41. To Make Holes in Sheet-Metal. Fig. 13. Holes may be punched in sheet-tin, copper, zinc, etc., in the following manner: Set a block of hard wood, W, on end; that is, place it so that you will pound directly against the end of the grain. Lay the metal, T, to be punched, upon this, and use a flat-ended punch. A sharp blow upon a good punch with a hammer will make a fairly clean hole; that is, it will cut out a piece of metal, and push it down into the wood. A sharp-pointed punch will merely push the metal aside, and leave a very ragged edge to the hole. A punch may be made of a nail by filing its end flat.
42. To Punch Holes through Thick Yokes, etc. As soon as 5 or 6 layers are to be punched at one operation, the process becomes a little more difficult than that given in App. 26. If you have an anvil, you can place the yoke over one of the round holes in it, and punch the tin right down into the hole, the ragged edges being afterward filed off. Hold the yoke as in App. 79 or 80 for filing. As you will probably have no anvil, lay an old nut from a bolt upon the end of the block of wood (App. 26), place the metal to be punched over the hole, and imagine that you have an anvil. Very good results may be obtained by this method. The size of nut used will depend upon the size of hole wanted.
43. To Straighten Wires. It is often necessary to have short lengths of wires straight, where they are to be made into bundles, etc. To straighten them, lay one or two at a time upon a perfectly flat surface, place a flat piece of board upon them, then roll them back and forth between the two. The upper board should be pressed down upon the wires while rolling them. If properly done, the wires can be quickly made as straight as needles.
44. Push-Buttons. Nearly every house has use for one or more push-buttons. The simple act of pressing your finger upon a movable button, or knob, may ring a bell a mile away, or do some other equally wonderful thing.
45. Push-Button. Fig. 14. This is made quickly, and may be easily fastened to the window or door-casing. One wire is joined to A and the other to C. B is a strip of tin or other metal, about ⅝ in. wide and 2 in. long. It is bent so that it will not touch A unless it is pressed down. This may be placed anywhere, in an electric-bell circuit or other open circuit, where it is desired to let the current pass for a moment only at a time.
46. Push-Button. Fig. 15 and Fig. 16. By placing App. 29 in a box, we can make something that looks a little more like a real push-button. Fig. 15 shows a plan with the box-cover removed, and Fig. 16 shows a view of the inside of it, a part of the box being cut away. C, Fig. 15, is a wooden pill-box 1 in. high and 1¾ in. in diameter. Make a ¼ in. hole in the cover of C for the "button," G, which is a short piece of ¼ in. dowel. This rests upon a single thickness of tin, D, which is cut into a strip ⅜ in. wide and about 1¼ in. long. In the bottom of C are two holes just large enough to allow the screws E and F to pass through. The wires, A and B, pass from the binding-posts, X and Y, through small holes burned through the sides of the box, and are fastened under the screw-heads. The whole box is screwed to the wooden base, which is 3 × 4 × ⅞ in., by the screws, E and F. D should have enough spring in it to raise itself and G when the pressure of the finger is removed. The circuit will be closed only when you press the button.
47. Push-Button. Figs. 17, 18, 19. Fig. 17 shows a top view or plan of the apparatus. Fig. 18 is a sectional view; that is, we suppose that the button has been cut into two parts along its length and through the center line. Fig. 19 is an enlarged detail drawing of the underside of the spool, C. The same part is marked by the same letter in all of the figures.
Saw an ordinary spool, C, into two parts. One-half of C will serve as the outside case for the button. The part to be pressed with the finger is a short length of ¼ in. dowel. To keep this from falling out of the hole in C, a short piece of wire nail, N, has been put through a small hole in its lower end. A slot, F, has been burned or cut into the underside of C, so that N can pass up and down in it when D is raised and lowered. The rod, D, rests upon A, one of the contacts. This is a straight piece of tin, cut as shown in Fig. 17, the narrow part being ¼ in. wide and 1¼ in. long. The wide part is ¾ in. wide and 1 in. long. The other contact, B, is the same size as A. A deep groove, a little over ¼ in. wide, is cut into the base so that the narrow part of B can be bent down below the end of A. The base shown is 4 × 2½ × ⅞ in. The spool, C, is fastened to the base by 2 screws or wire nails put up through the base, their positions being shown by the dots at E, Fig. 17. X and Y, Fig. 18, are 2 screw binding-posts. It is evident that the current cannot pass from X to Y, unless the button, D, be pressed down so that the end of A will touch B.
