This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
By JOHN E. MAHLMEISTER
IN the construction of this clock one perfectly good and accurate alarm clock and the works of an old or discarded one are used. The clock for the accurate time is set into a frame, or casing, made of thin boards which have a circular opening cut in them to fit snugly on the outside casing of the clock. The back of the clock and casing are shown in Fig. 1. A circular line is drawn on the casing, about 1 in. larger in diameter than the clock, and brass machine screws with two nuts clamping on the wood back, as shown at A, are set at intervals so as to be opposite, or just back of, the hour marks 2, 3, 5, 6, 8, 9, 11, and 12. A contact spring, B, is shaped as shown and soldered to the knurled knob on the back of the clock used for setting the hands in a position where it will travel or be parallel with the minute hand. The end of the contact spring should be shaped so that it will slide over the points of the screws easily, but in good contact. The ends of the screws should be filed to a slightly rounding point. The wiring diagram for this part of the apparatus is clearly shown, and the terminals are connected to binding posts C and D. The binding post E is connected to the metal part of the clock.
Ill: The Alarm Clock in Its Case and the Location of the Contact Pins and Contact Lever
Ill: Location of the Clock Works, Magnets, Binding Posts, Gongs and Strikers on the Baseboard
The chime part is made entirely separate and can be located at any reasonable distance from the clock. It is propelled by the works from an old clock, as shown at F, Fig. 2. The old clock is prepared for use by removing the hands, balance wheel and escapement so that the wheels will turn freely. To prevent the works from running too fast, a piece of sheet brass, G, is soldered to the shaft running at the highest speed. The brass should be as large as the space will admit. It forms a fan to catch the air and retard the speed, and also provides a means of stopping the works by the electric mechanism.
The parts for the gongs and electrical apparatus are supported on a baseboard, 3/4 in.thick, 6 in. wide, and 18 in. long. The automatic switch is located at one end of the base, and consists of two sets of magnets, H and J, with an armature, K, to which is attached a stiff contact wire, L. This wire is to make contact with the spring M when the armature is drawn by the magnets J, and with N when drawn by the magnets H. The springs M and N are made of thin sheet brass, bent as shown, and mounted on the base.
A piece of wood, O, on which to mount the works of the old clock is mortised into the base. Another standard, P, of the same height as O, is also mortised into the base to provide a bearing for the end of the shaft which carries the wood disk Q, the opposite end of the shaft being connected by means of a ferrule and soldered to the end of the minute-hand shaft. The shaft should be well lined up, so that it will turn freely. The wood disk is 1/4in. thick and about 6 in. in diameter.
Mark four circles on the face of the disk, near the outside edge and 1/4 in. apart. Step off the outside circle into 150 parts and draw a radial line from each mark across the four circular lines with the straight edge on the center of the disk. An arc of the disk is shown in Fig. 3, where trip pins are driven in for making the electric contacts. This part of the arc shows the method of locating the pins for the hour from 3 to 4 o'clock, with the intermediate pins for the quarter, half, and three-quarter-hour contacts. The intermediate pins are arranged in the same manner for all hours, but the hour pins, on the second circle, run from 1 pin to 12 pins consecutively. Ordinary pins, with the heads cut off, are used and should be driven in accurately on the division lines to secure proper results.
The arrangement of the springs is shown in Fig. 4. These springs, when pressed together, will close the circuit for ringing the gongs. They are made of thin sheet brass, bent as shown at R, and fastened to a piece, or block, of hard wood with screws, as shown at
S. The springs numbered 3, 5, 7, and 9 are the ones made as shown at R for sliding over the pins in the disk Q, and their ends should clear the face of the disk about 1/8 in. The springs 1, 2, 4,
6, and 8 are about 1/2 in. shorter and have their ends bent up at right angles so that they will almost touch the long ones. The spring 1 should be a little shorter than 2. When fastening the the Pins arc Accurately Set in Four Circular Lines and on Radial Lines springs to the block of wood, be sure that no two springs touch and that each one is separated from the other to form no contact until the pins in the wheel force them together. The block is then fastened to the base under and parallel with the shaft carrying the disk Q, as shown.
The starting and stopping of the clockwork F is accomplished by means of a set of bell magnets, arranged, as shown at T, Fig. 2, with the wire attached to the armature bent to touch the brass wing of the fan G. The armature must not vibrate, but stay against the magnet cores while the current is flowing through them, thus allowing the clock wheels to turn, and as soon as the current is cut off, the armature will spring back and stop the wheels.
Ill: The Parts Constructing the Chime are Placed in the Clock Frame below the Works
Arrange four gongs, U, V, W, and X, as shown in Fig. 2, and also three bell magnets with clappers 1, 2 and 3. These gongs should be selected for tone as in a chime clock. The connections to the bell magnets 1, 2, and 3 should be direct to the binding posts so that the armature will not vibrate, but give one stroke. For instance, bell magnet 1 should produce one stroke on the gong U when the current is on, and one stroke on the gong V when the current breaks. The magnets 2 should cause the clapper to strike once on the gong V when the current is on, and to make one stroke on the gong W when the current is broken. The magnets 3 produce only one stroke on the gong X at a time, which is used to sound the hours.
Ill: The Contact Springs are Operated by the Pins on the Disk Wheel
The parts are connected up electrically as shown in Fig. 5. The lines between the clock, Fig. 1, and the bell-ringing part, Fig. 2, are connected from C to C, D to D, and E, Fig. 1, to the zinc of a battery and from the carbon to E, Fig. 2. Two dry cells will be sufficient for the current.
The working of the mechanism is as follows: Suppose the time is 6 minutes of 3 o'clock and the contact spring on the back is near the 11 pin. As soon as it touches the pin, the armature K of the switch will be drawn in contact with the spring N, then when the contact spring touches the 12 pin, the current will flow into the for the Location of the Wires on the Under Side of the Base magnets T and release the wheels of the clockwork F, which turns the disk Q, and the three pins in the second row will pass over the spring 5 and press it in contact with the spring 4 three times, causing the gong X to toll out 3 o'clock. As the contact spring B will be on the contact pin 12 for about 1 minute, the wheels of the clockwork F would continue to turn and the bells ring, if it were not for the stop pin located on the outside, or first, circle of the disk Q, which pin is set in line with the last pin in the set of pins for the hour, or, in this instance, in line with the third pin. When the stop pin has passed the spring, the connection through the magnets T is broken and the clockwork F stops instantly. When the spring B strikes the 2 o'clock pin, or 10 minutes after 3 o'clock, the armature K is drawn over to N, and at the 3 pin, or 15 minutes after 3 o'clock, the bells U, V, and W will ring and then the stop pin will break the current, and so on, at every 15 minutes of the 12 hours.
Ill: Fig.5 The Wiring Diagram