We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
about .2 % swell to approximately 3% shrinkage. Serious damage is done to the film unless the film sprockets are carefully designed to accommodate these varying conditions.
A good design, therefore, should produce a sprocket which will run with film having .2% swell to 3% shrinkage without destructive interference. Absence of interference does not mean that the best running conditions will exist throughout this entire range for the reasons which will be explained and illustrated by lantern slides.
A comparison of a large number of laboratory wear and tear tests indicates that with a large percentage of sprockets now in use, the least destructive effect is shown when the film being run has shrunken or has a shorter pitch than the "identical" or actual pitch of the sprocket. With this condition, the driving of the film is done by the leaving tooth so that we may assume this to be the best running condition, except the theoretical condition of perfect mesh or "identical pitches" for both film and sprocket, which rarely, if ever, exists.
There is one fact that should be considered and that is, only one tooth in each row of teeth of a sprocket within the arc of contact can possibly be in driving engagement with the film perforations, except under perfect condition, as aforesaid, when the pitch of the film being run is identical with that for which the sprocket is designed.
For the purpose of illustration, let us assume a condition of perfect mesh between film and sprocket, that is, where every tooth in the arc of contact is in perfect contact with the edge of the corresponding perforation, as shown in Figure 4. Now let us assume rotation
MOTION PICTURE FILM IN MESH WITH FILM SPROCKET
Ideal condition, perfect mesh, all teeth are drivers, pitch of film identical with that of sprocket.
Fig. 4.
to be given the sprocket. Also assume that the film has suddenly stretched or swollen so that the pitch (or distance from center to center of perforations) is longer than the distance from center to center of the sprocket teeth (measured along a circle approximately .003" above the base of the teeth) , then the only tooth bearing against the edge of a perforation would be the entering tooth as at "A", Figure 5. If the film should continue to elongate, there would then be interference on the back of the leaving tooth, CC", Figure 6. This is the condition which occurs when unshrunken film, or film having a small
57