I'm on a quest to get the backlash on my machine under 0.001" or as close as reasonably possible.

This is an older 8x30 knee mill with new Chinese rolled 1605DFU ballscrews and double nut.

With the ballscrew/double nut out of the machine and in my vise, I could feel some backlash between the two nuts, I was able to squeeze a 0.002" feeler gauge between the nuts. By adding a single 0.001" shim between the nuts the backlash is now about 0.001" so I think I have the ballscrew nut about as good as I can get it (it is what it is). That leaves the bearings......

With the original 6001Z bearings in the BK12 blocks and everything assembled, actual backlash is 0.004", so about 0.003" axial movement in the bearings. I ordered a random set of 7001AC bearings. These are not a matched set. so as I understand it I will need to shim them to get close to zero. I measured all five bearings and in all cases the inner race is wider than the outer race by between 0.0006" and 0.0022" Seems to me like it would make more sense to ship these with narrower inner flanges so tightening the retaining nut would allow the end user to torque these to zero or near zero backlash. Does that make sense?

So at this point, with what I have, I think my only option is to add a shim between the outer rings?

If I try that I'm thinking of using say a 0.005" shim, and then in theory I can take out the remaining 0.001" or 0.002" by torquing the retaining nut, does that make sense?

I realize ordering a matched set of ACB's might be a more sensible approach, but I would like to give the shim approach a try.

Comments, suggestions, expertise is most welcome as this is all new to me.

Any wild guesses on how much torque will be required on the retaining nut to take up the remaining slack?

This is an older 8x30 knee mill with new Chinese rolled 1605DFU ballscrews and double nut.

With the ballscrew/double nut out of the machine and in my vise, I could feel some backlash between the two nuts, I was able to squeeze a 0.002" feeler gauge between the nuts. By adding a single 0.001" shim between the nuts the backlash is now about 0.001" so I think I have the ballscrew nut about as good as I can get it (it is what it is). That leaves the bearings......

With the original 6001Z bearings in the BK12 blocks and everything assembled, actual backlash is 0.004", so about 0.003" axial movement in the bearings. I ordered a random set of 7001AC bearings. These are not a matched set. so as I understand it I will need to shim them to get close to zero. I measured all five bearings and in all cases the inner race is wider than the outer race by between 0.0006" and 0.0022" Seems to me like it would make more sense to ship these with narrower inner flanges so tightening the retaining nut would allow the end user to torque these to zero or near zero backlash. Does that make sense?

So at this point, with what I have, I think my only option is to add a shim between the outer rings?

If I try that I'm thinking of using say a 0.005" shim, and then in theory I can take out the remaining 0.001" or 0.002" by torquing the retaining nut, does that make sense?

I realize ordering a matched set of ACB's might be a more sensible approach, but I would like to give the shim approach a try.

Comments, suggestions, expertise is most welcome as this is all new to me.

Any wild guesses on how much torque will be required on the retaining nut to take up the remaining slack?

This is a companion discussion topic for the original entry at https://www.cnczone.com/forums/linear-and-rotary-motion/468778-angular-contact-bearings-experts-new-post.html