Film-Tech Forum ARCHIVE: Intermittent Sprocket Cling

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Posted by Christopher Duvall (Member # 284) on 06-24-2001, 04:43 AM:

Due to circumstances beyond my control, I had to run my booth tonight and I saw something a bit troubling. What got my attention, was some "chatter" like noise and I pin pointed to the intermittent. It appeared that the film was clinging (or catching) to the sprockets on the intermittent. This caused the sound loop make the noise I was hearing. I checked the pad and it was lined up almost perfectly with enough space for the film to go through and it had enough tension. The intermittant spockets had no residue or stickyness but they were covered lightly with fine shedding probably due to the clinging. I felt the the sprockets and they felt rough.

Now the questions,
1. What would cause that kind of wear on intermittent sprockets?
2. What can I do to fix this problem?

While I am at it, I had a different projector that had an intermittent pad that was bent and causing minor shedding on a print. I replaced the pad. To me this sounds like one of my guys abused the projector for that to get bent. Does anybody have thoughts on this as well?

As for the shedding...thank the film Gods (Brad) that we have Film-Guard. (Does that plug work for you Brad?)

------------------
Chris Duvall
General Manager
Regal Cinemas Colonnade14
Las Vegas, NV

Posted by Jerry Chase (Member # 660) on 06-24-2001, 08:05 AM:

Just want to positively eliminate the common cause first...

Is there any undercutting at all of the sprocket teeth? As a side note, I wonder if there is any difference in sprocket wear from polyester as opposed to c. acetate film?

Posted by John Walsh (Member # 168) on 06-24-2001, 09:31 AM:

Yes, check the sprocket teeth. If you run a lot of film, the sprocket teeth can wear and become "hook" shaped. It can also happen sooner than normal if someone always keeps the gate tension set too high. You can easily see this by looking at the teeth and compairing one side to the other. A quick fix is to simply remove the sprocket, turn it around, and reinstall it so the other side of the teeth are used.

It also possible that the teeth got damaged because something leaned against them while the projector was running.

Here is where it helps to know what kind of projector you have. For example, the newer Simplexes have a easily removable gate assembly that swings on one pivot to open and close. This gate includes the intermittent pad shoes (half moon shaped pads that hold the film around the intermittent sprocket.) If someone removed the gate for cleaning, and dropped it, the shoe could get bent.

A Century gate (well, it's actually the trap) slides in or out for cleaning. I've seen people who weren't paying attention, missed the dovetail-shaped slot it fits into, and bangs one or two teeth on the intermittent sprocket. Now those teeth have a burr which chews the film.

Posted by Christopher Duvall (Member # 284) on 06-24-2001, 10:59 AM:

I guess I should have mentioned it...the projector is a Simplex and it is relatively new. The gate does not swing open, but slide horizontally out. The pad is on a seperate assembly to itself. Very much like a 35/70 capable Century I used to work with yearrs ago. I also should have mentioned when talking about the sprockets I was referring to the teeth. Upon closer inspection, there was a bit of a hooking action on the teeth.

So, if there is hooking on the sprocket teeth on the intermittent, it could have been caused by high tension in the gate? Damn, I knew that polyester film was tough but not that damn tough. These projectors are only 2 years old.

OK, what now? Should I or could I flip the intermittent sprocket around in the assembly, replace it or or have somebody who knows what they are doing file down the rough hooked edges on the teeth?

------------------
Chris Duvall
General Manager
Regal Cinemas Colonnade14
Las Vegas, NV

Posted by Jerry Chase (Member # 660) on 06-24-2001, 12:01 PM:

Arrgh!!! put away the file! Flip the sprocket for now. You'll eventually need a new sprocket, but flipping is common practice.

Loose that gate tension. Use only the least amount of tension that will prevent jitters. Anyone who ever ran a DP-75 with plastic shoes and thin metal bands learned this tip real quick.

Posted by Darryl Spicer (Member # 711) on 06-24-2001, 12:35 PM:

You say this is a simplex projector head with the intermitent shoe seperate from the gate trap. It is only two years old. Hmmmm I thought all the new simplexes had the swinging gate assembly. Of course this could be that model they tried to make that incorporated both simplex and century design into one. They called it the mellinium I think but not sure. Things I have heard about these have not been good.

I have been using two models of simplex projectors at two diferent theaters I am working at right now. They are the 1050's with the sliding gates for removal and the model 1060 with the pivote gates. The 1050's are 11 years old and show no signs of hooking on sprockets and the 1060's are 6 years old and show no signs of hooking.

You should not have to run the tension on the straps past 3 to get a steady picture. If you are running past 3 it will require the intermittent to pull harder. The straps may need to be changed if no jitter free picture can be obtained.

Posted by Brad Miller (Member # 2) on 06-24-2001, 12:48 PM:

Yes, just remove the sprocket and flip it around so that the other side of the teeth are doing the pulling. Make sure after you do this that everything lines up in respect to the trap and shoe. The cause is definitely too much gate tension and running film that is not lubricated enough. That polyester film when ran "dry" can become awful tacky.

Posted by John Walsh (Member # 168) on 06-24-2001, 04:12 PM:

Yes, it does sound like it's a Millennium projector. I do like the seperate pad roller for the intermittent sprocket. It's harder to control the film while threading with the older "one-peice" gate design.

Did you ever notice on a Millennium that when the film is centered in the aperture, it is not centered in the framing window? It's not off by a lot, but is more than any other projector I've seen.

