The Boy Mechanic Part 121

[Ill.u.s.tration: An Easily Made Wondergraph]

a grooved block attached to the ruler. A strip of wood, MN, is fastened to one end of the board. This strip is made just high enough to keep the ruler parallel with the face of the table, and a row of small nails are driven part way into its upper edge.

Anyone of these nails may be used to hold the other end of the ruler in position, as shown in the sketch. If the wheels are not true, a belt tightener, B, may be attached and held against the belt by a spring or rubber band.

After the apparatus is adjusted so it will run smoothly, fasten a piece of drawing paper to the table with a couple of thumb tacks, adjust the pen so that it rests lightly on the paper and turn the drive wheel. The results will be surprising and delightful. The accompanying designs were made with a very crude combination of pulleys and belts, such as described.

The machine should have a speed that will cause the pen to move over the paper at the same rate as in ordinary writing. The ink should flow freely from the pen as it pa.s.ses over the paper. A very fine pen may be necessary to prevent the lines from running together.

The dimensions of the wondergraph may vary. The larger designs in the ill.u.s.tration were made on a table, 8 in. in diameter, which was driven by a guide wheel, 6 in. in diameter. The size of the driver has no effect on the form or dimensions of the design, but a change in almost any other part of the machine has a marked effect on the results obtained. If the penholder is made so that it may be fastened at various positions along the ruler, and the guide wheel has holes drilled through it at different distances from the center

[Ill.u.s.tration: Diagrams Showing Construction of Wonder graphs]

to hold the peg attaching the ruler, these two adjustments, together with the one for changing the other end of the ruler by the rows of nails, will make a very great number of combinations possible. Even a slight change will greatly modify a figure or give an entirely new one. Designs may be changed by simply twisting the belt, thus reversing the direction of the table.

If an arm be fastened to the ruler at right angles to it, containing three or four grooves to hold the pen, still different figures will be obtained. A novel effect is made by fastening two pens to this arm at the same time, one filled with red ink and the other with black ink. The designs will be quite dissimilar and may be one traced over the other or one within the other according to the relative position of the pens.

Again change the size of the guide wheel and note the effect. If the diameter of the table is a multiple of that of the guide wheel, a complete figure of few lobes will result as shown by the one design in the lower right hand corner of the ill.u.s.tration.

With a very flexible belt tightener an elliptical guide wheel may be used. The axis may be taken at one of the foci or at the intersection of the axis of the ellipse.

The most complicated adjustment is to mount the table on the face of another disc, table and disc revolving in opposite directions.

It will go through a long series of changes without completing any figure and then will repeat itself. The diameters may be made to vary from the fraction of an inch to as large a diameter as the size of the table permits. The designs given here were originally traced on drawing paper 6 in. square.

Remarkable and complex as are the curves produced in this manner, yet they are but the results obtained by combining simultaneously two simple motions as may be shown in the following manner: Hold the table stationary and the pen will trace an oval. But if the guide wheel is secured in a fixed position and the table is revolved a circle will be the result.

So much for the machine shown in

[Ill.u.s.tration: Specimen Scrolls Made on the Wondergraph]

Fig. 1. The number of the modifications of this simple contrivance is limited only by the ingenuity of the maker. Fig. 2 speaks for itself. One end of the ruler is fastened in such a way as to have a to-and-fro motion over the arc of a circle and the speed of the table is geared down by the addition of another wheel with a small pulley attached. This will give many new designs. In Fig. 3 the end of the ruler is held by a rubber band against the edge of a thin triangular piece of wood which is attached to the face of the fourth wheel. By subst.i.tuting other plain figures for the triangle, or outlining them with small finishing nails, many curious modifications such as are shown by the two smallest designs in the ill.u.s.trations may be obtained. It is necessary, if symmetrical designs are to be made, that the fourth wheel and the guide wheel have the same diameter.

In Fig. 4, V and W are vertical wheels which may be successfully connected with the double horizontal drive wheel if the pulley between the two has a wide f.l.a.n.g.e and is set at the proper angle.

A long strip of paper is given a uniform rectilinear motion as the string attached to it is wound around the axle, V. The pen, P, has a motion compounded of two simultaneous motions at right angles to each other given by the two guide wheels. Designs such as shown as a border at the top and bottom of the ill.u.s.tration are obtained in this way. If the vertical wheels are disconnected and the paper fastened in place the well known Lissajou's curves are obtained.

These curves may be traced by various methods, but this arrangement is about the simplest of them all. The design in this case will change as the ratio of the diameters of the two guide wheels are changed.

These are only a few of the many adjustments that are possible.

Frequently some new device will give a figure which is apparently like one obtained in some other way, yet, if you will watch the way in which the two are commenced and developed into the complete design you will find they are formed quite differently.

The average boy will take delight in making a wondergraph and in inventing the many improvements that are sure to suggest themselves to him. At all events it will not be time thrown away, for, simple as the contrivance is, it will arouse latent energies which may develop along more useful lines in maturer years.

** How to Make a 110-Volt Transformer [439]

Secure two magnets from a telephone bell, or a set of magnets wound for 2,000 ohms. Mount them on a bar of bra.s.s or steel as shown in Fig. 1. Get an empty cocoa can and clean it good to remove all particles of cocoa and punch five holes in the cover, as shown in Fig. 2. The middle hole is to be used to fasten the cover to the bra.s.s bar with a bolt. The other four holes are for the wire terminals. A piece of rubber tubing must be placed over the wire terminals before inserting them in the holes. Fill the can with crude oil, or with any kind of oil except kerosene

[Ill.u.s.tration: Parts of the Transformer]

oil, and immerse the magnets in it by fitting the cover on tight (Fig. 3). The connections are made as shown in the diagram, Fig.

