y-axis ballscrew binding

[crazyman]

Anyone have problems with the x or y axis ballscrew binding slighly when installing?
When I turn the pulley gear by hand using low amount of tourque i sometimes run into a slight resistance that requires more torque to breakthrough. When applying the extra torque I hear a "click" "click" as if the bearings are getting jammed slightly and then letting go. prelaod is set as per the IH website .2turns past first resistance feel by hand.
Anyone have this issue and what was done to fix it?

[dfurlano]

Sounds to me like you lost a ball bearing. That can happen if you put the ball nut on the screw yourself.

[chipsinpan]

You did not say if you were installing a new ball screw , or just doing maintenence on an old one .
Anyway I will share my experience with the things I learned on my (Milltronics CNC ).
First of all , the ballscrew assembly is fairly bullitproof and is usually not prone to problems. I have found the end thrust bearing to be the culprit most of the time . It is important to note ( in my case ) that the end thrust
bearing is an "angular contact precision Ball bearing ". This means that there is only one proper direction to install the bearing . The preload to eliminate the backlash depends on the proper relationship of this bearing in the housing .
This bearing is usually the one nearest the drive pulley . The one on the other end is a "floater" and serves only to hold the ballscrew up .
I know this is fairly generic info , but may be of some help .

[wildcat]

You will have some clinking on a new ball screw as the balls recirculate. Losing one is probably no big deal... if you lost several you might want to find them

Do you feel the resistance when the trust bearing is not so tight? Maybe you just need to back it off a little.

Have you checked that the ballscrew is installed straight? Move to one end of travel and measure from the ballscrew in both dimensions to a reference point. Move to the other end of travel, repeat the measurement and compare. If the ballscrew is not straight I would expect your binding would occur only at one end or the other.

Good luck

[crazyman]

To answer a few questions:
No bearings were lost when installing(rebuilding) the new ballnut on the ballscrew...I'm becoming an expert at rebuilding these now after so many teardowns.

The prelaod is set as per the IH instructions (.2turns) if I lossen it it will probably bind less, but that will just mask the problem. I have the Y axis working at the same preload with no binding. Gene wants me to try backing off the preload a bit but i would rather be certain the ballsrew is aligned perfectly b4 trying that.

wildcat, good suggestion on checking the ballsrew alignment i will do this next. I was trying to determine a good way to check the aligment previously.
The funny thing is I get binding on two far ends at time while the middle travel is fine. So that makes me think the ends may be out a bit. For that to be so the ballscrew may be slightly bend ( which seems to be the case when I turn the screw i notice a very slight wobble at free floating end. I though that this would not be an issue since the screw is quite flexible on the floating end.
What prelaod setting are you guys/gals using? Gene tells me you don't really need the full .2 turns? If your using less preload that .2 turns, any issues?

Also, the coolar on my ballnut seems to wiggle back and forth a bit on the two pins. Anyone see an issue with that in terms or backlash?

[wildcat]

To check the alignment just use a caliper and measure the free end of the ballscrew to the casting in both dimensions with the saddle at both ends of its travel. A small difference is fine... but if you could measure the difference with a tape measure there is a problem If there is an alignment problem you could drill out the holes on the mounting plate (or drill new holes) and/or put a spacer under the ball nut mount.

If it is binding at both ends then perhaps you have a combination of a misaligned ballscrew and tight spots on the ways...