Some ideas to Back to back double ball nut (no flange type) for my lathe.. possible?

Hi!

I'm converting my mini lathe to a bigger (but still small - 10mm diameter) ballscrew lead screw.

I want to have a double nut back to back configuration for reducing backlash. I've searched a lot for examples and with the standard flange nut, I can screw one ballnut to the nut block, and the other one would be "floating" fixed only by screws on the fixed nut-block assembly, and by means of springs or tightening these screws a preload would be achieved to reduce backlash.

something like this in the first picture:

https://www.cnczone.com/forums/attac...d=451980&stc=1

But as my mini lathe has space constraints, I need to use a flange-less type of ballnut, like this one on the second picture:

https://www.cnczone.com/forums/attac...d=451982&stc=1


So, I thought about creating a balnut block where I could screw one nut on one side, and the other one on the other side, but then, how would I be able to make them a little apart or a little bit closer to decrease backlash?

I thought then about using a belleville washer on one side to act as preload, or spring to make both nuts apart, so backlash would be reduced.

These ideas are drawn below:

https://www.cnczone.com/forums/attac...d=451986&stc=1

My space constraints are tough. I can't mill the nut block to a higher diameter then the outer diameter of the ballnut external case.

In my case I plan to use a 1002 ballnut/screw. It has an external diameter of 19.5mm, and I have 21 mm of height under the lathe's bed only.

Anyone has any ideas if this would work? If not, does enyone has a better idea to couple two flangeless ball nuts in my space constraints?

Thanks for reading!

Yes it works. I have done that. Just used set screws against the nut housing, no springs.

Quote:

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Originally Posted by Jim Dawson

Yes it works. I have done that. Just used set screws against the nut housing, no springs.

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Thanks Jim!

But I'm having a hard time to ..visualize that in practice in my case......

As the nut housing will be the same diameter (or just 1mm bigger than) of the outer diameter of the nut, where could I put those set screws and how would I adjust them? I have more space laterally than vertically. Laterally I could make a housing a little bit larger.. maybe 2 or 3mm bigger in each side...

Regards, Rodrigo

One of my machines had nuts like you show in your last picture. One nut was screwed tight into the nut housing, the other was screwed in and fixed in position with 2 set screws on the sides. You could also just use shims that fit over the threads on the nut to get the correct spacing.

Sorry I don't have any pictures.

Quote:

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Originally Posted by Jim Dawson

One of my machines had nuts like you show in your last picture. One nut was screwed tight into the nut housing, the other was screwed in and fixed in position with 2 set screws on the sides. You could also just use shims that fit over the threads on the nut to get the correct spacing.

Sorry I don't have any pictures.

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Ok, thanks Jim!

What do you think about this new design? Two long (20mm) M2.5mm setscrews that I can adjust from both sides of the fixed nut that push the other nut on the other side.

Would it be a good set-up?

Would there be any risk of this other nut with time and use and friction..... unscrew from the housing??

Thanks for your help!

https://www.cnczone.com/forums/attac...d=452012&stc=1

An interesting idea, and I think it would work fine. The set screws lock the adjustable nut, so I think there is no problem.

Maybe some blue loctite on the threads of the nuts would be helpful.

Hi Jim!

I've been thinking.. the set screws design would prevent the nut from .. screwing in the screw, but only the glue would prevent it from screwing out, right?

What do you think of this other design option? A spacer to a determined thickness and then screws to lock the nut from it's ending. So the spacer wouldn't let the nut screw in, and the screws (with a little flange) wouldn't let the nut screw out.

Check in the picture, what do you think?

Or it's too much for it, and just the set screws would be good enough? I'm afraid that, if I use only the set-screws design, and if I glue also the adjustable one, and adjust it wrongly by mistake, it would be a pain to remove it to readjust it...

https://www.cnczone.com/forums/attac...d=452228&stc=1

I think either way would work. I also think the spacer is not required. Once the set screws are tightened, just the friction on the nut threads will prevent the nut from coming loose.

I've just built this for a double nut setup. The rear flange is able to float 15mm longitudinally so I can set the two nuts up on the same plane. Not sure if this kind of thing will work. The slots are 15mm my own pitch is 10mm so should be ok. https://uploads.tapatalk-cdn.com/202...adf1179945.jpghttps://uploads.tapatalk-cdn.com/202...20dd07c5d0.jpg

Sent from my SM-N970F using Tapatalk

Quote:

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Originally Posted by Jim Dawson

I think either way would work. I also think the spacer is not required. Once the set screws are tightened, just the friction on the nut threads will prevent the nut from coming loose.

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HI! It took a long time to make my setup real, but I'd like to share some info and ask for more help...

My initial setup with only one flange, with two screw-type ballnuts on either side of the same flange, didn't work. I couldn't see the obvious.

The thing is: When you start to screw the second ballnut (the adjustable one) on the flange, as soon as it starts to engage in the opposite side of the flange's threads, it makes so much pressure between them and the internal balls lock, with no movement at all.

Eventually I could find a spot where it worked, but, as only the beginning of the threads were engaged, the second (adjustable) nut eventually came loose and disengaged from the flange.

So I decided to mill another smaller flange to screw in the second nut, and then I can adjust both flanges pressure against it other freely, and lock them with M3 nuts.


My doubt now is... how much ... pressure against each other can be set, to reduce backlash without wearing the ballnuts balls?

Are both ball nuts, against each other, supposed to move as freely as an only-one-setup would? Or in a double setup like this, naturally there would be more ... drag....

How can I know if I'm putting too much pressure against each other?

In my test right now, I reduced the backlash from 0.05mm to 0.02mm, and the nuts don't move as freely as only one would.

Thanks for reading!


https://www.cnczone.com/forums/attac...d=459178&stc=1

Hi Rimbaldo

This is my way to adjust the backlash?

Several of my screw nuts have a large backlash. I used two old nuts in series to form a double nut structure, which can auto eliminated the backlash well.
working well.

uugp
Attachment 460932
Attachment 460934

Quote:

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Originally Posted by uugp

Hi Rimbaldo

This is my way to adjust the backlash?

Several of my screw nuts have a large backlash. I used two old nuts in series to form a double nut structure, which can auto eliminated the backlash well.
working well.

uugp
Attachment 460932
Attachment 460934

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Do you have something to stop the second nut rotating?

You need to preload and keep the nuts from rotating relative to each other.

Hi pippin

One fixed nut and one floating nut.
The floating nut clings to the fixed nut by the torsion force of the torsion spring. No need for additional any blocking structure.
Locking or preloading depends on the torsion force of the torsion spring.
The pre-load force does not need to be too large, just overcome the movement friction force.
Spacer is rigid. Only required when flange face to flange matched for put in the torsion spring. My another device is like this.

When rotating forward, the floating nut pushes the spacer and the fixed nut to move together. This is easy to understand.
When reversing, the fixed nut is activated, while the floating nut is just under the influence of the friction force-tighten to the fixed nut.
Therefore, they will not rotate relative to each other.

Operating note: clean lubrication is required, and the lead tolerance of the screw is relatively stable. Only ball nut are valid.
Since there is no backlash,
Wear will increase slightly, and there is an impact when the power is turned on and initialized, as I use a stepper motor?

Try it if you are interested.

Regards

uugp