The Boy Mechanic Part 39

The hasp, if that be the name for the double toothed arrangement that catches into the lock, was to be secured by only three bra.s.s screws, which seemed to be insufficient, says a correspondent of the Metal Worker; therefore a piece of heavy tin was formed over the front of the trunk, which is only 3/8-in. board, the hasp tinned and soldered to the back of the now U-shaped tin, and the tin placed over the board and all fastened in position. The tin is 4 in. wide, 16 in. long and when placed over the board, it laps down about 8 in. between the boards, and the same distance inside of the new board, as shown by the heavy line in the cross section, Fig. 1. Wrought nails are used which pa.s.s twice through the tin and both boards, and then well clinched. The three screws were then put in the hasp.

The k.n.o.b on the dial extends out too far, which may be filed off and two holes subst.i.tuted, as shown, with which to operate the dial. An old key is filed down in the shape shown in Fig. 2 to fit the two holes.

As the dial is convex it will need protection to prevent injury by rough handling. A leather s.h.i.+eld may be used for this purpose, which is cut with two holes, one for the key and the other to permit the operator to observe the numbers on the dial. The s.h.i.+eld answers a further purpose of preventing any bystander from noting the numbers on the dial.

** AN ELECTRIC ILLUSION BOX [135]

The accompanying engravings show a most interesting form of electrically operated illusion consisting of a box divided diagonally and each division alternately lighted with an electric lamp. By means of an automatic thermostat arranged in the lamp circuit causing the lamps to light successively, an aquarium apparently without fish one moment is in the next instant swarming with live gold fish; an empty vase viewed through the opening in the box suddenly is filled with flowers, or an empty cigar box is seen and immediately is filled with cigars.

These electric magic boxes as shown are made of metal and oxidized copper finished, but for ordinary use they can be made of wood in the same shape and size. The upper magic boxes as are shown in the engraving are about 12 in. square and 8-1/2 in. high for parlor use and the lower boxes are 18 in. square and 10-1/2 in. high for use in window displays. There is a part.i.tion arranged diagonally in the box as shown in the plan view, which completely divides the box into two parts. One-half the part.i.tion is fitted with a plain, clear gla.s.s as shown. The part.i.tion and interior of the box are rendered non-reflecting by painting with a dull, not s.h.i.+ny, black color. When making of wood, a door must be provided on the side or rear to make changes of exhibits. If the box is made large enough, or in the larger size mentioned, openings may be made in the bottom for this purpose, and also used in case of performing the magic trick of allowing two persons to place their

[Ill.u.s.tration: Construction of Magic Boxes]

heads in the box and change from one to the other.

The electric globes are inserted as shown at LL through the top of the box, one in each division. When the rear part is illuminated, any article arranged within that part will be visible to the spectator looking into the box through the front opening, but when the front part is illuminated, and the back left dark, any article placed therein will be reflected in. the gla.s.s, which takes the same position to the observer as the one in the rear. Thus a plain aquarium is set in the rear part and one with swimming fish placed in

[Ill.u.s.tration: Four Electric Magic Boxes Complete for Use]

the front, and with the proper illumination one is changed, as it appears, into the other. When using as a window display, place the goods in one part and the price in the other. Many other changes can be made at the will of the operator.

Electric lamps may be controlled by various means to produce different effects. Lamps may be connected in parallel and each turned on or off by means of a hand-operated switch or the b.u.t.ton on the lamp socket, or if desired a hand-operated adjustable resistance may be included in the circuit of each lamp for gradually causing the object to fade away or reappear slowly.

Instead of changing the current operated by hand, this may be done automatically by connecting the lamps in parallel on the lighting circuit and each connected in series with a thermostatic switch plug provided with a heating coil which operates to automatically open and close the circuit through the respective lamp.

When there is no electric current available, matches or candles may be used and inserted through the holes H, as shown in the sketch, alternately.

** Replace Dry Putty [136]

Painting over putty that has not become dry will cause scaling or cracking around the edges of the putty.

** Photo Print Was.h.i.+ng Tank [136]

The accompanying sketch shows a simple form of a print was.h.i.+ng tank that tips from side to side by the weight of the water. For prints 4 by 5 and 5 by 7-in. a tank 2 ft. long and 1 ft. wide will be about the right size. This tank is then divided with a part.i.tion placed exactly in the center. This part.i.tion should extend 3 or 4 in. above the top of the tank. The part.i.tion may also extend below the tank about 1-1/2 in., or a piece of this width put on the bottom, as shown at A in the sketch.

[Ill.u.s.tration: Keeps Prints Constantly Moving]

A row of holes about 1/2 in. in diameter is bored through each end of the tank, as shown at B. These holes will allow the water to spill out while the opposite side is filling. The tank may be made from 1/2-in. material and when completed as shown, lined with oil cloth to make it watertight. The tank is placed with the part.i.tion directly under a water tap and the flow of water will cause it to tip from time to time, keeping the prints constantly moving about in the water.

** Home-Made Soldering Clamps [137]

Take a cotter pin and bend it over a small rod to bring the points together, as shown in the sketch. This will make a spring clamp that is opened to slip over the articles to be clamped together by inserting a scratch awl or scriber between the legs at the bowed portion. To make a more positive clamp before bending the legs to a bow, slip a short coil of wire over the pin, pa.s.sing it down to the ring end. Wire 1/32 in. in diameter wound over a wire slightly larger in diameter than that of the cotter will do. In soldering, smoke the legs well to avoid solder adhering to them. The clamp is tightened by pus.h.i.+ng up the coil ring toward the bow of the legs and then twisting it like a nut, the coil being wound right-handed, so that it will have a screw effect.

