A Workshop Accessory
Page 40
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of All-round Value
MHE advantages of an electric motor for small machine tools, etc., which will maintain an absolutely constant speed without the necessity of a hand or foot-operated rheostat are obvious. Such a motor has lately been put on the market by a French concern, the Socie'te de Recherdes Mecaniques et Physiques, 40, Rue de l'Echiquier, Paris.
This appliance is fitted with a centrifugal governor, controlling the current, and as the spring tension of the governor can be varied, the motor can be set to turn at any desired speed. By reason of the governor the speed is not affected by the varying resistances which the tool may encounter during its operation. Cylinder grinding may be taken as a case in point, where the R.M.P. motor makes for greater accuracy.
The ordinary electrically driven grinding wheel starts on its travel turning at a certain speed, but if the resistance to be overcome increases, the resulting cylinder bore will be slightly conical as the grinding wheel will lose speed. The 826 governor of the R.M.P. motor adjusts this automatically.
This constancy of speed is of value in various forms of laboratory work, and an example may be found in the Stroborama or stroboscope lighting apparatus, which is also manufactured by the same concern. Here, the governed motor is employed to turn the rotary interrupter of the synchronizer. An interesting demonstration of the Stroborama was given during the Paris Aviation Salon. Two large " windows " had been cut in the head of a cylinder from a Clerget aviation oil engine and fitted with special glass..
An electrically driven air pomp brought the pressure up to the required point, and the jet of heavy oil was injected by a normal type of fuel pump. The " windows " were placed on opposite sides of the cylinder and the stroboscope lighting entered through the rear window, brilliantly illuminating the interior of the cylinder head.
The fuel jet could be ,seen slowly emerging, an event which, actually, takes only an infinite fraction of a second. Owing to the stroboscope, it appeared to take several seconds, and the form of the jet could be studied in detail.