I don't think it's near as easy as it may seem, at least beyond test samples. When manufacturing film, you want to be especially careful that the punched chips (all of them) are completely removed. And that the perforations are clean, with no ragged edges or broken chips laying near the edge. Anything left behind has the potential of ending up in a good frame during the exposure. Or remaining trapped in the edge of the film gate for the rest of the roll.
Originally Posted by AgX
In order to punch clean perforations, the punch and die set needs to have a certain clearance, which depends on how the film base shears. And if it is to be a commercial product, the perfs ought to conform to the ANSI/ISO standards for size and spacing, etc. I can probably dig up some of these dimensions (older ANSI specs), if anyone needs them.
A machinist who maintained some of this gear for a manufacturer once explained some of the difficulties to me; some extraordinary precision is called for. (I wonder if any of the perfing machines showed up in the book, Making Kodak Film.)
We are not speaking of a commercial product here to my understanding. I know the specification of the perforations and I know the industrial perforators, but I also know how to get some perforations into the base. Between that there is a wide span.
But who would even shoot the film, aside from testing, if there was even a slight risk of loose film chips in the roll?
I can understand shooting on hand-coated emulsions, with intermittent defects. But a single small chip, caught in the film gate, could scratch the entire rest of the roll.
Yesterday at GEH I actually got to lay eyes on an old Kodak perforater. Unfortunately it's in the collection so that means it'll never be used again, but, I agree with AgX that it should be a relatively simple task for anyone who is good at milling and machining.
In fact, although not for making perfs, in the labs down here I've come across these two little film splitters with stickers that say RIT on them. They are for splitting 4" film down to 35mm, and the other is for splitting 35mm down to 16mm. The bigger is driven by a motor and the smaller by hand crank. My point in mentioning these is that the construction of them is very simple, but they are also incredibly well made, with very high tolerances, and they work like a charm.
If somebody at a technical university can put these things together, a film perforater for medium quantity production would be easy enough me thinks.
It's not precision which stops loose pieces from the perforations from appearing on the film, it's clever design. Putting thought into the method and designing a mechanism which takes away all the loose pieces effectively shouldn't be too difficult.
If it has been done before, it can be done again.
Well, it's both. I had a special tour, for a specific purpose. They let me perforate a couple thousand feet of film in the process so that I would understand the issues. A guy who worked on them answered a lot of questions for me, so I'm working from that understanding. I'll just repeat that I think it's much more difficult than meets the eye. If one were to punch ROUND holes, and didn't mind the occasional perf hanging by a stretched bit of base, it would probably be a lot easier. I don't want to say too much more than I have.
Originally Posted by Steve Smith
Originally Posted by michaelbsc
Good points. I mentioned 35mm because that's my need :). It's also narrower and more rolls could come out of a single product run of what might be an expensive product. The paper backing would present issues if the film were stockpiled already rolled. If this were treated somewhat similar to 35mm one could spool it with re-used paper as it was needed. Your camera is already able to advance just the right amount of film between exposures, all the numbers do is help the aging brain keep track of how many times it has done its job. Perhaps buy a couple thousand feet of this paper from Kodak's supplier and re-use it until the zombies are at the door. If there was a little polyester in the paper it might not have to be so disposable.
No, this is not trivial. Think of it as keeping the glass plate guys from having the last laugh. (I could coat microscope slides and use them in my Nikon as a one-shot.) :p
I can immediately think of two perfectly good ways to perforate film. The first would be a matching set of male and female rotating dies which pull the blank film in and push it out with holes in it. The other way would be a flat male and female die which cuts a small lengh of the film which is then indexed along and uses the last two perforations cut to register the next set.
The rotating dies method is the way to go if you are doing a lot of film and want to run fast. The flat die method would be easier for a hand operated, low quantity production run. We have small hand operated machines at work similar to this for punching polyester sheet.
If you were happy with round perforations, a pair of drilling heads and an automatic advance mechanism would work but I would rather deal with perforation sized pieces than the swarf from drilling.
Actually, with holes under about 3mm diameter, the shape doesn't matter much. 2mm punches in a steel rule die type of tool do not last very long. In a two part male and female die set, it doesn't matter much what the shape is.
Originally Posted by Mr Bill
What we need to do is scale it up. Make film just over four inches wide and perforate it with larger holes to make easily advanced rolls of film for large format cameras!
It's fantastic to see these older threads get up on their legs and run again. The Big Wheel keeps turning. The newest photographers get acquainted with the vocabulary and culture and materials of the older photographers, all with an eye on the potential for the latest technology to keep the older technologies alive -- at least as artisan niches. And, besides, it gives us something to talk about!
I'll throw in a couple of thoughts. 1) I don't think backing paper is an issue. Thin, acid-free, black paper is available from the Paper Art world.
2) When you're designing a sprocket hole puncher, keep in mind that it will probably work best to first coat and dry the film and then slice and punch it. Otherwise, you'll fill the sprocket holes with emulsion, which is nearly as hard as PET. (I'm assuming small scale machinery all along the process.) That means the hole punching will have to be done in the dark, and care taken to prevent scratches on the emulsion.
Originally Posted by dwross
Can you point out which exact paper you are talking about? For a while, I've been contemplating to try to make a few rolls of 122 film for my Kodak 3A camera. It should not be difficult to manufacture spools from 120 leftovers, and I think I have most of the ingredients for the emulsion, but the lack of backing paper has been stopping me.