I want to share my experience with the D-Curler design above. I downloaded the .pdf and built a couple of them according to the plans. No real trouble with the build, though it's not an inconsequential effort.
One note on the window films. There are two types and they're not clearly marked as to which is which. One is the static cling type and the other is actually adhesive based. The smoke color mentioned in the pdf is a static cling type. I mistakenly bought an adhesive based one because it was the size that best fit my plans. Wound up trashing it and it cost $18. Anything that is frosted or claims to have metal content is probably not the right kind.
It's a very clever plan and yields a very workable arrangement. The vinyl makes a nice surface for the print to lie on and the static cling film works perfectly to hold the print in place while you go do something else. It takes only a moment really to flatten the print. No need to leave it for a long time. I'm using about a 2" diameter piece of pvc pipe and it seems about perfect.
However, there is one major problem that I have been unable to solve. Because of the bump formed on the roll where the print meets the roller, the device will leave a subtle crease in the print each time the leading edge rolls over the print. With my roller, that meant a crease about every 6" or so. Nothing I have found so far has eliminated that crease. No amount of increasing or decreasing pressure or loosening the tension on the roll has solved the problem at all. You won't see the crease in good flat light but with any oblique light source it will be painfully obvious. And there seems to be no way to remove it once it's there.
I would, of course, welcome input from anyone who has solved this problem because the device is fast and easy to use and removed the roll from a print almost immediately. But the crease has been a fatal flaw for me. I have not tried the side strips mentioned above. They might just work as they could prevent the paper from touching the rest of the print. It's worth a try, but I suspect there might still be an issue. The leading edge of the paper wants very badly to pull away from the roll and that's what causes the crease.
What has, however, worked very well for me is simply to spray a very light mist of water on the back of the print. I am working with a heavy watercolor paper. This would obviously not apply to a conventional photo paper. But then the photo paper may not crease either. I haven't tested it. Anyway, the mist of water caused the print to relax almost immediately. I've been putting a piece of foam core and a little weight on the print while it dries but it hardly seems necessary.
There tends to be a little residual curl at the edges of the sheet and the D-Curler does a very nice job of removing that. Just don't roll past the point where the leading edge of the paper rolls over onto the rest of the print.
I hope this is helpful to people considering making the device. It has it's place in removing the curl at the edge of the sheet and it may work with less fragile papers such as conventional photo papers but it will not solve the issue of flattening fine art papers unless you plan to mount the print, thus removing the subtle crease.