Chapter XXIV: Part II: Construction (1)

Transformers may be divided into two main groups, the classification being made according to the relation between the magnetic circuit of the transformer and the primary and secondary windings. When the two windings surround the magnetic circuit of a transformer, as indicated in Fig. 9, the transformer is said to be of core type. If the magnetic circuit surrounds the windings, as indicated in Fig. 10, the transformer is said to be of the shell type. The following instructions are for a shell-type transformer.

Any mass of magnetic material, such as a piece of soft iron, when placed in a magnetic field that is produced by an alternating current, will be rapidly magnetized and demagnetized, the rapidity of the change depending upon the frequency of the current producing the field. When a piece of iron is magnetized and demagnetized, as just stated, there will be a certain amount of heat generated in it and this heat represents energy that must come from the electrical circuit producing the magnetic field in which the iron is placed.

The heat that is generated in the iron is due to two causes: First, the hysteresis loss which is due to a property of the iron that causes the magnetism in the iron to lag behind the magnetizing influence, or the changes that are constantly taking place in the field strength due to the alternating current. This loss cannot be entirely eliminated, but it may be reduced to a very low value by using a soft grade of iron, or one having what is called a low hysteretic constant. Second, the eddy-current loss which is due to the circulation of currents through the mass of metal. These currents are due to unequal electromotive forces set up in the different parts of the piece of metal when there is a change in the strength of the field in which the metal is placed. This loss cannot be entirely eliminated, but it can be greatly reduced by breaking the mass of metal up into parts and insulating these parts from each other, which results in the paths in which the eddy currents originally circulated being destroyed to a certain extent.

The breaking up of the metal is usually made in such a way that the joints between the various parts are parallel to the direction of the magnetic field. When the joints are made in this way, they offer less opposition to the magnetizing force. This is one of the principal reasons why induction-coil cores are made up of a bundle of wires instead of a solid piece. These wires are annealed or softened to reduce the hysteresis loss that would occur. The combined hysteresis and eddy-current losses, which are spoken of as the iron losses, will of course be very small in the transformer you are going to construct, but the above discussion is given to show why the magnetic circuits of transformers are built up from sheets of soft iron, called laminations. The core is said to be laminated.

The dimensions of the complete magnetic circuit, of the transformer you are going to construct, are given in Fig. 11. The primary and secondary windings are both to be placed about the center portion C, and it is apparent that the winding of these coils would be very tedious if the wire had to be passed back and forth through the openings A and B. This procedure in winding can be prevented by first forming the part of the magnetic circuit upon which the windings are placed; then wind on the coils and, after they are completed, finish building up the magnetic circuit with pieces cut to the proper size and shape.

Procure a small quantity of soft, thin sheet iron and cut out a sufficient number of rectangular pieces, 3 in. by 4-1/4 in., to make a pile 3/4 in. in height when firmly pressed together. Now cut a rectangular notch in each of these pieces, 2 in. wide and 3-5/8 in. long. The sides of this notch can be cut with a pair of tinner's shears, and the end can be cut with a sharp cold-chisel. Be careful not to bend either piece any more than you can help. The outside piece, or the one in which the notch is cut, should have dimensions corresponding to those given in Fig. 12. When all of these pieces have been cut, as indicated above, the rectangular pieces, 2 in. by 3-5/8 in., that were cut out to form the notch in the larger pieces, should have two of their corners cut away, so as to form pieces whose dimensions correspond to those given in Fig. 13. These last pieces are to form the core and part of the end of the transformer. Now make sure that all the edges of the pieces are perfectly smooth and that they are all of the same size; then give each one a coat of very thin shellac.

Now cut from a piece of insulating fiber, that is about 1/16 in. thick, two pieces whose dimensions correspond to those given in Fig. 14. When these pieces are completed, the core of the transformer can be assembled as follows: Place the T-shaped pieces, whose dimensions correspond to those given in Fig. 13, through the openings in the pieces of insulation, alternate pieces being put through the openings from opposite sides. The distance from outside to outside of the pieces of insulation should be exactly the same as the length of the vertical portion of the T-shaped pieces forming the core, or 3 in.

Cut from some soft wood four pieces having cross sections whose dimensions correspond to those given in Fig. 15, and of such a length that they will just slip down between the two pieces of insulation. These pieces should now be placed on the four sides of the iron core and covered with several layers of heavy insulating cloth. Each layer of the cloth should be shellacked as it is put on, which will increase the insulation and at the same time help in holding the wooden pieces in place. You are now ready to start winding the transformer.

The secondary, which is the low-voltage side in this case, as you are using the transformer to reduce or step down the voltage, will have the smaller number of turns, and larger wire should be used in winding it than in the primary, as it will carry a larger current. On account of the secondary being of larger wire, it will be placed on the core first. For this winding you will need a small quantity of No. 26 B. & S. gauge, single cotton-covered wire. Drill a small hole through one of the insulating washers, down close to the cloth covering the core, being careful at the same time to keep the hole as far from the metal part of the core as possible. Pass the end of a short piece of No. 18 or 20 B. & S. gauge, double cotton-covered wire through this opening and solder it to the end of the No. 26 wire. Insulate the joint with a piece of paraffin paper or cloth, and bind the piece of heavy wire to the core of the transformer with a piece of linen thread.

