X3 mill with rails, ATC, new motor

[Jonathan]

Believe it or not, I found some time to work on this project again!
Decided I should do some sort of drawings for the X & Y axes, so here's the rough idea. I say rough as most of these parts are just blocks to show the general arrangement of things - I've not added detail:



The X axis uses a bed from a different machine. I'm adding HSR35-1100mm rails to this and SHS25 rails to Y. These rails sizes are based on what I've got good deals on. For the ballscrews I'll be buying TBI DFU ballscrews, similar to Z, sized to get a reasonable stiffness for each axis.

As a 'first pass' look at it, I've tabulated the stiffnesses of each component, then combined these (as springs in series) to get a value for the stiffness of each axis:



This implies that the stiffness is dominated by that of the ballscrews, as these are by far the smallest numbers in the table, so it is worthwhile to invest more in 'large' ballscrews as improving these should have the biggest effect on the overall stiffness of the axis. For the table above I've calculated the stiffness's based on DFU2005 on X and Y, with angular contact bearings on both ends of the X-ballscrew, to compensate for the lower stiffness of such a long ballscrew.

This analysis is still too basic though, as it assumes the forces are all applied at the respective axis center of stiffness, since moments aren't considered, so I need to re-calculate including the 'pitch' and 'roll' stiffness of each axis. If this shows that the ballscrew stiffness is still significantly lower than the linear bearing stiffness, then I'll consider using even bigger ballscrews.

So far I've started machining the bed and steel spacer strips to mount the rails, that's about it...