Page:Popular Science Monthly Volume 91.djvu/622

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��Popular Science Monthly

��A New Type of Acid-Proof Brush for Soldering Flux

THE use of non-corroding paste in soldering has, in many cases, done away with the disagree- able and dangerous acid brush. There are still a few jobs, however, which require an acid flux for soldering. To those who have occasion to use sol- dering acid of any kind, the non - corrosive acid brushes shown in the il- lustration should prove serviceable.

Both of the brushes shown employ a small piece of rubber sponge for the brush proper, while the handles are made as illustrated, one from an old rubber pen barrel and the other from a section of tubular porcelain insulator.

The piece of sponge mentioned is forced into one end of the rubber or porcelain handle, as shown. — R. U. Clark.

���A discarded fountain pen case and a section of tubular por- celain insulator for brush handles

��good insulation from the motor shaft with extreme lightness.

To make an arm embodying these fea- tures, proceed as follows: From a piece of fiber or bakelite of suitable length and }4 in. thick, cut a strip to the shape shown at A. The widest part should equal the diameter of the shaft-bushing, so as to fit flush. The dimensions will, of course, vary with the size of your ring; but in any event the length of this piece should be }/i in. less than the distance be- tween faces of opposite studs. Holes B and C are for fastening to the hub on the motor-shaft. Holes D and E, tap 2-56, are for screwing on the aluminum strip shown at

��a point

��Construction of a Rotating Arm for a Rotary Gap

TO those amateurs employing a rotary spark-gap of the type having the studs arranged in a ring about a revolving

���F. This piece is 1% in. longer than the fiber. At from each end bend the aluminum at right angles. This forms the sparking surface. Now, about }4 i n - W from the bend on both ends, curve the strip as at G. Screw it down, as shown, to the fiber arm. After screwing on the hub, mount it as shown at H.

The proper adjustment of distance be- tween electrodes is accomplished by chang- ing the stationary studs. This type of rotating arm is not only extremely light, allowing a quick start, but also has the advantage of cooling rapidly, owing to the exposed surface curving away from the fiber strip. This curve should be at least 1 in. from the center for good insulation.


A light rotating arm constructed so that it is well insulated from the motor shaft

arm, the construction of this arm often presents difficulty; for it must combine

��Using Resistance in Field Wiring on an Automobile Dynamo

MANY times the car owner is not en- tirely familiarwith the lighting system and does the wrong thing when trouble occurs. Cars are equipped with a gener- ator that will carry about six 12 c. p., 8-volt, tungsten filament bulbs. Each bulb takes about 1 x /l amperes. If it is desired to use only a part of the bulbs at a time it is necessary to connect in the line a resistance equal to that used by the bulbs cut out of the circuit. This resistance should be put in the shunt field wiring to prevent the voltage from running too high.

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