48. Sifter for Iron Filings. Fig. 20. In making magnetic figures with iron filings, it is an advantage to have the particles of iron fairly small and uniform in size. A simple sifter may be made by pricking holes in the bottom of a pasteboard pill-box with a pin. The sifter may be put away with the filings in it, provided you turn it upside down.
49. Sifter for Iron Filings. Fig. 21. Punch small holes in the cover of a tin box with a small wire nail. If you have occasion to use sifters for other purposes, the different sizes can be made by using larger and smaller nails to punch the different tin covers. But one size of nail should be used for one sifter.
50. Sifters may be made by pricking holes in an envelope. A sifter with very small holes can be made of a piece of muslin cloth. This can be used in the form of a little bag, or a piece of it can be pasted over the open bottom of a pill-box.
51. To Cut Wires, Nails, etc. If you have no wire-cutters, or large shears, you can cut large or small wires by hammering them against the sharp edge of another hammer, an anvil, or a piece of iron. Do not let the hammer itself hit upon the edge of the anvil. The above process will make a V-shaped dent on one side of even large wires, or nails, when they may be broken by bending back and forth.
CHAPTER IV.
SWITCHES AND CUT-OUTS.
52. Switches, Cut-Outs. Where apparatus is to be used frequently, such as for telephone and telegraph lines, it pays to make your switches, etc., carefully. The use of these switches, etc., will be shown in the proper place. Their construction only will be given here.
53. Cut-Out. Fig. 22. Details. X, Y, and Z represent 3 binding-posts like App. 42. These are fastened to a wooden base that is about 3 × 5 × ¾. The ends of the wires shown come from and go to the other pieces of apparatus. Q shows a stout wire or strip of 2 or 3 thicknesses of tin. Suppose we have an apparatus, as, for example, an electric bell, which we want to have ring when someone at a distance desires to call us. If we use a telephone or telegraph instrument we shall want to cut the bell out of the circuit as soon as we hear the call and are ready to talk. Suppose the current comes to us through the wire, A, Fig. 22. It can pass by the wire, C, through the bell and back to X. If we wanted simply to have the bell ring, the current could pass directly from X into the earth, or over a return wire back to the push-button at our friend's house. If, however, we are to use some other instrument, by lifting the end of Q out of X and pushing it into Y, the bell will be cut out, and the current can pass on wherever we need it.
54. Cut-Out. Fig. 23. The main features of this are like those of App. 36. The three binding-posts are like App. 46. Instead of a band of metal to change connections, as Q in App. 36, a stout copper wire is used. This can be easily changed from one of the upper binding-posts to the other, thereby throwing in or cutting out any piece of apparatus joined with the upper connectors.
55. Switch. Fig. 24. This simple switch has but one contact point, D, which is a screw-head. This switch may be used anywhere in the circuit by simply cutting the wire carrying the current, and joining the ends of the wire to the binding-posts X and Y. The metal strip, E, is made of 2 or 3 thicknesses of tin. It is ⅝ in. wide and about 5 in. long, and presses down upon D, when swung to the left, thus closing the circuit. The short metal strips shown are ⅝ × 1¼ in. The upper strip is joined to the end of E by a coiled copper wire, C W. (See App. 50.) If the current enters by the wire, A, it will pass through C W, E, D and out at B. The strip E is pivoted at F by a small screw. The base may be 3 or 4 × 5 × ⅞ in.
56. Switch. Fig. 25. By increasing the number of contact points and the wires leading from them, a switch may be made to throw in one or more pieces of apparatus. This variety of switch is useful in connection with resistance coils (Index). By joining the ends of the coils with the points 1, 2, 3, etc., more or less resistance can be easily thrown in by simply swinging the lever, E, around to the left or right. The uses of this will be again referred to.
