ACCORDING to the author, gear clatter and clash caused by metal-to-metal contact develops into an annoying whir or howl at high gear-speeds, and a material was sought that is flexible and resilient enough to absorb the vibrations or change their frequency to a pitch inaudible to the average human ear. Since vibrations in the crank, the cam and the generator shafts are transmitted to the timing-gears, which run at high speeds, a material was needed that would silence the consequent noise and provide a noiseless timing-gear train. A great variety of materials was investigated and the development of laminated, phenolic, condensation products resulted; these have proved mainly suitable for timing-gear-blank stock and stock for other gears such as those suitable for crankshafts and generator shafts. A further development was that of the flexible-web cam-gear made of the composition material.
The product described is made by bonding together in laminated form various bases such as paper, linen, canvas, or sheet asbestos, depending upon the grade that is to be produced, with a synthetic, phenolic, condensation resin. This resin can be hardened, made insoluble, infusible, and chemically inert to a high degree by the application of heat. Therefore, when once so hardened, it cannot afterward be softened or dissolved. Canvas-base material is the grade used in the manufacture of timing-gears, and the paper is confined to it. The other grades of the product are made in much the same manner except that other materials such as linen and paper are substituted for the canvas.
Gears made of the composition material, will, it is claimed, obviate unsatisfactory service and noise; they admit of quantity production, reduce expensive tear-downs on the production line to the minimum and assure silent, positive operation after a car is in service. Such gears can be machined with the same equipment that is used ordinarily for machining metal gears, a high peripheral speed and a coarse feed being used to obtain the best results. The peripheral speed should be about 250 ft. per min. and the lateral feed about 0.025 in. per revolution, plenty of clearance being given to the cutting-tool. Ordinary, standard hobs are used for hobbing these gears; the highest possible peripheral speed should be used, with a feed of 0.075 to 0.100 in. per revolution.