The Boy Mechanic Part 94

** Electric Alarm that Rings a Bell and Turns on a Light [337]

The ill.u.s.tration shows an alarm clock connected up to ring an electric bell, and at the same time turn on an electric light to show the time. The parts indicated are as follows: A, key of alarm clock; B, contact post, 4 in. long; C, shelf, 5-1/4 by 10 in.; D, bracket; E, electric bulb (3-1/2 volts) ; S, bra.s.s strip, 4-1/2 in. long, 3/8 in. wide and 1/16 in. thick; T, switch; F, wire from batteries to switch; G, wire from bell to switch; H, wire from light to switch; I, dry batteries; J, bell; X, point where a splice is made from the light to wire leading to batteries from bra.s.s strip under clock. Push the switch lever to the right before retiring.

To operate this, set alarm key as shown in diagram, after two turns have been made on the key. When alarm goes off, it turns till it forms a connection by striking the contact post and starts the electric bell ringing. Throw lever off from the right to center, which stops bell ringing. To throw on light throw levers to the left. The bell is then cut out but the light remains on till lever is again thrown in the center,

[Ill.u.s.tration: Details of Alarm Construction]

In placing clock on shelf, after setting alarm, be sure that the legs of clock are on the bra.s.s strip and that the alarm key is in position so it will come in contact with the contact post in back of clock. The contact post may be of 1/4-in. copper tubing, or 1/4-in. bra.s.s rod.

The advantage of this is that one can control the bell and light, while lying in bed, by having the switch on the baseboard, near the bed, so it can be reached without getting out of bed.

--Contributed by Geo. C. Brinkerhoff, Swissvale, Pa.

** How to Hold a Screw on a Screwdriver [337]

A screw that is taken from a place almost inaccessible with the fingers requires considerable patience to return it with an ordinary screwdriver unless some holding-on device is used. I have found that by putting a piece of cardboard or thick paper with the blade of the screwdriver in the screw head slot, the screw may be held and turned into places that it would be impossible with the screwdriver alone.

--Contributed by C. Chatland, Ogden, Utah.

** How to Make a Lead Cannon [338]

Any boy who has a little mechanical ability can make a very reliable cannon for his Fourth-of-July celebration by following the instructions given here:

[Ill.u.s.tration: Lead Cannon Construction]

Take a stick--a piece of curtain roller will do--7 in. long. Make a shoulder, as at A, Fig. 1, 4 in. from one end, making it as true and smooth as possible, as this is to be the muzzle of the cannon.

Make the spindle as in Fig. 1, 1/4 in. in diameter. Procure a good quality of stiff paper, about 6 in. wide, and wrap it around the shoulder of the stick, letting it extend 3/4 in. beyond the end of the spindle, as at B, Fig. 2. Push an ordinary s.h.i.+ngle nail through the paper and into the extreme end of the spindle, as at A, Fig. 2. This is to form the fuse hole.

Having finished this, place stick and all in a pail of sand, being careful not to get the sand in it, and letting the opening at the top extend a little above the surface of the sand. Then fill the paper cylinder with melted lead and let cool. Pull out the nail and stick, sc.r.a.pe off the paper and the cannon is ready for mounting, as in Fig. 3.

--Contributed by Chas. S. Chapman, Lanesboro, Minn.

** Homemade Electric Bed Warmer [338]

The heat developed by a carbon-filament lamp is sufficiently high to allow its use as a heating element of, for instance, a bed warmer. There are a number of other small heaters which can be easily made and for which lamps form very suitable heating elements, but the bed warmer is probably the best example. All that is required is a tin covering, which can be made of an old can, about 3-1/2 in. in diameter. The top is cut out and the edge filed smooth. The lamp-socket end of the flexible cord is inserted in the can and the shade holder gripped over the opening. A small lamp of about 5 cp. will do the heating.

A flannel bag, large enough to slip over the tin can and provided with a neck that can be drawn together by means of a cord, gives the heater a more finished appearance, as well as making it more pleasant to the touch.