Now wind the No. 26 wire on the core as evenly as possible, to within about 1/8 in. of the end of the spool. Place over the first layer two layers of paraffin paper and wind on a second layer of wire. Three layers should give you the required number of turns in the secondary winding and a resistance of approximately 3-1/2 ohms. The end of the secondary winding should be terminated in the same way as the winding was started. Outside of the completed secondary winding place at least six layers of paraffin paper, or several layers of insulating cloth. The paraffin paper used should be approximately five mills in thickness. You can make your own paraffin paper by taking a good quality of writing paper about two mills thick and dipping it into some hot paraffin, then hanging it up by one edge to drain.

The primary winding is to be made from No. 34 B. & S. gauge, single silk-covered copper wire. The inside end of this winding should be started in the same way as the secondary, but at the end opposite to the one where the secondary terminated. Wind about 240 turns on each layer and place one layer of paraffin paper between each layer of wire. The primary winding should have at least 12 layers, and the outside end should be terminated as the inside end. Outside of the completed windings, place several layers of insulating cloth to serve as an insulation, and at the same time provide a mechanical protection for the windings.

The outside part of the magnetic circuit can now be put in place. When the U-shaped pieces are all in place, the magnetic circuit will have the form and dimensions shown in Fig. 11. A clamp should now be made for each end of the transformer, to hold the pieces forming the magnetic circuit together, and at the same time give an easy means of mounting the transformer. Cut from a piece of sheet iron, about 1/16 in. in thickness, two pieces whose dimensions correspond to those given in Fig. 16, and two pieces whose dimensions correspond to those given in Fig. 17. Drill the holes in these pieces as indicated, and bend the larger ones into the form shown in Fig. 18. These pieces can now be clamped across the ends of the transformer with small bolts, as shown in Fig. 19.

A box should now be made from sheet iron to hold the transformer. The box should be of such dimensions that it will be at least 1/8 in. from the transformer at all points. This box should be provided with a cover that can be easily removed.

Now mount the transformer in the box by means of small bolts, that pass through the holes in the supports and holes in the bottom of the box. Two binding-posts can now be mounted on one end of the box, and insulated from it, to serve as terminals for the secondary winding. Two pieces of stranded No. 14 B. & S. gauge, rubber-covered copper wire should now be soldered to the terminals of the primary circuit and passed out through insulating bushings mounted in holes cut in the end of the box opposite to the one upon which the binding-posts were mounted. These heavy wires should be firmly fastened to the iron part of the transformer inside the box, so that any outside strain placed upon them will not, in time, break them loose from the smaller wires. Be sure to insulate all joints and wires well inside the box.

A circuit can now be run from a 110-volt lighting or power circuit, observing the same rules as though you were wiring for lights, and connected to the heavy wires, or primary circuit. The binding-posts, or secondary winding should be connected to the bell circuit and the transformer is complete and ready to operate. You may have to change the adjustment of the bells, but after a little adjustment they will operate quite satisfactorily.

Mirror Hinged to Window Casing

A shaving mirror is usually placed on a window sash to avoid shadows as much as possible. This is very inconvenient and many times the mirror is broken by a fall. A good way to avoid shadows and have the mirror handy is to hinge it to the window casing. This can be done with screweyes, A, and screwhooks, B. The screweyes are turned into the frame of the mirror and the screwhooks into the window casing. Two screwhooks can also be turned into the casing on the opposite side of the window, if desired, so that the mirror can be used on either side.--Contributed by James D. McKenna, New Britain, Conn.

A Cleaning Bath for Silverware

A good way to clean silverware of all coloring by eggs or other substances is to place the silver articles in a kettle of boiling water containing a few pieces of zinc. An electrolytic action is produced by the zinc, water and silver which decomposes the sulphides on the silver and leaves it well cleaned. No silver is taken away by this method.--Contributed by Loren Ward, Des Moines, Iowa.

To Prevent Poultry Water from Freezing

The method shown in the sketch is used by me in cold weather to keep the drinking water for the poultry from freezing. The device consists of a part of a barrel inverted and set over the fountain, and a tubular lantern. A small opening is cut in one side of the barrel through which the fowl can reach the water.--Contributed by P. C. Fish, Kansas City, Mo.

How to Make a Letter Scale

A reliable letter scale that can be easily made is shown in the sketch. It consists of a wide-neck bottle filled with water into which the weighing device is inserted. This latter part is made of a light piece of wood weighted on the lower end, to keep it in a stable, upright position, and a piece of cardboard is tacked to the other. The wood is placed in the water, and known weights are used on the cardboard while calibrating.

