Baer Charlton
SPFG, Supreme Picture Framing God

Don't you just love when you mouth writes a check, that you body can't cash..... without a lot of learning up-curve.
By the way.... did I mention I hate.... er..... HATE math. So I did it with string and a pencil...... don't laugh - it worked.
Oh, and then there was the V-nailer.....

Yes, that is 1/4" thick foam core. No, I have no idea what the angles are - - other than they are the ones that work.
Cut square... draw line from point to point.... align frame miter to the line and the jaw point - - draw a line. Repeat on other side. nail