Details. The base of the one shown in Fig. 25 is 4 × 5 × ⅞ in. thick. The switch, E, is a band of 2 thicknesses of tin ⅝ in. wide. It is pivoted at F with a screw. To the end of E is fastened a copper wire, which leads to the upper binding-post, X (App. 46). The apparatus has 5 contact points, marked 1, 2, 3, etc. These consist of brass screws and copper washers. With F as a center draw the arc of a circle that has a radius of 4 in. Place the screws 1, 2, etc., along this arc, and about ⅝ in. apart, center to center; that is, the screws are all 4 in. from F, and are, therefore, in the form of a curve.
The last screw forms a part of the binding-post, Y. Suppose 4 pieces of apparatus, marked A, B, C, and D, be connected with 1, 2, etc., as shown. These may be, for example, coils of wire to be used as resistance coils. If the current enters at X, it will pass along at E and be ready to leave at Y, as soon as E touches one of the contact points. If E be placed upon 1, the current will be obliged to pass through all of the coils, A, B, etc., before it can get to Y. In this case the resistance will be greatest. If E be now moved on to 2, only A will be cut out, and the total resistance reduced. By placing E upon 4, but one coil, D, will be in the circuit. When E is upon 5 the current will pass through the switch with practically no resistance. This is the principle upon which current regulators work. (Study resistance in text-book.) When E is in the position shown in Fig. 25 no current can pass.
CHAPTER V.
BINDING-POSTS AND CONNECTORS.
57. Binding-Posts are used to make connections between two pieces of apparatus, between two or more wires, between a wire and any apparatus, etc., etc. They are used simply for convenience, so that the wires can be quickly fastened or unfastened to the apparatus. There are many ways of making them at home. The following forms will be found useful and practical. Although some that are given are really connectors instead of binding-posts, we shall give them the general name of binding-posts.
58. Binding-Post. About the simplest form is a screw, or a nail with a flat head. The bare wire may be placed under the head of the screw or nail before forcing it entirely into the wood. This will keep the end of the wire in place, and another wire may be joined electrically to the first by merely touching it to the screw-head, or by placing it under the screw-head.
59. Binding-Post. Fig. 26. This consists of a screw and a copper washer or "bur." The screw is a "round-headed brass" one, ⅝ in. long, number 5 or 7. The copper burs are No. 8, and fit nicely around the screws. By using 2 burs instead of 1, several wires may be easily joined together at one point. Scrape the covering from the ends of the wires, and place them between the burs.
60. Binding-Post. Fig. 27. A coiled spring serves very well as a connector. One end should be fastened to the apparatus, as shown, by clamping it under a screw-head. The other end of the coil should be pulled out a little, away from the other turns, so that you can stretch the spring in order to put the bare ends of wires between the turns. Any number of wires placed between these turns will be pinched and electrically connected. The coil should be about ½ in. long and less than ½ in. in diameter. You can make a coil by tightly wrapping stiff iron wire around a pencil. The steel wire springs taken from old window-shades are excellent for this purpose. They may be cut into lengths with tinner's shears.
61. Binding-Post. Fig. 28. Two copper or tin strips fastened at one end by a screw, the upper strip being bent a little at one end, make a connector that is useful for some purposes, where you want to make and break the connection frequently. The bare end of the wire which belongs to the apparatus is fastened under the screw-head. The outside wire, or wires, to be connected are pushed between the strips of metal. Another way is to fasten the outside wire to a strip of metal about ½ in. wide, and then push this between the strips shown in the figure. The strips shown should be about ¾ in. wide and 1¼ in. long.
62. Binding-Post. Fig. 29. A combination made between App. 42 and 43 does well. Fasten a metal strip, ¾ in. × 1¼ in., to the apparatus by means of a screw. The apparatus wire should be fastened under the screw-head. A short length of spring may be pushed upon the upright part of the strip, as shown. Into this you can quickly fasten the outside wires.
63. Binding-Post. Fig. 30. This makes a very simple and practical binding-post for home-made apparatus. It consists of a screw-eye, preferably of brass. The circle or eye should be about ⅜ or ½ in. in diameter. The thread on such a screw-eye will be about ½ in. long. Two copper burs are used to pinch the wires.
64. Binding-Post. Fig. 31. This consists of a screw, screw-eye, bur and a metal strip, ¾ × 1¼ in. The apparatus wire should be fastened under the screw-head. Any outside wires which are to be joined to the apparatus should be clamped under the bur by turning the screw-eye. A small hole should be made in the wood before putting in the screw-eye. (See App. 25.) Do not turn the screw-eye too hard, or you will spoil the thread made in the wood.
