Author Topic: Ballscrews On Manual Lathe and More  (Read 253 times)

Offline Buell

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Ballscrews On Manual Lathe and More
« on: October 06, 2018, 10:34:13 AM »
So I have a Sieg Mini Mill that Im trying to get sorted. My questions are..Could I replace if i can shoe horn in ! a pair of linear bearings and a Ballscrew assembly to stop with all the Backlash issues, on both the x and Y ? My thought was because these screws are 90% efficient...less effort to crank and if i could in the future may attach a couple of steppers to use as power drives and when Im really daring convert to cnc !
 
My thought was I cannot because there is no load or friction to hold the screw in place at any given time it would just go in any direction ? That being said is the only reason the ballscrews on cnc dont move because the Steppers constantly Lock them in Place ?

Its a sx2 plus and at the moment Im building a Column support and base to try and stiffen it up there, any info on Mods would be great ..I know its been a while since I was on here but the lathe is great now i got it all sorted.
If you don't succeed ...try try try again...you can't fail trying.

Offline philf

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Re: Ballscrews On Manual Lathe and More
« Reply #1 on: October 06, 2018, 11:12:20 AM »
Buell,

You're right in thinking you will need either a stepper motor or brake to stop your table moving under the cutting forces. Servo motors often have an integral brake.

My CNC uses normal dovetail slides and the table can quite easily be pushed along by hand if the steppers aren't energised.

Backlash can be a pain but most manual machines have some backlash. If there's too much it can be detrimental when climb milling.

A DRO gets round accuracy and repeatability problems without having to compensate for backlash which can vary along the length of a leadscrew.

Hope this helps.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline Buell

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Re: Ballscrews On Manual Lathe and More
« Reply #2 on: October 06, 2018, 01:51:25 PM »
I thought as much with the stepper motor ! I guess Im gonna Invest in a Dro. And do some mods to the Leadscrew thats there. Anyone had any luck with making it slick ? All the mods I have seen seem to be for the X2 which is different to the x2plus typically the one I have is Based on the X1 begs the question why they called it an X2 never mind.
Heres a stand Im trying to beef it up with..
If you don't succeed ...try try try again...you can't fail trying.

Offline hanermo

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Re: Ballscrews On Manual Lathe and More
« Reply #3 on: October 15, 2018, 11:15:01 AM »
The x axis ballscrew on my (very good) lathe was a vast improvement.
The stepper I used then == 2004 acted as a tiny brake when disabled, and as a break when powered.

The 3/4" 0.750" roton ballscrew was == 14 x more rigid than the original 16-17 mm acme screw on a 12x industrial lathe.
And had vastly less stiction and about 5x more power due to lower losses.

Now I use an ac servo of 750W for much more accuracy and rigidity.
I use servo-disable signal to turn it off for manual turning and enable it when I need a solid break.

Now finalising move to a new 32/5 mm ballscrew of much higher quality.
And direct drive vs HTD 8-30 mm belts at 1:2.
And 25 mm linear guides on x, and 270 mm movement for  gang tools and 2 toolchangers vs 140 mm movement on gibs.

Either the belts or pulleys were inaccurate, and movement was not linear to a high accuracy with the bigger belts and pulleys in htd 8/30.
Part of the problem was likely the roton rolled ballscrew.
And the weak yoke linkage (rubbery) in version 3 of x axis mount.

So I had "bounce" where the x movement was sometimes erratic in unpredictable ways.
After 3 weeks and 150+ hours the new x axis is nearly done.
(temporary) Yoke needs fixing and then the servo needs a mount point.