Second ballnut for improve accuracy

[ian]

It is doable to get it close.
I've got my machine down to 0.025mm. It uses gibs/ways so is fairly tight unlike linear rails and my longest is X at 800mm.
I did 2 things.
1: Used decent angular contact bearings size 12x32x10mm in custom made mountings for my 1605 DFU screws.
2. I packed (shimmed) the double nuts with thin (0.01mm) aluminium foil (tin foil) between the back nut and center spacer until they were slightly bitey.

These 2 ways seemed to be key. You have to be carefull where you buy your screws as some don't bother with the spacer bit so it's useless.
My Y screw needed packing by 0.04mm and my X needed 0.07mm. Bit of a difference there. I reckon your X will take a fair bit.
It's well worth taking the time to do these.

You can still have issues with spindle run out too especially with ER collets. Generally I can get it to 0.01mm in the ER collets or 0.004mm direct collet.
I generally add 0.01mm oversize to my drawings and it comes out pretty bang on.

Otherwise you may have to get some proper expensive grounded C3-C5 type screws. And angular contacts to fit them.

Thanks - it is good to know it is achievable and realistic - I wasn't sure whether I had the wrong expectations of what can be realistically achieved. I'm settling in for some time consuming fiddling to get it dialed...

Did you tension your ballscrew axially?
Do you ha e a picture or design for the contact bearing housing and mount?

Thanks in advance

Ian