The Boy Mechanic Part 126

Place the quill on top of the penholder C, so that its small end rests against the pen immediately above its eye. Pull the string through this eye. Securely bind the quill to the pen and holder with a thread, as shown, first placing under it a wedge-shaped support of cork or wood, D, hollowed on both sides to fit the curved surfaces of the quill and holder. The ill.u.s.tration shows the detail clearly.

To fill the reservoir place the pen upright on its point and dip a small camel's-hair brush or cloth-bound toothpick into the ink bottle and "sc.r.a.pe" off the ink it will hold on the inner edge of the quill. Cork tightly, and the device is ready for use. When not in use place the holder at an angle with the pen uppermost.

--Contributed by Chelsea C. Fraser, Saginaw, Michigan.

** How to Construct a Small Thermostat [455]

By R. A. McCLURE

It is a well known fact, that there is a change in the dimensions of a piece of metal, due to a change in its temperature. This change in dimensions is not the same for all materials; it being much greater in some

[Ill.u.s.tration: Simple Thermostat; Couple and Mounting Strip]

materials than in others, while in some there is practically no change.

If two thin, narrow strips of different metals, that contract or expand at different ratio due to a variation in temperature, be rigidly fastened together at their ends, and the combination then heated or cooled, the combined piece will have its shape changed.

One of the pieces will increase in length more than the other, due to a rise in temperature, and this same piece will decrease in length more than the other when subjected to a decrease in temperature.

If one end of this combined piece be rigidly clamped to a support, as shown in Fig. 1, and the combination then have its temperature changed, the free end will move to the right or left of its original position, depending upon which of the pieces changes in length the more. If there is a rise in temperature and the right-hand piece B increases in length faster than the left-hand piece A, the free end of the combined piece win move to the left of its original position. If, on the other hand, there is a decrease in temperature, the right-hand piece will decrease in length more than the left-hand piece, and the upper or free end will move to the right of its original position.

Such a combination of two metals const.i.tutes a simple thermostat.

If the movement of the free end of the combination be made to actuate a needle moving over a properly calibrated scale we have a simple form of thermometer. If two electrical contacts, CC, be mounted on the right and left-hand sides of the upper end of the combined piece, as shown in Fig. 1, we have a thermostat that may be used in closing an electrical circuit when the temperature of the room in which it is placed rises or falls a certain value.

These contacts should be so arranged that they can be moved toward or away from the combined piece independently. By adjusting the position of these contacts, the electrical circuit will be closed when the temperature of the thermostat has reached an experimentally predetermined value.

The following description is that of a thermostat, constructed by the author of this article, which gave very satisfactory results.

First obtain a piece of steel, 6 in. long, 5/8 in. wide and 2/100 in. thick, and a piece of bra.s.s, 6 in. long, 5/8 in. wide and 3/100 in. thick. Clean one side of each of these pieces and tin them well with solder. Place the two tinned surfaces just treated in contact with each other and heat them until the solder on their surfaces melts and then allow them to cool. A better way would be to clamp the two thin pieces between two heavy metal pieces, and then heat the whole to such a temperature that the solder will melt, and then allow it to cool. This last method will give more satisfactory results than would be obtained if no clamps are used, as the thin metal pieces are liable to bend

[Ill.u.s.tration: Support for Couple, and Needle-Mounting Strip]

out of shape when they are heated, and as a result they will not be in contact with each other over their entire surfaces. After these pieces have been soldered together forming one piece, which we shall for convenience speak of as the couple, two small holes should be drilled in one end to be used in mounting it, and a notch cut in the other end, as shown in Fig. 2.

Cut from some thin sheet bra.s.s, about 2/100 in. in thickness, two pieces, 1/4 in. wide and 1/2 in. long. Bend these pieces of bra.s.s over a piece of hatpin wire, thus forming two V-shaped pieces. Cut off a piece of the hatpin, 5/8 in. long, and fasten it across the notched end of the couple by means of the U-shaped piece of bra.s.s, which should be soldered in place as shown in Fig. 3. All superfluous solder should then be cleaned from the couple and the steel pin. Now bend the couple so as to form a perfect half circle, the bra.s.s being on the inside.

