International projectionist (July-Dec 1934)

NEW 0.945 SPROCKET CUTS FILM MUTILATION James J. Finn THEORETICALLY there is no connection between the super-sensitive ears of some motion picture projectionists and the introduction by International Projector Corp. of a new 35 mm. feed sprocket having a diameter of 0.945 inch. But, practically there is a direct connection — and therein lies a tale. The reasons back of the introduction of this new sprocket are of particular interest to the projectionist, the producer, the film manufacturer and the projector manufacturer. The base of this whole sprocket problem is none other than our old acquaintance and consistent troublemaker— film mutilation. For years now the standard sprocket has had a diameter of 0.935 inch. The reason for such a diameter is not quite clear — it just is, that's all. Of late, however, the consistent trickle of complaints anent film mutilation has steadily been enlarged into a raging torrent, fed by innumerable protests from theatres throughout the world. Obviously, something had to be done about the matter. But what? Widespread Film Mutilation First in line to receive the full impact of these complaints was the Eastman Kodak Company, which for many years has borne the brunt of this critical deluge. The Eastman technical force experimented lavishly, neglecting no possible fault-producer. Out of the welter of such intensive and prolonged work finally came the answer to the problem — a clear-cut declaration of the guilt of the sprocket, which was destroying hundreds of thousands of dollars worth of film stock yearly as it whirred unceasingly in picture theatres throughout the world. Eastman Kodak then turned to the International Projector Corp. Couldn't something be done about this matter of sprockets? Yes, answered International, something could be done, but time was necessary in which to conduct certain tests and carefully check the whole problem in terms of ten-thousandths of an inch, or even less. That something was done, and the result is now in hand in a new standard feed sprocket. 1 Sprocket Dimensions, J. Soc. Mot. Pict. Eng., XXLI (January, 1934), No. 1, p. 20. Into the Fall (1933) meeting of the S. M. P. E., held in Chicago, walked Mr. Herbert Griffin, technical pontiff of International Projector Corp., who proceeded to set the air in motion by voicing the results of an exhaustive investigation conducted by his company into this whole matter of sprockets. "Exhaustive" is certainly the word, for Mr. Griffin's paper1 ran to some 30 pages and contained 19 illustrations. Briefly summarized, Mr. Griffin said that it was time for a new deal in sprocket dimensions — and he proceeded to tell why. Months of work, scores of drawings and the records of extensive and exhaustive tests buttressed the Griffin statement, which figuratively mopped up the sprocket situation, particularly as it affects film mutilation, until the topic was as dry as a sunbaked bone. The New 0.945 Sprocket The net result of all this activity is a new sprocket of 0.945 inch diameter. Had Mr. Griffin taken into consideration the very important matter of film shrinkage, which vitally affect sprocket dimensions? He had; and to prove it he submitted a chart (Figure 1) which dealt conclusively with this angle. Were there any more questions? There were; and all were satisfactorily answered. It was shown, for example, that the 0.945 sprocket matched precisely the pitch of a film that had shrunk 0.15% and therefore had clearance all the way down the line. Theoretically, at this point all the sprocket teeth are in Fig. 1. Chart showing interference and slippage in relation to base diameter of feed sprocket, and shrinkage of film. Figures above heavy line indicate inters ference in inches between edge of perforation and entering tooth. Figures below heavy line indicate slippage in inches from leaving to entering tooth engagement, which constitutes an ideal condition. With the 0.945 sprocket the tooth that does all the work is the last tooth in contact with the film before it enters the lower loop — in other words, the outgoing tooth. This really is an ideal condition, because it constitutes a direct "pulling" action on the film. With the 0.935 sprocket, however, it is interesting to note that practically all the work is done by the incoming sprocket tooth (at the intermittent sprocket tension shoe), which gives poor results because it constitutes a very positive "pushing" action and causes "cramming" of the film. This snubbing action becomes more pronounced as the sprocket diameter is decreased within the range from 0.945 down to 0.935. Would the 0.945 sprocket help to effect a sharp decline in film mutilation? It certainly would and does, as has been conclusively established by an exhaustive series of test runs with long, short and medium-size lengths of film. Added up, the net result of these tests was that the 0.945 sprocket extended the average life of film at least six times beyond that possible through use of the 0.935 sprocket. Eliminated was that pushing, cramming and ripping action of the latter sprocket. Then, everything is fine, is it not? The answer is, "No, it isn't fine"; and the reason why it isn't fine is Mr. Projectionist of the group recently cited as the possessors of supersensitive ears. What is this heresy? What is the pseaNT 5H2//V/(A<5£ SP£<XK£7£>M. /A////C//£S. .345 .344 .343 .342 .34/ .340 o.o .OOO 23 .00047 .OOO 6 6 .00086 .00/06 .00/26 0./3 .00004 . 00023 .00042 .00062 .00082 .00/02 OJ5 .ooooo .000/3 .00038 . OOO 58 .00078 .00O98 0.2 .00003 .OOO/ o .OOO 2 9 .00043 .OOOG3 .00089 0.3 .00028 .00003 .OOO/ O .0OO3O .00050 .00070 0.4 .00047 .00028 . OO0O9 .OOO// .0003/ .OOOS/ O.S .OOO 65 .00048 .00029 .00007 .OOO/ 3 .OOO 33 0.6 .00084 .0004,5 .00046 .oooez .00006 .OOO/ 4 0.675 .00038 .0OO73 .OOO&O .00040 .00020 .OOOOO /.S .O0252 .00233 .002/ 4 .00/34 .00/74 .00/S4 [16]