Discover how much more there is to know about escapements by creating your own drawings. The purpose of this project is to introduce the reader, whether professional or hobbyist, to a hands-on method for drawing a mechanical clock or watch escapement. While it is more obvious that a manufacturer needs to know how to design a pallet, the repairman could do a better repair with an improved understanding of design theory. The ability to draw an escapement enables one to experiment more easily with the effects of changing the variables and to compare different types of escapements, their similarities and differences. Watch Escapements:
The most important reason for careful attention to design is efficiency. The escapements most frequently encountered at the bench are the Recoil, the Graham (or dead-beat), and the Swiss Lever. These all have efficiencies below 50%. This means that more than half the power is lost in the escapement alone, after all the power losses in the gear train.
Modern Swiss Lever
Drawing watch escapements requires much more detail than drawing the Graham (clock) escapement. I will pay most attention to the modern Swiss watch with the club-tooth escape wheel as it is the most commonly encountered at the bench. If you are a clockmaker or watchmaker who understands everything summarized in this introduction, you probably do not need this book. If you do not understand all of it, the cost of this book would be the cheapest escapement course you ever took.
Watch and clock escapements are similar in that they should have symmetrical designs, so that the impulses the pallets receive would be equal. The efficiency of the escapement should be the same for both pallets. The impulse face of each pallet should have an angle of 45º relative to the direction of the force that the escape tooth applies to the pallet during impulse if the angle between this force and the force that acts to rotate the pallet were 90º. If the pallet's impulse face angle were not correct, there would be a considerable loss of efficiency, or the ability of the balance wheel to receive impulses from the escape wheel. This is covered in detail in Chapter 4 of the Clock Escapement section.
The most significant difference between clock and watch escapements, such as the Graham escapement and the Swiss Lever, is that the clock's pendulum is not independent of the pallets, whereas the watch's balance wheel is independent of the pallets most of the time. This means that the clock escapement should have pallets with curved locking faces to achieve a dead-beat, so that there would be no recoil as the escape tooth slides along the pallet locking face. The watch escapement, however, should have pallets with locking faces that allow the escape tooth to move forwards slightly as it slides up the pallet's locking face, so as to create draw. The draw is a small binding action that helps to keep the pallet fork over to the side, against the banking pin, until the balance wheel's roller jewel returns, so that the fork's guard pin would not rub against the balance wheel's roller table and thereby interfere with the freedom of rotation of the balance wheel. Since watches require draw, the equidistant lock of the pallets is desirable in order to have equal draw for both pallets. This is covered in detail in Chapter 9 of the Clock Escapement section.
If you are a watchmaker with no interest in clocks, I would recommend that you consider reading the chapters concerning clock escapements because the logic behind the drawings is the same, and it is easier to introduce a reader to the drawing techniques with less difficult examples, (in other words, examples of simpler escapements that apply to clocks). It would be necessary to understand the basic principles behind escapement drawings before attempting to draw complicated watch escapements that would work in a simulation on a computer.
Go to Chapter 1
Escapements in Motion
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