The Boy Mechanic Part 24

[Ill.u.s.tration: Cabinet Holding 32 Records]

1/4 in. deep and 3/4 in. apart on one side of the top and bottom shelves, as shown in Fig. 2, and on both sides of the middle shelf. The shelves should be s.p.a.ced 9-5/8 in. for 10-in. records and 5-5/8 in. for 6-in. records. A neat scroll design is cut from a board 25 in. long to fill up and finish the s.p.a.ce below the bottom shelf.

--Contributed by H. E. Mangold, Compton, Cal.

** A Battery Rheostat [80]

In a board 7 in. long and 5 in. wide bore holes about 1/4 in.

apart, in a semicircle 2 in. from the bottom, and cut notches in top end to correspond with the holes. From a piece of bra.s.s a switch, C, is cut with a k.n.o.b soldered on at the end. Nails for stops are placed at DD. Two binding-posts are placed in board at A and B. With about 9 ft. of fine iron wire attach one end to the bottom of post A and run through first hole and over in first notch to back of board and then through second hole and over second notch and so on until E is reached, where the other end of wire is fastened. Connect switch to post B.

--Contributed by Edmund Kuhn, Jr., East Orange, N. J.

[Ill.u.s.tration: Battery Rheostat]

** Automatic Time Switch [80]

This device may be used to either open or close the circuit at any desired time. An alarm clock is firmly fastened to a wooden bracket and provided with a small wood or metal drum, A, to which is fastened a cord, B. The other end of the cord is tied to the switch handle so that when the alarm goes off the switch is either opened or closed, depending on whether the cord is pa.s.sed over pulley C or pulley D.

When the cord is pa.s.sed over pulley C, as shown in Fig. 1, the circuit will be closed when the alarm goes off, but if it is pa.s.sed over D the circuit will be opened. Pulley D is fastened to a piece of spring steel, E, which in operation is bent, as shown by the dotted lines, thus causing the switch to snap open quickly and prevent forming an arc.

--Contributed by Douglas Royer, Roanoke, Va.

[Ill.u.s.tration: Will Open or Close Circuit as Desired]

** How to Make a Rotary Pump [81]

[Ill.u.s.tration: Details of Rotary Pump]

A simple rotary pump is constructed on the principle of creating a vacuum in a rubber tube and so causing water to rise to fill the vacuum. Figs. 3, 4 and 5 show all the parts needed, excepting the crank and tubing. The dimensions and description given are for a minimum pump, but a larger one could be built in proportion.

Through the center of a block of wood 4 in. square and 7/8 in.

thick (A, Figs. 1, 2 and 3) saw a circular opening 2-7/8 in. in diameter. On each side of this block cut a larger circle 3-1/4 in.

in diameter, having the same center as the first circle (Fig. 3).

Cut the last circles only 1/4 in. deep, leaving the first circle in the form of a ridge or track 3/8 in. wide, against which the rubber tubing, E, is compressed by wheels. Bore two 1/4 in. holes (HH, Fig. 1) from the outside of the block to the edge of the inner circle. Put the rubber tube, E, through one of these holes, pa.s.s it around the track and out through the other hole. Notice the break (S) in the track; this is necessary in order to place in position the piece holding the wheels.

Fig. 4 shows the wheel-holder, B. Make it of hard wood 3-1/8 in.

long, 1 in. wide and a little less than 7/8 in. thick, so that it will run freely between the sides (Fig. 5) when they are placed.

Cut two grooves, one in each end, 1 in. deep and 1/2 in. wide. In these grooves place wheels, CC, to turn on pins of stout wire.

These wheels should be 3/4 in. in diameter. When placed in the holder their centers must be exactly 2 in. apart, or so arranged that the distance between the edge of the wheels and the track (K, Fig. 1) is equal to the thickness of the tubing when pressed flat.

If the wheels fit too tightly, they will bind; it too loose, they will let the air through. Bore a hole through the middle of the wheel-holder and insert the crankpin, D, which should be about 1/2 in. in diameter. The crankpin should fit tightly; if necessary drive a brad through to keep it from slipping.

In the sides (Fig. 5) bore a hole in the center of the crankpin to run in loosely. Now put all these parts together, as shown in the ill.u.s.tration. Do not fasten the sides too securely until you have tried the device and are sure it will run smoothly. For the crank a bent piece of stout wire or a nail will serve, though a small iron wheel is better, as it gives steadiness to the motion. In this case a handle must be attached to the rim of the wheel to serve as a crank. The drive wheel from a broken-down eggbeater will do nicely. For ease in handling the pump, a platform should be added.

To use the pump, fill the tube with water and place the lower end of the tube in a reservoir of water. Make a nozzle of the end of a clay pipe stem for the other end of the tube. Then turn the crank from left to right. The first wheel presses the air out of the tube, creating a vacuum which is immediately filled with water.

