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410
Transactions of S.M.P.E., August 1927
Take-up sprocket holds film against rewind tension by leaving tooth D and allows clearance to entering tooth C. This condition holds until film is shrunk 0.78 per cent.
ecpecsc/^Ts a condition witm film shbunkcn i.so t euNNiNO ON speocKtTs with dimensions as
PeOPOSCD AT PAQIS CONFCeCNCC
ZCQO
SO % SMBUNK SMOMTi
CtlABT V
I— C55 TOOTH THICK NC5S
CHART V
Sprocket dimensions proposed by Paris Congress
Tooth pitch same as perforation pitch of film shrunk 0.78 per cent.
Film shrunk 1.5 per cent; i.e., old film.
Intermittent sprocket engages film at leaving tooth B leaving clearance at entering tooth A. This good running condition occurs at 0.78 per cent shrinkage and holds until film has shrunk 2.89 per cent.
Take-up sprocket engages film at entering tooth C. When next tooth E engages film, either (1) film is pushed forward, (2) film chmbs sprocket tooth or (3) perforation is torn. This condition occurs at 0.78 per cent shrinkage and is more aggravated the greater the shrinkage.
The Committee finds that the maximum shrinkage of useful film is 1.5 per cent and recommends a take-up sprocket designed accordingly. The shrinkage of newly processed film for which the feed and intermittent are designed is 0.13 per cent. These latter sprockets as has already been shown will accommodate film shrunk as much as 2.92 per cent without damage. Dimensions of sprockets to produce these results are illustrated in Charts A, B, and C. The essential dimensions are:
For take-up Base diameter 0.9321 in. (23.67 mm.)
Sprocket Tooth 0.050 in. (1.26 mm.)