The Boy Mechanic Part 19

A small kiln for baking clay figures may be built at a cost of $1.

The following shows the general plan of such a kiln which has stood the test of 200 firings, and which is good for any work requiring less than 1400 C.

Get an iron pail about 1 ft. high by 1 ft. across, with a cover.

Any old pail which is thick enough will do, while a new one will cost about 80 cents. In the bottom of this cut a 2-in. round hole and close it with a cork or wood plug, A, Fig. 1, which shall project at least 2 in. inside the pail. Make a cylindrical core of wood, B, Fig. 1, 8 in. long and 8 in. across. Make a

[Ill.u.s.tration: Homemade Pottery Kiln]

mixture of clay, 60%; sand, 15%; and graphite, 25%, kneading thoroughly in water to a good molding consistency. Line the pail, bottom and sides, with heavy paper and cover the core with same.

Now pack the bottom of the pail thoroughly with a 2-in. layer of the clay mixture, and on it set the paper wrapped core, carefully centering it. The 2 in. of s.p.a.ce between the core and the sides of the pail all around is to be filled with clay, C, as is shown in the sketch, using a little at a time and packing it very tight. In like manner make the cover of the kiln, cutting the hole a little smaller, about 1 in. At the edge or rim of the cover encircle a 2-in. strip of sheet iron, E, Fig. 2, to hold the clay mixture, C.

Set aside for a few days until well dried.

While these are drying you may be making a m.u.f.fle, if there is to be any glazing done. This is a clay cylinder (Fig. 3) with false top and bottom, in which the pottery to be glazed is protected from any smoke or dust. It is placed inside the kiln, setting on any convenient blocks which will place it midway. The walls of the m.u.f.fle should be about 1/2 in. thick, and the dimensions should allow at least 1 in. of s.p.a.ce all around for the pa.s.sage of heat between it and the walls of the kiln. By the time the clay of the kiln is well dried, it will be found that it has all shrunk away from the iron about 3/8 in. After removing all the paper, pack this s.p.a.ce-top, bottom and sides with moist ground asbestos. If the cover of the pail has no rim, it may be fastened to the asbestos and clay lining by punching a few holes, pa.s.sing wire nails through and clinching them. Fit all the parts together snugly, take out the plugs in the top and bottom, and your kiln is ready for business. The handle of the pail will be convenient for moving it about, and it can be set on three bricks or some more elaborate support, as dictated by fancy and expense.

The temperature required for baking earthenware is 1250 degrees--1310 degrees, C.,; hotel china, 1330 degrees; hard porcelain, 1390 degrees-1410 degrees. These temperatures can not be obtained in the above kiln by means of the ordinary Bunsen burner. If will be necessary either to buy the largest size Bunsen, or make one yourself, if you have the materials. If you can get a cone which can be screwed into an inch pipe, file the opening of the cone to 1/16 in. diameter, and jacket the whole with a 2-1/2-in. pipe. The flame end of this burner tube should be about 4-1/2 in. above the cone opening and should be covered with gauze to prevent flame from snapping back. When lighted, the point of the blue flame, which is the hottest part, should be just in the hole in the bottom of the kiln. Such a burner will be cheaply made and will furnish a kiln temperature of 1400 degrees, but it will burn a great deal of gas.

A plumber's torch of medium size will cost more in the beginning, but will be cheaper in operation. Whatever burner is used, the firing should be gradual, and with especial caution the first time. By experiment you will find that a higher temperature is obtained by placing a 1-in. pipe 2-ft. long over the lid hole as a chimney. It would be still more effective to get another iron pail, 2 in. wider than the kiln, and get a down draft by inverting it over the kiln at whatever height proves most suitable. --G. L.

W.

** How to Make a Small Medical Induction Coil [63]

The coil to be described is 3-1/2 in., full length of iron core, and 3/4 in. in diameter.

Procure a bundle of small iron wire, say 1/4 in. in diameter, and cut it 3-1/2 in. long; bind neatly with coa.r.s.e thread and file the ends smooth (Fig. 1). This done, make two wood ends, 1-1/4 by 1-1/4 in. and 3/8 in. thick, and varnish. Bore holes in the center of each so the core will fit in snugly and leave about 1/4 in.

projecting from each end (Fig. 1).

After finis.h.i.+ng the core, sh.e.l.lac two layers of thick paper over it between the ends; let this dry thoroughly. Wind two layers of bell magnet wire over this, allowing several inches of free wire to come through a hole in the end. Cover with paper and sh.e.l.lac as before. Wind about 1/8 in. of fine wire, such

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

as used on telephone generators, around the coil, leaving long terminals. Soak the whole in melted paraffin and let cool; bind tightly with black silk.

The vibrator is made of a piece of thin tin to which is soldered the head of an iron screw and on the other side a small piece of platinum, which can be taken from an old electric bell (Fig. 2).

Of course, a regulator must be had for the vibrator; this can be accomplished by bending a stout piece of copper wire as shown. The connections and the base for setting up are shown in the figures.

