Funny you should say that, I was just tending towards one screw.

I've read some more threads, especially the kingcreaky ones where he seems to just weld up a steel frame a whack the rails on it. OK, he's probably an expert welder. But still, I might be worrying too much about getting the rails straight and flat. Which means the earlier steel frame is, well, back in the frame.

I can't use any 3D drawing packages yet, but that's fine, you have to decide the general configuration before you draw the details.

I'm still interested in the best way to do make this, but it might be academic by tomorow. I'm likely going to order a 1800x900 machine from Eric at stepmores.