Author Topic: 3D Printed Ball Nut for the Insane  (Read 11491 times)

Offline Joules

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3D Printed Ball Nut for the Insane
« on: August 19, 2016, 10:57:35 AM »
With all the new CNC stuff kicking off and wanting a better understanding of how things work I thought I would have a go designing and printing my own ball nut.  I got some off cuts of 1205 ballscrew to use for setting up the future mill project.  First job was always going to be a 3D model of the parts, so might as well start with the ballscrew.



Measurment of the OD and radius of the raceway indicated 11.86mm and 2mm ballbearings.  The centre of the balls are at 12mm and the ballscrew has clearance, hence the 11.86mm OD.



To model this I start off with a 12mm rod, wrap a helical curve round the rod (5mm pitch).  In Rhino I can use the pipe command to create a 2mm pipe along the curve, thats going to be our raceway.  Next, create another rod, but this time it's 11.87mm diameter.  Move the pipe from the centre of the 12mm to the new, now delete the pipe from the new rod.   Easy, created the ballscrew, well as much of it as we need for modelling.

To create the nut I need a part I can work from in the form of a tube with the raceway cut out of that.  The tube I generated has a 12.23mm bore and 19mm OD, just rough values to get started.  This time we take pipe away from the tube to get its internal raceway.



A sectioned tube shows the internals that I will use in modelling the nut, and thats as far as we are at the moment.

I am interested in how these work and how bad a printed nut will be, if it can be tweaked to be of any use in light applications or the CAD model will just be used for designing the mill setup and any future CNC machines that need parts modelling.  In the mean time it's a fun challenge to get me thinking.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #1 on: August 19, 2016, 11:44:27 AM »
As just brought to my attention, the ballscrew works by having the balls run on the radius edge (the radius I ignored) forming two contact points (low friction).  In this case the poor printed nut would be eaten away in a few revs, so with tongue in cheek I will continue with the idea of a 2mm ball having lots more contact  :thumbup:   Will it be better, or worse than a full contact plastic nut  :scratch:

See, isn't learning great    :)
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Offline DMIOM

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Re: 3D Printed Ball Nut for the Insane
« Reply #2 on: August 19, 2016, 11:48:43 AM »
Joules - if the balls are "full contact", I wonder what effect the inevitable "corrugations" resulting from FDM 3D printing will have?

Dave

Offline John Stevenson

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Re: 3D Printed Ball Nut for the Insane
« Reply #3 on: August 19, 2016, 11:59:29 AM »
Personally I think that it's a load of balls.
John Stevenson

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #4 on: August 19, 2016, 12:19:03 PM »
Dave, I expect some Shake, Rattle and Roll  ah-ha....   I am anticipating the balls rolling a smooth-er path through the nut, getting "A" tolerance will be fun.  Graunchy start and see where it goes from there.  I recon John sums up the eventual out come of this.
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Offline DMIOM

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Re: 3D Printed Ball Nut for the Insane
« Reply #5 on: August 19, 2016, 12:29:42 PM »
........Graunchy start and see where it goes from there. .......

Where next -  :proj: - if you find that FDM doesn't give a smooth enough ball raceway, then obviously the next step is to upgrade the printer - some sort of selective laser sintering unit?  :headbang:

Dave

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #6 on: August 19, 2016, 03:15:59 PM »
That would be robot arm operated MIG welder then. 
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Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #7 on: August 21, 2016, 08:21:42 AM »
I finished up the nut design this morning.  I like little exercises like this as they make you think and keep the drawing skills sharp.



I took the sectioned nut and made a start on the recirculation path for the balls.  The balls have to come off, and return to the ballscrew at the helix angle, I also added an incline of the same angle to increase clearance over the existing raceway in the nut.  The pipe command is used on the curve I generated and a good radius for the bends.



This is the internal raceway once I have cleaned up the nut of the excess raceway exiting the nut and combined the pipe we added earlier.  The raceway has also been trimmed where it breaks the surface of the nut.



So we end up with a basic nut like this, with the exposed raceway where we can load the balls later.  Finally for this part we need to cap that open raceway.



The cap is nothing fancy, but having a flat face helps printing it later.



