Good Ballscrew for 7x14 Lathe?

[The New Steve H]

I used the Steele plans to turn a 7 x 14 into a CNC lathe. I quit fooling with it because the leadscrew was not accurate. It doesn't use a ballscrew. It uses a very expensive screw with a plastic nut from McMaster-Carr. I would like accuracy no worse than 0.005". I don't see how I can cut usable threads if it's less accurate than that.

I would like to give it another shot, with a real ballscrew, but I don't know of a good source for such a screw at a reasonable price. I don't want junk, but it doesn't have to be from Tiffany's, either. Can someone recommend a good vendor? Thanks for any help you can offer.

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[The New Steve H]

I didn't realize this question was too hard to answer when I posted it.

[cyclestart]

The Steele plans aren't public domain so it is a tough question.
Thomson and Roton have compact flange-less ball nuts compared to the common flange type from China.
Thomson has 3/8 diameter screws, possibly Roton as well.
Check their drawings to see if .anything fits ? Make your own flange.

.

[jfong]

CNC Lathe

Here's my conversion using some thk ballscrews found on eBay

[cyclestart]

The UK prices in this link are a bit of an eye opener but give an idea of how small these flangeless ballnuts get.

R12-04C1-RSW

I'm surprised you're getting such poor performance from acme screw and (assuming) anti-backlash nut..
The problem could be bearings in the fixed end support or the motor coupler ?

[The New Steve H]

Thanks for the link, Jfong. I have seen your project before. It looks like the left end of the lead screw is not supported. Is that correct? I was thinking it would be necessary to support the left end in order to apply rightward pressure on the screw and reduce longitudinal movement in the right-hand bearing. If you're getting good results without doing that, then I would rather do what you did and avoid the hassle of aligning two bearings and the nut.

Cyclestart, you are probably right. I had some wobble in the lead screw support and had to tighten it up.

[Al_The_Man]

When I retrofitted Lathmaster 9"x30" mine I used a Hiwin from Taiwan, very high quality/precision for the price, double pre loaded nut, but the shaft was very hard and did not appear to be surface hardened, but hardened all the way through, I had to get a friend to turn in down with ceramic tooling.
At the time there was a guy on ebay that was bringing them in in the box full.
Lathemaster 9x30 First Chips!
Al.

[jfong]

The right bearing block takes up all the load. I believe there is two angular contact bearings in the THK support block. It came with a left side support with just a single radial bearing but I never installed it. The ballscrew doesn't spin very fast so it wasn't required to limit screw whipping. It wasn't meant to limit longitudal movement.

[The New Steve H]

It looks like there are a few Hiwin deals on Ebay. Also the linearmotionbearings2008 guy.

[lixingwen1987]

Luoyang Derun Precision Machine Tool Bearings co.,ltd.

Add: Derun technology area , huaxia road, New technology zone,,Luoyang, Henan

TEL?+86-0379-65112328

FAX: +86-0379-65112392

TEL:+86 17184625318

Email:drzbearing@163.com

Web:http://www.DRZbearing.cn
http://www.DRZbearing.com

[Norvegicum]

what sizes ball screws are you using for your 7x14? z: 1605 500mm? x: 1204 25mm or 20mm?

[joeavaerage]

Hi,
to get that sort of accuracy you want a ground ballscrew. There is no such thing as a cheap ground ballscrew......rolled yes.....ground no.

overstock & surplus automation products: Motion Control, NSK Precision Ground & Rolled Ballscrews

Craig