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1952 Theatre Catalog, 10th Edition, Page 299 (263)

1952 Theatre Catalog, 10th Edition
1952 Theatre Catalog
1952 Theatre Catalog, 10th Edition, Page 299
Page 299

1952 Theatre Catalog, 10th Edition, Page 299

I theatres over several years have shown

I that this new sprocket gives longer film life and less sprocket wear than the older 0.935-inch base diameter sprocket. The new sprockets are now being supplied as regular equipment by a few projector and parts manufacturers and it is expected that the new standard will soon be accepted universally.

Even the new sprocket does not fit present day low shrinkage films in the manner shown by Figure 23 but it does approach this desirable condition. The new 0.943-inch diameter sprocket has been chosen as a standard on the basis of the best performance now available within the limits of designs that have been proven by extensive trade usage. It is quite possible that further work. and further improvements in film may suggest a still larger diameter sprocket at some future time.

/ / Film Loops

Excessively large loops not only result

FIG. 23. Illustration of excellent fit of older type FIG. 24. Illustration showing poor fit of present t ' r. i n and in some instances film having higher shrinkage with a standard 0.335 low-shrink film with standard 0.935 inch d ameter lgdno'isy ope a? b t l 1

inch diameter sprocket. v sprocket. Note interference at top tooth. 51 BVV 155 unSted IneSS; u may a so a ' from the pull-down edges of the per-fora- FIG. 25. Exposed edges of film damaged during shipment, or when unevenly wound rolls are forced

. r i t "d' h d" . tions and well in from the corners. These m o a 15 a case

small cuts quickly develop into more serious damage which can soon result in complete breakdown. In Figures 22C, D, E and F, examples are shown of the more severe types of tooth damage found on intermittent sprockets from theatre service. Figure 22A shows a new tooth and Figure 22B illustrates the typical slightly curved face cut commonly seen on normally worn sprocket teeth.

0.943-lnch Base Diameter Sprockets

A great deal of work has been done by the motion picture industry which has shown that the projection life of film is considerably prolonged if the intermittent sprocket is at least as large or larger than that required to give perfect mesh of the sprocket with the film being driven. Obviously, the conditions for perfect mesh of the film with the sprocket are intimately associated with the shrinkage of the processed film. In recent years, the shrinkage characteristics of motion picture films have been greatly improved, so that a sprocket of greater base diameter is now preferable to the 0.935-inch base diameter intermittent sprockets previously accepted as the standard size for older type films having greater shrinkage properties. Figure 23 illustrates how well the older type films having higher shrinkage characteristics than present day materials, fit the previously accepted 0.935-inch base diameter sprocket when that standard was adopted. Figure 24 shows how present day lower shrinkage films no longer fit this earlier type sprocket. Note that it is the entering tooth which contacts the perforation edge and moves the film rather than the leaving tooth, as in Figure 2: .

In 1947, an intermittent sprocket having a 0.943-inch base diameter was approved by the Society of Motion Picture Engineers and the American Standards Association. Careful laboratory tests as well as comparative tests in many

1952 Theatre Catalog, 10th Edition, Page 299