No "precision guides" just mark the roll, hold it in hand and saw. The margin of error is huge (millimeters) for my Horseman backs. I can do the cut by hand with the night-vision. I just cut a guitar saddle to 1/64" by hand yesterday. I'd use the same saw. I could probably do the cut in the dark by propping the saw up horizontal on a piece of appropriately sized wood.
Originally Posted by AgX
Now the 'dust' may spoil the edge of the film, but I'm thinking of something like a 'surplus' or 'free' roll of 70mm that would be otherwise useless. Not something that cost $500