Why do we find wheels having such defective teeth? This is probably due to their rapid manufacture, as they very likely had the correct shape when first cut, but by careless grinding and polishing they were given improper forms, careless treatment being very evident at tooth F, which we find on examination has a feather edge at the point as well as at the heel of the tooth. If we grind these edges of the tooth with a ruby file, by placing it in the position as indicated by dotted lines h and h¹, and afterwards polishing the tooth point, we will find that the balance makes a better vibration. A wheel, having teeth like E, can still be used, but the balance will have a very poor motion, due to the fact that the impulse angle of the wheel tooth is too small; the impulse faces of the teeth having so small an angle, are nearly incapable of any action. With a tooth like G, if we should remove its bent point at the dotted line d, then the tooth would be too short, and as the inclination of the impulse face is incapable to produce a proper action, a new wheel must be used, having teeth as shown at [Fig. 55].
The reasons why a tooth, having the shape as shown at F and G ([Fig. 59]), will cause a bad action of the escapement and also why in such cases with a greater force acting on the wheel, causes a stopping of the clock, I will endeavor to explain with the aid of the illustration [Fig. 60]. Here we clearly see the curved points of the teeth resting against the outer and inner walls of the cylinder while the escapement is in action.
Teeth H and H¹ represent the defective tooth, while K and K¹ shows a correctly formed tooth for a wheel of the same size, the correct depth and positions where the tooth strikes the inner and outer walls of the cylinder. It will be readily seen that the position of the tooth point upon the cylinder (at c) is most favorable in reducing the resistance to the least possible amount. But in the case of the teeth H and H¹ the condition is entirely different. We find that it was necessary to set the escapement very deeply in order that it could perform its functions at all, and, as a consequence, we have a false proportion; the effects being considerably increased by the worst possible position of the teeth H and H¹, where they touch the cylinder. While the cylinder c is turning in the direction shown by the arrows i i¹, the tooth does not affect the cylinder to any extent; but during the reverse movement of the cylinder, in the direction of o o¹, an excessive amount of engaging friction must take place. A close inspection of the drawing will enable us to see that there is a great tendency of the cylinder to drag the tooth along with it during each of these motions. It is evident that in such a case the friction will eventually become so great as to lock the escapement, and if greater pressure is applied by any means to teeth H and H¹, it is easily seen that this effect will take place much more rapidly. Replacing the escape wheel with one of correctly formed teeth and size is the best means at our disposal.
Fig. 60.
CHAPTER XIII.
THE DETACHED LEVER ESCAPEMENT
AS APPLIED TO CLOCKS.
As the clock repairer is almost of necessity a watchmaker, or hopes to become one, and as he must enter deeply into the study of all questions pertaining to the detached lever in its various forms before he can make any progress at all in watchmaking, it would seem unnecessary to repeat in these pages that which has already been so well said and so perfectly drawn, described and illustrated by such authorities as Moritz Grossman, Britten, Playtner and the various teachers in the horological schools, to say nothing of an equally brilliant and more numerous coterie of writers among the French, Germans and Swiss, so that the reader is referred to these writers for the mathematics and drawings which already so fully cover the technical and theoretical properties of the detached lever escapement. A few words as to its adaptation to clocks may, however, not be out of place.