An Analysis of the Lever Escapement

Excerpt

PREFACE.

Before entering upon our subject proper, we think it advisable to explain a few points, simple though they are, which might cause confusion to some readers. Our experience has shown us that as soon as we use the words “millimeter” and “degree,” perplexity is the result. “What is a millimeter?” is propounded to us very often in the course of a year; nearly every new acquaintance is interested in having the metric system of measurement, together with the fine gauges used, explained to him.

The metric system of measurement originated at the time of the French Revolution, in the latter part of the 18th century; its divisions are decimal, just the same as the system of currency we use in this country.

A meter is the ten millionth part of an arc of the meridian of Paris, drawn from the equator to the north pole; as compared with the English inch there are  inches in a meter, and there are 25.4 millimeters in an inch.

The meter is sub-divided into decimeters, centimeters and millimeters; 1,000 millimeters equal one meter; the millimeter is again divided into and the into of a millimeter, which could be continued indefinitely. The  millimeter is equal to the of an inch. These are measurements with which the watchmaker is concerned.  millimeter, written , is the side shake for a balance pivot; multiply it by and we obtain the thickness for the spring detent of a pocket chronometer, which is about the thickness of a human hair.

The metric system of measurement is used in all the watch factories of Switzerland, France, Germany, and the United States, and nearly all the lathe makers number their chucks by it, and some of them cut the leading screws on their slide rests to it.

 In any modern work on horology of value, the metric system is used. Skilled horologists use it on account of its convenience. The millimeter is a unit which can be handled on the small parts of a watch, whereas the inch must always be divided on anything smaller than the plates.

Equally as fine gauges can be and are made for the inch as for the metric system, and the inch is decimally divided, but we require another decimal point to express our measurement.

Metric gauges can now be procured from the material shops; they consist of tenth measures, verniers and micrometers; the finer ones of these come from Glashutte, and are the ones mentioned by Grossmann in his essay on the lever escapement. Any workman who has once used these instruments could not be persuaded to do without them.

No one can comprehend the geometrical principles employed in escapements without a knowledge of angles and their measurements, therefore we deem it of sufficient importance to at least explain what a degree is, as we know for a fact, that young workmen especially, often fail to see how to apply it.

Every circle, no matter how large or small it may be, contains ; a degree is therefore the 360th part of a circle; it is divided into minutes, seconds, thirds, etc.

To measure the value of a degree of any circle, we must multiply the diameter of it by 3.1416, which gives us the circumference, and then divide it by 360. It will be seen that it depends on the size of that circle or its radius, as to the value of a degree in any actual measurement. To illustrate; a degree on the earth’s circumference measures 60 geographical miles, while measured on the circumference of an escape wheel 7.5 mm. in diameter, or as they would designate it in a material shop, , it would be 7.5 × 3.1416 ÷ 360 = .0655 mm., which is equal to the breadth of an ordinary human hair; it is a degree in both cases, but the difference is very great, therefore a degree cannot be associated  with any actual measurement until the radius of the circle is known. Degrees are generated from the center of the circle, and should be thought of as to ascension or direction and relative value. Circles contain four right angles of each. Degrees are commonly measured by means of the protractor, although the ordinary instruments of this kind leave very much to be desired. The lines can be verified by means of the compass, which is a good practical method.

It may also be well to give an explanation of some of the terms used.

equals the amount of freedom which is allowed for the action of pallets and wheel. See , .

—In the ratchet tooth or English wheel, the primitive and real diameter are equal; in the club tooth wheel it means across the locking corners of the teeth; in such a wheel, therefore, the primitive is less than the real diameter by the height of two impulse planes.

equals the depth of locking, measured from the locking corner of the pallet at the moment the drop has occurred....