Here we see the finished components, the cap had a lip extruded round it and trimmed to take a matching cut out of the nut for alignment and gluing in when the nut is assembled.  The pipe we drew earlier was used to trim the raceway in the cap.  The nut is stood vertical ready to be printed with the cap at its side.

In all honesty as a printed part this just wouldn't work.  I would need to add clearance to the raceway in the nut for the balls to move, the error in my printer layers would most likely mean the raceway at one end won't line up with the raceway on the ball screw.  However it has given me insight into how a nut works and can be designed, much respect for the companies that make these things and the precision they achieve.   If I happen on a bag of 2mm BB's I may have a go at printing this with some tweaking of the tolerances to line things up.  My thoughts are as the ball screw is hard it would peen the soft nut raceway into a good surface, not sure about the raceway tube, that might need to swell a little to allow free movement without too much bunching.

I'm still pretty chuffed that I managed to draw up a reasonable model that I feel would work and write up the results here in just a few hours.  CAD is all about doing, making virtual swarf.

For those curious to take a closer look I have just posted an STL file on GrabCad

https://grabcad.com/library/3d-printable-ballnut-for-1205-ballscrew-1

Please add a LIKE if you download it.   :thumbup:
« Last Edit: August 21, 2016, 08:50:55 AM by Joules »
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Offline awemawson

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Re: 3D Printed Ball Nut for the Insane
« Reply #8 on: August 21, 2016, 08:43:34 AM »
Pretty darn impressive Joules  :thumbup:
Andrew Mawson
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Offline DMIOM

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Re: 3D Printed Ball Nut for the Insane
« Reply #9 on: August 21, 2016, 09:35:41 AM »
+1   :thumbup:  :clap:

Dave

Offline spuddevans

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Re: 3D Printed Ball Nut for the Insane
« Reply #10 on: August 21, 2016, 10:56:57 AM »
+ 2  :thumbup: :thumbup:
Measure with a micrometer, mark with chalk, cut with an axe  -  MI0TME

Offline PekkaNF

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Re: 3D Printed Ball Nut for the Insane
« Reply #11 on: August 21, 2016, 10:59:54 AM »
There are few methods and variation on ball circulation.

http://www.linearmotiontips.com/three-ball-nut-recirculation-methods/
http://www.barnesballscrew.com/how-a-ball-screw-works/

I don't think this will be highly succesfull on other than demostration and a learnig curve - but that is prett much.

Pekka

Offline nrml

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Re: 3D Printed Ball Nut for the Insane
« Reply #12 on: August 21, 2016, 01:24:39 PM »
I can't wait to see your printed prototype. That would be a very cool toy to have on your desk :thumbup:. If you fill the raceway with something like PTFE grease before packing the balls, wouldn't it to a limited extent fill the print corrugations and make them act like oil grooves on a slide-way? With the fine resolutions you achieve on your prints I would be very surprised if this printed ball screw doesn't work.

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #13 on: August 21, 2016, 01:35:28 PM »
Thanks Pekka, the tangential ball return got my attention, it would make for a much simpler nut with inserts at each end for the raceway pickups.

nrml, pretty sure if I printed a section of ball screw it would all work, but matching the precision of the metal would be a tall order.  No doubt the plastic raceway would deform to accommodate.

https://simplybearings.co.uk

« Last Edit: September 13, 2018, 06:10:24 AM by Joules »
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Offline hanermo

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Re: 3D Printed Ball Nut for the Insane
« Reply #14 on: August 21, 2016, 02:28:31 PM »
Excellent work .. and is the kind of thing 3d printers will some day be good for.

Fwiw..
It is usually an ogive arch, and has three points of contact.
Goal is to have a arch a little bit smaller than the ball, so the ball is in compression with zero play.

We made some nuts, for a customer demo, who manufactures lower-accuracy (motive) ballscrews industrially.
Used an ST30Y, with live tools, and back-broached the path for the balls from HS to TS end.
Using custom ground carbide tool tips (12€ each).

Worked perfectly well.
Errors were way under 0.01 mm on customer go-no go gages.
Took about 5-8 minutes per nut, using about  0.02 mm cuts, in a softer material similar to phospor bronze, I think.

