956
��Popular Science Monthly
��B B, equal to width of V-ring. Connect lines B and C on both sides, extending lines to A A. Call this intersection point F, or "apparent apex of cone."
Using F as the center and B as the radius, describe a large arc. Repeat this operation using C as the radius. This gives us proper curve and width of the
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��Method of laying out a pattern for cutting the mica V-rings used on armatures
mica V-ring, but to eliminate waste the length should also be known; the exact length is not needed and would be im- practical for two reasons; first, it would involve too much figuring for the average armature winder and take up too much time; second, because provision must be made for welding mica V-ring ends to- gether.
Therefore the exact length would be too short. To get the required length, en- circle the large end of a V-ring with a piece of banding wire, allowing an extra inch for welding. Set this measurement on the large arc, and mark off the points, D D. Connect points D D with the apex, F. The V-ring is now all laid out and ready- to cut.
��A Holding Clip for Making Tests on Spark Plugs
WHEN testing the spark on a set of exposed sparking plugs most car owners feel the need of special clips to grip the plugs, which have a habit of tumbling out of contact, more particu- larly when single plugs are being tested with the engine running. Under these
��circumstances, too, there is a risk of straining the magneto or coil if a plug swings past its wire without a ground. An ordinary bicycle pump clip of the double spring type makes an excellent plug holder. One end may be sprung over any convenient pipe or bolt and the inverted plug dropped into the empty end.
Controlling an Oil Cup by Means of an Electromagnet
THE magnetically operated oil cup described herewith will be found to be a very convenient means of controlling oil feed in partially inaccessible places.
An electromagnet is used in this scheme, as shown in the sketch. To open the oil cup, energize the magnet by control switch or push button. The iron disk, ad- jacent to the electromagnet, becomes mag- netized and draws up the iron cap on the top of the oil feed pipe, and the oil will commence to drip. Upon breaking the circuit, the disk is demagnetized and the oil feed pipe, being no longer attracted, again falls and closes the feed hole.
Regulation of the flow can be obtained by adjustment of the iron disk, which is
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-—Oil feed pipe -- Oil cup
��A serviceable elec- tromagnet that draws the oil cup plunger by electric current controlled at a convenient point
��connected to a screw rod, as shown. A small electromagnet and a rheostat in series in the circuit will render the control of the oil cup quite precise. This device has considerable worth.— Peter J. M. Clute.
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