Film-Tech Forum ARCHIVE: film uneven on takeup platter

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Posted by Megan Penmann (Member # 233) on 04-03-2000, 11:39 PM:

One of our prints of Romeo Must Die is wrapping unevenly on the takeup platter. (Film sticking up in various places; it looks like it's the same places every time). I know it's not the platter system because we've run this particular print in different auditoriums. What causes this? I know I've seen this before, but I don't remember what caused it or how we fixed it.

Posted by Randy Stankey (Member # 64) on 04-04-2000, 09:33 AM:

I know there are a lot of different causes of this kind of thing but MOST of the times I've seen this it was becasue of some kind of film damage or becase of static.

Static: The "layers" of film stick together and an extra "loop" of film tries to go into the brain, sometimes casing a wrap. Answer: Get FilmGuard.

Damage: Usually becasue somebody mis-threaded the projector somehow. As the film rewinds on the platter it will seem to grow in diameter. It will also be kind of "spongy". That's becasue the sprockets in the projector have jumped the track, so to speak and have put little "dents" in the film. These dents push the layers apart becasue they act like "spacers" betwen them. Answer: Inspect the film. If it's damaged you'll have to get a new print.

There may be other casues, but these are my two best guesses.

Posted by Ken Layton (Member # 133) on 04-04-2000, 09:42 AM:

A bent or out-of-round takeup ring on the platter could be a problem, too.

Posted by Colin Wiseley (Member # 247) on 04-04-2000, 10:43 AM:

The only time I have seen this was also with a damaged print. It had small cuts between the sprocket holes for the entire length of reel 2. As the platter would take it up, the cuts would sometimes lock together and the tension would pull the film up. It made payout a headache as well.

------------------
Colin Wiseley
Lyric Theatre
Blacksburg, VA
www.thelyric.com

Posted by John Pytlak (Member # 331) on 04-04-2000, 12:35 PM:

Megan:

Excessively dry conditions in the booth can also cause winding problems. When the relative humidity is very low (e.g., in the winter when the heat is on, or in a desert climate), the gelatin emulsion on the film loses moisture to the dry air and shrinks temporarily. Since the polyester film base doesn't change much with humidity, the shrinking emulsion pulls in, causing the film to cup or curl excessively. Severe curl or incorrect winding tension may cause the film roll to wind unevenly, or take on the shape of a polygon ("spoking") instead of a perfect circle.

Kodak recommends maintaining a relative humidity of 50 to 60 percent in the projection room. At very high humidities (greater than 65%), the gelatin emulsion may actually get more soft and sticky, and the film can have "negative curl". At very low humidities, the emulsion shrinks so the film will have excessive "positive curl", and the film surface becomes less conductive, so static dissipates more slowly.

Every projection room should have an accurate humidity gauge to measure relative humidity. The low cost digital gauges sold by Radio Shack (e.g. Model 63-855) and Edmund Scientific are surprisingly accurate. Another quick gauge is to simply observe a short clip of free-hanging print film. It should have a very slight amount of "positive" curl, where the edges of the 35mm film curl upward only a few millimeters.

If the humidity is too low, use a humidifier to add moisture to the air. In moist or tropical environments, a dehumidifier or air conditioner may be needed to keep the humidity under 65%. Adjusting the HVAC system balance may help too.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

Posted by John Walsh (Member # 168) on 04-04-2000, 01:06 PM:

Try threading the film onto the take-up deck with the soundtrack down to keep it even.

A year or so ago, we had a print that would "cone" upwards so much, it would pick up the take-up ring way past the two pins that hold it from spinning.

Posted by Brad Miller (Member # 2) on 04-04-2000, 02:13 PM:

Ok, I guess I'll ask it. What kind of platter?

I find this to be from print damage in the sprockets 99% of the time. I have also seen this from excessive takeup tension on an older SPECO with the single elevator roller.

