Novel construction leads to novel clamping
Bill Tindall, E.Tn.
I was suspecting the difficulties I was having building a corner cupboard were the result of not knowing how to build one. The day in the Headley shop confirmed this fact. But I press onward.
Conventionally the top, bottom and shelving hold the cupboard together. In my case daughter wanted adjustable shelving, and I built the front mitered vertical framing first instead of last. For the rest of the project I suffer these decisions.
What is most critical is a square frame for the doors. To that end I glued up the front door frames. But, there is little that holds them together at that point. I temporarily added a strip along the bottom(white piece of poplar in PIC) and a piece of plywood where the doors will go to hold the frame square until the face frame glue cured and this assembly glued to the case top and bottom.
One of the joys of building this thing is that there is nothing orthogonal to clamp to. This obstacle was overcome with the arrangement shown. Once I install the case sides it will become rigid.
A trammel is positioned across a diagonal in the door opening. The trammel is how I determine if something is square; use the trammel to measure diagonals. In this case they matched to within 1/16"- success!