Film-Tech Forum ARCHIVE: CHRISTIE MUT -- Question about rollers

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Posted by Manny Knowles (Member # 1171) on 03-21-2003, 03:57 PM:

I'm still trying to track down this back-tension problem I'm seeing with these MUT's...

How many High-Speed Rollers is the Christie MUT supposed to have?

Both of them? Or just the one at the bottom?

For Clarification: High-Speed roller is the one with the race bearing (as opposed to the regular ones with just a nylon (?) sleeve).

Posted by Chris Markiewicz (Member # 1415) on 03-21-2003, 05:07 PM:

Our Christie MUT has high speed rollers top and bottom with needle roller bearings, and no back tension problems. I did leave the brain spring bands in; when I removed them the run from the platter to the projector was bouncing too much. Distance from platter to projector is about 6 feet to allow the 16mm Eiki to slide in when needed.

Posted by Brad Miller (Member # 2) on 03-21-2003, 05:13 PM:

Manny, is your problem building up or breaking down?

Chris, someone has been lazy and dragged their fingers through the 3 brain rollers to thread. That damages the rollers and causes them to wobble. It can also knock out any of the 3 digital formats from tracking properly. I would highly recommend you toss those and get new "green" rollers for your brain, then of course take that evil spring out. [Smile]

Posted by Manny Knowles (Member # 1171) on 03-21-2003, 06:34 PM:

Brad:

The problem is with making up. The movies are VERY TIGHT -- I was actually called in to remove a centre ring that had collapsed completely during a fast buildup. That was an extreme case. Always, though, this tension results in a bulge that DOES NOT GO AWAY after regular showings/rewinding. I shudder to think it but it appears that film is being stretched slightly.

I adjusted the speed controller so that the platter no longer goes at warp speed and I've personally built up movies with no problem by going to 6000' reels and using a low speed. No bulges on those movies. But the projectionists freaked when they saw how slow I was going. I was going unrealistically slow but my aim at the time was to narrow the problem down to the MUT itself and either speed or back-tension.

Actually, Brad...now that I think about it...the problem is with break-down, too. I've been changing belts and re-tightening that big aluminum wheel a lot.

What do you think? Could it be that I need two high-speed rollers and not just the one at the bottom?

Posted by Daryl C. W. O'Shea (Member # 1303) on 03-21-2003, 06:41 PM:

Having never seen a Christie MUT, I'm under the understanding that the belt gets dragged along while you build up. If this is the case, and you've been having to replace belts, I would expect that the belt is too tight and causing too much tension.

What I do know for sure -- if the bulge doesn't go away after playing, the film has been damaged. Usually it's either sprocket hole damage or a stretched edge (or two). In this case it would be a stretched edge.

Is it possible that whoever is building up prints has the MUT positioned so that the film has to twist through some excessive angles which would put more stress on one side of the film causing it to stretch?

Posted by Brad Miller (Member # 2) on 03-21-2003, 07:02 PM:

Manny, the problem isn't with the speed, it's your guys flipping the speed to 100% without "ramping" it up to speed. That is without a doubt what is creating your problem. Tell your guys to cool it and gradually increase speed. Also, building to large reels and then transferring to the MUT will make that issue mostly go away too. No one should be building from the shipping reels to the platter anyway. It's a poor film handling practice.

On breakdown, when is the last time you checked the axle bearings on the decks? Are your center rings circles, or ovals? Also, are your guys flipping the speed up without ramping on breakdown too? That can cause the film to get "smashed" onto itself in the first reel. The newer rings have a latch, but for older rings, we usually stick a regular sized cd case in the opening as we takeup the last show. The cd case prevents it from collapsing.

Are your MUT rollers black or green? Do they wobble?

Posted by Manny Knowles (Member # 1171) on 03-21-2003, 08:03 PM:

The rollers are green.

The MUT that I looked at today had wobbly rollers. The bearings had actually dislodged themselves from the high-speed roller and I had to replace it.

After replacing that h/s roller I noticed a "bounce," which was due to the spindle being slightly bent. Not that I have a spare of that part, but I tried removing the spindle and found that I couldn't because it is currently frozen in place.

The centre rings are round with a little gap that you squeeze to make it smaller when removing. It tends to collapse down to its smallest size when they build up movies.

The other roller on the MUT (the top roller) is a bit ratty looking, too. But I couldn't replace that one because I didn't have one like it in my spares kit. That's when I started wondering whether that was the right type of roller in the first instance.

Which leaves your question about the platter axle and bearings -- I heard a bad throbbing sound today as the speed increased. (Dare I say, the thing was purring?) I generally kept the speed down so as to eliminate that noise and hopefully some of that awful back-tension, too. It's been a while since that particular platter got a full shakedown and, after all, it is the one they seem to use all the time for their buildups. I will service the platter axle and bearings (and the little rubber tires) this weekend. Even if everything is fine, it would still be good to eliminate that as a possible cause.

Posted by Daryl C. W. O'Shea (Member # 1303) on 03-21-2003, 09:13 PM:

Since a collapsed center ring is no longer circle but oval, you're going to have uneven tension as you build up which will cause the film damage you are having. It might be a good idea to jam a cd case in there, to keep the ring circular, when building.