The first line is marked at the water level when there is no weight on the cardboard, and then a known weight placed on the top and another mark made at the water level, and so on, until a sufficient number of 1/2-oz. and ounce-divisions have been marked. The wood should be well coated with shellac varnish before it is placed in the water.--Contributed by Francis Chetlain, Chicago.

Summer Dish Washing

A labor-saving method in dish washing for a summer day is as follows: Construct a substantial wood frame and cover it with galvanized wire mesh. Attach legs and put it in a convenient place on the back porch. Wash the dishes on one end, and wipe the silverware dry. At the outer end spread a towel over the wire and place the dishes turned down upon it to dry, and cover them with another towel.--Contributed by L. Alberta Norrell, Tifton, Ga.

Nozzle Angle for Lawn Sprinkling

Where there is no prop or water sprinkler at hand for tilting the nozzle of a hose, start to tie a knot in the hose, as shown in the sketch, but do not draw it up tightly. The hose nozzle can be tilted to any angle in this manner.--Contributed by S. J. Eddy, Portland, Oregon.

Simple Methods of Connecting Call Bells

The following diagrams will indicate a few of the various methods that may be employed in connecting up electric bells for different purposes, A, B and C representing the push buttons; D, the bells; E, the batteries, and G, the ground. The simplest possible connection is shown in Fig. 1, the bell D, battery E, and push button A, are all connected in series. The operation of the bell is independent of the order in which the bell, battery, and push button are placed, so long as there is a complete circuit when the push button is pressed. One of the wires in this circuit may be done away with by completing the circuit through the ground, as shown in Fig. 2. Connecting a bell as shown in this diagram often results in quite a saving of wire. The proper connections for operating one bell from either of two push buttons, A or B, is shown in Fig. 3. Two bells, D, operated from a single push button, C, are connected as shown in Fig. 4. The two bells, D, are shown connected in parallel, which requires more wire than if they were connected in series. If they be connected in series, one or the other should have its make-and-break contact closed. The bell whose circuit remains unchanged will intercept the current for the other bell in series with it. The operating of the bells is more satisfactory, however, when they are in parallel, and each taking current from the battery independent of the other.

The diagram, Fig. 5, shows the proper connections for operating two bells from two independent push buttons, each push button operating a particular bell. Any number of bells operated from any number of push buttons, all of the bells being rung from any one of the push buttons, are connected as shown in Fig. 6. Such a circuit can be used as a fire alarm or time call in a factory, the operation of the circuit being controlled from any one of a number of different points.

The proper connections for what is called a return-call circuit is shown in Fig. 7. The circuit is so arranged that the bell at one end is controlled by the push button at the other end. Such a circuit can be used in transmitting signals in either direction. A ground return-call circuit is shown in Fig. 8. In the circuits shown in Figs. 7 and 8, only one battery is needed.

The connections of a two-wire metallic return-call circuit are shown in Fig. 9. A special push button must be used in this circuit, and in this case two batteries are used instead of one, as in Figs. 7 and 8. This circuit may be changed to a ground return-call circuit by using the earth as a conductor instead of either wire. There are, of course, numerous other methods that may be used in connecting call bells, but the connections shown in the diagrams are perhaps the most common.

Refrigerator for Dry and Warm Climates

Set a bowl containing butter, cream or fruit in a saucer and cover the bowl with a moistened napkin, allowing the edges to hang in a larger saucer filled with water, and place the whole in the air out of the sun's rays. The article to be kept cool may also be placed in a pan with an earthenware crock turned over it and covered with a small towel or cloth, the edges of which extend into another outer pan partly filled with water.

The method can be applied on a larger scale by using a shallow galvanized pan which will contain many articles and more water. This manner of cooling is especially adapted to camping parties and will prevent sloppy butter, sour milk and spoiling fruit. The articles are also kept free from ants and flies.--Contributed by C. B. Hosford, Swansea, Ariz.

Pencil-Sharpening Guide

The sketch shows how a guide for making a true point on a lead pencil may be made of a block of wood. The hole, which should be large enough to allow the pencil to be turned easily, is bored at the proper angle to form the desired point on the pencil. The long side of the block serves as a guide for the knife blade, while the projection at the bottom acts as a stop. The guide insures an even point and is easily manipulated. It is held in the palm of the left hand and the pencil is turned with the thumb and forefinger, while the knife is held against the face of the block, cutting edge downward, and worked up and down with the right hand.

Homemade Hinges

When making a chicken house recently I had forgotten to procure hinges. When searching the "junk" box I found some little metal brackets such as used for holding spring roller shades. Attaching these as shown, I made a good substitute hinge. A pair of the brackets having no slots were selected. A 2-1/2-in. wire nail with a washer was placed in the hole and driven into the top of the door, 1 in, from its back edge. The other bracket was placed on the bottom of the door in a similar manner. The door was placed in an open position and the prongs of the brackets were nailed to the door post. The bottom bracket may also be nailed to the floor and the top one to the lintel.--Contributed by Robert Smith, E. Burnaby, B. C.

