Popular Science Monthly 



137 



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 



i.iiiniim 



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. 



