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It seems there were 2 versions of pad rollers on the Cat 700 / 701 readers: one type (and I think that is the later one) can touch the film surface only on the edges, and the other ( which I have) can touch the film well within the area between perforations. When the film is properly tensioned it doesn't touch at all but I still don't like the idea. Has anybody experience with this problem? Or isn't it a problem at all?
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The normal film clearance of the pad rollers to sprocket film supporting edge is two film thicknesses. So an overlapping cement splice might touch, but a tape splice should not, unless of course it's incredibly sloppy. But we all make perfect splices, don't we.....? I remember there also being two types of rollers, but that they went to the single contact rollers pretty early on. Also any parts ordered from Dolby for repairs would get you the single contact rollers. BACP may have new parts available if you contact them. -
Because the film is under tension in a penthouse/davis loop type system, the double flange pad rollers should not pose an issue. LaVezzi had three pad roller options. The plastic ones could be had in either single or double-flange. The problem with double flange plastic rollers is that they are seamed and the control over the inner flange was not good. In applications were the film is not well tensioned (input feed sprocket on a platter system on say a Simplex on the lead-in roller the film could curl and touch the inner flange and create a scuff. Conversely, in a 4-star soundhead (gearbox) on the upper sprocket, the film is again not under tension and, depending on the size of the isolation loop to the lower sprocket, the film would not only curl enough to hit the inner flange but it would also rub in the picture area if an inner flange was not used.
I always recommended the metal pad roller for 4-star soundheads on that upper sprocket. The metal version (SOR4-22) is machined/polished and won't yield the same scuffs as the plastic roller and are FAR more preferable than the scuff down the middle of the image. Furthermore, the single flange plastic rollers would chamfer and induce the film to curl. Mind you, it was easy enough to thread the film so it would tend to not curl. The only reason for the dual sprocket in the 4-star soundhead was to isolate the sound reproduction from the take up system. You only needed a slight curl between the upper and lower sprocket. You don't want the film applying any pressure to pop open the lower pad roller but that is about it. It should look like a very slight "reverse-C." Most people made this WAY too large and that would induce the above mentioned curl.
However, in a penthouse, the film is under tension so the curling aspects are not nearly as present. So the inner flange shouldn't play much of a roll.Comment
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Originally posted by Steve Guttag View Post
Would that roll be cinnamon or crescent?
Sorry, eating breakfast while browsing and couldn't resist.
I do remember changing out a bunch of pad rollers from the double to single flange for a certain theatre chain in my service days, due to the threading habits that were causing a lot of scratching issues.
My own projectors over the years always ran singles. I'll have to take a closer look at my P35GPS and see what rollers it has. Someday soon I may finally get around to building my screening room.
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Christie started with all metal pad rollers (SOR4-22). I don't recall if they switched to plastic.Comment
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No, they always used the SOR4-22's. Except on the Cine-X35 where they had custom metal rollers.Originally posted by Steve Guttag View Post
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Steve and Mark, thanks for the follow up info. That projector, which I painstakingly restored before moving out here, has unfortunately been stored in my non climate controlled outbuilding, and will need a through cleaning and restoration all over again when I get into my next house (which I hope to start building next spring.)
I hope to include a proper projection room and nice viewing room in the new floor plan.
My CAT 701 will also need some TLC.Comment
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