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #15 on: August 21, 2016, 03:28:08 PM »
hanermo, thank you, detail like that is very useful.  I literally just sat down and from what I had seen and perceived of ball screw nuts designed this as a starter to increase my understanding and knowledge.  Details like yours and the others help greatly.
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Offline hanermo

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Re: 3D Printed Ball Nut for the Insane
« Reply #16 on: August 22, 2016, 11:24:45 AM »
Welcome.
I help where I can, when I think It might be helpful.

I also learned from others with more experience.

As my area straddles industrial and commercial stuff, sometimes my posts get mis-interpreted as erroneous, arrogant, or boasting, which is never my intention.
Most customer-related stuff is off-limits, as they donīt want their confidants to spread info.
(I was the commercial mgr for Haas Spain, 2011-2012).

I respect that, leading to, mostly, unfortunately few details.
Some customers have given explicit permission.

The ballscrew model I liked, as one of the challenges I mention in CAD-CAM posts is modelling a ballscrew.
Accurately (less than 1 micron error, so it could be made-from-model).

So it can be made (cannot have abrupt cut-off in groove, for example (or how will it be cut ?).
And my challenges are;
1. make a model
2. how long will it take You ? (estimate before starting). How accurate was Your estimate ?
3. how accurate will it be ? Sure ? Explain sure.
4. how large will the model be ?

I made my model in rhino 3d, in 2014/2015 or so, V5, in about 1 hr, for a 30MB file of accurate solids.
1 hr of research (but I knew a lot about ballscrews).
(Sufficient resolution and scaling for 1 micron modelling accuracy.)
I used an ogive arch, so its theoretically somewhat correct, but I did not look for a "correct" arch.
I suspect it does not really matter.

A 5-axis grinder with plunge grind and shape dressed via diamond  could finish the screw, correctly. Imho.
Grinder or live tool lathe or cnc lathe could rough the screw (hardness and support considerations).

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #17 on: August 22, 2016, 01:02:04 PM »
That's some going hanermo doing a nut in 1hr to 1 micron.  I don't work to those tolerances as the work I current do is happy at 50 micron, that being half the resolution I print at.  When the detailing is needed I switch to my 5 axis needle files   :lol:
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Offline ddmckee54

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Re: 3D Printed Ball Nut for the Insane
« Reply #18 on: August 23, 2016, 04:41:09 PM »
It amazes me every time I think about 3D printers.  The 3D print resolutions that you're talking about, from reasonably affordable printers, were the minimum sizes for cutting edge integrated circuit devices when I was in school for my BSEE.

Don
Too many irons, not enough fire.

Offline hanermo

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Re: 3D Printed Ball Nut for the Insane
« Reply #19 on: August 24, 2016, 11:24:29 AM »
My goal was to make a model that could be used directly in a cnc grinder.

The most accurate grinders I have seen, were at a customer, at 0.7 microns.
Envelope.
5 axis.

They use them to grind solid carbide.
For tuna cans.
Of all things..

They are the punches, ie molds, and run about 400 times/minute.
Single punch = can.

20 l paint cans run at 80/min.

Apparently, they need 1-2 microns accuracy.

Another most unbeliavable anecdote, of their 50 machines, +/-, are made by about 45 different manufacturers.
But really nice guys.

Offline John Stevenson

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Re: 3D Printed Ball Nut for the Insane
« Reply #20 on: August 24, 2016, 01:07:01 PM »
Well they have to work to microns Hannu or they wouldn't appear on your radar.

Post us a picture of a finished ball nut or the drawing like Joules has.

 :worthless:
John Stevenson

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #21 on: August 26, 2016, 02:37:54 AM »
 :poke:  I got some stick for not printing a nut.   So I am going to man up, and order some BALL's then start on getting a working print done.
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Offline John Stevenson

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Re: 3D Printed Ball Nut for the Insane
« Reply #22 on: August 26, 2016, 04:25:48 AM »
At least you will print and show yours. You will never see anything that Hannu has 'made' as its all virtual.
This guy has been on the Mach3 forum for years spouting his sub microns accuracy designs and other than a crude jig he showed once made out an old pallet and a length of stuffing, no one has seen any of these futuristic machines he's only months away from marketing.