** Making a Fire with the Aid of Ice [338]

Take a piece of very clear ice and melt it down into the hollow of your hands so as to form a large lens. The ill.u.s.tration shows how this is done. With the lens-shaped ice used in the same manner as a reading gla.s.s to

[Ill.u.s.tration: Forming the Ice Lens]

direct the sun's rays on paper or shavings you can start a fire.

--Contributed by Arthur E. Joerin.

** How to Make a Crossbow and Arrow Sling [339]

In making of this crossbow it is best to use maple for the stock, but if this wood cannot be procured, good straight-grained pine will do. The

[Ill.u.s.tration: Details of the Bow-Gun and Arrow Sling]

material must be 1-1/2 in. thick, 6 in. wide and a trifle over 3 ft. long. The bow is made from straight-grained oak, ash, or hickory, 5/8 in. thick, 1 in. wide and 3 ft. long. A piece of oak, 3/8 in. thick, 1-1/2 in. wide and 6 ft. long, will be sufficient to make the trigger, spring and arrows. A piece of tin, some nails and a good cord will complete the materials necessary to make the crossbow.

The piece of maple or pine selected for the stock must be planed and sandpapered on both sides, and then marked and cut as shown in Fig. 1. A groove is cut for the arrows in the top straight edge 3/8 in. wide and 3/8 in. deep. The tin is bent and fastened on the wood at the back end of the groove where the cord slips out of the notch; this is to keep the edges from splitting.

A mortise is cut for the bow at a point 9-1/2 in. from the end of the stock, and one for the trigger 12 in. from the opposite end, which should be slanting a little as shown by the dotted lines. A spring, Fig. 2, is made from a good piece of oak and fastened to the stock with two screws. The trigger, Fig. 3, which is 1/4 in.

thick, is inserted in the mortise in the position when pulled back, and adjusted so as to raise the spring to the proper height, and then a pin is put through both stock and trigger, having the latter swing quite freely. When the trigger is pulled, it lifts the spring up, which in turn lifts the cord off the tin notch.

The stick for the bow, Fig. 4, is dressed down from a point 3/4 in. on each side of the center line to 1/2 in. wide at each end.

Notches are cut in the ends for the cord. The bow is not fastened in the stock, it is wrapped with a piece of canvas 1-1/2 in. wide on the center line to make a tight fit in the mortise. A stout cord is now tied in the notches cut in the ends of the bow making the cord taut when the wood is straight.

The design of the arrows is shown in Fig. 5 and they are made with the blades much thinner than the round part.

To shoot the crossbow, pull the cord back and down in the notch as shown in Fig. 6, place the arrow in the groove, sight and pull the trigger as in shooting an ordinary gun.

The arrow sling is made from a branch of ash about 1/2 in. in diameter, the bark removed and a notch cut in one end, as shown in Fig. 7. A stout cord about 2-1/2 ft. long is tied in the notch and a large knot made in the other or loose end. The arrows are practically the same as those used on the crossbow, with the exception of a small notch which is cut in them as shown in Fig.

8.

To throw the arrow, insert the cord near the knot in the notch of the arrow, then grasping the stick with the right hand and holding the wing of the arrow with the left, as shown in Fig. 9, throw the arrow with a quick slinging motion. The arrow may be thrown several hundred feet after a little practice.

--Contributed by O. E. Trownes, Wilmette, Ill.

** A Home-Made Vise [340]

Cut two pieces of wood in the shape shown in the sketch and bore a 3/8-in. hole through both of them for a common carriage bolt.

Fasten one of the pieces to the edge of the bench with a large wood screw and attach the other piece to the first one with a piece of leather nailed across the bottom of both pieces. The nut on the carriage bolt may be tightened with a wrench,

[Ill.u.s.tration: Details of a Home-Made Bench Vise]

or, better still, a key filed out of a piece of soft steel to fit the nut. The edges of the jaws are faced with sheet metal which can be copper or steel suitable for the work it is intended to hold.

** Temporary Dark Room Lantern [340]

Occasionally through some accident to the regular ruby lamp, or through the necessity of, developing while out of reach of a properly equipped dark room, some makes.h.i.+ft of illumination must be improvised. Such a temporary safe light may be made from an empty cigar box in a short time.