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690 HANDBOOK OF PROJECTION FOR
use worn film for this purpose) in the mechanism with the gate open. Place it on the intermittent sprocket and close idler bracket. Engage sprocket holes on film with teeth of upper sprocket and turn flywheel backward until film is stretched tightly, being careful that teeth are in centre, sidewise of sprocket holes. If sprockets and aperture are not in perfect alignment the fact is readily detected by the film edge not being in line with tracks on aperture plate, or aperture not being central in film.
If film seems to bear equally on both edges of both sprockets and the aperture tracks are not straight with film, it would indicate aperture plate out of true. Gently drive its top one way or the other, as is required, to square it with the film. The first thing to do, however, before making the test is to be certain your intermittent sprocket shaft 666, P-2, is in exact alignment with camshaft 675, P-2.
INSTRUCTION NO. 37— REMOVING THE FRAMING CARRIAGE. — To remove the entire framing carriage of the mechanism, first remove the aperture plate (see Instruction No. 16) and the gate (see Instruction No. 11). Next remove the screw 741, P-4, turn the machine around and, looking in through the lens hole, you will see two perpendicular rods the top ends of which are held in cast lugs. Loosen the set screws in these lugs and in similar lugs at their lower ends, and pull these perpendicular rods out from below. Next remove horizontal bar 683, P-3, by taking out screw 731, P-3. The carriage may then be taken from the machine.
INSTRUCTION NO. 38— LUBRICATING GEARS.— See
"Gear Lubrication,'' under General Instruction No. 1.
INSTRUCTION NO. 39— TO THREAD THE MECHANISM.—See General Instruction No. 20, with the notation that if there be a loop setter the film must pass under its roller, A, P. 10, and should just clear it when the lower loop is at its shortest.
INSTRUCTION NO. 40—THE LOOP SETTER.— The Powers loop setter, illustrated in Plate 10, is a simple device which operates well. It automatically re-sets or re-forms the lower loop whenever it is "lost" by reason of any one of the several causes which may be responsible for this very annoying thing. Plate 10 shows the film forming the lower loop around roller A. When the loop is lost (drawn taut), the roller is necessarily elevated, thus causing a slight ro