Electric Bells and All About Them

oils, the iron becomes, for the time being, powerfully magnetic (see § 13). A piece of soft iron (known as the armature), supported by a spring, faces the magnet thus produced. This armat

current the iron may lose its magnetism, and allow the spring to withdraw the clapper from against the bell. This device is known as the "contact

actical knowledge of what are the requisites of a good bell, and where defects may be expected in any he may be called upon to purchase or examine, than he can obtain from

exchange, but their performance is always liable to variation and obstruction, from the following causes:-To insure a steady, uniform vibratory stroke on the bell, its hammer must be nicely adjusted to move within a strictly defined and limited space; the least fractional departure from this adjustment results in an unsatisfactory performance of the hammer, and often a total failure of the magnet to move it. In bells constructed on the old plan, the wooden base is liable to expansion and contraction, varying wi

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ts of my readers; for instance, a worker in sheet metal may find it more convenient to manufacture his bell out of the parts sketched in Figs. 17, 18, 20A, 21, 23, 24A, and 25; but, on the other hand, a smith or engineer might prefer the improved form shown at Fig. 31, and select the parts shown at Figs. 20A, 22, 19, choosing either to forge the horse-shoe magnet, Fig. 20, or to turn up the two cores, as shown at Fig. 21 (A), to screw into the metal base, Fig. 21 B, or to be fastened by nuts, as shown at Fig. 19. The result will be the same in the end, if good work

ke the cores of such a magnet, to ring a 2? in. bell, get two 2 inch lengths of 5/16 in. best Swedish round iron, straighten them, smooth them in a lathe, and reduce ? in. of one end of each to 4/16 of an in., leaving a sharp shoulder, as shown at Fig. 21 A. Next, get a 2-in. length of angle iron, drill in it two holes 1? apart, of the exact diameter of the turned ends of the cores, and rivet these securely in their places; this may be done by fastening the cores or legs in a vice whilst they are being rivetted. Two holes should be also bored in the other flange to receive the two screws, which are to hold the magnet to the base, as shown at Fig. 21 B. The magnet is now quite equal to the horse-shoe form, and must be made quite soft by annealing. This is done by heating it in a clear coal fire to a bright red heat, then burying it in hot ashes, and allowing it to cool gradually for a period of from 12 to 24 hours; or perhaps a better guide to the process will be to say, bury the iron in the hot ashes and leave it there until both it and they are quite cold. The iron must be brought to a bright cherry red heat before allowing it to cool, to soften it properly, and on no account must the cooling be hurried, or the metal will be hard. Iron is rendered hard by hammering, by being rapidly cooled, either in cold air or water, and hard iron retains magnetism for a longer time t

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urse the bobbins become fixtures on the magnets. There are some persons who are clever enough to make firm bobbins out of brown paper (like rocket cases), with reel ends, that can be slipped off and on the magnet cores. To these I would say, "by all means at your command, do so if you can." The size of the bobbins for a 2? in. bell should be: length 1? in., diameter of heads ? of an in., the length increasing ? of an in. and the diameter ? of an in. for every additional ? in. in the diameter of the bell. The holes throughout the bobbins should be of a size to fit the iron cores exactly, and the cores should projec

nductors or insulators, the best conductors being arranged from the top downwards, and the bad conductors or

ors. In

Paraff

. Gutt

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Metals.

olutions.

alts. Silk

e. Dry C

od. Dr

irt an

t given at § 5 for a more comp

ant, as the current has less effect on the iron if removed further from it, the decrease being as the square of the distance that the current is removed from the wire. Magnets coiled with silk-covered wire admit also of better finish, but for most purposes cotton-covered wire will give satisfaction, especially if well paraffined. This wire must be wound on the bobbins, from end to end regularly, with the coils side by side, as a reel of cotton is wound. This may be done on a lathe, but a little practice will be necessary before the inexperienced hand can guide the wire in a regular manner. If, however, the spool of wire have a metal rod passed up its centre, and this be held in the hand at a distance of a foot or more from the bobbin on the lathe, the wire will almost guide itself on, providing the guiding hand be allowed to follow its course. With a little care, the wire for these little magnets may be wound entirely by hand. Before commencing to wind on the bobbins, just measure off 8 in. of the wire (not cutting it off) and coil this length around a pencil, to form a small coil or helix. The pencil may then be withdrawn from the helix thus formed, which serves to connect the wire with one of the points of contact. This free end is to be fastened outside the bobbin by a nick in the head; or the ? in. length, before being formed into a helix, may be pushed through a small hole made on the head of the bobbin, so that 8 in. project outside the bobbin, which projecting piece may be coiled into a helix as above described. The wire should now be wound exactly as a reel

