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View Full Version : New interesting answer to screw whip.



alboy
26-01-2018, 07:17 PM
Had to post this guys. On a face book forum I was trying to explain why a ballscrew on a large machine is not really feasible, I of course mentioned screw whip. Here is the answer given by someone on the forum ........

If you go longer than 4' on a ballscrew, just turn the nut instead of the screw. Whipping gone.

What do you think. Interesting but difficult to implement?

magicniner
26-01-2018, 08:11 PM
Erm, Preaching to the Choir there mate.
Lots of threads here on Rotating Ballnuts ;-)

alboy
26-01-2018, 09:25 PM
Will have to do a search then. My inquiring mind is activating once more :-)

JAZZCNC
26-01-2018, 10:32 PM
Had to post this guys. On a face book forum I was trying to explain why a ballscrew on a large machine is not really feasible, I of course mentioned screw whip.

They are pefectly feasible. It's all about how you do it and often it's done wrong.

alboy
26-01-2018, 10:48 PM
They are pefectly feasible. It's all about how you do it and often it's done wrong.

Oh that applies to so many things in life lol. How are you, long time no speak. The CS labs controller has been working great by the way.

It just got me thinking that on a large machine, which is better ballscrew with rotating ball nut or R&P. In my mind (not always the best place to be :-) ) I would think that R&P would be cheaper to implement with better stability and speed (accuracy?) on larger machines. Now I am up for being proven wrong in my assumptions, best way to learn something :-)

JAZZCNC
26-01-2018, 11:54 PM
Oh that applies to so many things in life lol. How are you, long time no speak. The CS labs controller has been working great by the way.

It just got me thinking that on a large machine, which is better ballscrew with rotating ball nut or R&P. In my mind (not always the best place to be :-) ) I would think that R&P would be cheaper to implement with better stability and speed (accuracy?) on larger machines. Now I am up for being proven wrong in my assumptions, best way to learn something :-)

Well it's no brainer really the Ballnut wins every time if talking which is best. R&P doesn't come close in terms of accuracy or efficiency.
However rotating nut is more involved than rotating just the screw.

That said R&P comes with its own problems so can be just as involved. For instance, a ratio is required to get required resolution, which brings its own complexities. Then some mechanism is prefered to help reduce backlash by keeping constant engagement of the pinion with the rack which again brings some complexitys.
Also, careful positioning of the rack is required to avoid chips and dust from interfering with motion. Care is needed to keep rack clean so much more maintenance for the user than is with ballscrews.

Then you have to factor in the lower efficiency of R&P so larger more expensive motors/drives are required. All this soon gets expensive fast.

In performance terms then R&P can allow higher feeds for less cost but this does come with a cost of resolution. But the same can be said for ballscrews because very difficult or should say expensive to have high feeds and high resolution.

Take your pick but ballscrews will win every time in which is best battle.

alboy
27-01-2018, 12:40 AM
Thanks for that explanation, glad I have learned something new today, I assume (again) that the higher resolution of ballscrew would not be so important to a large woodworking cnc router as compared to the accuracy required of a cnc mill. I would hate to think what 2x 3mtr ballscrews would cost, I take it a support system to prevent screw whip would add to that cost as well I know that double pinion anti backlash and larger steppers would add to the cost of R&P (that's what I have on my machine) but do not have a clue as to what the price difference would be. I know my machine is accurate enough for the type of work I do even fairly detailed relief carving but I suspect the precision would be insufficient if I were to attempt cutting or milling to tight engineering tolerances. Thanks again oh wise one for your enlightenment. :-) :-) My inquisitive mind a satiated lol.

JAZZCNC
27-01-2018, 01:24 AM
I would hate to think what 2x 3mtr ballscrews would cost, I take it a support system to prevent screw whip would add to that cost as well

Not much as you probably think if got from China. If done correctly no support system is required and no whip will occur.
If wanting really high rapid feed rates then does start falling in R&P favor because does get difficult to handle whip with ball screws without going to rotating nuts.
But if can live with 15-20mtr/min rapids then ball screws can be made to do this without the whip and no pratting with rotating nuts etc.