65. Binding-Post. Fig. 32. The size of the bolt used in this form of binding-post will depend somewhat upon the thickness of the base of the apparatus. In general, a ¾ or ⅞ in. base should be used where screws or screw-eyes are necessary. With this kind (Fig. 32) a thin base can be used. The head is shown counter-sunk into the bottom of the base. This is not necessary, provided at least 3 heads are placed far enough apart to form legs for the apparatus to stand on. Strips of wood may be nailed upon the underside of the base to make room for the heads in case they are not used as legs. The wires should be pinched between the nut and the copper bur shown. If the bolt is too large for a bur, an iron washer may be used. A washer may be made of tin, or two nuts may be used.
66. Binding-Post. Fig. 33. This is a suggestion for a combination of App. 44 and 47. It is useful in school apparatus. Wires may be permanently fastened on the right, under the nut, and a spring, as in App. 44, may be slipped on the metal strip at the left, which is held under the head of the bolt.
67. Mercury Connector. A cup of mercury may be used as a connector. Make a small hole about ¼ in. in diameter and depth, in a piece of wood, and place 2 or 3 drops of mercury in this. The ends of wires dipped in this will be electrically connected.
68. Connector. Fig. 34. This shows how a wire may be fastened to one end of a short strip of tin. At the other end of the strip a slot is cut. This may straddle the body of a screw, or when left plain may be used to slip between the two metal strips shown in App. 43.
69. Binding-Post. Fig. 35. The ends of two or more wires may be quickly joined electrically by placing them between the nuts of a short bolt. By using 3 nuts the bolt will more easily connect a large number of wires.
Make Additional Notes and Sketches Here.
CHAPTER VI.
PERMANENT MAGNETS.
70. Permanent Magnets may be made in many ways and from many different kinds of steel. The steel used for needles, watch and clock springs, files, cutting tools, etc., is generally of good quality, and it is already hard enough to retain magnetism. (See Retentivity in text-book.)
71. Bar Magnet. A straight magnet is called a bar magnet. Magnetize a sewing-needle. For some experiments a needle-magnet, as we may call it, is better than a large magnet.
72. Bar Magnet. A harness-needle, which is thicker and stronger than a sewing-needle, makes an excellent bar magnet.
73. Bar Magnet. For long slim magnets use a knitting-needle. Some knitting-pins, as they are sometimes called, break off short when bent, but most of them will bend considerably before breaking. These slim magnets are excellent for the study of Consequent Poles. (See text-book.)
74. Flexible Bar Magnets. It is often necessary to have flexible magnets so that they may be bent into different shapes. These may be made from watch or clock springs, as such steel, called spring steel, will straighten out again as soon as the pressure is removed from it. Corset steels, dress steels, hack-saw blades, etc., make good thin flexible bar magnets.
75. Strong Bar Magnets may be made from flat files. The handle end may be broken off so that the two ends of the file shall be nearly alike in size. These should be magnetized upon an electro-magnet.
76. Compound Bar Magnets are made by first magnetizing several thin pieces of steel, and then riveting them together so that their like poles shall be together, and pull together. To make a small compound bar magnet, magnetize several harness-needles, or even sewing-needles, and then bind them into a little bundle with all the N poles at the same end. Melted paraffine dropped in between them will hold them together. Rubber bands may be used also, or, if but one end is to be experimented with, the points may be stuck into a cork, and the heads used to do the lifting.
77. Small Horseshoe Magnets may be made from needles or from other pieces of steel used for bar magnets. They should be annealed (App. 21) at their centers at least, so that you can bend them into the desired shape. In the case of bright needles, like harness-needles, the part annealed will become blackened. If you heat the center only, and the ends remain bright for about ½ inch, you will not need to harden the needle again. It is an advantage to have the center of the magnet a little soft, as it is not then liable to break. The ends alone may be hardened by holding the bent portion away from the candle or gas flame, while heating the ends. The bent steel should be magnetized by drawing its ends across the poles of a horseshoe magnet.
78. Flexible Horseshoe Magnets may be made of thin spring steel. The distance between the poles can be regulated at will by bending the steel more or less. The poles may be held at any desired distance apart by thread or wire, which should be wound around the legs of the magnet a little above the poles. This will keep the steel from straightening out.
