Did something very similar for years before the CMC.cheater method
Take the cutout and sandpaper the edge and tape back in and cut to final size. Cost is free.
That's the way I did it for 25 years before I got the CMC. I thought sanding was an easier concept to explain, and would work.Did something very similar for years before the CMC.
If it's cheating then I guess I cheated for about 30 years........
Instead of sanding, I would take the center and just flip it over, put it back in the mat cutter and reverse cut the bevel but not all the way down.
Just cut about half of the bevel to slightly reverse it and tape it back in to cut the opening for the degree.
Just another thing.
Mark the mat and the center with a pencil line before cutting for orientation to tape the center back in the same way it came out.
Cutting on a manual mat cutter can be a little imperfect and the center will probably fit back in better if it's put back the same way it was cut out.