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e bobbins should stand uppermost, as shown at Fig. 22 A. A short length of the lower free ends of wire (near the base or yoke) should now be bared of their covering, cleaned with emery paper, twisted together tightly, as shown at Fig. 22 B, soldered t

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iding joins, taking care that the direction of the winding in the finished coils be as shown at Fig. 22 B; that is to say,

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s, and these are soldered into it. The top strip is then bent back over the armature to form the contact-spring, the other strip being soldered or rivetted to a small bracket of angle brass. In either case a short rod of stout hard brass wire is rivetted or screwed into the free end of the armature, and to the end of this rod is screwed or soldered the metal bead, or bob, which forms the hammer or "clapper" of the bell. The next portion to be made is the contact pillar, or bracket, with its screw, as shown at Fig. 25. This may either be a short stout pillar of ? in. brass rod, about 1 in. high, tapped on one side to receive the screw, which should be fitted with a back nut; or it may, as shown in the figure, be made out of a stout piece of angle brass. The exact size and length of the screw is immaterial; it must, however, be long enough to reach (when put in its place behind the contact spring) the spring itself, and still have a few threads behind the back nut to spare. The screw should be nicely fitted to the pillar, and the lock nut should clench it well, as when once the adjustment of the parts is found which gives good ringing, it is advisable that no motion should take place, lest the perfection of ringing be interfered with. Some makers use

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. 28). The bell must be adjusted on its pillar (see Fig. 29A), which is itself screwed into a hole in the base-plate, where it is held by a nut. The adjustment of the bell is effected by placing it over the shoulder of the pillar, and then clenching it down by screwing over it one or other of the nuts shown at Fig. 29. The bell should clear the base, and should be at such a height as to be struck on its edge by the hammer or clapper attached to the armature, Figs. 23 and 24. We still need, to complete our bell, two binding screws, which may take either of the forms shown at Fig. 27; and an insulating washer, or collar, made of ebonite or boxwood, soaked in melted paraffin, to prevent the contact pillar (Fig. 25) making electrica

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the metal base-plate by washers, as shown at Fig. 30 (similar washers must be used for the two binding screws if the whole base-plate be made in metal). This being done, the metal frame, Fig. 18, is put in position on the wooden base, as shown at Fig. 17, and screwed down thereto by the screws indicated at s s s. The magnet may then be screwed down to the metal frame as shown. The small bracket of angle brass marked B, in Figs. 23 and 24, is ne

proceed to test the working of the bell by connecting up the binding screws with the wires proceeding from a freshly-charged Leclanché cell. If all have been properly done, and the connections duly made, the armature should begin to vibrate at once, causing the "bob," or hammer, to strike the bell rapidly; that is, provided the platinum tipped screw touches the platinum speck on the contact spring. Should this not be the case, the screw must be turned until the platinum tip touches the platinum speck. The armature will now begin to vibrate. It may be that the clapper runs too near the bell, so that it gives a harsh, thuddy buzz instead of a clear, ringing sound; or, possibly, the clapper is "set" too far from the bell to stri

