Hi Neil,

I think in all that energetic exchange no-one picked up your enquiry in post #189. You were asking about getting the rails parallel to each other (in plan view). In building mk3 (WIP) I did something similar to you in fixing the 'primary rail' and using the gantry to help set the other rail before marking, tapping and bolting it down. In addition to that to make sure the first rail was straight I clamped a flat hard plate of steel against the outside of the extrusion (with a bit sticking up) to form a stop to push the side of the rail up to.

It turned out that the secondary rail fitted gently against the edge of the other extrusion so all that time spent cutting the crossmembers carefully etc. and building the squarest bed I could had paid off.

I also design and make RC planes - so balsa, liteply, and ply are the usual materials being cut. Will be watching your build with interest.