Skimmer for Bottled Milk

The cream that rises on the milk in an ordinary milk bottle cannot be removed easily. Where a small family desires to use the cream for coffee, the skimmer shown in the sketch is very handy.

The cone is made of metal--tin, brass or copper--which can be nickelplated, the seam being soldered. The cone is 2 in. deep with a diameter at the top of 1-3/8 in. A handle can be made of a discarded sugar or teaspoon, which is soldered to the cone. Insert the cone in the bottle far enough for the cream to flow into it and then withdraw. Cream will gather about 3 in. deep on rich milk. The milk can be used for cooking. A piece of wire can be used for a handle instead of the spoon.--Contributed by Victor Labadie, Dallas, Texas.

How to Preserve Putty

Having some putty left over after a job of glazing and wishing to keep it without its becoming dried up, I tried wrapping it in paraffin paper such as used to wrap butter. I found this method to be a decided success, the oil being prevented from drying out.--Contributed by Levi R. Markwood, Fairview, Pa.

How to Build a Simple Electric Motor By A. G. McClure

An exceedingly simple and inexpensive motor that may be used in operating small toys can be constructed as follows: First procure a good permanent magnet, about 5 in. long and about 1-1/2 in. between the inside edges at the open end. This magnet should be at least 1/2 in. thick, and if it cannot be had in one piece, two or more may be placed side by side, like poles being placed together. The writer was unable to procure ready-made magnets, so one was formed and magnetized. Obtain a piece of tungsten or some other good-grade steel, 1/2 in. by 1/2 in., and about 11 in. long. Bend this piece into the form of a U, with the inner edges 1-3/4 in. apart. Square off both ends and drill two small holes in the outside surface of each end, at AA, about 3/8 in. from the end. Tap these holes for small machine screws. Drill the hole B with a small drill, about 1/16 in., in the center of the lower portion of the U and ream it out. The piece should now be clamped with a good pair of blacksmith's tongs,--a block of iron being placed between the ends to keep the pressure of the tongs from drawing them together--heated to a cherry red and then plunged into a bath of oil. It can then be magnetized by placing it in contact with a permanent magnet.

Next obtain a piece of 1/8-in. brass, about 1/2 in. wide and 5-1/2 in. long. Drill two holes in each end of the piece to match those drilled in the ends of the magnet, also one in the center, and tap it for a 1/8-in. machine screw. Now bend this piece into the form shown. Provide a machine screw, S, for the hole C and drill a small tapered hole in the end of the screw.

Obtain a small quantity of soft sheet iron and cut a sufficient number of pieces similar to that shown at D to make a pile 1/2 in high. Cut two pieces of the same size from some thin sheet brass. Now place all of these pieces in a pile, the brass pieces being on the outside, and clamp them securely, then drill the two small holes, E and F. Place two small copper rivets in these holes and rivet the heads down before removing the clamp. Drill a 1/8-in. hole, G, through this piece, the armature, for the shaft to pass through. Procure a piece of 1/8-in. steel rod, about 6 in. long. Sharpen one end so that it will enter the hole B, then cut the other end off and sharpen it so that it will enter the opening made in the end of the screw S. The armature may now be soldered to this shaft, its left-hand surface being flush with the ends of the magnet.

A small commutator, H, should now be made as follows: Obtain a piece of thin brass tubing about 5/8 in. in diameter. Turn down a piece of hard rubber so that the tube will fit tightly on it. Drill a hole in this piece of rubber of such a size that it will have to be forced on the steel shaft. Saw two longitudinal slots in the brass tube diametrically opposite each other and then bind these two pieces in place on the piece of rubber with some heavy linen thread wrapped around each end. The armature is now ready to wind. Get a small quantity of No. 22 gauge cotton-covered wire, solder one end to one of the segments of the commutator, then wind one end of the armature full and cross over and wind the other end full, soldering the end of the wire to the second commutator segment. Make sure to wind both ends of the armature in the same direction so the current in both parts of the winding produces magnetizing effects in the same direction. Insulate the winding from the core and the different layers from each other with a good quality of thin writing paper.

Two small brushes should now be made from some thin spring brass and mounted on the brass piece as shown. These brushes should be insulated from the piece of brass and two small binding posts should be provided for making connections to them. The position of the commutator and brushes should be such that the brushes move from one segment to the other when the ends of the armature are directly in line with the ends of the permanent magnet.

A small pulley should be mounted upon the shaft to be used in transmitting the power. The whole device may be mounted in a horizontal position on a wooden base as shown, and the motor is complete.

