Rotating Ballnut - design ideas

**JAZZCNC** · 20-05-2020

Originally Posted by Heavyweather

You probably didn't understand the name of the site where the bamboo machine is shown.
I don't see anything wrong with combining wood with a 3m screw driven nut. The nut is a proven design running in EMS machines for years.

What's wrong with 16mm screws?

We will have to agree to disagree regards a wooden CNC machine.!!

Regards the 16mm screw then it's too flimsy over 3mtr and thou it it doesn't rotate it will still vibrate at higher feeds. Now you probably don't believe me because your thinking well it's under tension how can it.? But let me assure you that it will vibrate because even the 25mm screws I fit and put under heavy tension still vibrate at high feeds when the machine approaches the ends of travel and changes direction quickly. A 16mm screw will twang like a skipping rope.!!

**Heavyweather** · 20-05-2020

The site is about wooden machines.

On the EMS machines the two screws on the y axis are supported. It's obviously a compromise since the machines should stay affordable.

Would the 20mm screw be ok for my 2m travel?

**JAZZCNC** · 20-05-2020

Originally Posted by Heavyweather

The site is about wooden machines.

On the EMS machines the two screws on the y axis are supported. It's obviously a compromise since the machines should stay affordable.

Would the 20mm screw be ok for my 2m travel?

I wouldn't even use a rotating nut over 2mtr, simply use 20mm pitch with a 2:1 ratio which brings it back in line with 10mm speeds and resolution but halfs the screw speed.

But to answer your question then yes it would be ok over 2mtr. . . . . Now my question to you is why are you wanting rotating nuts with only 2mtr travel.?

**Heavyweather** · 20-05-2020

I've not decided yet. The other option is rack&pinion.

**Boyan Silyavski** · 23-05-2020

Originally Posted by Heavyweather

I've not decided yet. The other option is rack&pinion.

The only option is to do it right.
Why to invent the hot water again when it was explained here in the forum hundred times how to do it properly. Ball screw prices from China are very good price and if you are making a big machine means you will make money from it. Hobby or not.

The example machines with the rotating ball nut you linked were made from people that have Zero understanding of Inertia, Acceleration, Snappines and so on.

People giving you advice here have though and forgotten already what you still don't even know about CNC.

Nothing personal against you but i am seeing a tendency here in the forum. People with Zero knowledge come here ask questions, dont listen to the answers and try to promote their own truth. And waste their and our own time. I have not answered in detail at least in 20 questions lately cause i see people will not listen or do what i am saying so why waste my breath.

I am saying it again in other words: Do something that is proven that works well, don't fancy yourself an engineer, cause if you were, you wouldn't be asking questions, or if you were -you would be listening to the answers. So you will finish with successful build and will be extremely happy to have listened to my friendly advice.

**JAZZCNC** · 23-05-2020

Originally Posted by Boyan Silyavski

The only option is to do it right.
Why to invent the hot water again when it was explained here in the forum hundred times how to do it properly. Ball screw prices from China are very good price and if you are making a big machine means you will make money from it. Hobby or not.

The example machines with the rotating ball nut you linked were made from people that have Zero understanding of Inertia, Acceleration, Snappines and so on.

People giving you advice here have though and forgotten already what you still don't even know about CNC.

Nothing personal against you but i am seeing a tendency here in the forum. People with Zero knowledge come here ask questions, dont listen to the answers and try to promote their own truth. And waste their and our own time. I have not answered in detail at least in 20 questions lately cause i see people will not listen or do what i am saying so why waste my breath.

I am saying it again in other words: Do something that is proven that works well, don't fancy yourself an engineer, cause if you were, you wouldn't be asking questions, or if you were -you would be listening to the answers. So you will finish with successful build and will be extremely happy to have listened to my friendly advice.

No sorry Boyan that's not the correct attitude. I do understand your frustration and what your saying and won't lie I've felt the same before many times but If I had done that or Jonathan etc who helped you all those years ago then you would have a very different machine now or possibly not at all because you might have given up.!!

We all have our own way of learning and building, just because it works for you doesn't mean it works for others or your design suits or is better than the other.

