Part 14 (2/2)

** How to Make Small Gearwheels Without a Lathe [46]

To make small models sundry small gears and racks are required, either cut for the place or by using the parts from an old clock.

With no other tools than a hacksaw, some files, a compa.s.s,

[Ill.u.s.tration: Making Model Wheels]

and with the exercise of a little patience and moderate skill, very good teeth may be cut on blank wheels.

First take the case of a small gearwheel, say 1 in. outside diameter and 1/16 in. thick, with twenty-four teeth. Draw a circle on paper, the same diameter as the wheel. Divide the circ.u.mference into the number of parts desired, by drawing diameters, Fig. 1.

The distance AB will be approximately the pitch. Now describe a smaller circle for the base of the teeth and halfway between these circles may be taken as the pitch circle.

Now describe a circle the same size as the largest circle on a piece of 1/16-in. sheet metal, and having cut it out and filed it up to this circle, fasten the marked-out paper circle accurately over it with glue. Saw-cuts can now be made down the diameters to the smaller circle with the aid of a saw guide, Fig. 2, made from 1/16-in. mild steel or iron. This guide should have a beveled edge, E, from F to G, to lay along the line on which the saw-cut is to be made. The straight-edge, CD, should be set back one-half the thickness of the saw-blades, so that the center of the blade, when flat against it, will be over the line FG. A small clearance s.p.a.ce, FC, must be made to allow the teeth of the saw to pa.s.s.

The guide should then be placed along one of the diameters and held in position until gripped in the vise, Fig. 3. The first tooth may now be cut, care being taken to keep the blade of the saw flat up to the guiding edge. The Model Engineer, London, says if this is done and the saw-guide well made, the cut will be central on the line, and if the marking-out is correct the teeth will be quite uniform all the way round. A small ward file will be needed to finish off the teeth to their proper shape and thickness.

In making a worm wheel the cuts must be taken in a sloping direction, the slope and pitch depending on the slope and pitch of the worm thread, which, though more difficult, may also be cut with a hacksaw and file.

A bevel wheel should be cut in the same manner as the spur wheel, but the cut should be deeper on the side which has the larger diameter. To cut a rack the pitch should be marked along the side, and the guide and saw used as before (Fig. 4).

** How to Make Four Pictures on One Plate [46]

Secure two extra slides for the plate holders and cut one corner out on one

[Ill.u.s.tration: Four Photos on One Plate]

of them, as shown in Fig. 1. Make a hole in the other, as shown in Fig. 2. With a lead pencil draw on the ground gla.s.s one line vertical and one horizontal, each in the center. This will divide the ground gla.s.s into four equal parts.

Focus the camera in the usual manner, but get the picture desired to fill only one of the parts on the ground gla.s.s. Place the plate-holder in position and draw the regular slide; subst.i.tute one of the slides prepared and expose in the usual way.

If a small picture is to be made in the lower left-hand corner of the plate, place the prepared slide with the corner cut, as shown in Fig. 1. The slide may be turned over for the upper left hand corner and then changed for slide shown in Fig. 2 for the upper and lower right-hand corners.

** Electric Blue-Light Experiment [47]

[Ill.u.s.tration: Electric Blue-light]

Take a jump-spark coil and connect it up with a battery and start the vibrator. Then take one outlet wire, R, and connect to one side of a 2-cp. electric lamp, and the other outlet wire, B, hold in one hand, and press all fingers of the other hand on globe at point A. A bright, blue light will come from the wires in the lamp to the surface of the globe where the fingers touch. No shock will be perceptible.

** Interesting Electrical Experiment [47]

The materials necessary for performing this experiment are: Telephone receiver, transmitter, some wire and some carbons, either the pencils for arc lamps, or ones taken from old dry batteries will do.

Run a line from the inside of the house to the inside of some other building and fasten it to one terminal of the receiver. To the other terminal fasten another piece of wire and ground it on the water faucet in the house. If there is no faucet in the house, ground it with a large piece of zinc.

Fasten the other end to one terminal of the transmitter and from the other terminal of the same run a wire into the ground. The ground here should consist either of a large piece of carbon, or several pieces bound tightly together.

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