International projectionist (Jan-Dec 1946)

TH •^r^;. ■•• — "1 FIGURE 2. Schematic of main drive shaft. and simply removed or replaced in operating position. The soundhead's drive unit is locked into the socket shaft by the set screws [items 2 and 5] and the heavy-duty pinion | item 4] is fixed on the tubular shaft by the item 6 key. The large end of the shaft is provided with a belt groove for driving lower magazine takeups when the projector is operated with certain older sound reproducers having no takeup drive facilities of their own. This drive construction eliminates the possibility of damage to projector gears due to poor alignment between the projector and soundhead. There are no long sleeve bearings to bind from inadequate lubrication, and since the drive shaft requires no additional lubrication during the long life of its sealed ball bearings, the risk of damage to soundhead optical components from excessive oiling and oil leaking is eliminated. Charting the Film Path The extreme roominess of the AA provides for threading simplicity. The film enters the projector from the upper magazine through a fire-trap unit having four quenching rollers running on greaselubricated pivot bearings. Between both upper and lower rollers there is a long chute to aid in the quenching action. From the fire trap the film passes to the upper feed sprocket, upon which it is held in place by the combined action of the sprocket's pad roller and the hardened steel guide roller just above and to the right of the sprocket. The film is thus guided smoothly over the sprocket, engaging six full perforations, and there is thus no tendency for it to jerk or slap because of uneven holdback tension from the magazine. This increases film life. The film loops upward from the upper feed sprocket and then passes down through the gate to the intermittent sprocket, around which it passes in a clockwise direction to form the lower film loop. For best alignment and for proper engagement of the sprocket and film, the tension shoe assembly is made part of the intermittent assembly itself. The leaving-end of the lower film loop passes over the lower feed sprocket clockwise, and the film then travels downward to the sound reproducer. Double pad rollers on this sprocket insure sufficient engagement between sprocket teeth and film perforations to block the pulsating film travel produced by the intermittent movement. The film is fed smoothly to the reproducer, thus the film motion stabilizing system does not have to cope with the irregularities produced by the intermittent action. A distinguishing feature is that the film path below and to the right of the lower feed sprocket is completely clear of all obstructions except for the cast stripper for this sprocket. This allows plenty of lual addition ol such auxiliary equipmi nl as double-film attachmenl and controltrack; pickup facilities. For the former, the strippei mounting boss is so located and designed as to permit the substitution of another doubli pad roller assembly for the stripper, so the bottom of the feed sprocket may be used to feed the separate sound Hack film in the sound reproducer, with the picture film going across the top of the sprocket and thence by an external chute, to the picture film takeup magazine. There is likewise adequate clearance below the feed sprocket to accommodate the feed and guide rollers of a new doublefilm type of sound reproducer requiring no external chute and no projector modifications. The Film Gate Assembly The film gate of the AA, when opened forward, provides a full inch clearance between tracks and tension shoes, thus allowing really adequate finger room for threading and for routine cleaning of aperture, tracks, shoes and guide rollers [Fig. 3]. The two long film-tension shoes extend the full length of the film tracks, and for perfect alignment they are combined into a single rigid unit of hardened steel. The film contacting surfaces are ground and polished. This unit is held to the gate assembly by studs at the top and the bottom which engage a unique gunlock mechanism within the gate body. The studs snap into operating position as they enter their locating slots in the gate body face. They space in this region for the possible even FIGURE 3. Film gate, shown closed here, opens a full inch for threoding. Top knob at right is the lens lock, lower knob is for lens focus, both being on front of the head. To the right of these knobs, but not shown here, is knob for shutter setting. INTERNATIONAL PROJECTIONIST December 1946 13