I make quite a few frames to go on prints that I sell. I use Polycore and glue ( high viscosity super glue)and wedge each corner.
Glueing each piece individually before joining is tedious and time consuming and if a number of pieces are glued at the same time the glue can drip .
I have made this jig that holds about ten pieces at a time and keeps the surface level while applying a drop on each with glue on therefore no dripping while going through them. It also holds the L shapes as seen on the same basis for gluing.
Simple I know but might help someone out .
Cheers
James