Motion picture projection : an elementary text book (1928)

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MOTION PICTURE PROJECTION 551 proper position. Now replace gear G-112-G, P.4, making sure that the squared-off face on inner side of gear locks into position with corresponding square clutch facing of main driving clutch C-126-A, P.4. Failure to properly engage these two clutch facings will result in both gears only partially meshing with resultant damage to teeth. Now replace screw S-209-G, P.3 and close both left hand doors of mechanism. This completes all of the operations on the left hand side of the mechanism. Now push locks L-116-B, P.2 back into place so that they engage with framing ring, R-133-A, P.l, and tighten up screws S-157-B, P.2, after which the collar C-192-G, P.2 is placed upon shaft of intermediate gear G-134-G, P.3, making sure that set-screw in collar is tightened against the flat surface of shaft. ADJUSTING THE STAR AND CAM The intermittent star and its mate, the cam, can easily be regarded as the most important units in the entire mechanism. The function of these two accurately-finished and almost microscopically-measured working parts is to pull the film down before the aperture position and hold it rigidly in a standing position while it is being exposed upon the screen. This means that during the showing of 1000 feet of film the intermittent movement must start and stop without back-lash or vibration 16,000 times. As can be imagined, this constant start and stop imposes a tremendous strain upon these two finely-adjusted and perfectly-finished parts, yet they are so constructed and of such splendid material that the well-known