The Boy Mechanic Part 67

Clean the metal thoroughly, using powdered pumice with lye. Cotton batting fastened to the end of a stick will make a good brush.

Upon the cleansed metal put a lacquer to prevent tarnishing. Metal clips may be soldered to the back to hold the picture in place and also a metal strip to hold the frame upright. These should be placed before the metal is lacquered.

** Finding the Horsepower of Small Motors [238]

A small motor often excites curiosity as to its true horsepower, or fraction of a horsepower. Guesses in this direction vary remarkably for the same motor or engine. It is comparatively easy to determine the horsepower put out by almost any machine by the following method which is intended for small battery motors and small steam engines.

Before giving the description, it may be well to know what horsepower means. Horsepower is the rate of work and a unit is equal to 33,000 ft. lb. per minute, or 550 ft. lb. per second.

That is lifting 33,000 lb. 1 ft. in one minute or 550 lb. 1 ft. in one second. This may be applied to the problem of finding the horsepower of a motor by fastening a piece of twine about 25 ft.

long to the shaft of the engine or motor to be tested in such a way that when the shaft revolves it will wind up the string similar to a windla.s.s. Place the motor in such a position that the twine will hang freely without touching anything: out of a high window will do. Fasten a weight to the other end of the line as heavy as the motor or engine can lift and still run. It must weigh enough to slow the power down a little, but not to stop it. Mark the position of the weight and start the motor, at the same time accurately measuring time in minutes and seconds it takes to lift the weight from the lowest point to the highest. Next measure accurately the distance in feet covered by the weight in its ascent and obtain the correct weight in pounds of the weight.

Multiply the weight by the distance covered and divide the result by the number of minutes or fraction of a minute obtained and divide this last result by 33,000 and the quotient will be the horsepower of the motor or engine.

Perhaps an ill.u.s.tration will make this solution much plainer.

Suppose the motor will lift a weight of 1 lb. and still revolve, 30 ft. in 10 seconds or 1/6 of a minute. Multiplying 1 by 30 we get 30, which divided by 1/6 gives 180. This in turn divided by 33,000 equals in round numbers 1/200 part of a horsepower.

--Contributed by Harold H. Cutter.

** Illusion for Window Attraction [239]

Gold fish and canary birds, living together in what seems like one receptacle, make an unusual show window attraction. Secure two gla.s.s vessels having straight sides of the same height, one 18 in.

in diameter (Fig. 1) and the other 12 in. in diameter (Fig. 2).

The smaller is placed within the larger, the bottoms being covered with moss and aquarium decorations which can be purchased at a bird store. Fill the 3-in. s.p.a.ce between the vessels with water.

Cut a piece of galvanized screen into circular form to cover the larger vessel, and hang a bird swing, A, Fig. 3, in the center.

Place the screen on top of the vessels so that the swing will hang in the center of the inner vessel. A weight--a box filled with sand will do--should be placed on top of the screen, over the smaller vessel, to keep it from floating. Moss should be put over the top of the screen so that the two separate vessels can not be seen.

[Ill.u.s.tration: 18 in. Diameter; 12 in. Diameter]

[Ill.u.s.tration: Birds and Fish Apparently Together]

Place the birds in the inner vessel and the fish in the water. The effect is surprising. To complete the effect and aid the illusion the vessels can be set in a box lined with black velvet, or on a pedestal.

--Contributed by J. F. Campbell, Somerville, Ma.s.s.

** Cleaner for White Shoes [239]

Finely ground whiting mixed with water to the consistency of paste makes a very good coating for white shoes. A brush can be used in applying the mixture which will dry in a few minutes. It is best to mix only as much paste as required for immediate use.

--Contributed . by L. Szerlip, Brooklyn, N. Y.

** Crossing Belt Laces [239]

Belt laces should never cross on the side next to the pulley as they will cut themselves in two.

** How to Make a Candlestick Holder [240]

A candlestick of very simple construction and design can be made as follows: Secure a piece of bra.s.s or

[Ill.u.s.tration: Candle Holder Complete]

copper of No. 23 gauge of a size sufficient to make the pieces detailed in the accompanying sketch. A riveting hammer and a pair of pliers will be needed, also a pair of tin shears and a piece of metal upon which to rivet.

Cut out a piece of metal for the base to a size of 5-1/2 by 5-1/2 in. Trim the sharp corners off slightly. Draw a pencil line all around the margin and 5/8 in. away from the edge. With the pliers shape the sides as shown in the ill.u.s.tration.

Next lay out the holding cup according to the plan of development shown, and cut out the shape with the shears. Polish both of these pieces, using any of the common metal polishes. Rivet the cup to the base, and then, with the pliers, shape the sides as shown in the photograph. The manner of making and fastening the handle is clearly ill.u.s.trated. Use a file to smooth all the cut edges so that they will not injure the hands.

In riveting, care should be taken to round up the heads of the rivets nicely as a good mechanic would. Do not be content merely to bend them over. This rounding is easily accomplished by striking around the rivets' outer circ.u.mference, keeping the center high.

A good lacquer should be applied after the parts have been properly cleaned and polished, to keep the metal from tarnishing.

[Ill.u.s.tration: Details of Candle Holder]

** A Home-Made Duplicator [240]

The usual gelatine pad, which is the princ.i.p.al part of the average hectograph or duplicator, is, as a rule, unsatisfactory, as it is apt to sour and mold in the summer and freeze in the winter, which, with other defects, often render it useless after a few months service.

A compound that is almost indestructible is the preparation sold at art stores as modeling clay. This clay is as easily worked as a putty and is spread into the tray, which may be of wood or tin, and the surface leveled by pounding with a mallet or hammer, then by drawing a straightedge over it.

The surface of the pad is now saturated with pure glycerine. This is poured upon the surface after it is slightly warmed, covering the same and then laying a cloth over the pad and allowing it to stand long enough for the clay to absorb the glycerine, after which it is ready for use.

The original copy is written with a copying pencil or typewritten through a hectograph ribbon. A sheet of newspaper is laid upon the pad and a round stick or pencil is pa.s.sed over it to make the surface level and smooth. Remove the newspaper and place the original copy face down on the leveled surface and smooth it out in the same way so that every part touches the pad. Remove the copy in about five minutes and place the clean sheets of paper one after another on the surface and remove them. From 50 to 75 copies of the original can be made in a short time.

This compound is impervious to water, so the negative print is removed by simply washing with a damp sponge, the same as removing writing from a slate. This makes it possible to place another original on the pad immediately without waiting for the ink to vanish by chemical action as in the original hectograph.

The action of the weather has no effect upon this compound and it is proof against accident, for the tray may be dropped and the pad dented or cut into pieces, and the clay can be pressed back and leveled. The only caution is to keep it covered with a cloth saturated in glycerine while not in use.

--Contributed by A. A. Houghton, Northville, Mich.

** Paper-Clip Bookmark [241]

The combination of a paper clip and a calling card makes a good bookmark.

[Ill.u.s.tration: Bookmark]

The clip and card can be kept together by piercing the card and bending the ends of the wire to stick through the holes. The clip is attached to a page as shown in the sketch.

--Contributed by Thos. DeLoof, Grand Rapids, Mich.

** Aerating Water in a Small Tank [241]