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A NON-CINCHING FILM REWIND MACHINE* L. A. ELMER**
Summary. — Cinching, or the sliding between layers of film within a reel, produces scratches and surface abrasions which increase the film noise level. Cinching is] more likely to occur in rewinding than anywhere else in the normal usage of sound-film. At the beginning of rewinding, when the supply reel is full and the take-up reel is'i empty, a small amount of torque is nseded for rotating the take-up reel. Under this\ condition the film will be wound rather loosely. When the supply reel is nearly\ empty, relatively high film tension is required to produce a given torque on the supply] reel. The torque to be applied to the take-up reel will then be high, on account on both the high film tension and the large radius arm of the film spiral on the reel. Thisl high torque is almost certain to cause cinching in the loosely wound bottom portion 0/1 the reel. The conditions to be satisfied if cinching is to be avoided are analyzed. A jj power-driven rewind is described which meets these requirements. The film tension is\ controlled by the weight of the film on the supply reel at all times during the rewind.-!
It is generally known that a sound-film record becomes more noisy ; with successive play ings. Some of this increased noise is the result ! of dust and grease which accumulate on the film while it passes through the projector. More of it is caused by scratches and abrasions on the film. In modern projectors and sound-heads and other film-handling machinery, that area of the film which carries the sound record never comes into contact with anything which could mar its surface except the adjacent layers of film on the supply andji take-up reels. The sound record areas of film, therefore, should '. suffer very little damage during projection if sliding of the layers of ffilm within the reels is prevented. In every operation involving the ; handling of stereophonic films, care was taken that this sliding or, cinching did not occur.
A rewind machine was needed that could handle a 2000-f t reel of film rapidly and protect the film from cinching and exposure to even small amounts of dust. A commercial automatic rewind machine j was found where the film was wound directly from the upper supply j
* Presented at the 1941 Spring Meeting at Rochester, N. Y. ; received March 14, 1941.
** Bell Telephone Laboratories, New York, N. Y.
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