How to measure radius of curved corners?

[H2OPlayar]

Last min thought, You also want it like a 1/8th or a 1/16th smaller than the total dimensions so it drops in place easily, not 100% exact or it will be to tight of a fit. You don't wanna have to shove it in or pry it out.

We usually do an offset all the way around in CAD. So something like .050" offset all the way around so you get an even gap.