Film-Tech Forum ARCHIVE: Cause of loose film.... any suggestions?

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Posted by Chris Rhode (Member # 448) on 05-10-2004, 12:42 PM:

Hi,

It has been a long time since I have posted something to this forum (mainly because I have been burnt out with my job and my managers don't care,) but things seem to be taking a turn and I had a question for all of the film experts out there.

My theater (Muvico Centro Ybor 20 in Tampa, FL) runs Century SA-TA model projectors attached to Strong Super Highlight 2 lamp houses. We are having a problem with one of our projectors stretching any print that runs through it.

The best I can describe it to you guys is like this: when I go to break down trailers and what not as I roll them up onto the plastic cores I notice that the trailer is VERY LOOSE. As I go to squeeze on the trailer I notice that on the non-soundtrack side it seems as if it has been stretched out. The soundtrack side of the film seems to be fine. I was thinking it may be incorrectly installed tension bands. Other people I work with have said things that range from "its the aperture plate" to "its the humidity." I don't quite understand how the humidity could be affecting only one side of the print and not the other and as far as the aperture plate goes, the film runs perpendicular to the plate not to mention the fact that it doesn't seem to be in contact with the non-soundtrack side of the film whatsoever.

So, any advise you all can provide will be more

[ 05-10-2004, 05:17 PM: Message edited by: Chris Rhode ]

Posted by Scott Norwood (Member # 30) on 05-10-2004, 12:52 PM:

Since your theatre is a 20-plex, I assume that you are using platters. What make and model are they? Do you have any unusually tight twists in your film path?

Also, please edit your subject header to something more descriptive. Thanks.

Posted by John Foley (Member # 1183) on 05-10-2004, 01:49 PM:

Let me understand... your film (when broken down) is loose on the sound track side ("spongy").

When a film has played in the projector in question and is at rest between shows, is it tight on the center ring or loose...if you push on the tail of the film in toward the center of the platter with the center ring in place, it should not give at all. if it is "spongy" and does allow you to push it in, I would guess sprocket damage.
Do the sprocket holes seem flat like the rest of the film, or are the flare out, as if excessive tension was applied by the teeth?
Any noticeable dents on the film by sprocket teeth that would prevent the film from laying flush on itself when wound

For your problem this to occur to every print, every show and not be consistent human error (ie treading mistake) could mean a sprocket issue (turn your motor on with no film and see if any of the sprockets have a wobble, as if they are on an angle instead of horizontal.) I have never seen this but i may be possible to have a bent sprocket shaft to explain the one side stretching.

Is the film warped? Is moisture damage a possibility? Condensation on the platters?

Are your sure it is only one side?

Do you always thread with one side down on the platter? Is it the non-soundtrack side?

any other sprocket issues...ie missing teeth, slippage? (USE CAUTION FOR THIS: hold each sprocket while you inch the film with the film advance knob.. any play and any sprocket, or are they all tight.

Posted by Chris Rhode (Member # 448) on 05-10-2004, 03:47 PM:

Forgive the non-descriptive title, I am not very good at creating subject lines.

John: There is no sprocket damage whatsoever. The film seems to be flat on both sides (soundtrack and non-soundtrack.) We always thread the film with the non-soundtrack side facing down.

As far as the film resting on the platter (we use Strong SCDC3 3-tier platter systems with no whacky twists,) the film is spongy at rest. There is a bunch of play with the film. There is so much play as a matter of fact that I can actually stick my finger into the film! After a few days worth of runs through the projector the film will actually start to rise up off of the platter from the center!! I have seen sprocket damage before at my theater due to operator error. We use SR-D at our theater and I see no damage of any kind to the digital soundtrack. Our tech has said that it was the humidity because this projector in question sits next to an exit door that leads to the outside and certain projectionists like to prop the door open when they take a smoke brake. It this was true, then wouldn't the humidity cause the film to become sticky?

