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22
Transactions of S.M.P.E., January 1927
Fig. 2 represents a condition with freshly developed film. You will note at the intermittent sprocket that the film is in theoretical contact with the teeth from *'A" to '*B", that is, four teeth are engaged. On the takeup sprocket you will note that the film is held by the leaving tooth *'D" and as the film is practically of normal pitch you will note a slight clearance at "C", so that the film is held against the rewind tension by tooth "D". As the film leaves the sprocket at ''D" it will be engaged by the next tooth. As there is no resistance of the film to be fed forward by the sprocket, the film will cam off the leaving tooth and creep so that the next tooth is engaged.
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Fig. 2.
Referring to Fig. 3, the condition as shown represents film when shrunk about 1.5%, and referring to the intermittent sprocket you will note that the film is engaged by tooth "B", and as the film cams off the tooth "B" it is engaged by the next tooth. The advantage of the film being pulled by the leaving tooth is on account of the snubbing action between the film and base diameter of the sprocket. You will note that the film at "D" of the takeup sprocket is engaged, and there is increased clearance at "C", there being no interference at the entering tooth.
Referring to Fig. 4, this represents a condition of film with 2.92% shrinkage. You will note that the film is being moved by the leaving