Posted by Paul G. Thompson (Member # 655) on 03-21-2003, 11:19 PM:

In my opinion, don't use standard rollers in place of high-speed rollers. There is a thread somewhere that has some pictures I posted where someone has done just that.

Posted by Manny Knowles (Member # 1171) on 03-22-2003, 12:03 AM:

Daryl -- you're right (!) and the circle-turned-oval is probably what's causing the throbbing sound, too.

This is one of the more interesting problems I've had to work on because now it seems like there are a lot of contributing factors.

Paul -- are you saying that the Christie MUT uses two high-speed rollers? I'm still awaiting a definitive answer to that question -- is the adjustable roller a standard (nylon centre) one or a high-speed type (with bearings)?

Oh...and Paul...you might consider changing that to read "Experience is inversely proportional to the amount of equipment ruined."

Posted by Daryl C. W. O'Shea (Member # 1303) on 03-22-2003, 12:12 AM:

quote:
Oh...and Paul...you might consider changing that to read "Experience is inversely proportional to the amount of equipment ruined."

Unless equipment is NEVER ruined that would be impossible! Since an inverse curve would mean that you've ruined less equipment as you gain experience, you would have to figure out some way to un-ruin equipment. Maybe "Experience is inversely proportional to the amount of equipment you remember ruining." would work. [Big Grin]

Posted by Manny Knowles (Member # 1171) on 03-22-2003, 12:29 AM:

I just KNEW that would take this thread off-topic.

Let's try to focus on the problem, mkay? [Wink]

Posted by Chris Markiewicz (Member # 1415) on 03-22-2003, 04:16 PM:

Both our MUT rollers are green high speed with bearings.

Posted by Manny Knowles (Member # 1171) on 03-22-2003, 04:38 PM:

Thanks, Chris.

Posted by Paul G. Thompson (Member # 655) on 03-23-2003, 12:25 AM:

OK Manny and Daryl....you win. [Big Grin]

Back to the subject. Yes, both should be high speed bearing type rollers. In addition to the speed, the loading is a little heavier during make-up and tear-down. Some of those roller pictures I posted some time ago were the standard rollers that were placed on the MUT for one reason or the other.

Posted by Manuel Francisco Valencia (Member # 710) on 03-23-2003, 05:52 PM:

You definately want the rollers will the bearings. We had a few of the regular rollers on the MUTs and after a while the friction of the high speeds began to bore out the center causing the roller to wobble like crazy but it didn't build the film tight. As far as the tension I have tried a few things in the past. Although others will disagree with this it is worth a shot. Try taking the belt off of the motor and wheel and see if that helps building up. On breakdown, see if you can separate the motor from the platter. CAUTION: This should leave you with no tension so you have to accelerate and decelerate very very slowly, otherwise your shit is going to fly everywhere. Alright guys, bash the hell out of me now.

Posted by Brad Miller (Member # 2) on 03-23-2003, 06:11 PM:

Never, ever, ever, ever pull back the motor from the platter during breakdown if you don't want to damage the film. (Christie, SPECO and Kinoton models only. All other platters are carelessly designed which frequently damages film during breakdown and as such this does not apply to them.) If you have to pull back the motor to solve some other problem, you need to solve that problem and not rig other things to get by. [Mad]

Also, loading tension isn't that big of an issue. If it winds a little loose, big deal. The film will pay out from the middle of the roll just fine if it isn't tight. This only affects the careless operators who build on one specific platter and then move the print before it is ran at least one time. Prints should always be built on the platter where it will run it's first showing.

Is that harsh enough for you? Don't make me add you to the "you suck" list. Be sure and slap your trainer next time you see him and tell him it was from me! [Wink]

Posted by Manuel Francisco Valencia (Member # 710) on 03-23-2003, 06:48 PM:

As I said I "tried a few things in the PAST." This isn't a practice of mine but I did do it so I will take the good with the bad, I am a big boy. Mistakes shouldn't be hidden but learned from.

Posted by Brad Miller (Member # 2) on 03-23-2003, 08:26 PM:

So did you learn from them? If so, it would be nice if you would refrain from posting known bad suggestions to the readers who may not know better. [Wink]

Posted by Manuel Francisco Valencia (Member # 710) on 03-23-2003, 08:44 PM:

My apologies. [Wink]

Posted by Paul Konen (Member # 41) on 03-24-2003, 09:04 AM:

Manny, I actually took the roller assy that adjusts to the deck that you are using and turned it upside down to replace the roller at the bottom of the MUT. This assy is a lot more studier than the roller on the thin piece of steel that would start to warp under tension.

So, my answer is TWO high speed rollers on my MUT.

Brad, Can you expand on lubricating the axle bearings? I don't think that anyone, including Christie, told us to do that.

Posted by Brad Miller (Member # 2) on 03-24-2003, 11:45 AM:

Take the decks off and lubricate the bearing that sits at the base of the axle (or sticks to the bottom of the deck, depending). I've been using high speed brake lube which has worked well for me.