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erating" operation, it would be necessary to provide a rack and pinion movement, the rack being attached to the body or head of the lathe and the pinion loosely mounted on the spindle that carries the sprocket wheel. An index disc should be attached firmly on the shaft that carries the sprocket wheel, the index being used for the purpose of changing the relationship between the sprocket wheel and the pinion. The pitch diameter of this pinion should be equal to the diameter of the sprocket wheel plus one-half the thickness of the film. The rack should be placed on the same side of the gear as the end mill for forming the teeth. Thus, the pitch line of the rack and gear would be the same as the pitch line of the film and the sprocket teeth.
It would be necessary to eliminate from the rack and pinion connection all possibility of lost motion and for this purpose it is probable that a double rack, adjustable endwise, such as is used on profiling machines, would be desirable for the purpose.
Fig. 8 Enlarged view of tooth and cutter only, with tooth in section, and on a line near the end of the tooth where it comes in contact with the matter.
It will be seen by the accompanying sketch that when the carrier of the sprocket tooth is moved up or down the connection of the gear with the rack will give the sprocket a rolling movement, and if the sprocket wheel and tooth are positioned so that when the center of the sprocket shaft reaches a point on a line horizontal with the center of the forming cutter, and the center of the sprocket tooth will at that time also be in the same line, the rolling motion given to the sprocket tooth as it enters and leaves the opening in the cutter will apparently form the tooth in accordance with the requirements.
It has been my opinion, and I believe it is generally agreed, that the best results can be obtained by the use of rectangular perforations because in that case after rounding the corners of the teeth with a forming cutter, the sides and ends of the teeth could be ground. This too
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