I have learned a few things about my derevaun film splitter after putting a couple rolls through it. I thought I would pass along the small modifications I have made for the benefit of anyone wanting to try this rather elegant solution to producing discontinued film formats from 120 roll film.
In the process of making my measurments with 120 film backing in place in the camera I noticed that the film rails in the camera are actually a bit wider than the film, so measuring for the position of the cutter starting at the side of the camera produced some inaccuracy.
Inserting the film leader in the take-up spool and advancing the film centers the film strip, and in this camera that means that the edge of the film is actually 2mm inward from the side of the camera. With the film backing in place, I dabbed a little white paint on the film rail along the border of the film backing; that gave me a starting point for measuring for the desired 46mm width needed for cutter placement. Accuracy in this regard is desirable, both for allowing the film to travel properly through the camera in which it will be used and also to ensure that the film will properly seat in the film processing spool.
I'm pleased with the outcome of my DIY splitter endeavor so far; it is going to give me a lot more choice in regard to film types in using my 127 cameras. The splitter could also be adapted to other formats, and even the left-over strip on the right side could be used for some of the subminiature formats. I am also currently discarding about seven inches of the 120 film strip which is not needed for the standard 127 film format. That extra amount could be made use of for a few more exposures in cameras not having a too-tight film compartment.