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This topic comprises 2 pages: 1 2
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Topic: Base side scratches
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 10-06-2000 07:20 AM
You need to be careful when running loops. Unless the loop is run in a straight line over undercut rollers, it is very easy to scratch the loop outside the projector path and be misled. I agree with Leo that running "virgin" film, stopping the projector, and then carefully examining the film with specular light, will reveal where in the film path the scratch is occurring.BTW, a really good way to see any scratches or abrasion on a piece of film is to hold it up in the concentrated specular beam of light coming out of a projector. A spare slide projector or spotlight shining down on the rewind bench produces a light that makes it very easy to find scratches during inspection. ------------------
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 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 10-08-2000 02:11 PM
Harry --- you've located where the abrasion seems to be occuring. You said the abrasions are on the back side, about 1 centimetre from one set of perfs, and some in the middle of the frame. Although slight abrasion of the film edges and perforations by the gate and intermittent sprocket shoe is common, abrasion of the central image area is unusual. Any chance the loop below the intermittent is the wrong size?------------------
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 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 10-09-2000 06:01 AM
Proper lubrication of film does help prevent abrasion. Kodak specifies "edge waxing" as part of the processing for print film, as this serves to reduce abrasion along the edges and perforation area of the print. But your image-area scratching is abnormal, and shows that something is contacting the image area of the film. I agree with Brad that your loop size is a suspect. The projector manual should have a threading diagram, or a description of the proper threading procedure. Another guide to proper loop size is that the distance between the picture aperture and the analog sound pickup should be 21 frames for exact sound sync, and 20 frames for sound to be in sync 50 feet from the screen. (Sound takes 1/24 second to travel about 50 feet).------------------
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 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
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Harry Robinson
Expert Film Handler
Posts: 155
From: Franklin Tennessee
Registered: Dec 1999
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posted 10-09-2000 07:09 PM
First of all, I want to thank you guys for your responses to my problem. This is the greatest site.
OK, I filed down the screws, buffed the gate door, shortened my loops, and nothing.
So...I re-threaded, ran the projector for about three seconds, shut it down, then marked the film with a felt pen at the top of the gate. I pulled the film out, then looked down the surface from the felt mark to the scuffing on the film.
I then marked the scuff. Then I re-threaded the projector. The scuff was right on top of the sound drum in the RCA 1040. And the scratches started after that. I had missread the film earlier.
The sound drum had been corroded when I got the unit, so I took to a garage and mounted it in a power drill, then scotch brited it till it was smooth...apparently not smooth enough.
I went back in today with the cotton buffing wheel and buffed the drum without removing it from the unit, letting it spin a little for even coverage.
I put a little spin on the flywheel, fired up the projector for three seconds and checked again. The scuff mark was about one third the size as before as were the tiny scratches. I will buff this thing as smooth as I can and see if I can completely eliminate the problem.
Any thoughts?
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