In the meantime we will resume our study of the cylinder escapement with particular reference to badly worn or otherwise ill fitting escape wheels, as many times, the other points being right, the wheel and cylinder may be such as to give either too great or too small a balance vibration.
A poor motion can also be due to a rough or a badly polished cylinder, but such a cylinder we rarely find. That with a wrong shape of the cylinder lips the motion is not much lessened can be seen in quite ordinary movements, where the quality is certainly not of the best neither are the lips correctly formed, nevertheless they have rather an excessive motion. To cover up these defects in such movements the cylinder wheel teeth are purposely given the shape as shown at B in [Fig. 56], and to give sufficient power a strong mainspring is inserted.
With an excessive balance vibration we can usually conclude that it is an intentional deception on the part of the manufacturer, while a poor motion can generally be ascribed to careless methods in making. The continued efforts in making improvements to quicken and cheapen manufacturing processes very frequently result in the introduction of defects which are only found by the experienced and practical watchmaker.
As to the causes which induce excessive balance vibrations? As this defect is generally found in the cheaper grades of cylinder escapements, having usually rather small, heavy, and often clumsy balances, those which have balances whose weight is probably less than they ought to be, need not here be further considered, and it only remains for us to look to the cylinder or the escape wheel for the causes which produce these excessive vibrations. It will be found that the cylinder is smaller in diameter than usually employed in such a size of clock; the escape wheel is naturally also smaller, and its teeth generally resemble B, [Fig. 56], while A shows the correct shape of a tooth for a wheel of that diameter.
In using small cylinders we can give the escape wheel teeth a somewhat greater angle of inclination than generally used, but that the proper amount of incline is exceeded is proved by the fact that the balance vibrates more than two-thirds of a turn. It can also be readily seen that with a tooth like B a greater impulse must be imparted than one with an easy curve like A, and the impulse is still further increased as the working width of the tooth B (the lift) is greater, indicated by line b, while the same line in a correct width of tooth, as shown at a, is considerably shorter.
In addition to what has been said of these escapements, we also find them provided with very strong mainsprings to give the necessary power to a tooth like B with its steeply inclined lifting face or impulse angle.
To decrease the great amplitude of the balance vibrations many watchmakers simply replace the strong mainspring with a weaker one. But this procedure is not advantageous as the power of the escape wheel tooth is insufficient to start the balance going and this is due to two causes. First, the great angle of the escape wheel tooth, and secondly, the inertia of the balance. It is only by violently shaking such a clock that, we are enabled to start it going. And the owner soon becomes dissatisfied from its frequent stoppage due to setting of the hands and other causes so that he will be often obliged to shake it until it starts going once more.
Fig. 57.Fig. 58.