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, converts them, pro tem., into a powerful magnet (see § 13); consequently, the armature, with its contact spring and hammer, is pulled towards the electro-magnets and at the same time gives a blow to the bell. Now, if instead of having the platinum speck attached to a flexible spring, it had been attached bodily to the rigid iron armature, directly the electro-magnets felt the influence of the current, the platinum speck would have also been pulled out of contact with the platinum screw, therefore the electro-magnet cores would have immediately lost their magnetism (see § 13, last five lines). This would have been disadvantageous, for two reasons: 1st, because the stroke of the hammer would have been very short, and consequently the ring of the bell very weak; and, 2nd, because, as even the softest iron requires some appreciable time for the electric current to flow rou

s, which greatly lowers the conductivity of the junction. Again, at the junction points of the wires with the contact angle brass and contact pillar, some workmen solder the junctions, using "killed spirits" as a flux. A soldered contact is certainly the best, electrically speaking, but "killed spirits," or chloride of zinc, should never be used as a flux in any apparatus or at any point that cannot be washed in abundance of water, as chloride of zinc is very deliquescent (runs to water), rottens the wire, and spoils the insulation of the adjacent parts. If solder be used at any parts, let resin be used as a flux. Even if any excess of resin remain on the work, it doe

reen, or turns black, it is not platinum; if it remains unaltered, it may be silver or platinum. After it has stood on the tip for a minute, draw it along a piece of white paper, so as to produce a streak of the acid. Expose the paper for a few minutes to s

l the armature with sufficient force to give a good blow; in the latter, the spring cannot return the armature, with its attendant contact spring, back to its place against the platinum screw. To ascertain which of these two defects obtains, it is only necessary, while the bell is in action, to press the spring lightly with a bit of wire, first towards and then away from the electro-magnets. If the ringing is improved in the first case, the spring is too strong; if improvement takes place in the latter case, the spring is too weak. The third source of inefficient action, defective insulation, is not likely to occur in a newly-made bell, except by gross carelessness. Still, it may be well to point out where electrical leakage is likely to occur, and how its presence may be ascertained, localized, and remedied. If the wire used to wind the electro-magnet be old, badly covered, or bared in several places in winding, it probably will allow the current to "short circuit," instead of traversing the whole length of the coils. If this be the case, the magnet will be very weak: the magnet of a 2?-in. bell should be able to sustain easily a 1 lb. weight attached by a piece of string to a smooth piece of ?-in. square iron placed across its poles, when energized by a single pint Leclanché cell. If it will not do this, the insulation may be suspected. If the wire has been wound on the bare cores (without bobbins), as is sometimes done, bared places in the wire may be touching the iron. This may be ascertained by connecting one pole of a bottle bichromate, or other powerful battery, with one of the wires of the electro-magnet coils, and drawing the other pole of the battery across the clean iron faces of the

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whether the board is warped or swollen, or whether it has shrunk. Warping or swelling will throw the electro-magnet too far from the armature, or "set" the pillar ou

, etc., will certainly militate against good contacts and good action if this important point be neglected. The cover or case generally takes the form of a shallow box, as shown at Fig. 32, and may be made from ?-in. teak, mahogany, or walnut, dovetai

sizes. It must be noted that if the bells are to be used at long distances from the battery, rather more of a finer gauge of wir

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a

observed in the differen

eter of Magnet Cores. Length of Bobbin. Diamet

5/16'' 1?

? 2

7/16 2

? 2?

/16 2?

? 3

11/16

? 3?

3/16 3

? 4

15/16

1 4?

-1/16

1? 5

-3/16 5

1? 5

-5/16 5

1? 6

1-7/16

1? 6

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, Fig. 34, the wires from the electro-magnet are connected directly to the two binding screws L and Z, so that when contact is made with the battery, the armature is drawn to the poles of the electro-magnet, and kept there so long as the battery current passes. By this means, only one stroke or blow is given to the bell for each contact of the battery. Of course, directly the connection with the battery is broken, the spring which carries the armature and clapper flies back ready to be again attracted, should connection again be made with the battery. To regulate the distance of the armature from the poles of the electro-magnets, a set screw Q takes the place of the platinum screw in the ordinary form, while to prevent the hammer remaining in contact with the bell (which would produce a dull thud and stop the clear ring of the bell), a stop (g) is set near the end of the armature, or two studs are fixed on the tips of the poles of the electro-magnets. The mode of adjusting this kin

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differs but little from the ordinary trembling bell. The chief difference lies in the addition of an automatic device whereby contact is kept up with the battery, even after the "push" contact has ceased. As it is desirable for the person in charge to be able to stop the ringing at will, without proceeding to the place where the "push" stands, so it is not usual to make the continuous ringing arrangement dependent on the "push," though, of course, this could be done, by causing it to engage in a catch,