How to Make a Humidity Indicator

A simple weather indicator that may be used in determining the condition of the atmosphere may be made as follows: Dress a small figure, in the form of a doll, with a piece of cloth, previously dipped in the following solution: Chloride of cobalt, 30 parts by weight; sodium chloride, 15 parts; gum arabic, 7-1/2 parts; calcium chloride, 4-1/2 parts, and water, 400 parts. This cloth will change color as the amount of moisture in the atmosphere changes, the change being due to the cobalt salt, which, in dry air, is lavender blue. As the moisture in the atmosphere increases, the color changes first to bluish red, then light red and finally pink, according to the amount of moisture. With a decrease in moisture, the colors change in the reverse order to that given above, and the blue color returns when the air becomes dry.

The "Q" Trick

Lay out the form of the capital letter Q with coins on a table and ask someone in the audience to select a number and then ask that person to count up from one until the number is reached, beginning at A and stopping on the circle, for instance at B, then counting back again beginning with one, but, instead of counting on the tail, pass it and go around the circle, say, to C. The performer gives these instructions to the person doing the counting. The one selecting the number must not tell the performer what the number is, and the latter is to leave the room while the counting proceeds. The performer, before leaving the room, is to tell which coin will be the last one counted.

Take, for example, the number 7. Counting from A to B there are just 7 coins and counting back the last number or 7 will be at C. Try 9 for the number and the last one counted will also be C. The number of coins in the tail represents the number of coins in the circle from the intersection of the tail and circle to the last number counted. For instance, the sketch shows 4 coins in the tail, therefore the last coin counted in the circle will be at C or the fourth coin from the intersection of the tail and circle.

By slipping another coin in the tail the location of the last coin counted is changed, thereby eliminating any chance of exposing the trick by locating the same coin in the circle every time. This can be done secretly without being noticed.

To Keep Ants Away From Food

Suspend a shelf, breadbox or rack with wire around which is tied a piece of cotton cloth, saturated with a mineral oil. The ants will not cross the oil-soaked cloth.

Some strong wire hooks attached to the rack or shelf answer well to hang small articles on, such as bacon, bags of sugar, syrup cans, etc.--Contributed by C. B. Hosford, Swansea, Ariz.

Vaulting-Pole Holder

An adjusting device for a vaulting pole that can be easily fixed at any point on a round pole by using a wedge and ring, is shown in the sketch. The wedge carries a pin on which to place the cross pole. The manner of using this device as well as its construction is clearly indicated.--Contributed by Sterling R. Speirs, St. Louis, Mo.

Flying Model Aeroplane for a Display

A novelty for a window display is made of a model aeroplane flying by its own power. To control the direction and make the model fly in a circle it is fastened to a long stick or beam which is pivoted in the center. The one shown was pivoted to a roller-skate wheel which in turn was fastened to a metal standard. The beam was attached to the skate wheel with two small bolts which were insulated and carried two brushes as commutator contacts.

The commutator rings were made of heavy brass strips, fastened to a round piece of wood which was attached to the metal standard. The wires from the current supply were connected to the commutator rings. From the brushes connecting wires were carried along the beam to the aeroplane motor which was a small battery motor with propeller.

The opposite end of the beam was weighted to balance it. The first sketch shows the parts and the manner of making the connections. The aeroplane is driven in a circular path by its own power in a realistic manner.

An Electric Time Light

Although the modern alarm clock is a wonderfully effective piece of mechanism, it is, to say the least, very abrupt in its manner. It seldom confines its efforts to the chamber of its owner, but spreads its disturbance all over the building. It is very easy for a person to arise early in the summer and no greater difficulty should be experienced in winter, if the bedroom is brightly lighted at the proper hour. To do this simply and automatically became the problem.

The first thought was to obtain one of those clock-actuated electric-light switches, such as the stores use, but this would not do, because it meant some unsightly wiring around the room. It was then remembered how, in the course of some experiments, an ordinary incandescent light was operated through a piece of No. 36 gauge wire without any sign of heating. If, then, a wire only 1/200 in. in diameter were of ample carrying capacity, surely a dollar watch would be sufficient to make the connection. Such being the case, the whole mechanism could readily be attached to the drop cord of a lamp directly above the socket, thus obviating any additional wiring. This all proved to be true, and the whole was made and attached in the course of a couple of hours.

While one might feel enthusiastic about this small and easily contrived affair, it is scarcely to be presumed that it would operate so effectively on one who had spent the larger part of the night tripping the "light fantastic," or in undue conviviality. An ordinary 16-cp. globe has thus far operated perfectly, and a 40-watt tungsten lamp would, if not too far away, surely awaken the hardest sleeper of sober habits.