The base upon which this couple is to be mounted should be made as follows: Obtain a piece of bra.s.s, 7 in. long, 3/4 in. wide, and 1/4 in. thick. In this piece drill holes, as indicated in Fig. 4, except A, which will be drilled later. Tap the holes B, C and D for 1/8-in. machine screws.

Cut from some 1/8-in. sheet bra.s.s a piece, 1-7/8 in. long and 3/4 in. wide, to be used as a support for the couple. In one end of this piece drill two small holes, as indicated in Fig. 5, and tap them for 3/16-in. machine screws. In the opposite end cut a slot, whose dimensions correspond to those given in Fig. 5. Now bend the piece, at the dotted line in Fig. 5, into the form shown in Fig.

6, making sure that the dimension given is correct. This piece can now be mounted upon the piece shown in Fig. 4, by means of two bra.s.s machine screws placed in the holes B. The slot in the support for the couple will permit its being moved along the mounting strip, the purpose of which will be shown later.

Next cut another piece of 1/8-in. bra.s.s, 2-3/4 in. long and 5/8 in. wide. In this piece drill two 1/8-in. holes, as indicated in Fig. 7, and then bend it at the dotted lines into the form shown in Fig. 8. Mount this strip upon the main mounting strip by means of two bra.s.s machine screws placed in the holes C, so that the upper part is over the center-punch mark for the hole A in the main mounting strip.

You are now ready to drill the hole A, which should be done as follows: Remove the piece you last mounted and then clamp the main mounting strip in the drill press so that the center-punch mark for the hole A is directly under the point of the drill. Then remount the piece you just removed, without disturbing the piece you clamped in the drill press, and drill a small hole through both pieces. This hole should be about 3/64 in. in diameter. After this small hole has been drilled through both pieces, a countersink should be placed in the drill chuck and the hole in the upper piece countersunk to a depth equal to half the thickness of the metal in which it is drilled. Unclamp the pieces from the drill press, turn them over, and countersink the small hole in what was originally the lower piece. The object of countersinking these holes is to reduce the bearing surface of a small shaft that is to be supported in the holes and must be as free from friction as possible.

We may now construct the needle, or moving portion of the thermostat, which should be done as follows: The shaft that is to carry the moving system must be made from a piece of steel rod, about 3/32 in. in diameter. Its dimensions should correspond to those given in Fig. 9. Considerable care should be used in turning this shaft down, to make sure that it fits perfectly in the small holes in the supporting pieces. The shaft should turn freely, but it must not be loose in the holes, nor should it have but a very small end play.

Cut from some 1/32-in. sheet bra.s.s a piece whose dimensions correspond to those given in Fig. 10. Drill a 1/8-in. hole, A, in this piece, and cut a slot, B, from one side of the piece into this hole, and a second slot, C, along the center of the piece as indicated in the figure. Considerable care should be exercised in cutting the slot C, so that its breadth is exactly equal to the diameter of the piece of steel wire fastened on the end of the couple. Also make sure to get the sides of this slot perfectly smooth. Cut from some 1/8-in. bra.s.s a disk having a diameter of 1/2 in., and solder it to the end of the needle. The dotted line in Fig. 10 indicates the proper position of the disk. Now drill a hole, D, through the disk and needle, of such a diameter that considerable force must be applied to the steel shaft you have already made, in order to force it through the hole. Force the shaft

[Ill.u.s.tration: Shaft for Needle and Needle]

through this hole until the needle is exactly in the center of the shaft.

The parts of the thermostat thus far made can now be a.s.sembled.

