BallNuts, 1,2 or a double.

Hello,

in my quest to get going on my lathe conversion i've been having a bit of a look at various ballnut sellers and have been left with some questions.

i'm looking to get as low a lash as is possible without going to bonkers on price :)

How many nuts should be used?

i see that some people use 2 non preloaded nuts with springs to preload between them,

then theirs the preloaded nuts(ones that are labled that way are much pricier)

and the double ball buts(2 seperate nuts packaged together and preloaded).

i have noticed that all the china sourced ball screws and nuts are a bit vague on their backlash specs, what sort of backlash should one expect due just to using a c7 roled ballnut of chineas origin?

Are the pre loaded nuts actualy naturaly backlash free in use?

The double nuts in a single package, beter value than 2 singles and making some sort of preload mount?

Ball returns, plastic tubes, external metal tubes or end circulation? Whats the deal, any difference or just cosmetic/down to space requirements?

Hope i'm not asking too many basic questions but i had a look at zap automation and they carry loads of different types of ball nut with little info for the noob on what makes them different(also many have very similar prices so that makes it even more confussing :)

Stuart

p.s. I found a referance to an faq on this site about stepper choice but i havn't been able to find it using the search box.

Backlash not really a problem on lathe as you're always approaching cut from same direction, so I wouldn't get carried away on this.

I'm trying to do a geometric capable build, so am interested in it being fairly low.

I can always limit it to plain turning if it doesn't work out well. :)

Stuart

The cheap double nuts are shimmed so the low backlash quoted lasts until it beds in.
Springing nuts is a right royal pain in the backside but if you have gone anal on backlash then you don't really have an alternative.

Ok so the pre-loaded ones arnt adjustable to take up ware in them?

(sorry if thats a dim question)
:)

Stuart

I may be out of date, been a few years since I bought ball screws.
You can fit oversize balls, that really stiffens them up, but nothing I know lasts, except springs.

The Chinese ball nuts are actually back slash free. I would get a double ball nut if i was so worried. These are not the Chinese ball nuts like before 4-5 years, when they were back slashing.

Quote:

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Originally Posted by silyavski

The Chinese ball nuts are actually back slash free. I would get a double ball nut if i was so worried. These are not the Chinese ball nuts like before 4-5 years, when they were back slashing.

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Hello,

thanks for the info.

what is cross compatability like? If i ordered screws and nuts and then decided somthing wasn't working so well would I be able to buy any brand and mix and match or would that be problematic?

Stuart

Quote:

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Originally Posted by Stupoty

Hello,

thanks for the info.

what is cross compatability like? If i ordered screws and nuts and then decided somthing wasn't working so well would I be able to buy any brand and mix and match or would that be problematic?

Stuart

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IME none mix n match well unless coming from same company and then depends how old.? Tooling changes etc make difference to screws/nuts.
For instance I've got some Old screws from China and decided to replace worn nuts from same supplier and the current nuts supplied while fitting were not a very good fit and needed larger balls. They Worked but not straight fit and needed tweaking.

Regards best way then I think is double nuts with springs washers but like robin says it comes with a price, thats being a royal pain to fit and get right also IMO slightly more wear due to higher constant friction.
Shimmed Double nuts are ok but they need servicing occasionally, which shouldn't really be a problem as it's a good idea, esp on lathe, to have strip down every 12-18months or so to give a good clean and fettleing.!

Quote:

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Originally Posted by JAZZCNC

IME none mix n match well unless coming from same company and then depends how old.? Tooling changes etc make difference to screws/nuts.
For instance I've got some Old screws from China and decided to replace worn nuts from same supplier and the current nuts while fitting were not a very good fit and needed larger balls. They Worked but not straight fit and needed tweaking.

Regards best way then I think is double nuts with springs washers but like robin says it comes with a price, thats being a royal pain to fit and get right also IMO slightly more wear due to higher constant friction.
Shimmed Double nuts are ok but they need servicing occasionally, which shouldn't really be a problem as it's a good idea, esp on lathe, to have strip down every 12-18months or so to give a good clean and fettleing.!

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Thats good to know (compatibility) i will make sure i get them all together, once iv'e waded through the billion and a half available options :)

Stuart

Stuart,

I did this a while ago so trying to remember the exact figure. Around 0.05mm (50 microns) from memory based on a 16mm diameter 5mm pitch chinese ballscrew and single nut. Measured this using a DTI on the Y axis and jogging it from Mach3 back and forth in 0.01mm steps.

I have a Chinese 12 mm ballscrew on my S7 cross slide, single nut and IIRC the backlash I measured when first installed was about 0.03 mm, 30 microns. My Novamill has about the same value using double nuts on 16mm screws, but that has had a lot more use! On a lathe it's nice to have low backlash if you want to do profile turning though would have to turn compensation on. I have tried compensation on the screws before but it doesn't work very well if the backlash is too large. In fact I found it didn't work at all!

Thanks for the info on backlash amount's that you guys have experienced, always nice to have an idea of what is achievable.

With regard to the preloaded nuts (either springs or balls oversized) is their any rule of thumb for the added drag/resistance in the system?

Stuart