The base of the mechanism is a small piece of 1/4-in. hard wood, upon which is fastened a small brass bracket, A, bent so as to hold the watch from slipping down. A small clip, B, was then arranged so as to grip the neck of the watch after its lower edge had been placed against A, and a small brad at either side prevented lateral movement. In this way the watch was held firmly, yet in a manner that would permit its being taken out instantly when necessary. The glass and minute hand were removed. The brass bolt from an exhausted dry cell was placed at C, so as to clamp a small copper washer to which was soldered a narrow strip of copper, D, about 1/16 in. wide and cut from a leaf of an old dynamo brush. This strip is arranged so as to wipe the hour hand as it travels past, but being so thin, it has no appreciable effect on the time keeping. As illustrated, the device is set for six o'clock, but by loosening the nut C an hour's adjustment either way may be had. It is a very simple matter, however, to arrange the device so it will operate at any hour. In connecting up, one end of the drop cord is removed from the socket and attached to A, which throws the current through the watch, thence along the hand and down D to C, from where it is carried by a short piece of wire to the socket again. As there are so many circuits through the watch, the small current required for one light does not affect it in any way. Thus far, no trouble has been experienced in making this delicate connection with 110 volts, but if any should develop, the contacts may be tipped with the small pieces of platinum taken from a burned-out globe.

* * * * *

The meat of a white English walnut may be easily
removed by heating the nut in an oven or on top of a
stove, then using a knife to pry the shell open.

A Small Shocking Machine

An amusing as well as instructive shocking machine, usually called a medical coil, can be easily constructed from a discarded buzzer or electric bell, four binding posts, some pieces of insulated wire, two carbon rods, and a rheostat.

A base for attaching the parts is made of a piece of poplar, 10 in. long, 5 in. wide, and 1/2 in. thick, which can be finished as desired, but a good method is to shape the edge like molding and give it a mahogany stain, and when dry apply a coat of white shellac, which should be allowed to dry a day, whereupon the surface is rubbed with prepared wax. When the base is ready, mount the buzzer at one end. This can be easily done by making an L-shaped piece of metal, A, which is fastened to the base with a screw, and to the yoke of the magnet coil with a small bolt. If the armature and its connections are also used from the buzzer, the height of the coils must be taken in consideration. These parts are fastened in position as shown, using an L-shaped piece of metal, B, for the spring end. The screw holding the armature spring to the base, as well as the vibrator screw, should be of such a length that it will enter the base far enough to permit a connection for a wire in a countersunk hole bored in the base from the under side. Binding posts are placed in the corners of the base in holes countersunk from the under side for the screw heads.

The rheostat is of the miniature-battery type, which has a round base and a coil of resistance wire with a lever passing over the coil. Such a rheostat can be purchased from an electrical store, but if the person constructing the shocking machine desires to make one, it is not difficult if a lathe is at hand.

To make the rheostat, turn up a disk, about 3 in. in diameter, from a piece of hard wood, such as oak, maple, or walnut, and form a circular groove in the upper surface, about 3/8 in. inside of the circumference. The groove is to admit a circular coil of resistance wire, and in making it, be sure to have it the proper size to take the coil snugly. The coil can be of any size, and to make it, resistance wire is wound around a piece of wire used as a mandrel. If the coil is 1/4 in., or a trifle smaller, in diameter, it will make a good size. Be sure that the depth of the groove is such that it will allow a part of the coils of the resistance wire to project above the surface of the wood disk. The coil of wire should be just long enough to fit in the groove and allow a 1-in. space between the ends, one of which is anchored to the base, at C, the other being attached to the binding post D. Drill a hole through the center of the disk and fasten a lever, taken from a switch, or one made of a piece of sheet brass, that will extend from the center to the outside of the disk, or over the resistance-wire coil. A small handle is attached to the outer end. A connection is made from the center support of the lever to the binding post E.

The connections for the buzzer and rheostat are made on the under side of the base, where grooves are cut to run the wires in, so that they will be below the surface of the wood. In the diagram, the binding post F is connected to the binding post D of the rheostat, which in turn is connected to the screw of the make-and-break point G. The other binding post H is connected to the bracket B supporting the armature spring. The binding post E of the rheostat is connected to the base binding post J. The magnet coils are connected, as shown, from K to L, and from M to B.

The two pieces of carbon, which are used for the hand pieces, are connected with silk-insulated wire. These connections are made to the binding posts F and H. The other two binding posts, J and L, are connected to a battery. The carbons used may be purchased, or taken from an old battery. Two or more dry cells are used for the current. The rheostat controls the amount of current passing through the hand pieces.--Contributed by Gilbert Crossley, Erie, Pa.

Secret Compartment in Ordinary Table Drawer

It is frequently desired to have some handy place for storing valuables where there is but little chance of discovering them. Secret drawers in tables usually require special and expensive changes, but with only a few simple changes on a regular drawer of any ordinary table, a secret compartment can be made which is as secure as can ordinarily be figured on, outside of a steel safe. Having chosen the desired table, a partition should be placed across the entire back part of the drawer, allowing for necessary space in the secret compartment. This partition should resemble the real back of the drawer as closely as it is possible to make it. The compartment must not be too wide, for the resulting small width of the front part of the drawer might then arouse suspicion. On the lower side of the secret compartment a strip of wood, A, should be attached with a screw, as shown in Fig. 1, allowing sufficient looseness so the strip may be turned end for end when necessary. With the strip set as shown, it will strike the front side B of the table when the drawer is pulled out, leaving the secret compartment still hidden. In order to expose this, it will be necessary to turn the strip, as shown in Fig. 2, when the drawer can be pulled out to its full length.

