Here we go again . . . MK4

[Jonathan]

Well that link is quite read.

Mm, it's good stuff.

I've only got so much space and I had wondered about an enclosure in the future so don't want to go past the edge of the table with any parts.

I wouldn't prioritize the enclosure over the stiffness of the machine. The 'sufficiently strong' machine in my sig. is currently enclosed with shower curtains and sitting in a paddling pool containing 240L of coolant, in my friend's living room of all places. It's as crazy as it sounds, but it does work!

To summarise I think what the article is saying is that because things will twist and rotate, you should put the ballnut in the centre of rotation (that is rotation of the structural parts caused by moments) so that the nut sees minimum binding loads etc.

I agree that the radial displacement effects on the ballnut will be minimal, but I was still thinking about stiffness - namely that the center of stiffness is (by definition) the point where when the ballscrew applies a force (which can easily exceed the cutting forces), no angular deflection will occur. Prizes for working out how big the effect would be...

Dean: thanks, noted. If I ever design a machine where their form is not a constraint, I'll consider using them.