Film-Tech Forum ARCHIVE: Scratch problems

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Posted by Masao Garcia (Member # 184) on 10-27-1999, 02:57 PM:

We have Christie P35C projectors with FM-35 failsafes and Christie AW3R platters, and for some reason we get these short, vertical, black scratches on our prints. These scratches only occur on certain projectors and never on others, and they're usually noticeable after 3 weeks or so. I'd say the scratches take up about a third of a frame at most, and they are usually off center. They also don't seem to be totally consistent throughout the whole print, but will appear on and off. I'm guessing they are base side scratches because they are always black (but they could be shallow emulsion side scratches...I'll check some old trailers to be sure).

I guess my question is, has anyone else experienced these scratches before? I've checked how all my Usher-bs thread, and they all have pretty much the same thread patterns (i.e. no one threads off the rollers or anything like that). I notice that some have bigger or smaller loops than others, but nothing extreme (as far as I know). I've heard the term, "standing scratches" before, and I was wondering if those are what I'm describing? What are "standing scratches"? Thanks for any info.

Posted by John Walsh (Member # 168) on 10-27-1999, 04:27 PM:

Seems like it must be something around the intermittent; upper loop, or right after the intermittent. I had a situation where a guy would thread a fairly large lower loop (after the intermittent on a Simplex.) Sometimes he had threaded out-of-frame. When he turned the framing knob to correct it, the lower loop was made bigger, and hit the projector casting. When the show was over, he would return the framing knob to center, but short scratches would be left on the film.

Question: Do Christie projectors have a framing method like a Simplex or Norelco, where the intermittent sprocket rotates around it's center, or does the entire intermittent assembly move up/down like a Century or Cinemecannica?

Posted by John Wilson (Member # 269) on 10-27-1999, 05:38 PM:

It sounds like one of your projectionists is making their loops too big.

Posted by Brad Miller (Member # 2) on 10-27-1999, 08:57 PM:

Altering the framing on a Christie will change the loop size. This is why I strongly recommend they be locked down. If the projectionist threads out of frame...then it is he who will have to suffer the embarassment of stopping it, framing it correctly and then restarting it. That'll only happen once.

Sounds like the lower loop is being made too big. On a Christie, you want that lower loop to be as big as possible WITH THE FILM TUGGING ON THE OPEN LOWER PAD ROLLER. With that pad roller in the open position turning the machine over by hand, if the film is not tugging gently on the pad roller, you WILL get standing scratches. However, make sure the loop is not too small. Basically make the loop just big enough so it doesn't tug and then lower it by one sprocket hole. That is optimum size.

Christie has come up with a nifty little addition that can be screwed underneath the Ultramittent to prevent this. It is a set of guide rails and their part number is #196189-001. See if your theater will let you requisition some.

Posted by Masao Garcia (Member # 184) on 10-27-1999, 10:48 PM:

Cool, thanks again for the suggestions. I'll look into my Usher Bs' threading habits and look into that Ultramittent part.

Posted by Jim Ziegler (Member # 86) on 10-28-1999, 02:35 AM:

Brad,

What do these add-ons look like? Are they standard on the projectors now, or are they optional?

Posted by Joe Redifer (Member # 3) on 10-28-1999, 04:12 AM:

It happens only on certain projectors but not on others? Not a loop size problem. Sounds to me like the screws inside the gate have become loose and are rubbing against the base side of the film. I have seen this happen occasionally. Check every single screw you can find in the gate/trap area and make sure they are tight.

Posted by Paul Konen (Member # 41) on 10-28-1999, 09:57 AM:

We had those too. They appeared on the right side of the print and were associated with one projector. We found that it see to be coming from the removable brain. It wouldn't drag around the bottom, but may have been dragging on something in the fingers.

Also, these scratches would wander, they weren't always in the same place. Just the right side of the image.

Posted by Jim Ziegler (Member # 86) on 10-29-1999, 04:19 AM:

Paul, I have had that happen twice now, as well. I haven't figured out what has caused it yet (not that I have looked into it much, the offending brains are on my workbench where they can do no harm). Anyone know which part of the brain is causing this problem?