It being necessary that the strip A be as long as the secret compartment is wide, to fully expose this, there may be cases where the drawer is not wide enough to allow the strip A to turn around. In that case the strip can be hinged to the back of the drawer as shown in Fig. 3. When it is hanging down, as shown by the dotted outline, the drawer may be pulled out to its full extent. When it is desired to lock the secret compartment, the hinged strip must be swung up in position, and fastened. An ordinary thumbscrew or eye can be used which, by a turn or two, will either release it or fasten it in place.--Contributed by Paul Durst, Detroit, Mich.

Inflating Handballs

When handballs become "dead," or no longer bounce freely, they may frequently be restored by inflating them with air. This can be done by means of a bulb attached to a hypodermic needle. The needle must be inserted through the soft plug which every inflated ball has, and which can be discovered by pressure. After the ball is inflated and the needle extracted, the soft rubber closes around the fine hole, preventing the escape of the air. If a leak is found, which allows the air to escape too rapidly, a repair can be made with a single-tube tire outfit.--Contributed by A. B. Wegener, Camden. N. J.

A Garden-Bed Scarecrow

A very neat and successful scarecrow for garden beds can be made as follows: A number of corks are procured, and a feather is stuck in each end of them, as shown. These are tied to a string, spacing them from 1 to 2 ft. apart, and the string is hung over the beds. The slightest breeze will keep them fluttering, and no bird will come to rest on the beds.--Contributed by M. T. Canary, Chicago.

Measuring the Length of Wire Wound on a Spool

When winding magnet spools on a lathe, the exact amount of wire used can be easily determined by means of the device shown in the illustration. The large reel from which the wire is obtained is conveniently placed on a loose mandrel, or rod, near the lathe, and in line with the spool which is to be wound. A grooved idler wheel, the exact diameter of which is known, is supported between the spool and wire reel so it may freely revolve; the number of its revolutions should be obtained, automatically, by a revolution counter. When using the device, the wire from the reel is placed once around the idler to insure the necessary grip to prevent it from sliding; then it is led to the spool. The exact diameter of the idler being known and the number of revolutions indicated, the true length of the wire wound on the spools can be easily determined by the following formula: Length of wire on spool in feet equals circumference of idler in feet times number of revolutions of idler.--Contributed by C. Swayne, St. Louis, Mo.

Homemade Lawn Sprinkler

With a short length of old hose, a serviceable lawn sprinkler can be quickly and easily made. One end is provided with a regular coupling for connecting it to the line of good hose. The other end is turned up for several inches, and securely wired to the main part, thereby shutting off any flow through it. Several cuts are made into it, about halfway across and 6 in. apart. If the water is forced in, the only means of escape will be through the slots, which will produce fine sprays, giving as good service as a manufactured sprinkler.--Contributed by A. B. Shaw, N. Dartmouth, Mass.

Homemade Toy Bank

The little bank illustrated is not exactly burglar-proof, but once put together it cannot be opened except by the destruction of one of the units of which it is composed. It requires but little skill to make, and would be a good problem for manual training, as it offers an excellent opportunity for teaching certain rudiments of woodworking by the application method.

In its construction, six pieces of hard wood, of the dimensions shown in the sketch, are required. White wood will do if there is no hard wood at hand. The coin slot is 1/8 in. wide by 1-1/4 in. long, and is cut in only one piece.

No difficulty will be experienced in putting the first five pieces together, but the sixth, or top, piece, shown in the sketch, will not go in, because the bottom edge of the raised side will strike the inside of the piece to the right. By beveling this edge with a chisel from top to bottom between the dadoes, or grooves, it can be forced down quite a distance and sprung in place by placing a block of wood on the high side and striking it a sharp blow with a heavy hammer.--Contributed by J. A. Shelly, Brooklyn, New York.

An Electric Anemometer By Wm. H. Dettman

The construction of this instrument is so simple that any amateur can make one and if accurate calibrations are desired, these can be marked by comparison with a standard anemometer, while both are placed in the wind.

The Indicator

The case of the indicator is built of thin wood--the material of an old cigar box will do--9 in. long, 6 in. wide and 1-1/2 in. deep. If cigar-box material is used, it must first be soaked in warm water to remove the paper. If a cover is to be used on the box, a slot, on an arc of a circle, must be cut through it to show the scale beneath. The arc is determined by the length of the needle from a center over the axis on which the needle swings. When the box is completed, smooth up the outside surface with fine sandpaper and give it a coat of stain.

The core of the magnet is made by winding several layers of bond paper around a pencil of sufficient size to make an inside diameter of slightly over 1/4 in., and a tube 2 in. long. Each layer of the paper is glued to the preceding layer.

