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THE PROJECTOR 217
movably. The picture is projected and the cycle of action is repeated.
Constructional Details
All reputable manufacturers use only the very finest materials in constructing their intermittent movements. The shape and diameters of the sprockets and the dimensions and spacing of the sprocket teeth are all measured in 10/1,000 of an inch. (38) Any sprockets, stars or cams failing to come within two 10/1,000 of an inch of the correct measurements are rejected.
All intermittent parts are finished by a very high speed, precisely accurate grinding processes. (39) In modern intermittent movements the cam and star are always hardened, but the intermittent sprockets sometimes are not because it was discovered that hardening causes undercutting in the form of a notch in the metal at the base of the sprocket teeth. Teeth not hardened wear off smoothly.
(40) Faulty functioning of the intermittent movement will be magnified on the screen, in the form of an up-and-down movement, as many times as 0.600 is contained in the height, in inches, of the screen image, provided the trouble is due to faulty rotation of the intermittent sprocket. Any lateral (sidewise) movement of the intermittent sprocket will be magnified on the screen as many times as 0.825 is contained in the width, in inches, of the screen image.
Intermittent Lubrication
(41) Considering the foregoing it is obvious that such movements must be lubricated with carefully selected oil. Many theatre managers refuse to buy high grade oil, and .then wonder why intermittent movements cost so much for repairs and replacements. It is best that projectionists use no oil in the intermittent movement oil well except that recommended by the manufacturer. Never use light household oils as they will bind up the intermittent movement quickly — and ruin it. The intermittent oil well should be drained and filled with fresh oil following each 100 hours of opera