He's been allowed to get away with it on the Mach forum as frankly he's amusing and every village needs it's idiot. However forums being what they are many can't see see through the bullshit
John Stevenson

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #23 on: August 28, 2016, 03:29:18 PM »
Look what turned up.



8 inches of 2mm ballbearings, better get a sealable box to play with them in, or they are going to get lost in no time.
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Offline awemawson

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Re: 3D Printed Ball Nut for the Insane
« Reply #24 on: August 28, 2016, 04:13:06 PM »
Looks like a load of balls to me Jules  :ddb:
Andrew Mawson
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Offline tom osselton

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Re: 3D Printed Ball Nut for the Insane
« Reply #25 on: August 28, 2016, 04:20:27 PM »
Looks like you are one short!   :beer:

Offline PK

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Re: 3D Printed Ball Nut for the Insane
« Reply #26 on: August 28, 2016, 04:25:42 PM »
You got 2 sizes?
Every second ball in a ball nut is a metric poofteenth smaller. This allows it to act as an idler between the load bearing balls.

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #27 on: August 28, 2016, 04:31:48 PM »
 :palm:  Oh no.....

I'll widen the raceway every 3mm, that way each one can be alternately idle.
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Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #28 on: August 28, 2016, 04:44:50 PM »
 :lol:   PK, I had to look that up as I thought you were pulling my plonker....

Well friction will take care of itself as the nut heats up.
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Offline awemawson

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Re: 3D Printed Ball Nut for the Insane
« Reply #29 on: June 04, 2017, 05:29:46 AM »
Resurrecting an old post here, but where are the pictures of the final result Joules  :scratch:
Andrew Mawson
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Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #30 on: September 09, 2018, 11:08:04 AM »
Revisit time for this mad project as I now have the 0.3mm nozzle.  First things first, find out what the real hole sizes are that I need for these bearings.  It's one thing doing a design in CAD but another doing the prints, so a ball gauge is needed with holes in Z and Y from 2-2.5 in 0.1mm steps.  Why Z and Y, because printers don't print true, they normally do a good round hole in Z, but you end up with a droopy ellipse in X and Y.  This will impact on the raceways within the nut.  As can be seen in the pictures, balls in the Z pass through at 2.4mm and pass at 2.3mm in the Y.  I was expecting the opposite result, however that sets my minimum hole size at 2.4mm.  That means the nut needs redesigning to take this into account.  I will also need to make some test nuts that just have the spiral raceway in to set them, it could be they have a different diameter or spacing from the holes depending on how the balls peen the printed surface.

I looked up ball options as per PK's original observation that I needed different size balls.  The nearest I can find are 2.45mm and 2.5mm, but in a printed nut you can't hold that close a tolerance so we go ahead with full contact balls of 2mm.
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Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #31 on: September 09, 2018, 12:49:22 PM »
Well that was interesting.  I printed my first test nut and found I printed a mirror of what I needed.  Doh....   So I tested the nut for fit on the lead screw noting the threads running in opposite directions and marked the nut as bad.  Then I had a thought, well a single bearing should cycle through nut with no motion.  It did, and I could feel the quality of the race within the nut and it was good, with no tight spots.  I will cycle this a few times more to see how it beds in.  The nut was tight on the shaft so the next MIRRORED nut has 0.3mm extra clearance but same thread profile and position within the nut.  No play between the nut and the shaft with the bearing inside, looking good.

Doesn't mean a whole bunch of balls won't lock up in the correct nut, but we should know in another hour or so.

Well bugger me !!!   loaded 13 balls in the test nut and it seems to be working, I wasn't expecting this.
« Last Edit: September 09, 2018, 01:46:14 PM by Joules »
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Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #32 on: September 09, 2018, 07:13:23 PM »
It works !!!  Loaded the balls and they are recirculating.  At the moment the ball nut is still a little rough, but the bearings are making the track smooth.  I have enough clearance using a 2.3mm track throughout.  No backlash in the nut, yet.
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Offline S. Heslop

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Re: 3D Printed Ball Nut for the Insane
« Reply #33 on: September 09, 2018, 10:04:46 PM »
That's pretty awesome! Interested to see how it holds up in testing.

