Duplex Escapement
This escapement is shown in a plan view in Fig. 116, while Fig. 117 shows an elevation of the staff and one tooth of the escape wheel. This escapement was no doubt so named on account of the double escape wheel, which was used in the earliest forms. Duplex is a Latin word meaning double, and there is but little doubt that this escapement derived its name from the fact of this double escape wheel, although some writers claim it was the invention of a watchmaker by the name of Dupleix, an Englishman, who was even but little known in his own country, and from whom the name was derived. Saunier says of this invention: "The first crude suggestion of the duplex escapement seems to have been made by Dutertre, a clever French watchmaker; but Pierre Le Roy was the real originator of this mechanism, having first constructed it about the middle of the last century." Some very good results were obtained from it, but on account of its susceptibility to wear at the pivots, as well as for other reasons, it has fallen into disuse, until it was modified and adopted by the Waterbury Watch Company, where it has proven very satisfactory. The impulse teeth rise from the plane of the body of the wheel and are represented in the black outlines of Fig. 116, while the long teeth are the locking ones. The center of the escape wheel and balance are planted close enough so that the circle of the escape wheel and the duplex roller intersect each other sufficiently that the escape teeth cannot pass except when the tooth drops into the notch of the roller and is traveling in the same direction of the escape wheel. At the instant that the tooth passes the notch the impulse tooth strikes upon the impulse pallet, thus imparting the power to the balance. In the return vibration the locking tooth falls into the notch, but the momentum of the balance overcomes that of the escape wheel, and no impulse is transmitted until both balance and escape wheel are moving in the same direction. The locking of the escape wheel in this form does not take place under favorable conditions, for when the balance is returning just prior to the receiving of an impulse the friction is engaging and when in this position, any slight roughness on the roller would cause a wedging action, causing the watch to stop. By reference to the figure it will be seen that the balance is at no time detached from the motive power, being more or less influenced by it during its entire vibration. In some of the older and finer specimens of the duplex the roller was made of ruby, but as now made it is always of steel. It will be noticed that at the time a tooth is unlocked the action is very much like the chronometer, and at the locking resembles the cylinder to a certain extent. The drop is changed by shifting the impulse pallet on the balance staff. If the drop is too great the impulse pallet is to be moved so that the angle between the roller notch and the impulse pallet is greater and if the drop is not sufficient they are to be moved closer together. When in beat the notch in the roller should point to the center of the escape wheel, although this point is varied by different workmen. Some authors say that this escapement requires considerable drop, sometimes as much as ten degrees. In this, as in the chronometer, the amount of drop should be the smallest amount possible to have a positive action of the impulse. All drop is just so much power wasted and the less we can have it the weaker mainspring we can have and in this respect is so much less power upon the train which could only cause it to wear away at the various points of contact. The balance jewels should fit the pivots accurately, as if they do not the tooth may catch or bottom in the notch of the roller when held in certain positions, and in others the tooth would not have sufficient hold on the roller for the safety of the locking. When cleaning it is necessary that the roller notch be thoroughly cleaned.
A balance spring having about ten coils is the best suited to this escapement. The watch previously referred to, which is made in this country, has proven that the duplex escapement, when well made, compares very favorably with the same grades of lever watches, and superior to the cylinder in point of timekeeping. The setting of the escapement, which in the older forms of the escapement has been well-nigh eliminated, there being no more difficulty experienced with this than any other watch. The workman who uses the same care when repairing one of these watches as he would in a lever, will have but little trouble in getting a satisfactory performance. Among the more prominent causes of stoppage in the escapement are, a roller which is not true, and this will most probably be found in one where some workmen has tried to pivot the staff and failed to get it properly centered, the teeth catching in the notch and a roller poorly smoothed, a point of a tooth may be slightly bent so that it cannot enter the notch or bind.