Straightness of steel/alumunium box section

[routercnc]

I'd also been playing around with a few ideas recently. Some of them are very similar to yours Ross!

First off, tried to get Z axis as close to gantry as possible (using profile rail, which I'm fortunate to have) and came up with the scheme below (LH image).

Also, playing with gantry sides idea using RHS, with an offcut from the gantry as a spacer to get the loads well into the RHS and avoid just locally distorting the wall (centre and RH image). Lower joint down to the X bearing is always an area for many ideas - thought using these bars each side were a bit neater than the usual double back to back plate arrangement.
Option of TIG-ing a closer plate over the sloping part of the RHS, but probably not worth the effort.


p.s. Looked at some of the steel box and RHS in the stores, and the ERW stuff would need grinding. The sides tend to cave in slightly relative to the corners.