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #34 on: September 10, 2018, 07:46:22 AM »
After hours of running the ball nut along the shaft it has flattened out all the internal imperfections.  The nut isn't as free running as a metal nut, it was never going to be.  It does have zero backlash and should maintain that in low load applications as the nut contains around 70 balls, lightly greased so they slide against each other, but don't seem to slip in the nut or on the screw.   I have published a couple of STL files on the GrabCAD site listed earlier in the thread.  They are this new nut and the ball gauge.  Don't just expect to print this nut and it to work.  The gauge was used to set the raceway dimensions based on this printer and filament.  The nut is scaleable if you have the CAD skills to draw the raceway, I think my 2mm balls are too small as they sit in the lead screw and they should ride on the edges.  But hey, it works for me, don't underestimate the importance of using a 0.3mm nozzle with balls of this size, that blob size will catch you out.
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Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #35 on: September 10, 2018, 12:45:38 PM »
Ahhhh, inspection time showed up a couple of flaws.  I had been stuffing balls in to reduce the gaps, still had about 1 balls worth of gap and I noticed the ball nut has started cracking.  Fair dues, it's not much thicker than 1mm at the thinest points between shell and outer, and it was designed rapidly last night as proof of concept.  I could print thicker shells as this is pretty thin, increase the raceway clearance a gnats or machine an alloy case to clamp the nut externally.  That last option isn't a bad idea as the nut becomes an insert that is easily replaceable.  Not quite an all printed solution though.  I have printed a second nut and taking extra care to prepare the internal raceway and scrape away as many fine blobs as I can find as I guess the pressure inside the nut must get pretty high as it's bedding in.

The cracked nut does feel smooth and still no backlash, time to pull it apart and inspect the raceway internally.

The nut internally is quite badly contaminated with PLA debris forced out of the raceway.  It was soft enough you didn't feel it, but I need to find a way of burnishing the race before assembly.   this nut is being cleaned up and I will carry on testing it.   The count was 74 balls in this nut, so thats about 150mm of raceway wrapped inside this tiny nut.  Need more balls for more nuts
« Last Edit: September 10, 2018, 01:22:12 PM by Joules »
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Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #36 on: September 11, 2018, 09:32:23 AM »
Problem solved with nut No. 4

It now has a thicker body by an extra 1mm, I was also able to increase the raceway separation to 1.5mm, from 0.7mm.  The new raceway was increased to 2.4mm, like I said it should have been in the first place  :palm:

The temperature I was printing at was the high temp I used for printing the shells, this was causing the extra blobs I was having in the raceway.  The nut has had some running in on the lathe at various speeds to bed it in.  The photo below was after the running, and no fuzz from the PLA, so it looks like the raceway got burnished properly this time.   Printing more nuts for future use, and get some balls ordered.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #37 on: September 11, 2018, 02:29:57 PM »



I figured I would print a window to show the balls recirculating and give some scale to the nut.   This is the new revision 4 nut, whilst assembling the new window I fumbled the nut and lost 8 or so balls.  I was working over a tray, but most of what fell out only a few inches above, made a mad bounce for freedom.   The new nut has 84 balls in it, I am down to 5 spare as every time I open this, I loose a ball or two, or "8"

This has been a long time in the making, from those first drawings to not really believing this would work, to not an insane Ball Nut anymore.   I will carry on refining this design and try to find a worthy project to make use of them, or see if anyone else runs with the idea.
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Offline awemawson

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Re: 3D Printed Ball Nut for the Insane
« Reply #38 on: September 11, 2018, 03:23:46 PM »
Looks excellent Joules, do you have a real life application for them, or is it just the joy of achievement that floats your boat?
Andrew Mawson
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Offline Joules

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Re: 3D Printed Ball Nut for the Insane
« Reply #39 on: September 11, 2018, 03:38:13 PM »
Design looking for a purpose.   I had an idea in mind but ball screws and commercial nuts put the project outside my play money.  I did still want to know if I could design and print a working version.   They might make a good alternative to belt drive or get a small desktop cnc working again.  I ordered some more balls, I should really print one and set it up with a thrust bearing then torque the ball nut to destruction.  I might also have come up with a serious use for IGUS filament.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup: