To make this frame:
I cut this one on the table saw - no router. I had a piece of black walnut 7/8 x 2 x 34". I ripped two stick 3/4" wide, then reduced the 7/8 to 3/4" on the saw. Then set the fence to 1/4" from the blade and cut a 1/8" wide slot 3/8" deep (makes a slot from 1/4" to 3/8" from edge). Then flipped the stick and cut another 1/8" slot on the perpendicular side. That made a 3/8"x3/8" rabbit in one quarter of the stick.
Use a machinist square to set the table saw angle guide to an accurate 45 degrees and cut the corner miters for sides at 12" and 9.5" to fit the 8.5x11 portrait. Glued the corner miters, then set the table saw blade so the top of the saw blade is at 4 1/32" - that puts the 45 degree tangent of the blade at 1/2" above the table. Set the fence back to 1/4" between blade and fence and with the frame on its side push it 1" into the saw blade. That makes an almost-diagonal through the corner that is 1/8" wide, extending 1" along each side of the frame. I had some 1/8" maple left over from one of the sword jobs, so used that for the diagonals in the corners. With the maple grain running diagonal to the walnut, the corners are pretty strong. I used Gorilla wood glue on it - it's pretty strong and set up in 30 minutes.
Anyway, I like the frame. Not very fancy, but the walnut makes a nice contrast to the BB Ply.
BTW - on the back, I had a small rectangle of 1/8" BB ply left over, so it is cut up and used as the brackets to keep the portrait in the frame.