Posted by Joe Redifer (Member # 3) on 04-04-2000, 06:05 PM:

I have had this happen a few times in the past on my Christie AW3's. I actually watched it occur once, and I could not find anything wrong with the thread or sprockets. My guess would be the humidity. It used to happen fairly often, but Lethal Weapon 4 was the last print that did it. It stopped as suddenly as it started. However, once the print was like that, it would never ever go back to winding evenly, no matter what.

Posted by Brad Miller (Member # 2) on 04-04-2000, 06:18 PM:

True, could be the print. I ran a print of "Basketball Diaries" that was absolutely perfect to look at on the bench (and on screen)...but would NOT wind flat, regardless of winding tensions/emulsion in/emulsion out/reels/platters/cores...NOTHING.

It was quite bizarre, but it was just that one print. I ended up saying "to hell with it" because it projected so beautifully.

Posted by Joe Redifer (Member # 3) on 04-04-2000, 06:22 PM:

Johnny Pytlak must have been experimenting with the chemical composition of the film stocks on certain prints back then. Maybe they were experimenting with their anti-stat coating? But yes, prints ran fine and had no other problems.

Posted by George Roher (Member # 91) on 04-04-2000, 10:09 PM:

I've also had a print "cone up" on the take-up platter. This print was shedding very heavily too. It almost popped out the center ring when running soundtrack down. When I ran it soundtrack up, the center would lie flat on the platter (AW3) but the outer reels would be sticking up. I never understood this.

Posted by Ian Price (Member # 14) on 04-04-2000, 10:27 PM:

I too had film "cone up" on my platter and this was the cause.

Speco platter #3 was a loose winding kind of platter and the projector in #3 was embossing the film because one of the pad rollers was too tight to the sprocket. When I moved the print to the platter in #5, also a Speco, but one that wound tight, the damaged film would "cone up."

I adjusted the pad roller and that was the end of that problem. How do you adjust the pad roller, you ask? You take two pieces of film and thread them over the sprocket like you would with one. Then you try to turn the pad roller. if it is too tight, you adjust the pad roller stop-screw. The pad roller should just be loose on two thicknesses of film, but tight on three thicknesses of film.

I hope this helps. I have Simplex machines, but I understand the theory works on all machines.

Posted by Joe Redifer (Member # 3) on 04-04-2000, 11:11 PM:

Actually now that it has been mentioned, I do remember the film actually lifting the entire ring out of the center. We had to suction cup it down from the inside of the ring. And as heavy as those Christie rings are (and for some stupid reason they are damn heavy and bulky, for a ring) that is quite a feat. Why are Christie rings so bulky and heavy anyway? It doesn't make them any tougher. We had one snap in half on us just last week, just from lifting it out of the print!

When you are talking about film thicknesses, what kind of film are you talking about? Acetate? Polyester? Fuji or Kodak (Kodak is thicker). Lots of variables.

Posted by Brad Miller (Member # 2) on 04-04-2000, 11:19 PM:

Basketball Diaries was Fuji. Isn't Romeo Must Die Miramax? They've been using Fuji lately too. Perhaps it's restricted only to the thinner Fuji print stock?

Posted by Ian Price (Member # 14) on 04-04-2000, 11:30 PM:

Too much information, I think my head is going to explode!

Posted by Megan Penmann (Member # 233) on 04-05-2000, 08:40 AM:

We've got Strong platters... But like I said before, it's just this print, and it does the same thing on another platter system. Humidity is a possibility. But the air conditioning is broken on that side of the booth, so wouldn't that make the air more humid? (It certainly does feel more humid on that half of the booth). The print is definitely "coning up" as you all describe. I'll check for damage to the film itself when I work next, but when I looked at it before I didn't notice anything right away. We'll see... And maybe I'll be adventurous enough to try winding the film soundtrack down.

Posted by John Walsh (Member # 168) on 04-05-2000, 08:51 AM:

Christie rings are made heavier because they are not "locked" together where the split is. Other rings (like a Xetron) have a latching mechanism to hold the two ends together, increasing it's strength. Christie rings rely only on spring tension to hold them in.

