Getting everything square

[BillTodd]

Was the glycol, to increase the viscosity of the water? or do something to the surface tension?

It wets the glass so reducing the meniscus.

[daveshorts]

It wets the glass so reducing the meniscus.

That makes sense, I was worrying about that.

[daveshorts]

The main thing I am worried about is that it won't be planar. You can take a rectangular frame, and twist it, just by rotating the joints. So quite a tiny error in the joints could produce a few mm error in the frame. This will mean that what you end up milling will not be flat either. I have a particular problem as the table I have just built for it is very definitely rough woodwork, so I definitely can't rely on that for a plane. Horizontal is just a convenient plane to use.