Richardson's handbook of projection (1927)

631 HANDBOOK OF PROJECTION FOR line. This may be roughly tested, so far as the intermittent and upper sprockets be concerned, as follows : Thread a piece of new film into the projector, engaging it with the teeth of the upper and intermittent sprockets, closing the idlers. Turn the fly-wheel backwards until the film is stretched tightly. If the upper and intermittent sprockets and the aperture are in the line with each other, that fact will be evidenced by the film-edge being out of line with the tracks on the aperture plate, or the aperture being out of center in the film. If the film seems to bear equally on both edges of both sprockets, and the aperture plate tracks are not straight with the film, it would indicate the probability that the aperture plate itself is out of true. In some propectors this may be easily remedied; in others the aperture plate cannot possibly be out of true, and the indication would be that both the upper and intermittent sprockets are too far over to one side. Before making this test you should be sure the intermittent sprocket shaft is in exact alignment with the cam shaft, because if one end of the intermittent shaft be high or low, the intermittent sprocket will not be square with the film. This condition is not possible except on projectors in which either end of the intermittent sprocket shaft may be raised or lowered independently of the other end. GENERAL INSTRUCTION NO. 5— ADJUSTMENT OF INTERMITTENT MOVEMENT.— When the intermittent movement is on the "lock" its adjustment should be such that there will be very little circumferential movement in the intermittent sprocket, but care must be exercised that the adjustment be not made too close or else there will be undue and unnecessary friction of the parts. These adjustments are usually made when the projector is cold, and it must be remembered that under the influence of the heat Figure 224.