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3D Printed Ball Nut for the Insane

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Joules:
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.

Joules:
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    :)

DMIOM:
Joules - if the balls are "full contact", I wonder what effect the inevitable "corrugations" resulting from FDM 3D printing will have?

Dave

John Stevenson:
Personally I think that it's a load of balls.

Joules:
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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