Watch Repair for Beginners by Kelly Harold C

Author:Kelly, Harold C.
Language: eng
Format: epub
Publisher: Skyhorse Publishing, Inc.

The chronometer escapement comprises the same mechanical principle as does this escapement by Galilei. It is a fact worth noting that the chronometer escapement, perfected 140 years later, is the most perfect timekeeping device that has ever been conceived. And yet, oddly enough, Galilei’s escapement was not divulged to the world, and the escapements that were eventually developed proceeded upon wholly different lines.

Verge Escapement

The first mechanical clocks — that is, those consisting of toothed wheels driven by a weight —date from the tenth century. The earliest escapement that attained any prominence was the verge. The inventor is unknown, although the name of Pope Sylvester II (950-1010?) has been mentioned.

Construction. The time counter for the earliest verge clocks was a horizontal bar called the foliot (Figure 14). It is a sort of balance upon which two weights are suspended from notches near each end. The weights can be moved toward or away from the center of the foliot for the purpose of regulating. The arbor for the foliot is secured to a cord at the top and a pivot at the bottom runs in a hole in the block A. The lower portion of the arbor carries two flattened steel pallets. The pallets and the arbor together are called the verge. The angle between the pallets is usually 90 to 100 degrees. In some cases, particularly those made in France, the angle is even greater, often as much as 115 degrees. These of the latter type must have the pallets planted much closer to the wheel, resulting in a longer vibration but less recoil.

The escape wheel must have an odd number of teeth in order to work at all. The usual number is 13 or 15 for watches and 21, 31, or 33 for large clocks.

Action of the escapement. In the illustration, the escape wheel is shown turning in the direction of the arrow. The tooth under pallet B is in the act of giving impulse. Pushing pallet B to the left, the tooth eventually escapes, permitting the escape wheel to turn until another tooth engages pallet C. After a recoil due to the inertia of the foliot, the tooth delivers impulse to pallet C, this time pushing the pallet to the right. Soon a tooth escapes and action is repeated when another tooth engages pallet B.

Figure 14. Verge escapement.

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