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THE PROJECTOR 237
Lubrication of Bearings
(103) One drop of oil, or two at most, is ample lubrication for any projector mechanism bearing. The mechanism will throw off more than that, making a dirty mess and spotting the film. Use a medium-sized oil can having a fairly long spout with a small opening. Invariably, except in the hands of a very careful man. a big oil can with a generous spout opening will result in overoiling.
Sprocket Idlers
(104) The function of holding the film close to the face of the various sprockets is performed by sprocket idlers, consisting either of one or two rollers per sprocket or a thin steel shoe. In all modern projectors one or two rollers are used for all sprockets except the intermittent. Here Simplex uses a thin steel shoe.
Whether it is a shoe, a roller or rollers (some projectors have two rollers to each sprocket and some only one), the rule is (105) that the distance from the face of the roller or shoe to the face of the sprocket must be approximately one and one-half times the thickness of the film. (106) To arrive at this lay two thicknesses of film on the sprocket and adjust the roller bracket or the shoe firmly against the film with the adjustment screw in firm contact with the stop it rests upon.
(107) If the shoe or roller is too close to the sprocket face it will pinch the film. It will then start a tendency to side-weave, causing the sprocket teeth to climb out of the sprocket holes. If the shoe or roller is too far away the same condition may be brought about, though for a different reason, resulting in the loss of one of the loops. Proper adjustment of sprocket idlers is important.
(108) It is also important that each end of the sprocket idler is exactly the same distance from the sprocket face, since any variation will cause the film to pull sidewise away from and off the sprocket teeth. (109) If the idler is a roller it must be kept well lubricated with a thin oil, else it will stick and quickly wear flat on one side. In that case it must be replaced imme