Before the first wheel releases the tube at the top, the other wheel has reached the bottom, this time pressing along the water that was brought up by the first wheel. If the motion of the wheels is regular, the pump will give a steady stream. Two feet of 1/4-in. tubing, costing 10 cents, is all the expense necessary.

--Contributed by Dan H. Hubbard, Idana, Kan.

** How to Make a Fire Screen [82]

[Ill.u.s.tration: FIG.2 Made of Strap Iron]

A screen which will not interfere with the radiation of the heat from the fire, and will keep skirts and children safe can be made at little expense out of some strap iron. The screen which is shown in Fig. 1, stands 20 in. high from the base to the top crosspiece and is made of 3/4 by 1/4-in. and 1/2 by 1/4-in. iron.

The top and bottom pieces marked AA, Fig. 1, are 3/4 by 1/4 in.

and are 30 in. long, bent at an angle to fit the fireplace 7 in.

from each end, as shown in Fig. 2. The three legs marked BBB, Fig.

1, are of the same size iron and each leg will take 34 in. of material. In shaping the feet of these three pieces give them a slight tendency to lean toward the fire or inside of screen, says a correspondent in the Blacksmith and Wheelwright. In the two cross bars 1 in. from each end, A in Fig. 2, mark for hole and 3 in. from that mark the next hole. Take the center of the bar, B, 15 in. from each end, and mark for a hole, and 3-1/2 in. on each side mark again and 3-1/2 in. beyond each of these two, mark again.

Mark the legs 2-3/4 in. from the bottom and 2 in. from the top and after making rivet-holes rivet them to the cross bars, AA, Fig. 1.

Cut six pieces, 17-1/2 in. long and punch holes to fit and rivet onto the remaining holes in cross bars, AA, Fig. 1. Clean it up and give it a coat of black j.a.pan or dead black.

** Trap for Small Animals [82]

This is a box trap with gla.s.s sides and back, the panes of gla.s.s being held in place by brads placed on both sides. The animal does not fear to enter the box, because he can see through it: when he enters, however, and touches the bait the lid is released and, dropping, shuts him in. This is one of the easiest traps to build and is usually successful.

[Ill.u.s.tration: Trap]

** Homemade Grenet Battery [83]

Procure an ordinary carbon-zinc, sal-ammoniac battery and remove the zinc rod. If the battery has been used before, it is better to soak the carbon cylinder for a few hours to remove any remaining crystals of sal-ammoniac from its pores.

The truncated, conical zinc required is known as a fuller's zinc and can be bought at any electrical supply dealer's, or, it may be cast in a sand mold from sc.r.a.p zinc or the worn-out zinc rods from sal-ammoniac batteries. It should be cast on the end of a piece of No. 14 copper wire. Amalgamation is not necessary for the zinc one buys, but if one casts his own zinc, it is necessary to amalgamate it or coat it with mercury. This may be done as follows:

Dip a piece of rag in a diluted solution of sulphuric acid (water 16 parts, acid 1 part); rub the zinc well, at the same time allowing a few drops of mercury to fall on a spot attacked by the acid. The mercury will adhere, and if the rubbing is continued so as to spread the mercury, it will cover the entire surface of the zinc, giving it a bright, silvery appearance.

Next procure what is known as a wire connector. This is a piece of copper tube about 1-1/2 in. long having two thumb screws, one on each end on opposite sides (Fig. 2). The upper screw is to connect the battery wire, the lower one to raise and lower the zinc. The battery is now complete, and the solution (Fig. 1) must be prepared. Proceed as follows:

In 32 oz. of water dissolve 4 oz. pota.s.sium bichromate. When the bichromate has all dissolved, add slowly, stirring constantly, 4 oz. sulphuric acid. Do not add the acid too quickly or the heat generated may break the vessel containing the solution. Then pour the solution into the battery jar, until it is within 3 in. of the top. Thread the wire holding the zinc through the porcelain insulator of the carbon cylinder and also through the wire connector. Pull the zinc up as far as it will go and tighten the lower thumb screw so that it holds the wire secure. Place the carbon in the jar. If the solution touches the zinc, some of it should be poured out. To determine whether or not the zinc is touched by the solution, take out the carbon and lower the zinc.

If it is wet, there is too much liquid in the jar. The battery is now ready for use.

To cause a flow of electricity, lower the zinc until it almost touches the bottom of the jar and connect an electric bell or other electrical apparatus by means of wires to the two binding posts.

This battery when first set up gives a current of about two volts.

It is useful for running induction coils, or small electric motors. When through using the battery, raise the zinc and tighten the lower thumb screw. This prevents the zinc wasting away when no current is being used.

--Contributed by H. C. Meyer, Philadelphia.

[Ill.u.s.tration: Fig.1 Details of Homemade Battery]