Film-Tech Forum ARCHIVE: Misbehaving AW-3 -- What causes this?

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Posted by Randy Stankey (Member # 64) on 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

Posted by Paul G. Thompson (Member # 655) on 02-03-2001, 11:25 PM:

Randy, it almost sounds like it is ready to run away from you. (over-feed) But yet the P/O control is having no effect, and there is enough impedance on the rest of the guidance hardware to keep the film sagging between the platter mast and the projector, which would allow the film to back up in the pay-out head. Might this be what you are saying? What happens if you put a little drag on the platter with your hand and fake an under-feed? Does the bubble go away? This one is a new one on me....so it is just a thought.

Posted by Darryl Spicer (Member # 711) on 02-03-2001, 11:25 PM:

Randy,

When you swap brains make sure you swap it with another christie platter. See if the problem moves with the brain. Check the theaters splicer to make sure it is splicing correctly. I had something like that happen years ago. I just took the brain aprart and cleaned everything and lubed everything. The problem went away. Note: the platter I had the problem with were the aw3's with the fixed brains so I do not know if the problem would have moved.

Posted by Brad Miller (Member # 2) on 02-04-2001, 03:06 AM:

Randy, this is actually an easy fix. Swap the two flangeless rollers on that one brain and the problem in most cases will go away. What is happening is one of those flangeless rollers is spinning freely and the other one is gripping it's shaft just a touch. I've seen it on many occasions and swapping them fixes the problem 90% of the time. For the last 10%, find a drill bit that is just BARELY (and I do mean barely) larger than the hole in the roller that fits snugly on it's shaft and drill it out. Just make SURE that you do NOT overdrill it out to the point that it wobbles when it turns. Of course an even easier fix is just to toss the roller and put another one on. Christie is pretty good about including a few extra rollers in each new complex.

Posted by John Eickhof (Member # 323) on 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

Posted by Brad Miller (Member # 2) on 02-04-2001, 08:02 PM:

I must disagree John. That tension spring in the center brain roller is the main source of dts dropouts and other problems. They must be CONSTANTLY lubricated and if the spring has any dent in it at all, you can expect it to put out uneven tension to the tune of violent bouncing and snapping. Most multiplexes do not have this much spare time to deal with such maintenance. Also I've seen booths where they ran a film for a week or two with the brain spring in place where the rollers weren't perfectly aligned and it stretched one edge of the film, causing focus problems as well as SRD and SDDS tracking defects. The only time removing the brain spring will ever cause any problem is with DTS on the older black rollers that have been mishandled. Many operators that I've seen are lazy and like to ram their fingers through the 2nd and 3rd rollers in the brain instead of carefully opening up the 3rd roller and "placing" the film into the track, and it knocks them "out of balance" (for lack of a better term) so that they wobble. It is that wobbling which causes dts problems on AW3 platters without a brain spring. Removing the brain spring has cured dts tracking problems 100% of the time in my experience. It also allows for the rollers to be fairly substantially out of alignment without film damage. If those aren't enough good reasons to remove those springs, the tension exerted has very high odds that it will cause scratching with a web cleaning machine. Sorry, but I completely fail to see your reasoning for running WITH the brain spring and highly recommend that they be removed.

By the way, for any theater that has wobbling black roller problems, replace them with Christie's green rollers and then you can forget about ever having to deal with it again.

Posted by John Eickhof (Member # 323) on 02-04-2001, 10:42 PM:

Hi Brad, my next question is to our friends at Christie...why then do they furnish these payout heads with springs in the first place?

------------------
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

Posted by Darryl Spicer (Member # 711) on 02-04-2001, 11:33 PM:

they probably still use them because they have thousands of them sitting around. From what I was told years ago the reason that christie decided to put the springs in the brains was for booth instalations that had the platters set up further than a few feet from the projector to prevent the film from sagging. The older aw3's with the fixed brains did not have these in them. The newer ones did. I had so much trouble keeping the roller turning and the spring lubbed. I just removed the springs and problem was solved. By the way it has been a long time since I worked with christies. Do they still use that cheap crappy green motor made in Mexico or did they go back to useing the larger black ones?

Posted by Brad Miller (Member # 2) on 02-04-2001, 11:42 PM:

They no longer use the crappy green motors. They are back to the good Bodine ones again.

On the springs, they were considered necessary for any installation where the platter was farther apart from the projector than 8 to 10 feet. Personally, I've set up platters about 15 feet away from the projector without the spring and all was just fine and dandy. However, I can remember one particular installation that even though it was a straight shot to the projector, required one jumper roller, as the film had to travel about 30 feet. A jumper roller in those instances is far better than having to deal with that #~(&!\@ spring. Ever notice that no Christie 70mm roller has the capability to have that spring in it? I can just imagine the number of film breaks that would've come from it back in the acetate days. Many theaters had enough trouble making it through a day's performances back then with 70mm. Most of it was due to poor gate/trap alignment and short twists between rollers, though...basically the installation engineer's goofup!

Then again, people seem to think that film cannot be stretched more than that golden 8 to 10 feet rule for interlocking either.

Posted by Randy Stankey (Member # 64) on 02-04-2001, 11:59 PM:

I took the brains apart, replaced all three rollers with new, cleaned the shafts, put a TINY dab of lubriplate on the shaft and reassembled.

I found that one of the spacer washers under the rollers was missing. Could this have been a factor? I was only able to stay for part of the first show of the day but I think it's okay now.

Thanks!

Posted by Michael Cunningham (Member # 210) on 02-05-2001, 12:15 AM:

Perhaps Christie insists on installing these springs for the same reason they keep using those crappy, sideways MUT's and motors that don't move away from the platters which causes too much film tension on breakdown. As to what this reason is...who knows?!? Go Strong!! Heh...

-Mike

Posted by Brad Miller (Member # 2) on 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.

Posted by Randy Stankey (Member # 64) on 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.

Posted by Randy Stankey (Member # 64) on 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.

Posted by Brad Miller (Member # 2) on 02-05-2001, 09:39 PM:

Yup, that is precisely the image that went through my head when I suggested you flip the two flange-less rollers. It has always completely solved the problem for me, but of course, cleaning up the shafts and getting the proper washers is important too.