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Matching the Escapement

From The American Horologist magazine, May1938

Matching the Escapement

THE term "matching the escapement" is used to designate the work of bringing the different parts of the escapement into correct relation to each other; in other words, to make the necessary moves in order to obtain the proper lock, draft, drop, slide, fork length, let-off, etc. The best way of learning to do this work is to have a competent instructor who is at hand ready to inspect and to give advice. The difficulties are not so great in doing this work, as In correctly determining what to do, in order to bring about certain results, and also to know when the escapement is in proper condition. It is difficult to give in writing a comprehensive idea of how to do this work.  We will, however, give a few points which we hope will be useful to the beginner.

The first thing to receive attention is the condition of the pivots on the escape pinion, pallet arbor and balance staff, to see that they are straight, and that they fit properly in their respective holes.  It is absolutely necessary that each pivot should have some side shake, but it is also very important to guard against too much side shake, as such an excess causes loss of power and uncertainty in the action of the escapement. A desirable amount of side shake is .01 mm., and it should not exceed .015 mm., and the amount of end shake should be from .02 to .05 mm. As soon as these points have been found to be correct, we are ready to try the "lock" and the "drop." In describing the pallet action, on page 7, we made the statement that the lock should amount to from 1 to 1 degree 30'.  This statement is, of course, of no practical use unless we are equipped with the necessary instruments for measuring this angle. We may, however. use the thickness of the pallet stones for comparison and obtain practically the same results, by making the amount of lock equal to 1/10 to 1/8 the thickness of the stone, from the locking to the let-off corner. This corresponds very closely to the above angular measurements. If the pallet stones are to be moved, in order to change the amount of lock, it is very important to first consider what will be the effect of a certain move, besides the alteration of the lock. The drop, for example, is effected very rapidly by moving the L stone. Hence, if the drops are equal, we should make the change in the lock by moving the R stone. If the lock is too strong, and the drop is larger on the outside, the L stone should be moved. If the lock is too strong, and the drop is larger on the inside, it is necessary to move both stones. Move the L stone out a small amount, and move the R stone in until the lock is correct. It is also well to recognize that the drop may be modified to a certain extent by moving the pallet stones, close to one or the other side, in the slots, as there is always some room allowed for the shellac which is used for holding the stones. The moving of the pallet stones in or out in the slots will also affect the draft feature of the escapement; this is a point which we should bear in mind whenever we make a change in the position of the pallet stones. The effect from moving the R stone out is to increase the draft on both stones, whereas if the L stone is moved out and the R stone in, it will decrease the draft. In order to ascertain that the escape wheel is correct, the lock and the drop should be tried with every tooth in the wheel on both pallet stones.  This should be done with the bankings adjusted close, so as to just permit the teeth to drop. And the best way to try this, is to move the balance slowly with the finger while the pallet action is observed through the peep holes. After completing the adjustment of the pallet action, the jewel pin action is next to be considered. The fork should swing an equal distance to each side of the center line when the pallet is banked to drop. If we find that it moves farther on one side than on the other, it will be necessary to bend the fork close to the pallet a sufficient amount to bring it in line. This is called, "to adjust the let-off." The test for the let-off is to see that when the pallet is banked to drop, the jewel pin is just as close to the corner of the fork, in passing out, on one side as on the other. This test is correct, provided that the fork is of equal length on both sides of the slot, as it should be. The test for the fork length is that it should allow the jewel pin to pass out on both sides when the pallet is banked to drop. This is the maximum length which is allowed for the fork.  The test for short fork is to move the balance so as to unlock the pallet, then reverse the motion and see that the pallet is carried back safely to lock by the jewel pin.. This should be tried on both pallet stones. It is however, customary to try the shake of the fork when the center of the jewel pin is opposite the corner of the fork, and not to allow the pallet to unlock from this shake. In order to ensure perfect freedom in the jewel pin action, the jewel pin should be from .01 to .015 mm. smaller than the slot in the fork. The safety action is also adjusted, while the escapement is banked to drop. The guard pin should be made just barely free from the roller when the fork is against the banking, and this should be tried carefully on both sides. If this is done correctly, the roller will have the necessary clearance when the bankings are opened to allow for the slide.

The operation of moving a pallet stone is one that requires a great deal of experience before one is able to do it satisfactorily except by repeated trials.  Special tools called "pallet warmers" have been devised for holding the pallet during this operation. In the simplest form this tool consists of a small metal plate, about as large as a 12 size barrel, with a wire handle by which it is held while it is heated. This plate should have one or more holes drilled in it as clearance for the pallet arbor. This tool is provided with a spring clamp for holding the pallet to the plate. The pallet is placed top side down against this plate, and the whole of it is warmed over the alcohol flame until the shellac is softened so the stones can be moved.

A good way of applying shellac for the fastening of pallet stones is to warm some stick or button shellac, over a flame, and pull it out in long threads of about .5 rom. diameter. Shellac in this form is very convenient to use, as it is only necessary, when the pallet is heated to the proper temperature, to touch the end of this thread to it at the place where the shellac is wanted. With a little practice one can learn to deposit just the right amount. After the pallet is cold, all shellac on the surface should be cleaned off carefully with a scraper made of brass or nickel.

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