--Contributed by J. T. R., Was.h.i.+ngton, D. C.

** Mechanical Trick With Cards [63]

The following mechanical card trick is easy to prepare and simple to perform:

First, procure a new deck, and divide it into two piles, one containing the red cards and the other the black ones, all cards facing the same way. Take the red cards, square them up and place in a vise. Then, with a plane, plane off the upper right hand corner and lower left hand corner, as in Fig. 1, about 1/16 in.

Then take the black cards, square them up, and plane off about 1/16 in. on the upper left hand corner and lower right hand corner, as in Fig. 2.

Next restore all the cards to one pack, taking care to have the first card red, the next black, and so on, every alternate card being the same color. Bend the pack so as to give some spring to the cards, and by holding one thumb on the upper left-hand corner

[Ill.u.s.tration: Card Trick]

all the cards will appear red to the audience; place thumb in the center at top of pack and they will appear mixed, red and black; with thumb on upper right-hand corner all cards appear black. You can display either color called for.

--Contributed by Ralph Gingrich, Chicago.

** How to Make a Rain Gauge [64]

An accurate rain gauge may be easily constructed from galvanized iron, as shown in the sketch herewith. The funnel, A, overlaps and rests on the body, B, and discharges into the tube, C, the area of which is one-tenth that of the top of the funnel. The depth of the water in C is thus ten times the actual rainfall, so that by measuring it with a stick marked off in tenths of an inch, we obtain the result in hundredths of an inch.

A good size to make the rain gauge is as follows: A, 8 in.

diameter; C, 2.53 in. ; length of C, about 20 in. It should be placed in an exposed location, so that no inaccuracy will occur from wind currents. To find the fall of snow, pour a known quant.i.ty

[Ill.u.s.tration: Rain Gauge]

of warm water on the snow contained in the funnel and deduct the quant.i.ty poured in from the total amount in the tube.

--Contributed by Thurston Hendrickson, Long Branch, N.J.

** How to Make an Aquarium [64]

In making an aquarium, the first thing to decide on is the size.

It is well not to attempt building a very large one, as the difficulties increase with the size. A good size is 12 by 12 by 20 in., and this is inexpensive to build.

First buy one length of 3/4 by 1/8-in. angle iron for the frame, F, Fig. 1. This can be obtained at any steel shop and should cost about 20 cents. All the horizontal pieces, B, should be beveled 45 degrees at the ends and drilled for 3/16 in. stove bolts. The beveling may be done by roughing out with a hacksaw and finis.h.i.+ng with a file. After all the pieces are cut and beveled they should be drilled at the ends for the 3/16-in. stove bolts, C. Drill all the horizontal pieces, B, first and then mark the holes on the upright pieces, A, through the holes already drilled, thus making all the holes coincide. Mark the ends of each piece with a figure or letter, so that when they are a.s.sembled, the same ends will come together again. The upright pieces, A, should be countersunk as shown in the detail, and then the frame is ready to a.s.semble.

After the frame has been a.s.sembled take it to glazier and have a bottom made of skylight gla.s.s, and sides and ends of double-thick window gla.s.s. The bottom gla.s.s should be a good fit, but the sides and ends should be made slightly shorter to allow the cement, E, to form a dovetail joint as shown. When the gla.s.s is put in the frame a s.p.a.ce, D, will be found between the gla.s.s and the horizontal pieces, B, of the frame. If this were allowed to remain the pressure of the water would spring the gla.s.s and cause a leak at E; so it is filled up with plaster of paris.

The cement, E, is made as follows: Take 1 gill of plaster of paris, 1 gill of litharge, 1 gill of fine white sand, and 1/3 of a gill of finely powdered rosin. Mix well and add boiled linseed oil and turpentine until as thick as putty. Let

[Ill.u.s.tration: Detail of Aquarium Frame]

the cement dry three or four days before putting any water in the aquarium.

In choosing stock for the aquarium it should be remembered that a sufficient quant.i.ty of vegetable life is required to furnish oxygen for the fish. In a well balanced aquarium the water requires renewal only two or three times a year. It is well to have an excess of plants and a number of snails, as the snails will devour all the decaying vegetable matter which would otherwise poison the water and kill the fish.

[Ill.u.s.tration: Aquarium Finished]

If desired, a centerpiece (A, Fig. 2) can be made of colored stones held together by cement, and an inverted jar can be supported in the position shown at B. If the mouth of the jar is below the surface of the water it will stay filled and allow the fish to swim up inside as shown. Some washed pebbles or gravel should be placed on the bottom, and, if desired, a few Chinese lilies or other plants may be placed on the centerpiece.

** Homemade Pneumatic Lock [65]

Mount an old bicycle hand-pump, A, on the door by means of a metal plate, B, having a swinging connection at C. Fasten the lever, D, to the door k.n.o.b, and make a hinge connection with the pump by means of a piece of sheet