Re: ballnut preload help

You probably need to quantify how much you have and then track down the source of it
one thing at a time.
What kind of machine is this on? Which axis?How much is it with a test indicator?
Backlash, play, endfloat, slop can come from a lot of different places.
1. Preload between ball nuts (or between ball nut and ballscrew)- measure this with the
ballscrew assembly by itself. Chuck the ballscrew in a lathe, set up the ballnut assembly so
that it won't rotate (possibly a capscrew through flange laying against crosslide tool post).
Put an indicator against end of ballnut and see how much you can move it. I know that
there are other ways, but if you have a lathe, it's a handy fixture for testing.

2. How's the connection between the mount for the ballnut and the section that it's bolted
to? How sturdy is the thing that the ballnut is mounted to? Is there any flex? I think that
Jon Elson commented about milling out a massive new steel yoke for his ballscrews on his
Bridgeport that didn't flex nearly as much as the ole yoke that came with the machine.

3. What kind of bearings are you using to contain the ballscrew on the ends? How are
they oriented? Good bearings for ballscrews are expensive. I had to do some hunting for
a project at work and the ones that I found for this application were in the $350-$400 per
set range. Angular contact duplex bearings, 65° contact angle, ABEC 5 and ABEC 7. Some
companies sold them in matched pairs (Bardon).
Once you have the bearings mounted, set up an indicator on the end of the ballscrew and
see how much you can push the table back and forth. The ballscrew should have a clamp
nut or device capturing the bearings. This reading with the indicator should be almost
nothing.

sorry for the long winded post, but I had to deal with this a couple weeks back on a big
machine at work. I have a crappy mill/drill in my home shop that I am working on right
now and it's a real eye opener to see what I did with it in the past, with what I had on
hand. No wonder I was dissapointed with it's performance....

Dan

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "tppjr" <tppjr@c...> wrote:
> Trying to get my conversion all finished up and doing a final reassembly
> after the move. Even with the ball nut preload set for the max recommended
> (.5 turns) I still have a bit of backlash. It isn't much but it is there,
> enough to feel by hand turning the bare timing belt pully. I though that it
> was in my bearing block and kept taking a half thou at a time off the
> retainer but was getting no change in the back lash. I then unbolted the
> bearing block from the table and moved the table off to the side so I could
> see the ball nut. With the bearing block just hanging on the screw I can
> still feel the backlash so it has to be in the nut.
>
> Any suggestions or comments?
>
> Thanks,
>
> Thomas