Two flanges or disks are attached to the tube to form a spool for the wire. The disks are cut from thin wood, 1-1/4 in. square, and a hole bored through their centers so that each will fit on the tube tightly. One of them is glued to one end of the tube and the other fastened at a point 1/2 in. from the opposite end. The space between the disks is filled with seven layers of No. 22 gauge insulated magnet wire, allowing sufficient ends of the wire to project for connections. The finished coil is located in the box, as shown at A, Fig. 1.

The core for the coil is cut from a piece of 1/4-in. iron rod, 1-1/4 in. long, and a slot is cut in each end, 1/4 in. deep, into which brass strips are inserted and soldered, or otherwise fastened. The strips of brass are 3/16 in. wide, one 1-1/2 in. long and the other 3/4 in. Two 1/16 in. holes are drilled in the end of the long piece, and one 1/16 in. hole in the end of the short piece. The complete core with the brass ends is shown in Fig. 2.

The needle B, Fig. 1, is made of a copper or brass wire, about 6 in. long, and is mounted on an axis at C. The detail of the bearing for the axis is shown in Fig. 3. The axis D is a piece of wood fitted in the U-shaped piece of brass and made to turn on brads as bearings, the center being pierced to receive the end of the needle. After locating the bearing for the axis C, Fig. 1, it is fastened in place so that the upper end or pointer of the needle will travel over the scale. The needle is then attached to the bearing after having been passed through the inner hole of the longer brass strip of the core, and the coil is fitted with the core in the manner shown at D. A light brass coil spring is attached to each end of the core, as shown at E and F, the latter being held with a string, G, whose end is tied to a brad on the outside of the box, for adjustment. A better device could be substituted by attaching the end of the spring F to a nut and using a knurled-head bolt passed through the box side. One of the wires from the coil is attached to a push button, H, to be used when a reading of the instrument is made. The connections for the instrument consist of one binding post and a push button.

The Anemometer

The anemometer resembles a miniature windmill and is mounted on top of a building or support where it is fully exposed to the air currents. It differs from the windmill in that the revolving wheel is replaced by a cupped disk, A, Fig. 4, fitted with a sliding metal shaft, B, which is supported on crosspieces, CC, between the main frame pieces DD. The latter pieces carry a vane at the opposite end. The frame pieces are 1/2 in. thick, 2-1/4 in. wide and 36 in. long, and the crosspieces have the same width and thickness and are 4 in. long.

A variable-resistance coil, E, is made as follows and fastened in the main frame. The core of this coil is a piece of wood, 2 in. square and 4 in. long, and wound with No. 18 gauge single-wound cotton-covered german-silver wire. The winding should begin 1/4 in. from one end of the core and finish 1/4 in. from the other, making the length of the coil 3-1/2 in. The ends of the wire are secured by winding them around the heads of brads driven into the core. A small portion of the insulation is removed from the wire on one side of the coil. This may be done with a piece of emery cloth or sandpaper. A sliding spring contact, F, is attached to the sliding shaft B, the end of which is pressed firmly on the bared portion of the wire coil. One end of a coil spring, which is slipped on the shaft between the pieces CC, is attached to the end crosspiece, and the other end is fastened to the sliding shaft so as to keep the shaft and disk out, and the flange H against the second crosspiece, when there is no air current applied to the disk A. The insulation of the standard upon which the anemometer turns is shown in Fig. 5. The standard J is made of a piece of 1/2-in. pipe, suitably and rigidly attached to the building or support, and the upper end, around which the anemometer revolves to keep in the direction of the air currents, is fitted with a plug of wood to insulate the 1/4-in. brass rod K. A bearing and electric-wire connection plate, L, is made of brass, 1/8 in. thick, 2 in. wide and 4 in. long. The bearing and connection plate M are made in a similar manner. The surface of the holes in these plates, bearing against the pipe J and the brass rod K, make the two connections for the wires from the variable-resistance coil E, Fig. 4, located on the main frame, to the wire connections between the two instruments. These wires should be weather-proof, insulated, attached as shown, and running to and connecting the indicator with the anemometer at NN, Fig. 1.

Two or more dry cells must be connected in the line, and when a reading is desired, the button H, Fig. 1, is pushed, which causes the current to flow through the lines and draw the magnet core D in the coil, in proportion to the magnetic force induced by the amount of current passing through the resistance in the coils on E, Fig. 4, from the contact into which the spring F is brought by the wind pressure on the disk A.

How to Make Stick Shellac

It is often desired to use shellac in solid or stick form, and to get it into this shape by melting and molding requires considerable time. A much quicker method is to place the shellac in a shallow box, spread it out in a thin layer and play the flame from a Bunsen burner upon it until the mass is melted and run together. Allow it to stand a few seconds, then, with moistened fingers, fold it over and over and shape it with the fingers. It is possible to make a stick 8 or 10 in. long and 5/8 in. in diameter in about 5 minutes.--Contributed by J. H. Beeber, Rochester, N. Y.

Substitute for a Hose Reel