5. This device may be used on 110-volt current for electro-plating and small battery lamps, provided the magnets are wound with wire no larger than No. 40.

--Contributed by C. M. Rubsan, Muskogee, Okla.

** Experiment with a Vacuum [439]

[Ill.u.s.tration: Experimental Apparatus]

Take any kitchen utensil used for frying purposes-an ordinary skillet, or spider, works best-having a smooth inner bottom surface, and turn in water to the depth of 1/2 in. Cut a piece of cardboard circular to fit the bottom of the spider and make a hole in the center 4 in. in diameter. The hole will need to correspond to the size of the can used. It should be 1 in. less in diameter than that of the can. Place this cardboard in the bottom of the spider under the water. A 2-qt. syrup can or pail renders the best demonstration, although good results may be obtained from the use of an ordinary tomato can. The edge of the can must have no indentations, so it will fit perfectly tight all around on the cardboard. Place the can bottom side up and evenly over the hole in the cardboard. Put a sufficient weight on the can to prevent it moving on the cardboard, but not too heavy, say, l lb.

Place the spider with its adjusted contents upon a heated stove.

Soon the inverted can will begin to agitate. When this agitation finally ceases remove the spider from the stove, being careful not to move the can, and if the quickest results are desired, apply snow, ice or cold water to the surface of the can until the sides begin to flatten. The spider with its entire contents may now be lifted by taking hold of the can. When the vacuum is complete the sides of the can will suddenly collapse, and sometimes, with a considerable report, jump from the spider.

The cause of the foregoing phenomenon is that the circular hole in the cardboard admits direct heat from the surface of the spider.

This heat causes the air in the can to expand, which is allowed to escape by agitation, the water and the cardboard acting as a valve to prevent its re-entrance. When the enclosed air is expelled by the heat and a vacuum is formed by the cooling, the above results are obtained as described.

--Contributed by N. J. McLean.

** The Making of Freak Photographs [440]

An experiment that is interesting and one that can be varied at the pleasure of the operator, is the taking of his own picture.

The effect secured, as shown in the accompanying sketch, reproduced in pen and ink from a photograph, is that made by the photographer himself. At first it seems impossible to secure such a picture, but when told that a mirror was used the process is then known to be a simple one.

The mirror is set in such a way as to allow the camera and operator, when standing directly in front of it, to be

[Ill.u.s.tration: Photographing the Photographer]

in a rather strong light. The camera is focused, shutter set and plate holder made ready. The focusing cloth is thrown over your head, the position taken as shown, and the exposure made by the pressure of the teeth on the bulb while held between them.

** Hand Car Made of Pipe and Fittings [440]

Although apparently complicated, the construction of the miniature hand car shown in the accompanying

[Ill.u.s.tration: Boy's Hand Car]

ill.u.s.tration is very simple. With a few exceptions all the parts are short lengths of pipe and common tees, elbows and nipples.

The wheels were manufactured for use on a baby carriage. The sprocket wheel and chain were taken from a discarded bicycle, which was also drawn upon for the cork handle used on the steering lever. The floor is made of 1-in. white pine, 14 in. wide and 48 in. long, to which are bolted ordinary f.l.a.n.g.es to hold the framing and the, propelling and steering apparatus together. The axles were made from 3/8 in. shafting. The fifth wheel consists of two small f.l.a.n.g.es working on the face surfaces. These f.l.a.n.g.es and the auxiliary steering rod are connected to the axles by means of holes stamped in the piece of sheet iron which encases the axle.

The sheet iron was first properly stamped and then bent around the axle. The levers for propelling and steering the car work in fulcrums made for use in lever valves. The turned wooden handles by which these levers are operated were inserted through holes drilled in the connecting tees. The working joint for the steering and hand levers consists of a 1/2 by 3/8 by 3/8 in. tee, a 1/2 by 3/8 in. cross and a piece of rod threaded on both ends and screwed into the tee. The cross is reamed and, with the rod, forms a bearing.

The operation of this little hand car is very similar in principle to that of the ordinary tricycle, says Domestic Engineering. The machine can be propelled as fast as a boy can run. It responds readily to the slightest movement of the steering lever.

** How to Make a Rustic Seat [441]

The rustic settee ill.u.s.trated in Fig. 1 may be made 6 ft. long, which will accommodate four average-sized persons. It is not advisable to exceed this length, as then it would look out of proportion, says the Wood-Worker. Select the material for the posts, and for preference branches that are slightly curved, as shown in the sketch. The front posts are about 3-1/2 in. in diameter by 2 ft. 4 in. long. The back posts are 3 ft. 4 in. high, while the center post is 3 ft. 8 in. in height. The longitudinal and transverse rails are about 3 in. in diameter and their ends are pared away to fit the post to which they are connected by 1-in. diameter dowels. This method is shown in Fig. 4. The dowel holes are bored at a distance of 1 ft. 2-1/2 in, up from the lower ends of posts. The front center leg is partially halved to the front rail and also connected to the back post by a bearer, 4 in.