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Author
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Topic: Intermittent Sprocket Cling
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Christopher Duvall
Jedi Master Film Handler
Posts: 500
From: Denver, CO
Registered: Dec 1999
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posted 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?) 
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Chris Duvall
General Manager
Regal Cinemas Colonnade14
Las Vegas, NV
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John Walsh
Film God
Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
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posted 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.
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Christopher Duvall
Jedi Master Film Handler
Posts: 500
From: Denver, CO
Registered: Dec 1999
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posted 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
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Randy Stankey
Film God
Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99
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posted 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. )
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 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
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