Posted by Brad Miller (Member # 2) on 10-29-1999, 05:02 AM:

I do believe the new guard rails are standard on all new Christie projectors. Bevan Wright from Christie (come on Bevan, you know you read the forum) could tell us for sure.

They basically just screw in underneath the Ultramittent. There is no technician required. It is a fantastic upgrade!

If any of you guys who are having these scratches can send me a trailer (or just several feet from one) that has these scratches on them, I should be able to track down the cause of them just by looking at it. The shipping address is at the bottom of the FilmGuard page on the site.

Posted by Jim Ziegler (Member # 86) on 10-29-1999, 01:42 PM:

The scratches comming from the top part of the brain rollers.. I am wondering if it is caused by that tension spring. I haven't really dug into it yet, as I have more pressing matters to take care of.

Posted by Brad Miller (Member # 2) on 10-29-1999, 02:54 PM:

Coming from the top part of the brain rollers? Not sure I understand. Are your scratches on the right, like Paul's? Do you run soundtrack up or down?

Paul is local. Perhaps he can save some samples for me. The Christie AW3 is the best platter on the market. I'm shocked to hear it would be scratching and would like to find out the cause.

Posted by Jim Ziegler (Member # 86) on 10-30-1999, 03:19 AM:

Yes, I am running soundtrack down, and they were on the right, so it had to be the top of the rollers.

Posted by Brad Miller (Member # 2) on 10-30-1999, 03:48 AM:

Unless the two white stationary stripper posts are too close together and clogged with dirt (which I doubt) there really isn't anything in the AW3 brain that could cause this, except...

Does the film drag around the back side of the brain during the movie? If so, it is possible the delicate emulsion side of the film is rubbing against the back side of the brain and causing your scratches. If it doesn't, I really don't think there is anything in the brain that could cause it. In that case, I'd check the projector.

Send me a sample if you can.

Posted by Jim Ziegler (Member # 86) on 10-30-1999, 02:08 PM:

I don't think I have any samples. However, I did trace this to the brain when we were screening a new print. Basically, I just followed the line on the film and it lead to the brain. When I switched brains, it stopped scratching. I had another print that was starting to show the same type of damage, and we pulled that brain and the damage stopped there as well. Both of these platters were paying out correctly, so that was not the cause.

Posted by Scott Shepard (Member # 196) on 10-30-1999, 04:48 PM:

In response to the film scratching problem with the Christie projectors I have found that I have seen the operators making there loops to big to begin with and explained the importance of starting the show in frame due to the fact that adjusting the framing knob will increase the loop under the intermittent and cause film scratching.
Scott

Posted by Paul Konen (Member # 41) on 01-13-2000, 10:13 AM:

Additional Information: While unfortunately having to change out a couple of reels because of looping scratches, I also discovered the source of the black vertical scratches that appear.

I strongly feel that they are coming from the first roller after the payout. Unless the film stays perfectly on the roller, it will either ride up towards the tree and with the Christie AW3, it will cause the film to scrape against the holder during payout.

We just had our tech come and do pm at our theatre and locked down all rollers on the tree. This way they cannot swivel and cause rideups while paying out. Also, he timed the platters such that the prints are fairly tight and much more pleasing to move.

I am trying to get the information on how he did this but he is not there by the time I arrive.

Posted by Brad Miller (Member # 2) on 01-13-2000, 04:24 PM:

Your tech sped them up, hence the takeup arm spring is being pulled tighter during the normal part of the run.

Be forewarned, timing like that makes it easier to toss a print!

If you're really worried about the takeup tension, leave the timing as it was before (so you don't dump prints) and go to the hardware store and get a similar, but shorter spring. Make sure you don't overdo this though.

Posted by Michael Cunningham (Member # 210) on 01-13-2000, 05:29 PM:

Hey Brad,

I really like the idea of locking the framing knobs and thereby assigning responsibility for mis-frames to the offending operator. The only problem I have with this is how to correct for differences in studio printing. From what I've observed, there is no "standard" center of frame for the various studios. Some seem to print slightly (maybe 1/8 the distance between sprocket teeth) high and some slightly low. On my pitifully small screens, this can make quite the difference in appearance. Any suggestions?