Place the steel shaft in its bearings and see that it turns perfectly free. Then place the steel pin, on the end of the couple, in the slot C, and fasten the

[Ill.u.s.tration: Wiring Diagram for One and Two Bells]

other end of the couple, by means of two machine screws, to the support made for the couple. Increase or decrease the temperature of the thermostat and note the results. If everything is working all right, the end of the needle should move when the temperature of the thermostat is changed. The amount the end of the needle moves can be easily changed by moving the support or the couple toward or away from the shaft supporting the needle, which changes the position of the steel pin in the slot C. The nearer the steel pin is to the shaft supporting the needle, the greater the movement of the end of the needle due to a given change in temperature.

A small piece of white cardboard can be mounted directly under the end of the needle by means of small bra.s.s strips, that in turn can be attached to the lower ends of the main mounting holes D, Fig.

4. A scale can be marked on this piece of cardboard by noting the position of the needle corresponding to different temperatures as determined by a thermometer. When this scale has been completed, you can use the thermostat as a thermometer.

Two contacts may be mounted, one on each side of the needle, in a manner similar to the method suggested for mounting the cardboard.

These contacts should be so constructed that the end of the needle will slide over them with little friction, and so that their position with respect to the end of the needle may be easily changed.

[Ill.u.s.tration: a.s.sembled Thermostat]

Both contacts must be insulated from the remainder of the thermostat, and may or may not be connected together, depending on how the thermostat is to be used.

It would be advisable, if possible, to have the part of the needle that touches the contact points, as well as these points, of platinum, as the arc that is likely to be formed will not destroy the platinum as easily as it will the bra.s.s. A small wooden containing case can now be made and the thermostat is complete.

There should be a large number of holes drilled in the sides, ends and back of the case so that the air inside may be always of the same temperature as the outside air.

In adjusting, testing, or calibrating your thermostat, make sure that it is in the same position that it will be in when in use.

The connections of the thermostat for ringing one bell when the temperature rises or falls to a certain value, are shown in Fig.

11. The connections of the thermostat for ringing one bell when the temperature rises to a certain value and another bell when the temperature falls to a certain value, are shown in Fig. 12. The complete thermostat is shown in Fig. 13.

** A Tailless Kite [458]

The frame of a 3-ft. kite is made of two sticks, each 3 ft. long.

These are tied together so that the cross stick will be at a distance of 15 per cent of the full length of the upright stick, from its end, or in this case 5.4 in. The sticks may be made of straight grained pine, 3/8 in. square, for small kites, and larger hardwood sticks, for larger kites.

The cross stick is bent into a bow

[Ill.u.s.tration: Plan and Dimensions for Kite]

by tying a strong cord across from end to end. The center of the bend should be 4-1/2 in. above the ends. The bend is shown in the sketch. Connect all four ends or points with a cord, being careful not to pull the bend of the cross stick down, but seeing that it remains straight across the kite. When this is done the frame is ready for the cover.

The cover will require 2-1/2 sheets of tissue paper, 20 by 30 in., which should be pasted together as the sketch indicates. Cut out the paper, allowing 2 in. margin for lapping over the cord on the frame. Place the frame on the cover with the convex side toward the paper and paste the margin over the cord, allowing the paper to bag a little to form pockets for the air to lift the kite. The corners should be reinforced with circular pieces of paper pasted over the ends of the sticks.

The flying cord is attached to the points A and B of the frame.

There is no cross cord. The kite will fly at right angles to the flying cord. It is easily started flying from the ground by laying it with the head toward the operator and pulling it up into the wind.

--Contributed by Chas. B. Damik, Cooperstown, N. Y.

** The Levitation - A Modern Stage Trick [459]

This illusion has mystified thousands of the theater-going public, in fact, it has been the "piece de resistance" of many illusion acts. The ordinary method of procedure is as follows: The person who is to be suspended in the air, apparently with no support--usually a lady--is first put in a hypnotic (?) sleep. She is placed on a couch in the middle of the stage, and in most cases the spotlight is brought into play. The performer then takes a position close to the couch and with dramatic