Page:Popular Science Monthly Volume 89.djvu/151

 Popular Science Monthly

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��Electric Striking Mechanism for Mission Clocks

MANY of those who possess a mis- sion wall-clock have no doubt wished that it could be made into a "striking clock." This transformation is not difficult with the following ma- terials: a single-stroke 'electric belt; a small dry battery; an old flat file; 12 pieces of brass for contacts; a small piece of copper for brushes; and several feet of copper wire, screws, staples, etc. The first thing to do is to make the large contact (Fig. l). This is made of pieces of an old file. The file should first be an- nealed, so that it can be cut up into twelve short pieces. An old file should be selected which has a filing surface on the edge; it is the cor- rugations of this edge that are to be used to interrupt the current for the striking mechanism. The pieces should be just long enough to include twelve notches or corruga- tions. The corru- gated edge of the pieces should be

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��Fig. 2. The brush that is fastened to the under side of the longer or minute hand

���Fig. 1. Making the large contact of pieces of an

old file HMJ LW<

Fig. 3. Contact connections A Mission clock with an electrical arrange- ment for striking the hour

��dressed down by filing or grinding, so that on the first piece only the center corrugation is left, on the second, the middle two, on the third, the mid- dle three, etc. The pieces are clamped together with insulating strips between, in the order of their respective number of corrugations — I, 2, 3, 4, 5, etc.

If the contacts are to be fastened on the outside of the clock, the hands can be used as contact-arms. The large contact plate should be fastened directly opposite 12 (not necessarily over it) and the small contacts opposite the hours. The hands shoulcl then be removed and a brush similar to the one shown in Fig. 2 made and fastened to the under side of the minute-hand. Before replacing the hands one of them should be insulated from the rest

��of the clock-frame by a small piece of thin silk, wrajjped around the stem under the hand. A small brush should be fastened to the under side of the hour- hand to make contact with the small con- tacts. The brush on [the minute-hand should be adjusted, so that each segment of it will come over a row of corrugations. The brush should be nearly perpendicu- lar to the face, as it goes over the large contact, to avoid touching two at a time. The contacts should then be connected, as shown in Fig. 3, by wires run on the back of the face.

In case the con- tacts are placed (jn the inside, it will be necessary to make two contact-arms corresponding with the hands. The.se will be on the inside and will work over the contacts, as the hands did in the other case. In con- necting up the con- tacts it must be re- membered that each piece of file (row of contacts) is to be connected with the small contact op- posite the corre- sponding hour. The heavy dash-dot line indicates the main wires; one is connected with the hisu- laled hand and the other with the frame of the clock. The bell and battery are coimected in series. In fastening the wires small pieces of muslin may be glued over them to hold them in place and to avoid using staples or brads in the clock face.

When the hour hand passes over the contact corresponding with, say, the hour 5, the row containing 5 corruga- tions is thrown in the circuit, and when the minute hand comes around to 12, its brush passes over the large contact. As the current is only in one piece of the file — i. e., the one corresponding with that hour, all the others are dead. The brush trips from one notch to the next, causing the single-stroke bell to strike five times.— R. L. Kenyon.

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