I think we are building a theater in your town, Chris. Is it near your place?

Posted by Randy Stankey (Member # 64) on 06-24-2001, 05:42 PM:

If you had a "Mommy" Simplex and a "Daddy" Century SA, then you put them together and they made "Baby Projectors" you would get a Simplex Milennium. I agree that's what you probably have.

I see this all the time. Just flip the sprocket, like everybody else says, order a new one (Part number G-2330 -- $107 list price) and when it arrives you can install it. If the old one isn't too badly damaged you can save it for an emergency backup. Or, if you can swing the $$ just order two of them now and save the extra.

Watch out for people who try to clean the projector with a toothbrush while the motor is running. The toothbrush has a tendancy to slip off and whack the intermittent pad shoes. When they get bent they'll grind off the edges of the sprocket teeth. You can (A) carefully bend the shoe back into shape, if it's not too badly damaged or you can (B) order a new one. I would recommend (C) Ordering a new one and bending the old one back until the order to arrives.

If you only need the center part of the intermittent pad the part number is PA-0194 -- $5 list price. You can take all the other parts from the old one and use them to make a new one. If they are torn up too badly to use again (or if you just don't want to spend the time) you can order the whole assembly. Part number C1-BB-28 -- $35 list price.

When you put the sprocket on the intermittent, take a metal machinist's ruler, (the thick, heavy kind) and use that to align the intermittent sprocket with the lower, holdback sprocket. It's not hard to do but you'll need to take your time to do it accurately. If you put the sprocket on and don't align it properly you'll probably just tear it up again in a short time, not to mention the film won't run correctly throught the gate, etc.

I'm sorry to say it but this kind of damage is common when you have inexprienced, uncaring people running the booth. (Not to say that's whay YOU have... just a general statement. )

Posted by Kevin Crawford (Member # 469) on 06-24-2001, 05:51 PM:

I would check to see if the intermittant shoe is loose. I have seen a couple of these come loose on the millenium.

Take a good look at the sprocket. If the intermittant shoe is loose it will have cut your sprocket teeth down the middle. I have had to change three at my theatre and two others at other theatres.

If this is your problem, flipping them over will not help. They will need to be changed. When you do change them, make sure that the intermittant shoe is tight, and does not rub the sprocket teeth. I would suggest running the motor with the shoe closed. There should be very little noise from it.

Posted by Christopher Duvall (Member # 284) on 06-24-2001, 10:25 PM:

Thanx guys for the info. It is a Simplex Milennium and yes, the tension was too high. I will flip the sprocket and have my tech bring out a new one. You think as long as I have been around this stuff I would have seen this happen before. Guess I have been lucky,

Now as for the bent pad...I may be reaming somebody here shortly. I think someone has been cleaning with a toothbrush with the motor running...AAAGGGHHHH!!! This has a way of bringing out the worst in me.

John Walsh wrote:
"I think we are building a theater in your town, Chris. Is it near your place?"

John, are you with the Brennan (spelling?) chain? I know they have one going up near the Rio casino. That would put them more than 10 miles away headind NE. I do know they have a target date set for December as well.

------------------
Chris Duvall
General Manager
Regal Cinemas Colonnade14
Las Vegas, NV

Posted by Randy Stankey (Member # 64) on 06-24-2001, 10:35 PM:

Just the sight you clanging down the booth hallway in that suit of armor, going after that guy who banged up the projector would be worth the price of a plane ticket to Vegas!

Posted by John Pytlak (Member # 331) on 06-25-2001, 09:03 AM:

Worn or hooked sprocket teeth are an often overlooked problem. Look back over twenty years to an early issue of Kodak's "Film Notes for Reel People" in the Film Tech Manuals section: Film Notes Issue #H-50-4 Troubleshooting and prevention of damage. I find a pocket microscope is an excellent way of examining sprocket teeth for wear. Even if the film still runs and is steady, the worn teeth are probably "plucking" and damaging the film perforations. Excessive gate tension greatly accelerates sprocket tooth wear --- use the least possible tension that still gives a steady and sharp image.

By the way, if you run 5 shows a day, in two years, you probably have run over 35 million feet of film though that projector! It deserves new sprockets.

------------------
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 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Will Kutler (Member # 770) on 06-25-2001, 04:27 PM:

My understanding is that VKF sprockets will resist hooking much more than the old style sprockets. For those of you who have the Christie Projector, beware of the Ultramittent. Many of these Ultramittents at the theater which I worked started making a "snapping" sound which sounded like the gate/band tension was too tight! According to our Area Tech, this was/is a normal design flaw? I have read some other posts about people now being able to service these units. This is news to me, as my old employer-and Christie were VERY strict on servicing the Ultramittent! Each of the Ultramittents had electronics style securtiy paint on the hardware as an anti-tamper device! I think other people told you to make sure the shoes are properly aligned and that you have the pads correctly set for film thickness.

Posted by John Pytlak (Member # 331) on 06-26-2001, 03:46 PM:

35mm sprockets are specified by standard SMPTE 242. Sprockets like the LaVezzi VKF ("Very Kind to Film") have a wider tooth face, which distributes the stress on the perfs over a wider area, reducing film wear. The lateral width of the type R tooth (VKF) is 0.072 inches (1.83mm). The lateral width of the old type S tooth (CS) is only 0.040 inches (1.02mm). The corners of the tooth also have a larger radius which reduces the chances of tearing the perforation corners if there is any misalignment or excessive tension.