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Arri SB Pressure Roller


Serge Gregory

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I have an intermittent problem when filming with my Arri SB. Several times in the middle of a roll nothing happens when I press the start button, indicating to me that there's a film jam of some sort. When I put the camera in a changing bag and open it up, I'm able to restart simply by opening and closing the pressure roller assembly. In a previous roll this happened only once and the developed film looked just fine. In the current roll, I've had to restart a couple of times and I'm beginning to find it annoying. Any ideas about what could be causing this? Would an inadequate top loop do this? Something's causing the pressure roller to pop open and prevent filming.

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I assume when you say "roller assembly" you mean sprocket drive, right? 

Depending on the year of your camera, I believe there is a little lever below the rollers that can shut off the camera if the bottom loop gets too small. Does your camera have that buckle switch? 

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Yes, I do have a buckle switch. I looked it up in the manual (ahem, maybe I should have gone there first. . .) So it looks like the buckle switch is kicking in because my bottom loop is too short. Before I shoot again, I'll open the camera up, enlarge the bottom loop and open/close the sprocket drive one more time. Hopefully that will solve the problem. I didn't think of this because I was sure that I had made the bottom loop plenty big when I first loaded the film. But perhaps not--I still find loading the Arri S properly a bit nerve wracking. Thanks for responding.

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I wrote this just as you posted your response Serge:

Read pages 15, 16 of the manual, regarding the buckle switch:

http://www.visualproducts.com/pdf/Arriflex16SManualArri16SManual.pdf

If the lower loop is too short (or the pressure roller assembly is opened) it will trip the buckle switch. Opening and closing the pressure roller assembly resets the switch.

If you think your loop is fine, it could be the pressure roller assembly is not properly latching closed for some reason and opening during filming, maybe the film is not correctly engaged with a sprocket roller.

 

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To finish up this thread, what I discovered after I successfully shot my roll and then examined the take-up film path in daylight is that the buckle switch is extremely sensitive. The slightest touch triggers it. Is this normal? Can the tension be adjusted? The lesson seems to be sure to make the bottom loop as generous as possible so as to keep it away from the switch. Do I need to be concerned about making it too big and scratching the emulsion?

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Yes it’s meant to be pretty sensitive. As long as you set the lower loop exactly following the white arrow (with the film pin registered in the gate) it should clear.

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2 hours ago, Serge Gregory said:

The lesson seems to be sure to make the bottom loop as generous as possible so as to keep it away from the switch

Yep, it's about making the bottom loop perfect. It's a very sensitive switch. You want it that way so when it looses the loop, generally by accident or if something goes wrong, that the camera won't just keep running. On the 35mm cameras that use it, this is very important because of the film speed associated. On the 16mm cameras, less important. 

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