-Mike

Posted by John Pytlak (Member # 331) on 01-13-2000, 08:18 PM:

Mike:

The slight shift in vertical position at reel changes usually is an indication that the print was made by a lab using bi-directional panel printers. The height of the BH-1866 perforation on the duplicate negative is 0.073 inches, and on the KS-1870 perforation on the print film is 0.078 inches. So there is a 0.005 inch shift in the vertical position of the image between reels where the printer sprocket drove the film heads-to-tails, as opposed to tails-to-heads. If the scene has a really "tight" composition, or if your scope aperture is higher than the standard 0.690 inches (sometimes showing the framelines), this shift can be annoying.

Other shifts can occur due to variations in the setup for any optical printing or digital effects.

------------------
John Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Research Labs, Building 69, Room 7419
Eastman Kodak Company
Rochester, NY 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243

Posted by John Pytlak (Member # 331) on 01-13-2000, 08:55 PM:

On the original topic of scratches:

Watch those loop sizes! Short vertical scratches always appearing at the same place on the frame usually indicate a loop that was too small or too big, such that it "flapped" on a projector component that scratched the film. Don't forget that the size of the bottom loop also affects analog sound sync.

When the film is excessively curled, it can "pull-in" to the center of an undercut roller or guide bar. Excessive curl is usually due to very dry booth conditions. Keep the relative humidity between 50 and 60 percent RH if you can. Use an accurate digital humidity gauge (Radio Shack and Edmund Scientific sell fairly inexpensive ones) to measure RH.

A clip of a piece of film from the leader is also a good humidity gauge. After the film equilibrates a few minutes to the booth environment, let it hang free and observe the curl. The film should cup VERY SLIGHTLY toward the emulsion side ("positive curl"). Very dry conditions cause the emulsion to shrink, causing excessive positive curl. Very moist conditions cause the emulsion to expand, causing the film to be sticky and limp, and with a slight "negative curl". You can see this effect by breathing on the hanging film strip --- the moisture from your breath will actually change the curl. Drying the film with a hair dryer will cause the film to curl in the other direction.

As often mentioned on Film-Tech forum, horizontal or slightly diagonal scratches usually are caused when the film is not properly guided onto the platter, so a burr or rough spot on the platter surface rubs across the film as the platter rotates. Misthreaded film riding up onto a roller flange will also cause diagonal scratches.

Horizontal "cinch marks" are caused by flattening a dished or unevenly wound roll. Vertical "cinch marks" are often caused by pulling on the end of the film to tighten a loosely wound roll. Carefully rewind loose or uneven rolls to avoid cinching. Use an on-line film cleaner to keep the film clean and minimize cinching from abrasive particles being wound into the film roll.

Posted by Randy Stankey (Member # 64) on 01-17-2000, 04:17 PM:

The first thing I do in the morn. is to look at my 'film barometer' hanging on the wall. We have a big booth and no way to control humidity. Console humidifiers next to every projector still can't heep the humidity up in the booth. I can look at the film on the wall and say whether or not it's going to be a 'bad film day'.

Posted by Dave Williams (Member # 299) on 01-17-2000, 06:59 PM:

We had a problem of intermittent scratches that came out of just one projector. We have four Simplex XL's and the one in our excellently tuned DTS theater was always scratching every print but only on one side. I spent about three hours diagnosing the problem when I found the culprit.

Although we installed platters over nine years ago, this one projector had its payout and takeup reels still attached, and rollers added to put the film straight through them. The takeup reel had a nice little metal roller on the bottom to feed it to the plastic roller, but alas the side of it had worn down so that it actually was in direct contact with half of the frame.

I do not know why these parts were left in tact but I removed them and installed the correct brackets and rollers in the right places. Absolutely no damaged prints since then.

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"If it's not worth doing, I have allready been there and done it"

Posted by Anthony Matarazzo (Member # 63) on 01-18-2000, 04:36 AM:

We were getting scratch on a few of our projectors at work. We did not know where they were coming from. The location tech readjusted the rollers to and from the projector and the problem stopped.