Nick
A low-cost and time trested solution is corner block and a Spanish
windless. Make-up four hardwood or better still plywood blocks in this shape:
-------------------
I . . . . . . . . . . I
I . . . o----------I
I . . . I
I . . . I
I . . . I
I . . . I
--------
The "o" represents a corner clearance hole drilled into the inside corner. A v-groouve is routed in both the outside edges (or sawn, chiselsd, doesn't matter what - it going to locate your string).
The frame is sawn/planed to size, the mitre faces coated with glue and it is placed on a flat surface. A corner block is put at each corner, outside the frame. Move the frame together and locate the corner pieces butting up against the outside of the frame. Run a string - polypropylene parcel wrapping string works well - round the outside several times then tie the ends togther. Take a length of dowel/whittling stick/dog's play stick an push through the middle of the string strands and use it to twist the sytring tighter, making sure that the string at the corners locates in the v-grooves. When tight enough gently rest the dowel against the frame and allow the glue to set. This technique is hundreds of years old and many hobby/arts/crafts shops sell low-cost plastic versions of it for a few pounds, but it's much more fun to make your own as it can be any size you want.
Alternatively use the 2nd fix trick - glue the long piece to the short piece using MitreMate 2-pack and a square piece of plywood as a squaring jig, repeat for other pair of pieces, then do same on two outside ends. Jobs done in 2 minutes :lol: Seen a 2nd fix chippie do 10 frames in an hour AND screw them to a wall on one job using this technique.....
