The best way to join a large frame?

[cff]

I have a job to do a large 4' x 4' frame for a mirror. I wonder if anyone has any advice about how to go about ensuring the joins are strong?

Jamuna

[Graysalchemy]

Personally I would Biscuit joint glue with PU adhesive and clamp, a ratchet strap is best for that then underpin and if you really want to be belt and braces put metal L brackets on teh back. The would probably be a little bit of overkill for a 4 x 4 ft, but is what I have used on 9ft x 7ft frames.

If you do use expanding PU glue go sparing with it as you don't want the foam to come onto the face of the frame as it is a b*gger to get of, but it is by far the strongest glue I have found.

[prospero]

My way is almost the same as A.G.'s above. Except I wouldn't use PU glue.

Biscuits will give the joint a lot of extra strength and the L plates even more. You can't beat a bit of over-engineering.