can cause the escapement to lock or unlock as it wishes with no control, a negative effect on time keeping would be a consequence of this. This can be adjusted by moving the pallet frame up or down on the pallet staff until the division is correct.
(d) Height of the guard pin and safety roller, (e) Clearance between the fork and underside of the roller, (f) Clearance between the bottom of the safety roller and the balance jewel setting, (g) Clearance at its extremity between the impulse pin (jewel) and the guard pin…
The second division to be checked is between the pallets and escape wheel, the escape wheel teeth should sit in the centre of the impulse faces of the pallet jewels. The main reason is stop the teeth and jewels from losing contact when both components are at there maximum end shakes. The escape wheel can be moved up or down to set the division by moving the top and bottom jewels by the same amount. Likewise the same can be done with the pallets but if this is done the division between the balance and horns/guard pin must be re-adjusted.
The horn shake is the amount of movement between the impulse jewel and the horn of the pallet lever. The horn shake should generally be less than half of the total depth of lock on the pallets. It can be a difficult thing to check, its done by stopping the balance at about 35 to 40 deg from either side of centre or rest position and observing the movement of the pallet lever. The tolerance should be equal on both sides. The horn shake can be adjusted by opening/closing the banking pins to increase or reduce the movement of the pallet lever. If a watch has solid banking pins, the pallet jewels can be moved in/out to reduce/increase the depth of lock which in turn reduces/increases the horn shake.
The last tolerance to check is between the guard pin and the safety roller (guard pin shake), the balance is turned 90 degrees using the same method as before, the tolerance can be checked and should be equal to or less than the horn shake. The guard pin can be shortened by stoning it down to increase the guard pin shake. It can also be bent slightly or stoned down more on one side to make the tolerance equal both sides.
The forthcoming Escapement exam involves setting up all of the above along with riveting, truing and poising a balance wheel in just 4 hours. Thankfully in practice it would be rare to have to adjust the majority of these things in just one watch but its important to know how to check them and adjust anything if necessary. The escapement controls the watches time keeping and faults here have a greater effect on this than in any other part of the movement. The added benefit of learning all this is a greater understanding of how a Swiss lever escapement works which is important as the majority of mechanical watches utilise this system. I have to say its a great feeling when you manage to set up an escapement perfectly for the very first time and hopefully I will be able t set it up perfectly during the exam!
Note- All diagrams taken from WOSTEP The Theory of Horology.