Smallest ball screws

[N4NV]

I am looking at converting a watch lathe so I need really small ball screws. What is the smallest practical ballscrews (with ball nuts) available?

Thanks

Vince

[LeeWay]

I have seen some nice tiny ones on Ebay at times.
I bought some precision acme screws with antibacklash nuts that seem pretty nice. They are 3/8" diameter.
I haven't actually used them yet, but may on a small build eventually.

[Jason3]

Hi Vince,

Sounds like a great project! Will there be a build thread?

What size ball screw would fit? I know Steinmeyer were offering 3 mm dia. ballscrews a few years back. From what I've seen, 10 mm is the small end of commonly available screws, but 6 and 8 mm can be found too. I had a couple of 8 mm ones, they were certainly nice and compact, and didn't feel too fragile... I threw them in with a lot of surplus used ballscrews I sold, otherwise I'd have given them to you

Best regards,

Jason

[N4NV]

Originally Posted by Jason3 Hi Vince, Sounds like a great project! Will there be a build thread? What size ball screw would fit? I know Steinmeyer were offering 3 mm dia. ballscrews a few years back. From what I've seen, 10 mm is the small end of commonly available screws, but 6 and 8 mm can be found too. I had a couple of 8 mm ones, they were certainly nice and compact, and didn't feel too fragile... I threw them in with a lot of surplus used ballscrews I sold, otherwise I'd have given them to you Best regards, Jason

As always, there will be a build thread (I have 4 others). I am looking for something close to 5mm, 6mm might do. The total x travel would be about 1", y 2". Very little load only light cuts. My Levin spindle is accurate to .00005" runout. I have turned some watch parts by hand that were .12mm in diameter, so this thing would have to be accurate. Still need a source for ballscrews.

Vince

[BobWarfield]

Vince, I hear you on the accuracy requirement. If you can find proper ballscrews, more power to you. Don't have anything to add there.

But, if you can't, consider an alternative. The forces involved on a tiny lathe are pretty small. Delrin nuts on an ACME screw such as what Widgitmaster uses on his router might actually work pretty well for you. The Delrin springs back after the cut, which pretty well takes out the backlash. The material has a built in lubricant (Teflon), so friction is low. The disadvantage is that enough force will either deform it, or wear it out really fast, but you don't have that problem.

You might take a gander at how Widgit approaches making them, or even get in touch with him about the backlash. He could certainly measure what he gets from one. You could make a neat little screw and nut combo up really quickly to try it too.

You could also make a preloaded double nut system out of Delrin on Acme pretty easily that would further remove any residual backlash.

Cheers,

BW

[N4NV]

I am using a Delrin nut on my Taig lathe CNC conversion. I was hoping for ball screws because of the forces involved. The steppers for this project will have to be pretty small. There is quite a bit of friction in a Delrin nut if you have it tight enough to prevent backlash and at those forces, I would have to build it much heavier than I would like to prevent an twisting.

Vince

[N4NV]

Bob, after your suggestion I looked into acme screws a little more and found that Nook has one that will work for me. It is 1/4-20 thread with plastic nuts. With my 200 steps per inch steppers, even without microstepping I will have an accuracy of .00025". The screws has an accuracy of .0003" which is better than rolled ball screws. The plastic nuts have a backlash of .006" so I am going to cut them in half and put a spring in between the two halve which will give me zero backlash with the light loads I will be seeing.

I bought some very low profile linear rails from eBay that will work for the carriage and cross slide.

It will be an interesting project, I just hope I can work on it along with all the other projects I am playing with.

Vince

[rowbare]

If you are going the ACME route, have you checked out http://www.dumpstercnc.com/ for anti-backlash nuts? He doesn't have 1/4-20 but he does have 1/4-16. That would still give you great resolution.

[N4NV]

Originally Posted by rowbare If you are going the ACME route, have you checked out http://www.dumpstercnc.com/ for anti-backlash nuts? He doesn't have 1/4-20 but he does have 1/4-16. That would still give you great resolution.

I already ordered the parts from Nook. I looked at DumsterCNC's website and what they are doing with their anti-backlash nuts is close to what I had in mind. The nuts from Nook were $28 each so they were a little more, but I will end up with a system that is closely matched.

Vince

[jdr]

Just read your postings.

You might want to try Starrett micrometer heads. Great for positioning small items. Very easy to mount.

Jack

[N4NV]

Originally Posted by jdr Just read your postings. You might want to try Starrett micrometer heads. Great for positioning small items. Very easy to mount. Jack

I have an XY positioning table that I purchased to convert that is set up that way. It just did not work out the way I wanted so I am going in a different direction.

Vince

[zephyr9900]

Originally Posted by N4NV I bought some very low profile linear rails from eBay that will work for the carriage and cross slide.

Vince, I'll be interested to see the mechanism you design. I built an X-Z mechanism for my carriageless Feeler lathe from two THK KR20 actuators, with size 10 (9mm tall) Thomson profile rails with preloaded carriages (overall height 15mm) in parallel with the slides. But that is a 4.5" center height.

Levin, that's a fine lathe. 8mm? How low of profile are your rails/carriages?

Randy