Film-Tech Forum ARCHIVE: Shedding Problem ?

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Posted by Glenn Conatser (Member # 970) on 06-04-2002, 02:28 PM:

Hello Everyone,

I just recently started having a shedding problem in one of my houses even with Film Guard runnig on this print its still shedding. The projector is a Christie P35C. It looks like its coming from the gate area mostly. Any help would be appreciated.

Cheers,
Glenn

Posted by John Pytlak (Member # 331) on 06-04-2002, 02:43 PM:

Back side or emulsion side of the film? Do you see obvious abrasion of the print? Where? Exactly where in the "gate area" - soundtrack side, opposite side, etc.? Any hard deposits on the film-contacting components? What film type (full magenta edgeprint identification)? If shedding just started, what has changed (assume new print would have started last week)?

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
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Posted by Brad Miller (Member # 2) on 06-04-2002, 03:05 PM:

You've got a pretty serious abrasion somewhere. Check the gate bands to make sure there isn't anything hard as well as pad roller clearance. You should be able to put two thicknesses of film between a closed pad roller and sprocket with the pad roller still able to spin, but not with 3 thicknesses. Finally make sure your intermittent shoe did not get out of alignment and isn't pressing hard up against the intermittent sprocket.

With that much abrasion, there should be a large deposit of purple emulsion shavings. Where is the pile?

What print is this? Did you receive it new?

Posted by Glenn Conatser (Member # 970) on 06-04-2002, 03:11 PM:

The shedding seems to be occuring at the bottom of the gate on the non soundtrack side and top of the ultramittent with alot of build up on the inner sprockets. Its on the base side with no visible damage to the film. Just alot of shedding. Hope this helps let me know if more info is needed.

Thanks for the quick reply John.

Glenn

Posted by Randy Stankey (Member # 64) on 06-04-2002, 03:22 PM:

I would put my money (if I had any) on the trap closure or the pressure bands.

If it's a flip-up style gate, like the Christies I know, there's not much that can go wrong with the closure setting. However, I have seen on several occasions where people slam the trap shut when they thread, the latch starts to get bashed up and the thing won't close properly.

Look at the hole on the inboard side of the trap where the locking pin goes in to hold the trap shut. The little "ledge" where the pin slides over can become worn and a little burr of metal builds up. This is because some people smack the trap and it flies shut. Instead they should push the thing shut with two fingers on the latching knob... slowly.

Once that hole starts to get worn, the gate will close too far. Then, the shoe (rails) will smack into the pressure bands, sandwiching them against the back of the trap casting. This puts dents into them. Film running over the uneven surface will be more prone to scuffing.

In extreme circumstances, the bands will become chipped and sharp little burrs will stick out. I have even seen where the rails of the shoe has burrs in it.

Examine your trap for this kind of damage. If you see any of it you'll have to make repairs. Most likely you will be ordering new bands and maybe a latch plate. (if you can't fix the old plate.)
In extreme conditions you will have to order, virtually, a whole new trap.

Secondly, I suggest you give the projector a cleaning within an inch of it's life. Christie projectors DO NOT like to be dirty. You have to keep them "hospital clean" or else they will start to spite you in one of a hundred different ways. It's funny... A Christie projector, kept clean, will run cleaner but once they start getting dirty they start running dirtier in a geometric progression. (Dirt makes it get dirtier and that dirt makes it get even dirtier, etc, etc, etc.)

Posted by Brad Miller (Member # 2) on 06-04-2002, 03:23 PM:

If it's only one side of the film, it's not the film's fault. Can you answer the other questions on this thread to help diagnose?

Posted by John Pytlak (Member # 331) on 06-04-2002, 03:25 PM:

When the gelatin emulsion is abraded by the projector, the shedding is often colored (has dyes in it). Since magenta is the top imaging layer, first sign of emulsion abrasion is often colored purple (magenta). One quick way to verify the debris is gelatin is to try to dissolve some in household chlorine bleach --- gelatin will dissolve, but film base will not.

Triacetate film base will not dissolve in bleach, but will dissolve in acetone or splicing cement.

Polyester (ESTAR) film base will NOT dissolve in most solvents.

One of the best ways to examine the film surface for scratches and abrasion is to illuminate the surface obliquely with a strong, specular light source. A desktop "tensor" light, or a spotlight works well. Holding the film in the beam of a projector in front of the lens will show even the tiniest scratch or abrasion because the light is so bright and specular.

Many have found that pre-show "rolling stock" ads tend to shed significantly. Has this changed recently?

Posted by Glenn Conatser (Member # 970) on 06-04-2002, 04:19 PM:

After doing a closer inspection im thinking its the imtermittent shoe that might be out of alignment. The gate seems to be a little stiff and the shoe doesent seem close all the way on the sprocket with out a little help. Pushing the shoe in or reclosing the gate a little harder gets it into place. Most of the deposits are on the inboard sprocket on the intermittent.

Posted by Glenn Conatser (Member # 970) on 06-04-2002, 07:04 PM:

I went and removed the gate arm to lubricate and inspect the shoe and noticed an abrasion in the shoe, and is hopefully the problem. But the plot thickens, after lubing the spring and shaft and cleaning everyhting the screw head decided to snap off. This was with mild pressure to. I was just making it snug enough to not move the gate arm and it snapped. My tech is coming in the morning to extract the left over piece.
Sounds like Murphy was a little bored and decided to pop in.

Ill be back with the details tomorrow.

Glenn

Posted by Manny Knowles (Member # 1171) on 06-04-2002, 08:38 PM:

John: I asked about this before in another thread...I've got purple stains on some of my machines. (Yes, they will indeed wipe away with a bleach/water solution!)

How do I stop this type of shedding from happening?

What are the usual suspects?

Posted by John Pytlak (Member # 331) on 06-04-2002, 09:58 PM:

Manny: First, look at the three S's. Try to determine if the film is being SCUFFED, SCRATCHED, or SKIVED.

Scuffing is usually from the film contacting components rubbing hard against the film, perhaps because of excessive tension in the gate. It's usually a general, "wide" abrasion, sometimes with small "plucked" sections. Kind of a film "brush-burn". Lower tension and proper print lubrication will help considerably. Be sure there's no buildup of hardened gelatin on the film contacting parts. Be sure all rollers are turning freely.

Scratching is a well defined scratch caused by a burr or something sharp in the film path. For example, a nick or burr on the film runner in the gate or on the intermittent sprocket shoe. Or diagonal "platter scratches" caused by the surface of the film being scratched by a nick on the platter surface as it rotates. Or "loop scratches" caused by a wrong-sized loop hitting a screw head or other sharp projector component.

Skivings are caused by something pinching or scraping against the side of the film. For example, studio guides set too tight, or a misaligned keeper roller pinching the film. Often skivings may look like short hairs under a magnifier. In rare cases, skivings can be very long and hair-like ("Angel Hair"). Freshly processed prints may skive a bit the first few times through a projector, as the gelatin emulsion swells during processing, and doesn't quite dry back to its original dimension, leaving a "proud" edge that a roller or sprocket tooth can knock off. But after the first few passes, there should be no more skivings. Always use on-line film cleaners to pick up any dirt generated or picked up.

Dampness is often a factor in scuffing and skiving. Gelatin emulsion absorbs moisture from the air, swelling and becoming softer and stickier. Ideally, keep the relative humidity in the range of 50 to 60 percent. Anything over 65% starts to bring problems. Living on an island, the sea air can bring lots of moisture at times, so use an accurate humidity gauge in the booth to keep an eye on humidity, and use a dehumidifier or air conditioning to remove excessive moisture from the air.