We have generally made a practice, upon the completion of the train for a fine clock, to put in the place of the escape-wheel a very light, well-balanced fly, to prevent “backlash,” and a very fine soft cord on the barrel; then hang on a very light weight; so slight that—all of the wheels being balanced, and no oil upon the pivots—the fly will move so slowly that its revolutions may be counted. By taking care that the weight be not too much in excess of the resistance, the least inaccuracy in the wheels and pinions may be discovered by the difference in the velocity of the fly, or by its suddenly stopping, which will be occasioned by any inequality in the train teeth, which would not have been discovered by the closest scrutiny. It was by means of this test that we discovered an inaccuracy in a pinion, caused by hardening, which could not have been discovered by a less delicate test.
The wheels in the train should be as light as possible, for as the whole train is stopped every time a tooth drops on the pallets, it is plain that the driving weight must overcome the inertia as well as the friction of the train at every beat. To this end it has been customary to “arm out” the wheels, leaving a very light rim supported by light arms, the wheels being generally of cast brass, turned up, and cut, then lightened. We followed this plan for some time, but abandoned it, as we found great difficulty in making a perfectly round wheel. The arms serve as posts to support the rim in cutting or turning, but the space between is very apt to spring down. We prefer making the wheels of fine hard-rolled sheet brass; it is superior to cast brass, much finer, harder, and more durable, and is freer from flaws. After the wheels are cut, they are turned out on each side, leaving a thin web in the centre; they can be made lighter, finished easier, and are round.
As to the shape of the teeth in clock-wheels, the subject has been so ably treated by Reid, Dennison, and Prof. Willis (who has invented an instrument to assist in laying out the curves for the teeth of wheels), that we shall not attempt it in this paper; besides, there is so little of the entire theory that can be applied to a clock-wheel of two and a half inches in diameter, with 120 to 140 teeth, farther than to leave the wheel and pinion of the proper diameter, that we consider it unnecessary; for if makers of regulators and other fine clocks will use pinions of 16 or 20 teeth, the friction or driving is all after the line of centres, and the whole subject of cycloids, epicycloids, and hypocycloids is reduced to a very small point, and might be said to “vanish into thin air.”
Having given only a few practical hints, and not yet crossed the threshold of the subject, we propose to continue from month to month—if the readers of the Journal do not weary—the discussion of the various parts that go to make the sum total of a fine clock, with notices of the various clocks made in this country.
It certainly comes within the province, and is the duty, of a journal devoted to Horology, to make a note of any and all the new improvements that pertain to the science. We give, then, some few, the merits of which have struck us as being a very important matter of consideration.
The best clock time-keeper is not absolutely perfect, so its rate must be kept; but the watchmaker ordinarily has no means of correcting the error of his regulator, until the accumulation renders it a serious inconvenience. Did he possess a Transit instrument, properly set and adjusted for meridian, together with the required books and knowledge of observing, he could from day to day correct his clock and keep accurate time; but these are all expensive, as well as involving time and labor. Suited to the wants of the artisan is a little instrument called the Dipleidescope; simple in its construction, and not liable to get out of position or order, it forms the best substitute for the transit we have seen. It is founded on the theory that the double reflection from the two surfaces of planes at an angle of 60° will coincide when the object reflected is in a true line with half the base of the whole triangle. Having a prism cut in an equilateral triangle, one angle is set directly down toward the centre of the earth, the base being brought parallel with the line of the horizon. Now, if the axis of the prism is in a line with the meridian, a reflection of the sun will appear, at the instant of crossing the meridian, on itself—that is, there would be but one image. If the instrument is well made, there can be no doubt of its accuracy and value to those who, wishing to verify their time, are not situated so as to use a transit.
Another improvement is a Bench-Key for watchmaker’s use. No one who has had any experience at the bench but will appreciate an article that facilitates the setting of time-pieces for his customers. In winding, it is equally valuable. It is not dependent for its strength of torsion on the spring-chuck principle, the power being applied close to the square by means of a pin that passes through the key.
Hall’s Patent Cutting Nippers are a positive desideratum; a large wire can be cut off without the least jar to the hand, the leverage is so great. The smallest sizes are suitable to the ordinary run of watch-work, and can be used in clock-work better than any cutting-plyers extant. Strong and durable, they possess one quality that all watchmakers will appreciate—if a cutting-jaw is broken it can be replaced by another.