79. Horseshoe Magnet. Fig. 36 and 37. Magnetize two harness-needles, and stick them into a cork so that the poles shall be arranged as shown. The distance between the poles can be regulated to suit. This forms a very simple and efficient magnet, with the advantages of a real horseshoe magnet.
80. Armatures. All home-made magnets should be provided with armatures, or keepers. These are made of soft iron on the regular magnets, and tend to keep the magnet strong. (See text-book.) For the bar magnets described, a piece of sheet-tin, upon which to lay them, is all that is needed for an armature. The lines of force will pass through this. For the horseshoe magnets described, strips of tin, soft iron wires, or even a wire nail placed across the poles will greatly aid in keeping in the strength. The little magnets should not be dropped or jarred. (Study the theory of magnetism in text-book.)
CHAPTER VII.
MAGNETIC NEEDLES AND COMPASSES.
81. Magnetic Needles and Compasses consist chiefly of a short bar-magnet. When used to tell the directions, north, east, etc., the apparatus is generally called a compass. When we speak of the "needle," we really mean the compass-needle. The little magnet may be almost any piece of magnetized steel, provided it is arranged so that it can easily swing around. There are several ways of supporting the compass-needle. It may rest upon a pivot, it may be hung from a fine thread, or it may be floated upon water with the aid of a cork, etc.
82. Uses. We all know that compasses are used to point to the north and south, and we speak of the "points of the compass." This, of course, is the most important use of the compass, and it has been known for centuries. In the laboratory it is used to show or detect the presence of currents of electricity, and, in connection with coils of wire, it may show the relative strengths of two currents, etc. When used for such purposes it generally has special forms and sizes. (See Galvanometers and Detectors.)
83. Compass. An oily sewing-needle will float upon the surface of water, when it is carefully let down to the water. A little butter may be rubbed upon the previously-magnetized needle to make it float better.
84. Compass. Fig. 38 shows a magnetized sewing-needle floated upon a cork. The needle may be permanently fastened to the cork with a few drops of melted paraffine.
85. Compass. Fig. 39. With a sharp knife make a cut part way through a flat cork. Into the cut push a short length of magnetized watch-spring. In the illustration the spring is shown partly removed from the cut. Float the cork.
86. Compass. Fig. 40. Stick a pin, P, into a pasteboard, cork, or wooden base, B. Bend a piece of stiff paper double, as shown, and then stick through it, on each side, a magnetized sewing-needle, S N. The north poles of the needles should be at the same end of the paper. Why? Balance the paper upon the pin-pivot, and see it fly around to the north and south.
87. Compass. Fig. 41. It is an advantage to have a magnetic needle that is always ready for use. The support is made by driving a pin through the top of a wooden pill-box, which should be about 1¾ in. in diameter. This gives plenty of room under and around the needle. If the pin be left too long, it will not be possible to put the bottom and top of the box together when you want to put the compass away. Cut the pin off (App. 35) at the right length, so that the magnetic needle can be safely put away in the closed pill-box.
88. The "Needle," that is the short bar magnet, may be made of watch-spring. As the spring is already quite hard and brittle, it may be easily broken into desired lengths. It is always better to make 3 or 4 needles at a time, as some will swing more easily than others, and time will be saved in making them. Break off 3 or 4 pieces of thin spring, each about 1½ in. long. Bend them as in Fig. 42. A good dent, not a hole, should be made at the center of each to keep them upon the support or pin-point. A "center punch," not too sharp, is the best tool to use, but a slight dent may be made with a sharp wire nail, provided the watch-spring is first annealed or softened. (See App. 21.) Do not place the spring directly upon iron or steel when making the dent, as these might injure the point of the punch, and the dent would not be deep enough. Fig. 42 shows a good way to make dents in steel springs. Place 2 or 3 layers of copper or lead between the anvil and the spring. A hammer or hatchet will do for the anvil. As the copper will give easily, a good dent may be made by striking the punch or nail with a hammer. If the spring has been annealed before denting it, it should be hardened again (App. 21) before magnetizing it, so that it will retain magnetism well. (See Residual Magnetism in text-book.)
