Hi Psiron,

I didn't mean twist in that way, that would be racking where one side moves more than the other. What I mean is physically twisting the 4x2 channel which will show up as little ridge lines on your cuts. When I first put my design up, Irving and a couple of others commented that as the rails were unsupported the gantry would twist and they were 100% correct, I soon changed to profiled rail mounted on the steel box section and all my problems went away. I think you'd see a similar situation midway across the table. I suppose a lot depends on what you want to produce witht he machine, as it's an 8 x 4 I presume you are looking at cutting sheet stock so this might not be much of a concern if it's just shapes you are cutting.

I'll have a look at the videos (didn't see them) and compare them with how my machine performs

Jeff.