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shunt wire), proceeding from the zinc of the battery. It will be seen, that if the battery current is by means of the push caused to flow through the coils of the electro-magnets, the armature is attracted as usual by them, and in moving towards them, releases and lets fall the lever contact, which, resting on the contact screw, completes the circuit

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es round the cores of the relay, thus converting it into a magnet. The armature a is thereby pulled to the magnet, and in so doing releases the detent lever, which falls on the contact screw, thus at one and the same time breaking the circuit through the relay, and making the circuit through the bell magnets B B′, back to the battery by Z. A second modification of this mode of causing an ordinary bell to ring continuously is shown at Fig. 38, the peculiar form of relay used therewith being illustrated at Fig. 39. Here, the relay is placed on a separate base board of its own, and could, if necessary, be thrown out of circuit altogether, by means of a switch,[13] so that the bell can be used as an ordinary bell or continuous action at will. It will be noticed that the relay has in this sketch only one core. But the delicacy of the action is not impaired thereby, as the armature, by means of the steel spring s, is mad

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e current flowing from C of the battery to armature A of the relay R, through contact post p, terminal L of the bell, through bell to terminal Z, and thence by the wire g to the zinc of the battery. Part of the current also flows along the wire from the bell terminal L through the relay coil b and switch W, to terminal Z of the bell, thus keeping the armature of the relay down, after the main circuit (through the push) has been broken; the bell continuing to ring until the shunt circuit is broken by moving the arm of the switch W over to the opposite (or non-contact) side. The bell can also be stopped by short circuiting the relay, which can be effected by an ordinary push. It will be seen that more than one bell can be rung from the same attachment, and the bell can, by moving the arm of

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pulling the ring outside the bottom of the core. The bell or bells then start ringing, as contact is established and kept up. The novelty lies in the fact that the duration of the contact, and consequently of the r

ial of the bell itself, the relative disposition of the parts, or some structural detail; but not upon the introd

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ded from a pivot and balanced by the hammer of the bell. At the back of the armature there may be a make and break arrangement, whereby a continuous succession of strokes is effected, or this may be omitted, in which case a single stroke is given when the contact with the battery is made, or both may be effected by separate wires, make contact with one wire, and a single stroke i

y power. The electro-magnetic apparatus being within the bell the latter forms a very effective and handsome shield f

act with an insulated metallic piece in the centre of the top of the bell. Both the wire and

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armature) with the core iron of their magnet. It is thus induced to perform the largest amount of work with the smallest electro-motive force. Instead of the armature and clapper being in a straight line attached to a rigid spring, which necessitates a considerable attractive power to primarily give it momentum, in the Jensen Bell the armature and hammer are in the form of an inverted U, and being perfectly balanced from the point of suspension, the lines of force from a comparatively small magnetic field suffice to set this improved form of armature into instant regular vibration. By using a flexible break and make arrangement instead of the usual armature spring and set screw (at best of most uncertain action), it is found that a much better result is attaine

ning bells the action is all enclosed in strong, square teak cases, to protect the movement, as far as possible, from the effects of the damp. All the parts are, for the same reason, made very large and strong; the armature is pivoted instead of being supported on a spring, the hammer shank being long, and furnished with a heavy bob. The domes or bells are from

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e screw touches, is soldered a speck of platinum. The wires from the electro-magnet are connected, one to the upper binding screw, the other to the brass case of the instrument itself, which is in metallic communication with the sheet iron disc. The return wire from the contact screw is shown attached to the insulated piece, and is fastened to another binding screw (not visible) on the base board. When contact is made with the battery, through the press or push, the magnet becomes energised, and pulls the iron disc or diaphragm towards it, causing it to buckle inwards. In doing this, contact is broken with the screw B; consequently the diaphragm a

iven to the parts covering the "movement," so as to imitate the head of an owl, etc. But bells with these changes in outward form will not pr

Amateu

ectrified body is said to be insulated when surro

ding directly over, but not touching, another stud, fixed to a base. The lower stud is connected to one terminal of battery, the spri

scribed

ent Making for Amateurs." Wh