At first I thought that Christie had a better idea, because you didn't need to unlatch anything to release the ring. But it can fall out fairly easily while moving a print. Now that we move prints a lot, I'd rather have the latching kind. I modified two Christie rings to maintain tension for when prints are moved.

I've had two break over the years, but when I looked at the break, it looked as if the casting was made wrong. They wouldn't replace them, even though they agreed it was manufactured wrong because the rings were several years old.

And don't replace those two nylon pins on the Christie ring with steel pins if they break. I did that, thinking I'll never have to fix those again. A week later, someone removed the ring by picking up only one side and bent/distorted the hole on the deck.

Posted by Randy Stankey (Member # 64) on 04-05-2000, 09:35 AM:

In my experience (on SPECO platters) if a print cones up (we call it "beehive") it's because the guide rods on the yo-yo/take-up control were dirty. If they get crummy, little "rings" of dirt build up and the yo-yo won't slide evenly. This causes the take-up platter to run at slightly erratic speeds.

Also, check that stupid adjustable caster/roller on the take-up. If it's slightly out of line it can cause a bit of beehiving too.

Since it doesn't happen on just one platter, I'd say people are right in suspecting something wrong with the film. My first guess, again, is sprocket damage. ("Spiked film") We used to have that a lot. We buckled down a lot at TT-17 and it's truely a rare occurence, now. Fire a couple of guys and that kind of stuff will STOP. (Or if you REALLY want to hurt a guy, demote him/her to USHER! :O )

Posted by John Pytlak (Member # 331) on 04-05-2000, 01:08 PM:

Megan:

Do get one of the Radio Shack or Edmund Scientific digital humidity gauges. If your air conditioning is "broken on that side of the booth", the humidity is probably too high (if the air conditioning is not removing moisture) or too low (if the room is getting hot). In either case, the film curl may be affected adversely. Remember, 50-60 percent RH is best for projection rooms.

Does the uneven wind affect all the reels, or is only one reel affected?

In addition to the "spocketing" or "run off" damage other posters have mentioned, is there any chance the print was "stretched" by abnormally high tension at some time? Excessive tension can deform the film enough so it won't wind evenly.

Posted by Brad Miller (Member # 2) on 04-05-2000, 03:31 PM:

Check to see if there isn't a roller out of line somewhere (probably in the takeup path). This can cause the stretching John mentioned above. It won't necessarily be far enough off to scratch the film, but it can stretch one side. Does the film lay flat between the projector and platter as it is running?

Posted by Chris Erwin (Member # 176) on 04-05-2000, 07:12 PM:

Stop me if I'm totally off-the-wall,but has anybody had leveling problems of the platter itself causing a wind problem?

--Chris

Posted by Megan Penmann (Member # 233) on 04-11-2000, 10:53 PM:

I inspected the film (or so I thought) and found no visible trace of any film damage. So I thought it was a humidity problem from the broken air conditioner. Today we got the air fixed, and the print sill sat uneven on the platter. So I inspected the film more closely and noticed a very small amount of sprocketing on the inboard side of the film. It's so slight that I could only tell by touching the film; the sprocketing is not really visible. Then I checked the projector where the unevenness originated and noticed that a pad roller was too tight. Thanks for everyone's suggestions!

Posted by John Pytlak (Member # 331) on 04-12-2000, 12:56 PM:

Megan:

To give an example of why even "a very small amount of sprocketing" on one edge of the film may cause uneven winding and dishing: Print film is approximately 0.0053 inches thick. If the thickness of the film pack on the platter is 12 inches, there are 12 / 0.0053 = 2264 convolutions of film stacked on top of each other in the roll. If the film has sprocket damage along one edge, the height of each perturbation in the surface is magnified by 2264! So if the sprocket teeth nicked the film surface by only 0.0001 inch, the film pack would be 2264 X 0.0001 = 0.2264 inches thicker on the damaged edge. That kind of thickness difference would cause the roll to "cone" or "dish" as it is wound.