This is topic Filter sliding down on Christie brain in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Manuel Francisco Valencia (Member # 710) on 05-14-2001, 03:20 PM:
I have this problem on two platters now. The arm on the brain always stops at about 50 degrees and cannot go any further because the filter has slid down its shaft and is hitting the take up bar. I always lift back up and tighten it into place but it always comes back down. When it happened to the second platter I felt an awful lot of what seem to be lubricant. Is it possible that the bearing above the filter broke and the lubricant ran out?
Posted by Paul G. Thompson (Member # 655) on 05-14-2001, 05:21 PM:
Sounds like a loose screw on a retaining collar around the shaft.
Posted by Randy Stankey (Member # 64) on 05-14-2001, 05:30 PM:
It's hard to say without looking at it. There could be any of a dozen things wrong with it.
First thing I'd do would be to take a look and make sure the screw that holds the filter card in place is securely tightened on the shaft. Tighten it and then wiggle it. Tighten it again if it needs to be. Sometimes if you get the thing on the shaft at a slight angle, the screw can't "grab" onto the shaft and will come loose later on. This is especially important for drive gears inside projectors and things but it is a habit for me to do this on almost everyting where a set screw is involved.On one occasion I found that somebody had done some work on the platter and removed the bearing. When it was replaced this person didn't make sure the bearing was seated all the way down in its "groove". A little bit later on, it decided to seat itself. (Because of the pressure of the brain pushing down.) When this happened the shaft moved down and messed up the payout.
Whatever the cause, you'll find it's a pain to work on the payout mechanism by reaching in through the little portal on the end of the support arm. Unless it's a quick repair, I take off the whole deck and remove the axle assembly by loosening the four bolts that hold it onto the arm. It's much easier that way. Just don't forget to put the three "donuts" (bearing rings) back on the axle and get them in the right order! 
Posted by Joe Grace (Member # 341) on 05-14-2001, 08:08 PM:
I have had this same thing happen to me a few times, but it doesent happen as often. Maybe try a new screw or a new filter. It could be that something like the threads are worn.
Joe
Posted by Jon Bartow (Member # 241) on 05-14-2001, 08:31 PM:
I have had several do just what you are describing. Take the axle assembly out and remove the filter (a.k.a. "variable density disc). Look at the shaft that the filter mounts to. Sometimes the set screw makes an indentation in the flat area of the shaft. If the indentation is deep enough then you will have a very hard time getting the set screw to tighten anywhere else. If that is the case order a new shaft and bearing.
Of course don't dissasemble anything unless you know how to put it back together properly 