32460Re: Ball screws
- Mar 2, 2013Since I mentioned it earlier and others have commented about using two standard ball nuts instead of the more expensive anti-backlash ones, I'd like to add this from what I have done and heard from others.
Oh and you can just use one standard ball nut, but you will have a small amount of backlash and it will increase over time, so if you just want to get it up and running, one will work for starting out.
Yes you can put spring pressure between them, this takes up the slack and keeps them close to zero backlash, and the spring pressure compensates for wear. But you need to use a strong spring or you can get bounce while cutting, so most normal coil springs won't work.
I've seen a lot of people use Belleville Washers which are heat treated as spring steel, and can have a spring force from like 10-35 pounds per washer (in the sizes used for a 1/2" - 5/8" screw) and these washers can be stacked for more pressure.
But what I did was made the mount that went to the table and one of the ball nuts was threaded into it and locked with three set screws to keep the ball nut body locked in the mount.
Then I just made a simple aluminum square piece with a hole in the center that was threaded for a ball nut and drilled holes for set screws from the sides to lock that ball nut, and cut a groove on one side to make tabs or ears to fit over the body of the ball nut on the mount.
I screwed the second ball nut into the square piece (smooth side) and started the ball screw in this one first, just enough for the ball screw to start out the other end of the ball nut, then holding this against the first ball nut (on the mount) so those tabs or ears were on both sides of the ball nut body I finished turning the ball screw through both ball nuts.
Now to take out the backlash I held the square piece of aluminum and unscrewed the second ball nut (away from the first) until there was tension but the ball screw still turned smoothly, think it was about 1/16 or 1/8 of a turn, then locked it in place with the set screws.
The way I did it will most likely get backlash over time, but for it being a hobby machine I think it will take a long time for this to happen, and I plan to redo it later (or buy a newer machine) once I get the hang of the programs.
Hope this rambling helps someone :)
--- In firstname.lastname@example.org, Jerry Durand <jdurand@...> wrote:
> On 03/02/2013 01:29 PM, Jim S. wrote:
> > Another poster's remarks about using two nuts per screw works. It is
> > much cheaper than any of the preloaded nuts sold commercially. You
> > mount them so they can be preloaded against each other to eliminate
> > backlash.
> I've seen products where the anti-backlash nut is just two nuts with a
> spring between them.
> You can also DIY nuts from acetal, someone had an instructional on doing
> Jerry Durand, Durand Interstellar, Inc. www.interstellar.com
> tel: +1 408 356-3886, USA toll free: 1 866 356-3886
> Skype: jerrydurand
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