Purchasing a z-axis?

[Tonyel]

Well, I did wonder! Zero backlash sounds like a hard thing to achieve in the real world.

The intention is to build the whole thing, more or less, from steel, on the grounds that it's cheap, can be easily welded by someone I know from work, and is about 3 times more rigid than ally. I appreciate that the associated 3 times higher density might compromise the acceleration of the moving bits and bobs, but I reckoned that it would be fairly easy to upgrade motors and drives in the future, but much harder to rebuild with a rigid frame.

The plan at present is to build the rectangular frame, get it welded as near plane as possible, then get it skimmed or ground to a true plane. A machine shop near me reckoned they could do it for about £160.

I've been thinking about the Z. Although the asymmetric design looks a bit dodgy, I think it should work. After all, the Z slide has to be rigidly constrained anyway, so the slight offset load from the ball screw ought not to bother it. Also, I wanted to minimise the offset of the Z direction load from the shear centre of the gantry box beam, so that it is less prone to bending, and can be lighter. I hacen't got as far as the milling head carrier yet, but intend it to be a channel, for rigidity.

By the way, I'm using the linear rails mainly because I got very lucky and found a load in a scrap yard! Otherwise, I think I'd be using round rails and bearings.

I enclose a close up of the gantry and Z FYI.

Thank you both for your comments and help - much appreciated! Most people just think I've gone mad...

Cheers,

Tony