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THE FILM ll|l
round 5/16 inch cold rolled steel or drill rod. Remove the old shafts and make the new one like them except in length. Pulleys can be secured by your hardware dealer, or can be made for you by your local machine shop. To increase the rewinding speed in an emergency it is only necessary to have an extra belt to reach directly from motor pulley M to pulley K.
(59) Immediately above the rewinder stretch a short length of film connected with the port fire shutter master control. A fire at the rewinder will burn the bit of film, thus instantly releasing the fire shutters.
Calculating Rewinder Pulleys
(60) As already noted, rewinding speed should not exceed the rate of six minutes for each 1,000 feet of film. The rule for computing the speed of pulleys is as follows: multiply the speed of the driving pulley per minute by its diameter and divide the sum by the diameter of the driven pulley. The result is the speed of the driven pulley.
The circumference of the driven and driver pulleys may be used for the calculation instead of diameters. The result will be the same. If we have a motor pulley two inches in diameter (diameter of the face of pulley) running 1,400 revolutions per minute, and propose to drive a countershaft pulley six inches in diameter, you have 2 X 1,400 = 466.6 revolutions the counter shaft would run per minute. If we then propose to drive a 10-inch diameter pulley mounted on a rewinder with a two-inch diameter countershaft pulley, the reel upon which the film is being rewound would run 466.6 X 2 = 933.2 -T 10 = 93.383 revolutions per minute.
Stated in proportions — the diameter of the driver pulley is to the diameter of the driven pulley as X is to the revolutions of the driver pulley. For the solution, multiply two extremes (end quantities) and divide by the known middle number. Result will be the revolutions per minute of the driven pulley.