Lathe cross slide conversion to a ball screw

**tonyfoale** · Jan 29, 2021, 04:40 PM

I had a lot of backlash in the cross slide feed screw, which made it inconvenient to use and difficult to turn accurately. I have had the notion to change it to a ball screw running around in my mind for quite some time and recently I bit the bullet.

Here is a video link:

The original lead screw was 15 mm in diameter, the ball screws came in 16 and 14 mm. I choose the 16 mm which was a mistake, you can see in the video how much I had to cut off the ball nut to get it to fit. The 14 mm size would have made that easier and still been perfectly adequate. We live and learn.

I am over the moon with the results of the conversion and have no hesitation in recommending it to anyone. There were some tricky setups needed to machine things accurately but they are fully explained in the video. Here are a few stills.

Lathe cross slide conversion to a ball screw-ballscrew_05.jpg

Lathe cross slide conversion to a ball screw-ballscrew_08.jpg

Click thumbnails for full size.

Lathe cross slide conversion to a ball screw-ballscrew_20.jpg

Lathe cross slide conversion to a ball screw-ballscrew_17.jpg

Lathe cross slide conversion to a ball screw-ballscrew_23.jpg

Lathe cross slide conversion to a ball screw-ballscrew_22.jpg

**DIYSwede** · Jan 30, 2021, 01:16 AM

Excellent work Tony - and explanations are very good throughout, IMHO.
For a while I've been on the lookout for LH <12 mm dia ball screws preferably with a ca 3 mm pitch w/o any success...
Q: Isn't the movement so darned smooth now, that the cross slide will move when turning due to the unbalanced improvised handwheel?

Keep up the good work and ATB

Johan

**tonyfoale** · Jan 30, 2021, 01:28 AM

Originally Posted by DIYSwede

For a while I've been on the lookout for LH <12 mm dia ball screws preferably with a ca 3 mm pitch w/o any success...
Q: Isn't the movement so darned smooth now, that the cross slide will move when turning due to the unbalanced improvised handwheel?
Johan

I have been unable to find a LH version also.
No, there is no problem with unwanted movements. The action is very smooth but not loose, there is enough friction from the dirt seals to prevent back driving and the unbalance from the handle is trivial in comparison.

**tonyfoale** · Jan 31, 2021, 04:42 PM

Paul Compton pointed out in the Youtube comments that LH ball screws are rare because these screws are mainly used in CNC machines and it is simply a matter of software as to which way they turn. So there is no need to make both RH and LH screws.

**gatz** · Feb 1, 2021, 05:54 PM

Great work, Tony
McMaster-Carr has a few English LH ball screws/nuts; probably not useful over in Spain

But, I did find this company that has LH metric.. might be worth a look.

https://us.misumi-ec.com/vona2/mech/...0029090%3A%3Ac

**dagrizz** · Feb 2, 2021, 04:11 PM

Originally Posted by tonyfoale

Paul Compton pointed out in the Youtube comments that LH ball screws are rare because these screws are mainly used in CNC machines and it is simply a matter of software as to which way they turn. So there is no need to make both RH and LH screws.

Umm, how'z about turning the ballscrew nut around. Then it'd run backwards! Same-o, same-o, right?

**tonyfoale** · Feb 2, 2021, 05:24 PM

Originally Posted by dagrizz

Umm, how'z about turning the ballscrew nut around. Then it'd run backwards! Same-o, same-o, right?

I am at a loss to decide if this is a serious comment or not.

**dagrizz** · Feb 2, 2021, 06:36 PM

Originally Posted by tonyfoale

I am at a loss to decide if this is a serious comment or not.

Definitely not serious; I just couldn't resist... Actually, I'd consider this upgrade for my Taiwanese 12 x 36, especially if the LH ball screw was available.
[edit]
I just checked at Thompson; they list a 5/8"LH w/ 0.2 lead, 6' long [https://www.thomsonlinear.com/en/product/190-9099]
The nut [https://www.thomsonlinear.com/en/product/8106-448-037] needs a screw-on flange [https://www.thomsonlinear.com/en/product/8105-448-002]. You'd have to machine the shaft to fit, and I haven't researched the fixed & floating bearing options.

**tonyfoale** · Feb 3, 2021, 12:59 AM

Originally Posted by dagrizz

I just checked at Thompson; they list a 5/8"LH w/ 0.2 lead, 6' long [https://www.thomsonlinear.com/en/product/190-9099]
The nut [https://www.thomsonlinear.com/en/product/8106-448-037] needs a screw-on flange [https://www.thomsonlinear.com/en/product/8105-448-002]. You'd have to machine the shaft to fit, and I haven't researched the fixed & floating bearing options.

Many thanks for that. BTW your links returned "product not found" responses but if I copied and pasted the PNs from your links in their search box it had no problem finding them. The screw on nut mounting is like I have on the Z axis of my mill, it would have been much easier to fit on the lathe than the flanged nut that I got.