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Pallet Stones

From The American Horologist and Jeweler magazine, March, 1942

Pallet Stones


Setting up the escapement is an adjustment that many of our younger watchmakers seem to fear and finding the cause for poor motions is quite often overlooked for want of experience, and perhaps, knowledge. The illustrations may prove helpful and assist the younger men with their work. 

Figure No. I - The escape tooth at rest against the receiving stone. The total lock, which means, initial drop and slide, should not be over one fourth the width of stone. For high grade watches, the total lock can be reduced so that it would be 1/5 to 1/6 the width of the pallet stones. 

The draft angle of the stone and the clearance on the face of the tooth is so that the toe of the tooth itself is resting an the face of the stone. Conditions of this kind are ideal, causing very little friction as the tooth is unlocked from the stone. There will be no oil adhesion.

Figure No. 2 - The discharged tooth after it has left the discharge corner of the discharge stone. The space between the corner of the stone and the heel of the tooth is called "drop" or clearance. The escapement should be examined carefully that the drops are equal for the receiving stone and the discharge stone.

Figure No.3 - Condition where the receiving stone has insufficient lifting angle and the sharp corner of the stone riding the face of tooth.

This is called "engaging friction." When conditions as in Figure No. 3 exist, very little power can be delivered from the receiving stone. A new stone substituted, having a greater lifting angle, will be required.

Fig. No.4 - Same condition and is commonly met up with, as many men are not aware that the discharge stone has a greater lifting angle than the receiving stone. If conditions are found in the watch, similar to figure No.4, it is safe to assume that a receiving stone has supplanted a discharge stone. Replace with a discharge stone.

Figure No. 5 - Shows tooth as it has passed beyond center of stone and is now giving the last half of its impulse.

Note the discharge corner of the stone riding up the incline of the tooth and the clearance between the heel of the tooth and the face af the stone. This is the correct action for our modern escapement.

Figure 6 - Shows the tooth midway across the face of the stone, the lifting angle of the tooth and the stone is parallel. This condition is often found and is especially detrimental in our small watches. If the oil in the escapement is heavy, there is strong adhesion between these two surfaces and the breaking of the oil adhesion retards the free action of the tooth and pallet.

Figure 7 - Shows the tooth at rest with the pallet stone setting at right angles with Tangent Line A.

The pressure of tooth resting on the face of stone creates a direct thrust to the pallet center and would act very much the same as a dead beat escapement. There would be no tendency of the pallet stones to slide down on the toe of the tooth, drawing the lever up to the banks. While conditions as severe as the illustration rarely exists, we meet up with watches where the pallet stones have been tilted sufficient to create a draw. If there is insufficient draw, the lever will not hold up to its banks, the guard pin will drag on the safety roller. creating a poor motion or possibly, stopping the watch entirely.

Figure No. 8 - Shows tooth at rest against the discharge stone. In this case the discharge stone has been tilted too much so instead of the toe of the tooth resting on the locking face of the stone, the corner of the stone is resting on front of the tooth. When conditions similar to Fig. No. 7 or 8 exists, it is possible to remedy the trouble by moving the stones sideways in the pallet frame and if results cannot be obtained, it will be necessary to enlarge the slots in the pallet frames so that the stone may be tilted sufficiently to create the proper draw, Fig. No. 7 and diminish the draw for Fig. No. 8.

Figure No. 9 - Shows the tooth as it has passed one half way across the face of stone. Note the condition that the toe of the tooth is riding the smooth lifting plane of the stone. This is an ideal condition where Fig. No.5 shows the path of the tooth after it has passed the center of stone and the discharge corner of the stone is riding the incline of the tooth.

Fig. No. 10 - Shows tooth at rest on the face of the pallet stone, however, note the toe of the tooth is worn. When a case of this kind exists, there will be no draw to hold the lever to its banks, allowing the guard pin to drag on the edge of the roller table, slowing up the motion of the balance. A case of this kind is best remedied by replacing escape wheel.

Figure No. 11 - When tooth of escape wheel is badly worn or damaged, the watch may run but we are only getting about one-half impulse, adjusting the pallet stones in such a case, would be of no avail. Replacing the escape wheel IS the best remedy.

Figure No. 12 - Shows tooth at rest with the receiving corner of the pallet stone chipped. This would cause the pallet to be thrown away from the banks, crowding the guard pin against the edge of the roller, causing' poor motion and many times, stopping the watch. The sharp edge of the stone would also be detrimental as it would soon cut the face of the tooth.

Figure No. 13 - Illustrates a narrow pallet stone, the position' of the stone indicates that the draw will be very strong and that the lifting angle will be excessive, causing a heavy drop lock on the discharge stone, being a narrow stone, the impulse would be considerably less then on the regular stone.

Figure No. 14 - Illustrates the pallet stone that is too wide. The slot in pallet frame has been spread to accommodate the stone. Illustration shows there will be no outside drop and very likely, the discharge corner of the stone would strike or be interfere with by the heel of the tooth.

The interference, however, slight it might be, will cause poor motion or stopping of watch.

Figure No. 15 - Before setting pallet stones to their proper positions, for drop lock and slide, the jewel pin and guard pin action must be adjusted. See that the jewel pin is set upright centered to the crescent, and the face of the roller jewel squared to center. Place balance in watch and turn the banking screws so the corner of the fork slot is brought close to the corner of the roller jewel. This is generally known as corner freedom and for the average watch, this corner freedom can be .001".

Fig. No. 16 - Now advance the roller and balance until the guard pin is out of the crescent. If the guard pin is tight against the roller, shorten it until there is a guard pin clearance or freedom. This freedom between the guard pin and safety roller should be .0005".

Fig, No. 17 - This rule applies on all watches so that should the lever get a jar and leave the bank, the guard pin will still hold the lever in the proper position so that the jewel pin will enter the fork slot freely.

When the jewel pin action and guard pin action have been satisfied, then the pallet stones are set so that there will be a safe drop lock and a visible slide. The banking pins are not adjusted ta create slide after the stones have been set. When replacing pallet stones, always order genuine pallet stones for the make and model of watch you are working on as each factory designs escapements to their specifications so that pallet stones a,re not interchangeable from one makers watch to some other makers watch. 

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