Well, I needed an 11.5" diameter prop, starting from a 12.25 x 3.75 APC (see picture) for my piped .46VF. I first had to drill out the center hole to fit a .250" dowel pin, and then made a template out of poster board. Scribed around the periphery (bottom surface) with a #11 (indexing off the hole and TE). Belt sander took the outline to the scribe lines, and I started scraping the top of the prop with a fairly sharp knife blade. I found out the APC material will actually file quite decently, but scraping works great, followed by a little sanding, balancing, and polishing. Works fine!
But yes, the next step is some 3 blade Brian Ether flat backs or maybe an UC. We'll see on that. But for now, I've got a pretty useful baseline prop.
Steve