89. Balancing. After a dent has been made, place the spring upon its support so that the pin-point shall be in the dent. It will, no doubt, need balancing. If one end is but slightly heavier than the other, the spring may be balanced by magnetizing it so that the lighter end shall become a north pole. This will then tend to "dip" and make the needle swing horizontally. If one end is much heavier than the other, it should first be magnetized and then balanced by cutting little pieces from the heavier end with tinners' shears, or by weighting the lighter end with thread, which may be wound around it. The finished compass-needle should swing very freely, and should finally come to rest in an N and S line after vibrating back and forth several times.
90. Glass-Covered Compass. A perspective view of this apparatus is shown in the tangent galvanometer. (See Index.) The outside band, E, is made of thick paper, 1 in. wide, and with such a diameter that it just fits around the glass. In this model, the glass from an old alarm-clock was used, it being 4 in. in diameter. Four pasteboard strips were sewed to the inside of the paper band E. They were made ⅞ in. long, so that the glass, when resting upon them, would be near the top of E.
The needle should be not over 1 in. long, if it is to be used in the galvanometer. A long slender paper pointer should be stuck to the top of the needle. Be careful to have the combined needle and pointer well balanced, so that it will swing freely. A circle graduated into 5–degree spaces should be fastened under the needle.
91. Astatic Needles. In the magnetic needles so far described, the pointing-power has been quite strong. By pointing-power we mean the tendency to swing around to the N and S. In App. 65 the 2 needle magnets had considerable pointing-power, because they helped each other. For some experiments in electricity a magnetic needle is required which has but little pointing-power; in fact, to detect the presence of very feeble currents by means of the needle, the less the pointing-power the better. Can you think of any way to arrange App. 65 so that it shall have very little pointing-power?
92. Astatic Needle. Fig. 43. Turn one of the needle magnets of App. 65 end for end, so that the N pole of one shall be at the same end of the paper as the S pole of the other. You can see that by this arrangement one needle pulls against the other. The magnetic field still remains about the little magnets, otherwise this combination would be of no value in the construction of galvanometers. The more nearly equal the magnets are in strength, the less the pointing-power of the combination.
93. Astatic Needle. Fig. 44. Magnetize two sewing-needles as equally as possible, by rubbing them over the pole of a magnet an equal number of times. Remove the covering from a piece of fine copper wire, say No. 30, and use the bare wire to wind about the needles, as shown. Be sure to place the poles of the little magnets as in the Fig. This combination may be supported by a fine thread. It is used for Astatic Detectors. (See Index.)
CHAPTER VIII.
YOKES AND ARMATURES.
94. Yokes are used to fasten two straight electro-magnets together to form a horseshoe electro-magnet. The reasons for using them should be understood. Soft iron should be used for yokes and armatures, as this is the best conductor of lines of magnetic force. Sheet-tin is made of thin iron, which is coated with tin. (Try a magnet upon a tin can.) This soft iron is very easily handled, bent, and punched, and is very useful for many purposes. The tin from old tomato cans, cracker boxes, etc., is just as good as any. The method of making your yokes will depend entirely upon the tools at your command. Several ways are given. Y, Fig. 47, shows the position of the yoke.
95. Yoke. For the experimental magnets (App. 89) a fairly large yoke is required in order to have the magnets far enough apart. If you have only a nail punch (App. 26) with which to make holes in tin, you will be obliged to punch but one thickness at a time. (See method of punching sheet-metal, App. 26.) Cut 5 or 6 pieces of the tin, 3¼ × 1 in. With a center punch (tools) or sharp-pointed nail make small dents (2 in. apart) in each piece to mark the places where the holes are to be punched. Punch 5⁄16 in. holes in each piece. If you do this carefully, the holes in the different pieces will match, and the bolts can be pushed or screwed into these. When screwing in the bolt magnets turn them by their heads; do not pinch the coils, as this loosens the wire.
If you have a good punch, it is better to make the yoke as in App. 27, instead of using separate pieces of tin.
96. Yoke. Fig. 45 and 46. Cut a strip of tin 6 in. long by 3¼ in. wide. Bend one end of it so that it will lap over ¾ in. (Fig. 46); hammer it down gently, then bend this over and over until the whole tin is used. The final result will be a flat roll, 3¼ by about 1 in. This should be hammered flat.