Rotating Ballnut - design ideas

[AndyGuid]

Hi Martin, welcome to the forum!

Afraid I don't have the knowledge to answer your question with certainty, but my gutfeel is that 2010 would be sufficient with the ballscrew being stationery as you plan on using a rotary nut.

Hopefully a knowledgeable member will notice your post and give you an authoritative answer over the weekend.

Jonathan's Rotating Ballnut is the only thread I've seen on this subject, so they seem to seldom be used on DIY builds.

[m_c]

2010 would likely be good enough, or even 1610.
To work that out, you really need to calculate the maximum forces involved.

The reason rotating ballnuts aren't popular, is spinning the screw is far easier.
Rotating ballnuts are far more elaborate, and for most applications aren't needed.

[JAZZCNC]

Hello guys.
My name is Martin and UI live in Norway.
I am currently designing a new big CNC Router with 1400x2700x200mm work area.
I want to use Rotary Nut and 2510 ballscrew together with 750W servo motor DMM.

My question is:
The Y axis is 3000mm long, and the ballscrew has to be 3100mm long in total.
Is 25mm ballscrew ok or is it OK to use smaller (2010 og 1610)

With rotating nuts things change with regard to pitch and diameter compared to rotating the screw.

It's a common mistake to think with a rotating nut setup that you don't get a screw whip because the screw isn't rotating and therefore you can use a smaller diameter screw, but in reality, what happens is that the screw actually bends under its own weight. So when the gantry is at the ends of travel the unsupported length of the screw starts to vibrate and oscillate from the vibrations of the machine and much like flicking one end of skipping rope when the motor starts to reverse travel direction it sets the screw off oscillating more and a thin screw oscillates with even a tiny amount vibration.
The answer and cure for this are to use a thicker diameter screw that doesn't bend quite as easily and put the screw under a little tension.

The next difference is the pitch.? Because a standard ball-screw nut is not designed to rotate then you need to lower the rotating speed of the nut to stop it from destroying itself, going with a higher pitch and gearing down is much less stressful on the nut and stops excessive wear.
This is even more important when using servos that spin at higher rpm because if you try to spin the nut at 1:1 ratio with 3000rpm you will destroy it very quickly.

My preferred screw this is 2525 with a 2:1 ratio for steppers or 3:1 with servos. The slower you spin the nut the longer it will last.
Lastly, try to get a ball nut type which as the flange located centrally as this helps support the nut better, this is another reason to use 2525 as most come with this nut type.

[Ale]

Hello!
I would like to get some input.
I have finished my build with rotating ball nut. Screws are 3m (y axis) and 1.7m (x axis) long, 32mm pitch, 32mm dia.
However, I do get some wobble when nut is rotating, I don't know is this something I should worry about. I did everything as flush and concentric as I could. Screws are tightened on ends, not too much tho.
Below are videos. Wobble is about 1-2mm.

[JAZZCNC]

Hello!
I would like to get some input.
I have finished my build with rotating ball nut. Screws are 3m (y axis) and 1.7m (x axis) long, 32mm pitch, 32mm dia.
However, I do get some wobble when nut is rotating, I don't know is this something I should worry about. I did everything as flush and concentric as I could. Screws are tightened on ends, not too much tho.
Below are videos. Wobble is about 1-2mm.

It's just a matter of fine adjustment of the alignment of the screw and the ball-nut and the rotating nut assembly.

Unless you machined the rotating nut shaft so it locates with the ball-nut body then it's very easy for the concentricity to be out a little bit so you will need to align them carefully. You are very close so a little adjustment here and there is all it will take to get it right.

[Dekata]

Do anyone have a working download link of the rotating nut cad design, or can post it/send it to me?