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1952 Theatre Catalog, 10th Edition, Page 298 (262)

1952 Theatre Catalog, 10th Edition
1952 Theatre Catalog
1952 Theatre Catalog, 10th Edition, Page 298
Page 298

1952 Theatre Catalog, 10th Edition, Page 298

FIG. 21. Intermittent film guide and bolder (older type).

ten be traced to an accumulation of dirt at the base of the intermittent sprocket teeth, rather than to low trap tension. Bands on new prints from the exchange usually carry a sticker, noting that it is a new print or that the tension should be reduced, but in the case of many older ty'pe projectors still in use, this means that the double-pronged springs would have to be removed and bent by hand. These springs would have to be bent back again for use with older film. Since they were never intended to stand such repeated bending, it is advisable to adjust them to give the minimum tension which will give good steadiness with older prints.

Tension on Upper Magazine Shaft

Proper adjustment of the spring tension on the feed spindle is important. If set too loosely, the film may come from the feed roll with a jerky motion. This is especially noticeable when the roll is loosely wound or if a bent reel is used, and is particularly bad for film in a noticeably worn or dried out condition. If the tension is too tight, the pull on the last forty or fifty feet might be sufiicient to cause serious perforation breakage, more so if a small-hubbed reel is used. It is not at all uncommon to lose the upper loop or for the film to break under this strain,

ln'l'ermii'II-eni' Film Guide

Considerable sprocket and film dainage may be attributed to improper setting of the intermittent film guide or shoe (Figure 21), the intended purpose of which is to hold the film snugly against the sprocket. The older type of guide holder shown can easily become sprung if excessive upward pressure is applied in attempting to remove a snugfitting trap door from the older type holder. When replacing such a door or plate, care should be taken to see that it is seated properly, otherwise the sprocket may be badly damaged. A loose-fitting holder should also be repaired, since this might allow the sprocket teeth to strike the inside walls of the guide due to the slightest side motion. It has been common practice to deliberately bend the older type guide holder by hand, either to insure better contact of the film with the sprocket, or to eliminate the "clickingil due to cons tact with the teeth. Improved design and construction and the two-stud trap door

locking arrangement on neWer projector models has greatly reduced the possibility of trouble from this source.

Some projectionists prefer to use a light guide spring, since they claim it is easier on the film and allows stiff splices to pass with less effort. Others insist that heavier pressure at this point gives a steadier picture, even though the trap tension might be lower than usual. Instances have been noted where two of the newer cone-type springs were nested together and used as a single spring in order to obtain heavier pressure against the film at the sprocket. It is obvious, however, that if the pressure at this point is unnecessarily high, the film wear will be greater and the sprocket may become rimmed in a short time.

Bad Sprockets

Through carelessness and neglect, intermittent sprockets are frequently kept

in service until they develop pronounced cuts or are otherwise so badly worn as to cause serious perforation damage. This is particularly true if the trap tension is excessive or if poor guiding allows the bad teeth to strike the perforations noticeably off center. Although present day sprockets are hardened in order to give longer service, the teeth are often so badly damaged that small pieces of film are torn from the pulldown edges of the perforations. Even the smaller cuts in worn sprockets result in noisy operation, since they prevent the film from leaving the sprocket freely. Noisy operation and serious film damage are even more liable to occur when an excessively large IOWer loop is used.

Sprocket teeth which have knifeslike edges resulting from contact with the inside walls of the metal guide, cause the small straight cuts parallel to the edge of the film, extending downward

FIG. 22. Intermittent sprocket tooth damage.

1952 Theatre Catalog, 10th Edition, Page 298