Straightness of steel/alumunium box section

[Ross77]

True, but it's not as strong and more easily transmits vibrations since it's less dense...

Personally for moving gantry with steppers I would go for Ali. Fixed gantry then heavy duty steel box...You pays your money you takes your chance.....

You can design for extra strength and reduce the vibrations in the first place and it dosnt become such an issue. (I'm sure someone will disagree with that.:naughty:)

This is what I was looking at, the idea was that the two horizontal box sections top and bottom with the c channel and vertical box in the middle would provide a pseudo I beam but with improved torsion due the central box, the c channel would house the Ball screw and there fore keep the z axis in tight to the gantry

The idea for the z axis was similar in that the spindle and hence cutting forces were in close to the gantry and the back to back rails to give an even load distribution. I figured that a wider z carriage was acceptable as the increase in rails needed is marginal compared to the bearings.

Anyway thats as far as i got and I know there are many improvements but hope it of some use or sparks another idea