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Author
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Topic: Misbehaving AW-3 -- What causes this?
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Randy Stankey
Film God
Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99
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posted 02-03-2001 10:52 PM
While working at one of my theatres I noticed one of the Christie AW-3 platters (a little over a year old) is doing something strange...Sometimes during the movie the film "bubbles" out from between the brain rollers and this loop of film sticks out. It's hard to explain. (I can't post a pic right now. Maybe later.) I'll try to explain in words... Show is threaded and started normally. Runs through trailer all right. The policy trailer runs and you recheck everyting before walking away. A while later you come back and you find that as the film goes between the first and second roller some "slack" has developed. Instead of going tightly around the middle roller, it sticks out a few inches to the right side and then goes back between the second and third roller and pays out normally (Most of the time) Sometimes a loop of film as big as six inches forms, which starts to get caught up in the roller shafts, causing catastrophe. Rollers are all good w/ no burrs. Springs are all tight and pulling the rollers closed. Rollers turn freely w/o binding or catching. (The "clock springs" under the middle roller have all been removed.) The funny thing is that it seems to happen only when the film is paying out from the middle deck. Could it be a "hitch" in the payout platter? Maybe there's a bad splice in the print that catches somehow? I will try swapping brains to see if that helps but I don't think it will. The same brain has been used on the top middle and bottom decks. Only happens on the middle, or so it seems. I have only seen it on the middle deck, anyway. I have also asked the regular Usher-B's if it has happened on other prints and they seem to think it has. My dominant theory is that there's a crummy splice somewhere. The reason it happens on one deck and not the other is because of the difference in film tension from deck to deck. Any idea
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John Eickhof
Jedi Master Film Handler
Posts: 588
From: Wendell, ID USA
Registered: Jan 2000
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posted 02-04-2001 03:14 PM
I too have seen this on AW3s that have had the tension springs inside the center roller removed, The spring that is placed inside the center roller is designed to pre tension the film as it pays out to the projector, This spring, if removed can result in erratic payout, bouncing of film, and possible troubles with digital readers, mainly DTSas the film needs top be fed steadily past the reader, what also happens is the platter is basically 'over feeding' the film through the first roller because the film is floating out of the second roller. Replace the internal spring, lubrcate the spring with vasoline or lubri-plate and your problem will go away. ------------------ John Eickhof President, Chief Slave Northwest Theatre Equipment Co., Inc. P.O.Box 258 Wendell, ID. 83355-0258 208-536-5489 email: jeickhof@nteequip.com
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Brad Miller
Administrator
Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99
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posted 02-05-2001 07:42 AM
I dislike the new horizontal MUTs, but Christie is going to continue to manufacture the standard table.Michael, the backtension is there for a reason. Shipping out a film that is not tightly and smoothly wound is just asking for trouble. I have never achieved what I consider to be an acceptable breakdown wind from any platter that disengages the motor for break down. I have also witnessed many prints broken down with the motor disengaged having cinch mark scratches on the print that were not there on the final showing, but some platters (example: Strong) were designed to be used in this manner. A hand is not good enough. I assume you learned on Strong platters, as most people who do not understand the reasoning for the backtension generally have learned on them and it is a new thing to them which just doesn't seem necessary. Strong's latest generation of platters certainly provide smooth payout and takeup operation, but I sincerely hope they will take this issue to the R&D table as the failure to not provide any form of backtension upon breakdown is the main reason why I will not install them.
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Randy Stankey
Film God
Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99
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posted 02-05-2001 11:23 AM
I had almost perfectly wound reels when breaking down with a Strong/Potts platter.It's all a matter of CLOSELY regulating the speed and using your hand (with appropriate padding, for safety) to apply just the right amount of "braking" pressure as the you slow the machine down. You have to start out VERY VERY slowly or you will "snap" the film upon start-up and then you GRADUALLY work up to normal working speed. ( Which, by the way should never be more than 2/3 to 3/4 of the top speed of the machine.) Use your hand to put just enough drag on the platter to keep the film tight. No more. When you're up to "working speed" you can take your hand away. When you get to the end of a reel you reverse the process... slowly bring the speed control down to a stop, applying just enough drag to keep the platter from over-spinning and backlashing the film. By the time you get to the splice you should already have the platter speed down to a "crawl". You should never have to "STOP" the platter with your hand. It should be almost ready to stop by itself. Like I said, your "braking hand" is only used to apply DRAG. It took me a while to figure this out but once I did, I can break down a 6 reel print in 20 minutes and all the reels will be wound nice and tight and even. I hardly EVER missed a splice because the film was moving slow enough to spot it instantly. (I only missed when I wasn't paying attention... even then it was only by a few feet.) If it weren't for all the splices and crappy, damaged film I had to deal with, some of the films would look like they just came from the lab.
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Randy Stankey
Film God
Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99
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posted 02-05-2001 05:11 PM
Okay, I just got the pic uploaded. Here it is: (The malfunction shown here was simulated in the interests of time and clarity.) I'm assuming that the cause was the 3rd roller was dragging just a little bit, creating a pinch point in the film path. When I disassembled the brain, I found that the 3rd roller (the one in back) had it's spacer washer missing. That and all the shafts were pretty icky-looking. I cleaned them up and reassembled with new rollers. I put the proper washers under each roller, too. Haven't heard any negative reports yet.
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