[Ill.u.s.tration: Clamp]

** A Telephone Experiment [137]

If the small apparatus, as shown in the accompanying sketch, is attached to the under side of an ordinary dining table, it will, if connected to a telephone circuit, set the table in vibration, so that any number of people who put their ears flat upon the table will hear the voice of a person speaking from a distance, apparently coming out of the table, says the Model Engineer. A small piece of wood, A, Fig. 1, is cut about 5 in. square, to the center of which is attached a small piece of soft iron wire, such as used for cores

[Ill.u.s.tration: Mechanical Table Talk]

of induction coils, about 4 in. long and bent in the form of a hook at the lower end, as shown at B. This wire is attached to the block of wood, A, as shown in Fig. 2. The end of the wire is soldered to a small bra.s.s plate which is set in the block so it will be level or flush with the top of the block and then fastened with two screws. The block A is fastened to the under side of the table with two screws. A small coil, C, is made by winding No. 24 silk or cotton covered wire around a small tube, either a piece of gla.s.s, a short straw or a quill. The coil is made tapering as shown without using wood ends. This coil is slipped over the wire B previous to soldering it to the small bra.s.s plate. The ends of the coil are connected to two binding-posts which are fastened to the block A. A small lead weight weighing 2 or 3 oz. is hung on the hook made in the lower end of the wire B.

When all connections are made, as shown in Fig. 1, and the block fastened to the under side of the table, the apparatus is ready for use, and has only to be connected to an ordinary telephone transmitter and batteries as shown. The apparatus will work to a certain extent even if the weight is removed, though not so clear.

** Wax Wood Screws [137]

Some workmen use tallow on lag or wood screws. Try beeswax for this purpose. It is much cleaner to use and is just as good if not better.

** How to Make an Induction Coil [138]

A small shocking coil, suitable for medical purposes, may be constructed of materials found in nearly every amateur mechanic's collection of odds and ends. The core, A, Fig. 1, is a piece of round soft iron rod about 1/4 in. in diameter and about 4 in.

long. A strip of stiff paper about 3/4 in. wide is covered with glue and wrapped around one end of the core, as shown at B, until the diameter is about 3/8 in. The portion of the core remaining uncovered is then wrapped with a piece of paper about 4 in. wide.

No glue is used on this piece, as it is removed later to form the s.p.a.ce, C, after the paper sh.e.l.l, D, has been wound upon it. This paper sh.e.l.l is made of stiff paper and glue the same as B and is made about 3/64 in. thick. Two pieces of hardwood, EE, 1-3/4 in.

square and about 5/16 in. thick, are drilled in the center and glued on the ends of the paper sh.e.l.l as shown.

The primary winding consists of 4 or 5 layers of No. 18 or 20 single cotton-covered magnet wire, the ends of which may be pa.s.sed through small holes in the wooden ends. If a drill small enough is not available, the holes may be made with a hot knitting needle or a piece of wire heated to redness. After the primary coil is wound it should be thoroughly insulated before winding the secondary.

This may be done by wrapping with 4 or 5 thicknesses of paper.

The secondary coil should be wound with single covered wire, preferably silk-covered, although cotton will do. The more turns there are on the secondary the higher the voltage will be, so the wire used must be fine. Number 32 to 36 will give good results, the latter giving more voltage but less amperage. Each layer of the secondary winding should be insulated from the others by a piece of thin paraffined paper wrapped over each layer as it is finished. It is well not to wind to the extreme ends of the paper insulations, but to leave a s.p.a.ce of about 1/8-in. at each end of the winding to prevent the wires of one layer slipping over the ends of the paraffin

[Ill.u.s.tration: Induction Coil]

paper and coming in contact with the layer beneath, thus causing a short circuit. The secondary winding should have at least a dozen layers and should be carefully wound to prevent short circuiting.

In order to reduce the strength of the current a piece of bra.s.s tubing, F, is pushed into the s.p.a.ce, C, surrounding the core, or if no bra.s.s tubing of the required size is on hand, roll a paper tube, cover with 4 or 5 thicknesses of tinfoil and then wrap with more paper, using glue to hold the tinfoil in place and to keep the tube from unwinding. When the tube is pushed all the way in, the current produced

[Ill.u.s.tration: Induction Coil]

will be almost unnoticeable, but when it is withdrawn the current will be so strong that a person cannot let go the handles until the coil is shut off. After the secondary coil is wound it should be covered with stiff paper, and the whole coil, including the wood ends, should then be enameled black.

It is then ready to be mounted on a wooden base as shown in Fig.

2. The secondary terminals are connected to the binding-posts, AA, which may be fastened on the base if desired. One wire from the primary is connected with the binding-post, B, and the other is connected with the armature, D, which may be taken from an old electric bell. The contact screw, E, also from an electric bell, is connected to the binding-post, C. The contact spring, F, should be bent against and soldered to the armature in order to make the vibrations more rapid.

If a false bottom is used on the base, all the wiring may be concealed, which adds greatly to the appearance and if desired a small switch may be added. The handles, which may be old bicycle pumps or electric light carbons, are connected to the binding-posts, AA, by means of wires about 3 or 4 ft. long. This coil when operating with the tube pulled all the way out and connected to a single dry cell will give a current stronger than most persons can stand.