Thread: Rotary ball nut?

Hi Glenn,


Rotary ball nut.... Are you talking about Ball Screws or something else?


Cheers
Kym

Hi Kym,

Rotary Ball nut is where the ball nut rotates around a fixed ball screw instead of the ball screw turning and moving the ball nut, hop ethat makes sense.

I found this video CNC router Rotating Ballnut drive first test - YouTube which shows a homemade one, little hard to see though.

They say they are good to use in areas where whiplash etc from high speeds over distance come into play

Cheers
Glenn

For the last 15 years, I've used two large commercial routers (~$150,000) that use rotating nut ballscrews. The screws were about 4.5meters long, and about 40mm diameter. We cut at 20M/min on the one at my current job, which is a Morbidelli. They work very well, but are very expensive.

Imo, it would be much cheaper to just use a screw with a large enough diameter, and high enough lead to prevent whipping. A 25mm screw with 25mm lead should be good for close to 3M long I would think.

Thanks Ger21 good to know and hear from someone with direct experience.

I guess one of the main reasons i was looking into it was more for positioning of the motor and compact design, more so than the worry of whipping (machine I'm looking at designing would be no longer then 1500 to 2000mm long).

In regards to increasing the lead, does this have any impact on accuracy? I've only ever used 5mm lead, I'll do a bit of research in this area.

Cheers
Glenn

Hi Glenn,

This an idea that Blurry customs has used on the Y axis. The picture is a little dark...looks like there is a pulley attached to the nut. IronMan XE24 CNC Router

Click on IronMan XE24 CNC Router and then find in Alternative views.

Cheers
Kym

IronMan XE24 CNC Router

Interesting Site Kym, yep that's the type of ball screw I'm interested in.
Might shoot them and email and see if they have an more detail on it.

Cheers
Glenn

Originally Posted by Lappy

In regards to increasing the lead, does this have any impact on accuracy?

Not accuracy, but possibly the resolution. Resolution depends on several different things.
If you plan on using steppers, then anytime you increase the distance traveled per stepper revolution, then you lose resolution. If you use servos, you can make up for it by using higher count encoders.

Hi Glen

My machine has rotating nuts (Thats a post you'd only seein a forum like this) on both x axis drives and also the Z. The 2.5m x drives are using a standard fixed nut but a drive that I made up while the Z is a stock rotating nut.

I'm happy with both setups as they removed weight and hieght in the case of the Z and rotational inertia in the X.

Here's some pics...
Yet another Aussie biuld log - Page 6 - CNCzone.com-The Largest Machinist Community on the net!

I'm on the central coast if you want to see the beast in the flesh.

Cheers

Mark

Hi Mark - nothing like a machine with rotating nuts!

Thanks for the offer that would be good, we have family up your way so next time we are due to visit I'll shoot you a note, be great to see your machine.

Cheers
Glenn