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MANAGERS WD PROJECTIONISTS
660
One essential requirement to accurate work is that some method he found hy means of which the projectionist may ascertain the precise point at which the intermittent sprocket starts and stops. Guess-work will not answer, nor is the sense
of sight or of touch sufficiently accurate.
One very effective method which is universally available for ascertaining the exact, precise point at which the intermittent sprocket starts and stops, is as follows : secure a light, flat, straight strip of spring steel. A corset steel will answer very well indeed. It should be not less than six inches in length, and may be longer, though added length is no advantage.
Place one end of this strip of metal against one of the intermittent sprocket teeth when the sprocket is ''on the lock," in such manner that when the sprocket starts to move the tooth will press against it. Place the other end against anyconvenient, immovable object, in such manner that the spring will be under slight tension — bowed slightly. See Fig. 230a.
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Figure 230a
Under this condition it is readily seen that when the sprocket moves, the spring will be bowed up, hence the movement of the spring will be instantly visible, either to sight or touch, and the precise instant the sprocket starts to move is thus disclosed.
Having the spring in place, move the flywheel slowly, in the direction it normally runs, until the spring starts to bow up. Then rock the wheel backward and forward until the