I have been investigating using a mechanism similar to a Mitchell BNC motion camera movement to provide perforating as a last step if one were to consider making roll film for 35mm use. The Mitchell BNC camera movement is (was) a very tough, well built design using reciprocating locating and registration pins, and a "D" shaped motion for advancing the film in the camera. You may have trouble finding original parts to pattern after, but you really don't need them. The concepts behind the design are what you are after.
To avoid errors in spacing the perforations the reciprocating speed of the punches is timed (gear train / sprockets) to the speed of the film strip. The perforator has very sharp tool steel (or stainless steel) punches with the cutting edge beveled at a bit more of an angle than done in normal practice and a longer travel. This is done to clear the punched waste completely and cleanly from the film path after the strike. Less force is required at the punch end if the cutting edge is beveled at an angle instead of flush - look at a three hole punch, or the end of a hypodermic needle for example (but not with as severe an angle). The side clearance between the punch and the die it fits into have to be specific to the substrate you are punching, so different punch / die combinations are required (acetate vs polyester, thickness, shear strength of each, etc). This takes into account the momentary distortion of the material that takes place during punching. Lavezzi sprockets can be used to provide a type of feedback to the drive controlling the punches. A similar kind of perforator might be made using the guts of an industrial sewing machine, but that's still at the "back of the napkin" stage. All of the parts are there, aside from timing, specific punches, support, etc. Aside from the sewing machine idea, other parts would need to be added, particularly for the film path (stability and steadiness) and in the punch (stripper plate, etc). All parts would have to be lapped to as smooth a surface as possible (almost to the point of looking like they were chrome plated) to avoid scratching. There are other considerations, but that is the gist of it. Things like reducing vibration during film travel are still being worked out. The perforator would have to be physically isolated from the drive motor(s) and gear train / guide sprockets to avoid shaking the film as it passes. This means using much thicker and heavier metal in the support / film path areas to soak up the vibrations created, as well as creating a 'guide channel' for the film strip itself.
Just one possible way of doing things...
Last edited by rmazzullo; 03-05-2011 at 06:32 AM. Click to view previous post history.