Joining A Mitered Corner

[TomFromStLouis]

I made a similar sized frame with ~1/2" oak glued into an L-shape profile. Butterfly keys in each corner with dovetailed brackets across the back. Here it is laid out to mark the tail mortises:

[Cecil]

Spline.  



Use a biscuit cutter for router.  The frame is big, so take the tool to the work.

Like Dennis said, it is overkill, but it works.  If you take your tool to the work it is not unwieldy.

[Steve N]

Tom, that is a great structure you've built. Support like a bridge. Bravo.

I agree that size is a tool to the work job, unless you do as John suggested and use a horizontal mortiser, you can go into the end of a phone pole, if you can lift it, and your bench will support the weight.

[ez-duzit]

I prefer to use a slip feather.

[Gary G™]

I made a 4' X 4' frame for a friend to hang his map in.
I reinforced the corners with flat L-brackets sunk into hand chiseled mortises cut across the corners created after the frame was glued together.
It worked fine.
Slipfeathers we're too difficult to handle on this large a frame.
YMMV.