Hope this helps (and thanks for the help and sorting through the mess that is my typing!!!) [Smile]

[ 05-10-2004, 05:18 PM: Message edited by: Chris Rhode ]

Posted by Brad Miller (Member # 2) on 05-10-2004, 06:59 PM:

Take your finger and thumb and gently run it across both edges of the film (over the sprocket holes) while the film is being pulled taught. Do you notice that the non-soundtrack edge is just a little more rougher than the soundtrack edge? I'm betting anything your inboard (non-soundtrack) sprockets are being stretched just ever so slightly. Be prepared to really look and feel carefully to find this. It's not an obvious thing, but please verify this first. I have seen this exact same thing happen in a booth equipped with exactly the same equipment and it was a one time threading error in the projector head.

Posted by Aaron Sisemore (Member # 145) on 05-10-2004, 06:59 PM:

Check EVERY sprocket and pad roller along the entire film path of the projector and soundhead.

The likely causes of 'Sponging' of prints will be one of the following:

-Misthreading (it only takes ONE mistake to permanently 'sponge' a polyester print)

-Pad roller misadjusted and compressing the film too tightly, causing the edge(s) to stretch

-Badly hooked sprocket(s) (You will also hear excessive 'buzz' as the film runs over the sprockets if this is the case)

-Misaligned intermittent shoe

-Failed bearings, missing snap ring (or both) on [Century] sound head mainshaft causing the sprocket to move slightly from side to side, usually putting undue stress on one edge of the film (This is the #1 offender in the few times I have seen this happen)

-Aaron

Posted by Chris Rhode (Member # 448) on 05-10-2004, 07:47 PM:

I happen to have a trailer off of an old print that came from that projector. I did what you asked Brad and I didn't notice any abnormality over the sprocket holes at all. I did however notice that the outer edge of the film on the inboard side is a little rough. When I ran my finger along the edge of the soundtrack side (isn't that called the reference side???) it was noticeably smoother than the inboard side.

I am not going to be back in the booth until Thursday but I have spoken with my friend who was there tonight and he told me that the sprockets seem to be in order (i.e. there is no play in them nor is there any wobble.) When I get in on Thursday I will thoroughly inspect the film path and to run a test trailer pack through it to see how long it takes this to happen.

Posted by John Pytlak (Member # 331) on 05-10-2004, 09:35 PM:

I agree that the film was either slightly stretched by excessive tension, or one side got slightly damaged causing a raised edge or perforations. Humidity control helps the film lie flat, but the humidity has to be way outside the recommended range of 50 to 60 percent to get winding problems due to abnormal curl alone.

Posted by Chris Rhode (Member # 448) on 05-11-2004, 08:27 AM:

I think that the film is being stretched by excessive tension from something, be it a sprocket or the tension bands. I just can't seem to figure out what exactly is causing them. I'll check it out on Thursday when I go back to work and let you all know what I find.

Thanks to all!!! [beer]

Posted by Chris Rhode (Member # 448) on 05-14-2004, 08:30 AM:

I finally checked out what was causing the film to be stretched on the outboard side. Arron, you were correct in saying that it might be a sprocket issue. I checked the feed sprocket in the sound reader right below the sound drum and noticed that the sprocket was wobbling ever so slightly. I had ran test trailers through without the pad roller on the sprocket and the film ran through fine. I ran the trailers through again with the pad roller down and the first run through the projector yielded the stretched out results that I was describing to you all.

I am not sure if the bearings have failed or what, but my co-worker is going to check it out. All I know for sure is that the sprocket that I am referring to is causing undue stress on the outboard side of the film as it runs over that sprocket.

Thanks to all who helped!!! You all are the best and this is why I go to this forum when I am looking for REAL answers!

Thanks again! [beer]

Posted by John Pytlak (Member # 331) on 05-14-2004, 09:21 AM:

Glad to have been of help. [thumbsup]