Elf ST/M - New motor belt = Faster sound speed!?!

[Dominique De Bast]

Maurice, I have not been explicit enough, I'm afraid. You're right about the 18 fps position. I have two Buckingham : one of them has a spare pulley that allows, in addition to the 24/18 fps to get a 16 fps speed (but I must admit I haven't tried it since it's complicated to change the pulleys). I was discussing this whith the French ninenfiver quoted in my preceeding message and he told me he got a 16 fps by changing the belt on the 18 fps position pulley. Some films shot at 16 fps have been projected at the monthly 9.5 projections in France, at 18 fps and it was noticeable. They were films without a sound strip, I can only imagine the sound would not have been correct. It may, as the films came frome the same filmmaker, depend on the camera (if it was shot at 15 fps, the film may look ok at 16 fps but not at 18 fps).

[Iain Warner]

My Elf RM3 double band projector was designed to project only at sound speed (24fps). The twin pulleys on motor are same size and cam tank pulleys also identical and the set up runs with twin belts. I presume this is to allow for the extra mechanical load imposed by the magnetic film drive which is driven by a flexible coupling on the feed sprocket shaft.
Anyway I inherited some film shot by my grandfather at silent speed, so taking a section of aluminium rod I turned up a smaller diameter double pulley to fit on the motor shaft, having calculated the required diameter to get 18fps. It is necessary to loosen the motor to change the pulleys but quite a simple job. It appears to work quite well and when the photo tachometer arrives I will be able to see how accurate my calculation was.
Most small engineering shops should be able to turn up a new pulley for the motor shaft, or even reduce the diameter of an original if you have a spare. I had to order a pair of shorter 'o' rings to use as drive belts as the cam tank pulleys were unaltered therefore the original sized belts would be too slack.
This may be a way for you to fine tune the projection speed.
Hope this is of interest.
Iain