Fig. 120. Brocot’s Calender: Wheels and Pinions
under the Dial with their Number of Teeth.
CHAPTER XX.
HAMMERS, GONGS AND BELLS.
Just as the tone of a piano depends very largely upon the condition of the felts on the hammers which strike the wires, so does the tone of a clock gong or bell depend on its hammer action. The deep, soft, resonant tone in either instance depends on the vibration being produced by something softer than metal. Ordinarily this condition is reached by facing the hammer with leather. The second essential is that the hammer shall immediately rebound, clear of the bell, so as not to interfere with the vibrations it has set up in the bell, wire or tube. As the leather gets harder the tone becomes harsher and “tinny,” sometimes changing to another much higher tone and entirely destroying the harmony. The remedy is either to oil the leather on the hammers, or if they are much worn to substitute new and thicker leathers until the tone is sufficiently mellowed, so that a vigorous blow will still produce a mellow tone of sufficient carrying power. A piece of round leather belting will be found very convenient for this purpose.
The superiority of a chiming clock lies in its hammer action. If this mechanism is not perfect, only inferior results can be obtained. The perfect hammer is the one that acts with the smallest strain and is operated with the least power. Heavy weights create a tremendous strain on the mechanism and bring disastrous results when one of the suspending cords break. The method of lifting the hammer is one of importance, and the action of the hammer-spring is but seldom right on old clocks brought in for repairs, especially if it be a spring bent over to a right angle at its point. If there are two springs, one to force the hammer down after the clock has raised it up, and another shorter one, fastened on to the pillar, to act as a counter-spring and prevent the hammer from jarring on the bell, there will seldom be any difficulty in repairing it; and the only operation necessary to be done is to file worn parts, polish the acting parts, set the springs a little stronger, and the thing is done. But if there is only one spring some further attention will be necessary, because the action of the one spring answers the purpose of the two previously mentioned, and to arrange it so that the hammer will be lifted with the greatest ease and then strike on the bell with the greatest force, and without jarring, requires some experience. That part of the hammer-stem which the spring acts on should never be filed or bent beyond the center of the arbor, as is sometimes done, because in such a case the hammer-spring has a sliding motion when it is in action, and some of the force of the spring is thereby lost. The point of the spring should also be made to work as near to the center of the arbor as it is possible to get it, and the flat end of the spring should be at a right angle with the edge of the frame, and that part of the hammer-stem that strikes against the flat end of the spring should be formed with a curve that will stop the hammer in a particular position and prevent it jarring on the bell. This curve can only be determined by experience; but a curve equal to a circle six inches in diameter will be nearly right.
The action of the pin wheel on the hammer tail is also of importance. The acting face of the hammer tail should be in a line with the center of the pin wheel, or a very little above it, but never below it, for then it becomes more difficult for the clock to lift the hammer, and the hammer tail should be of such a length as to drop from the pins of the pin wheel, and when it stops be about the distance of two teeth of the wheel from the next pin. This allows the wheel-work to gain a little force before lifting the hammer, which is sometimes desirable when the clock is a little dirty or nearly run down. We might also mention that in setting the hammer-spring to work with greater force it is always well to try and stop the fly with your finger when the clock is striking, and if this can be done it indicates that the hammer spring is stronger than the striking power of the clock can bear, and it ought to be weakened, because the striking part will be sure to stop whenever the clock gets the least dirty.
Gong wires are also the cause of faulty tones. In the factories these are made by coiling wires of suitable lengths and sections on arbors in a lathe. They are then heated to a dull red and hardened by dipping in water or oil. After cooling they are trued in the round and the flat like a watch hairspring and then drawn to a blue temper. The tone comes with the tempering, and if they are afterwards bent beyond the point where they will spring back to shape the tone is interfered with. Many repairers, not being aware of this fact, have ruined the tone of a gong wire while trying to true it up by bending with pliers. When the owner is particular about the tone of the clock, a new gong should always be put in if the old one is badly bent.
The wires are soldered to their centers and if they are at all loose they should be refastened in the same manner if it can be done without drawing the temper of the wire. When this cannot be done a plug of solder may be driven in between the wire and the side of the hole so as to stop all vibration or the solder already in place may be driven down so as to make all tight, as any vibration at this point will interfere with the tone.