I just had a new film holder made to use with my Nikon 4000ED scanner. The challenge I've found has been holding the film flat enough to have it sharp edge-to-edge. My previous holder I had made out of some aluminium and used screws to clamp the film. This works pretty well, and with practice loosening to move the film on and tightening didn't take too long. But the frame rounds of the corners of the negative, and getting the negative aligned properly is tricky. I tried a holder from filmscan-usa but found it did not hold the film flat enough. They do offer an option of ANR glass, but that would mean more surfaces to collect dust. Also it required adjusting the crop box in Viewscan for each frame. So I decided to try designing one and sending it to Shapeways to be printed. My first try was using the regular plastic in polished finish, but I found the tolerances weren't fine enough. So my second version was using the "fine detail frosted" plastic. This one had somewhat rough surface when it arrived, but some very fine grit emory paper made if much better. This time I decided to try some small magnets to clamp the film, though the friction fit seems like it might be enough by itself. Seen here along side my previous film holder.