You can not and should not say this design or your design is the only way it should be done, likewise, you can not criticize anyone who doesn't take the same path you did. We each make our own minds up based on our own requirements and you shouldn't try to force one plan onto anyone else.

Give them the benefit of your experience because that's the correct thing to do so we all learn together, but pushing YOUR WAY is the ONLY way is just wrong.

End of the day I see it that we just give our advice based on our experiences and it's down to the reader to act on it or not.
I've done this 1000's of times knowing the one asking the questions isn't listening or thinking they know better but yet I still do it because I know there will be 10 or 100 others in the background watching and listening who will take notice. This is also why I ALWAYS challenge BULLSHIT when i see it and will argue until my last breath when I know it to be wrong or Bad info.
Often I can turn them around and get them to see what I'm saying makes sense and is in there interest to follow, those that don't then good luck to them and if they come back and prove me wrong then that's good as well, because I learn from them. The Circle of CNC Life goes on and evolves...Lol

Just Chill mate and take another drink.!!. . . . . Just know we help more people than we realize or see, the Idiots who won't listen will always be idiots who can't be helped no matter what we say.

**Skid** · 05-06-2020

Gentleman, before I introduce myself I wanted to say thank you for all the knowledge you've put into the public domain with this thread. It has been extremely helpful and makes a lot of things very easy for my project, which I'll get to in a second.

So I'm Skid, new to the forums, and am based in the US. I have a BS in aerospace engineering have spent a lot of time in Part 23 aircraft over the years - both design and manufacturing. Currently though I run a small composites manufacturing facility where we do everything from tooling through final part fabrication for a variety of industries.

One of the big arrows in my tooling quiver is our CNC router table which we've been slowly upgrading and building. Due to capital availability we started small and have slowly been building the machine to really match our needs. It has a working envelope of 1600mm x 2500mm x 450mm. Primarily we machine medium/high density foam, tooling boards, high density urethanes, and aluminum. The big things that matter on the machine are smoothness and precision.

We started with a CNC Router Parts (Avid CNC now) 4x8 Pro machine. From there we did a lot of beef up the base frame and decked it with a single 1in MIC-6 plate full length. We've built a new Z-axis that gives us the travel we need along with a much stiffer cross section and higher quality components. We also swapped out the NEMA 34 steppers for 750W Technic SD Clearpath motors.

On the whole it does great but we're in the process of getting rid of the rack and pinion and moving to ball screws to get better precision and smoothness.

The x-axis I have ordered up a 1600mm, threaded length, 25mm screw with a 25mm lead from Thomson Linear so it's a 23um precision screw with less than .05mm backlash nut - I chose not to go preloaded for a couple reasons. We'll drive that screw with a 2:1 pulley reduction. That guy is pretty straight forward and I don't have any questions.

However, I do have a couple specific questions I'd like to ask about the y-axis which will be the same 25x25 screw and nut combination with a driven nut setup that I haven't found in the thread. I openly admit I may have missed them and re-reading the thread again to see what I missed. My questions are:

1) Are you doing anything unique at the screw supports to prevent rotation of the screw in the mounts? Keying, roll pins, set screws?
2) How much tension are you applying to the screws? Are you controlling this via torque on the end nuts or otherwise?
3) What is the preferred belt tooth profile and width these days? I know I've seen several HTD-5 references but some of those posts are a couple years old and I wasn't sure if some of the GTXXX profiles make more sense these days. Or something else?
4) Have there been any efforts at running double nuts to eliminate backlash in the system or are preloaded bearings the way to go here? My cutting thrust loads are fairly small when I'm doing the finish work which is why I forwent the preloaded nuts just to minimize running load on the system. A double nut on the X-axis is pretty straight forward but I wasn't sure what you guys have done with the driven nut setup or if you just back the second nut up to the other side of the bearing/pulley machining block.
5) Is there anything you didn't do but wish you had on your setups?

For the most part the drawings, models, and tech discussion makes it pretty straight forward for me to put together a bearing/pulley assembly with US sourced parts. I suspect I'll run into some more questions as I move forward but I think this gets me moving further forward. Again, thank you very much for all the information you've made public on this.