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The Light
on Your Screen
By CHARLES E. SHULTZ
[^Due to illness, Mr. Shultz has had to limit his department in this issue to the following article and "Reminders." — Editor.]
Putting a 1916 Projector Into Wartime Service
CLAUDE HARTMAN, JR. of
Hanover, Pa., writes, "I own a Powers 6-A mechanism. I rigged it up to show sound film and had to increase the speed from what the machine was normally designed to run. It's a 1916 model, according to the last patent date on the front plate.
"Here is the trouble: A slight loop forms between the bottom of the aperture plate and intermittent sprocket regardless of how tight the shoes are adjusted with the screw on the cooling ^late. When I add pressure with my finger at the top idler, or a little above this point against the upper part of the aperture, the loop disappears and the picture crawls down on the screen slightl3^ It does this with any film.
"The cam and cross are in good shape and the sprocket is not undercut. The bushings are not worn. There is one condition that exists that I think may cause the trouble, but don't want to make any changes until I'm sure. It's this:
"The surface of the aperture is about 1/16inch above the face of the sprocket: that is, when a steel rule is laid on one of the tracks of the aperture plate, it won't touch the sprocket, but will miss it by about that much. The film has to bend away from the tension shoes as soon as it leaves the aperture plate in order to hit the sprocket. I work in a machine shop and can make any changes that you may suggest. If this is the trouble, I can plane off the pads under the aperture plate.
"There is a slight unsteadiness to the picture when running normally and with any amount of pressure given to the shoes, but when extra pressure is added, the picture crawls down a little and becomes rock steady. By extra pressure, I mean pressure vvith the finger.
"A new aperture plate is masked to cut off the sound track; I had the shoes ground off straight and it fits evenly on the plate.
'The tension is so excessive when the shoes are in as far as they will go that I can hardly turn the flywheel by hand, but the loop still persists. Maybe this condition exists in all machines. However, there seems to be something radically wrong some place." ^ I believe you indicate that you have solved your own problem, Mr. Hartman, when you suggest that the trouble lies in the misalignment of the film tracks and intermittent sprocket face. This is definitely not supposed to be the case in any machine, and I say this after a careful checkup with the manufacturer of the projector.
If you work in a machine shop, you can correct this condition in exactly the manner that
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The Seventh Edition of this standard textbook on motion picture projection brings to all persons concerned with screening35 mm. film, up-to-the-minute guidance. Additionally, the Seventh Edition contains four chapters on Theatre Television, prepared for the practical Instruction of motion picture projectionists. Send your order to —
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BETTER THEATRES, JANUARY 6, 1945
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