International projectionist (Jan 1963-June 1965)

FIG. 3 — The Philips Norelco 70/35-mm projector cmploys a drive shaft instead of a pulley-and-belt arrangement for driving the takeup friction clutch. Construction of Tokeup Unit Fig. 1 shows ilif simple construction of a regular 35-mm projector takeup. A belt driven l>\ a pullej in the projector mechanism or soundhead runs the drive pulle) of the takeup at a constant speed. The reel shaft, or sj)in< I K-. i nut Fastened directlj to the drive pulley, however, but to a friction clutch which has the requi>ite degree of slippage. The clutch consists of two smoothfaced metal discs between which is a friction disc <>l leather, cork, or similar material. \\ ith no film in the projector, the coupling is complete, and the takeup spindle revolves at the same speed as the pullev . But when film is being taken up on a reel, the film, fed at a constant rate from the holdback sprocket of the soundhead, retards the rotation of the reel and causes the jriclion-dise and metal-flange clutch In slip while transmitting the rotary pouer. The larger the diameter of the roll of film on the takeup reel, the more slowly the reel revolves, and the greater the frictiondisc slippage. The Simplex projector, like most others, employs a leather friction disc. The Motiograph. however, uses a cork-faced discs to provide the same result. Leather discs should be relatively free from oil to work satisfactorily: cork discs should be soaked in projector oil. The speed at which the drive pulley of the takeup unit turns should be only very slightly greater than the speed International Projectionist November. 1963 required by the smallest reel-hub diameter used in the lower magazine. The high rotational speed required for the 1%-inch hub 1000 ft. reels (10 inches in outside diameter) places a great deal of tension on the film at the beginning, particularly when the tension spring of the takeup is adjusted to guarantee rotation of a fully loaded 2000-ft. reel. There is thus great danger that the teeth of the holdback sprocket will tear the perforations of the film at the commencement of a run when the diameter of the roll of film on the reel is small. In order to minimize this danger of damaging expensive film footage, pulleys should be selected which impart just sufficient rotational speed to the takeup spindle to wind up the film on reels having 31 ■_> or 4-inch hubs. When this is done, the projectionist should instruct his relief men never to use the small 10-inch (1000-ft.) shipping reels in the lower magazines. To disregard this precaution may result in a film jam-up or an ocean of loose film on the projection-room floor! Takeup Power Drive Most projectors have the old familiar pulley-andbelt transmission for the lower magazine film takeups. This type of transmission is capable of giving troublefree service only so long as the belt remains tight and firmh coupled by a strong, properly inserted metal staple. Cheap belting may be satisfactory on grandmothers sewing machine, but it simply is not good enough not reliable enough — for a motion-picture projector takeup. If the leather takeup belt stretches, it will slip on the pulleys and cause the film to wind up unevenly — or even to pile up in the lower magazine, jam the projector, Mi ip gears, and stop the show for the rest of the evening. \nd if the belt becomes so rotten that the coupling staple pulls out. the same dismaying result will ensure in an c\ en shorter time! A sprocket-and-chain transmission has been used FIG. 2 — The enclosed friction-disc clutch assembly of the Motiograph AA lower magazine takeup.