The Bioscope (Mar-June 1914)

THE Broscope, APRIL 30, 1914. stop governing the distance of the bearing roller from the sprocket drum is the film itself, and the film has to stand all the squeezing and grinding strain of a powerful spring. Fig. 1 illustrates the position the bearing roller should occupy in a machine designed with the object of minimising both film and mechanism wear. | Fig. 2 illustrates diagrammatically the type of roller mechanism sometimes employed, in which the full pressure of a powerful spring 1s acting on the surface of the film. If pressure b TENSION SPRING BEARING ROLLER ARM we FIG. 2. required on the film, why are sprockets 2mployed? We might as well return to one of the early experimental machines, in which the film was fed through by pressure rollers alone. The action of the bearing roller when prsss ing hard on the surface of the film as shown in’ Fig. 2 1s analogous to that of the steam roller, and, indeed, incredible enough though it szems. the pressure in many cases in relation to th2 area of contact and softness of emulsion is more damaging to the film than is the steam roller to the road surface. Why, then, employ such a barbarous method of engaging the film with the sprocket pins when actually no pressure whatever is required? The BEARING ROLLER SPrRock er FIG. 3. bearing roller has no need to press on the surface of the film, and its action should be just that of a guide, which to reduce friction is per' mitted to revolve.( 8) 33 ‘| ates this in section. US! oi tg re eS —o ei 5=5 Machines in which bearing rollers press on the film without any means of adjustment should either be avoided, or the manufacturers instructed to provide some means to give the necessary clearance between the roller and sprocket. Some projectors are constructed with rollers fitted so that they come to rest always at some predetermined distance from the sprockets, a simple method that has very much in its favour. Many projectors are fitted with an adjustment to regulate the distance between the roller and the sprocket drum. TI requently, however, this adjustment is altogether ignored. It 1s certain that a machine supplied with adjustable rollers should be used in conjunction with an operator well versed in the saison d'etre of the fitment, and the damage likely to occur if the correct ad justment be disregarded. Fig. 4 illustrates a sprocket with a bearing roller fitted with an adjustment incorrectly set, ApsJUS TING SCREW. BEARING ROLLER PRESSING ow SPROCKET. FIG. 4. INCORRECT SEFTING OF BEARING ROLLER ON SPROCKET \WHEEL. whilst Fig. 5 shows the same fitting, but with the adjusting screw set so that the roller allows ample room for the passage of the film. In connection with this, the adjusting screw should always be fitted with a lock-nut as illustrated, or there is danger of the screw working loose, so allowing the roller to press on the film. It is in connection with the adjustment that the human element plays an important part, and frequently operators totally disregard its importance. ‘Take care of the adjustment of the rollers, and the film will take care of itself,” is a fair truism, inasmuch as wear and consequent damage to the sides of the film is concerned. Another and important point regarding the life of the film is in connection with the size of loop used. Many operators employ an unnccessanily large one, the consequent flapping doing much to damage the surface of the film. A small loop just sufficient to allow of the frec action of the ‘ntermittert mechanism is all that is neéded!