Rotating nut conversion?

[Corvus corax]

Now that I have a functional ballscrew, its time to get it up and running- installed, as it were. The problem is, in my efforts to create wisdom through utter idiocy, I now have a screw with a moment of inertia that would make even a turbo diesel flywheel envious. I figured I could overcome this by using a larger stepping motor for this axis, and to some extent this is true, but after doing some quick calculations with Mariss, found the resulting force from the system to be far in excess of requirements. So the solution, it seems, is to set up the screw as a rotating nut system. Now I can have even more needless complexity! Yes! So, the question is: How do I accomplish this endeavor?

Or,should I go with the far more boring and monetarily wasteful option, adopting a toothed belt, or rack and pinion? I really don't think either of these will offer the accuracy I need. I am working with Aluminum, and require an absolute positional accuracy over the full completion of a job of no less than +/- .001 inch. Now, my needs are decidedly 2D, but as the pieces assemble into self aligning chassis systems, comprised of as many as 20 separate parts, any dimensional differences make themselves known VERY quickly. On top of all that, there are very few visible fasteners, and the majority of components are cosmetically sensitive.

[Pat2000]

I'm not sure of your m/c size n power but it must be pretty decent! I'd love to see some 'DIY' or 'simple rotating nut mechanism's - way to go IMHO.

if you can live with a toothed belt drive around the 'nut' - with appropiate belt teeth on the outside that seems to be one way to go, of course the bearings between the nut and carriage are going to need a hard looking at.

How do they typically 'drive the nut' on the commercial designs?

would love to see some 'simplish' designs.

keep that big shaft locked in place n stationary. obviously you add the stepper to the carriage weight.

[andy_ck87028]

I have no experience in this field but my first thought would be the introduction of a spring loaded tensioner on the belt. I don't know how big your ball screw is but there assumedly would be some lateral movement in the middle (ie away from the end supports) and this would have to be taken up otherwise you will get inaccuracies.

Apart from that it should be straightforward (imho).

Good luck

Andy

[Corvus corax]

Ballscrew is 1.25 inches, with a minor diameter of 1.00. Its a massive piece. great for big milling machines with limited transit and cutting speeds, running 1KW servo drives, not so great for nimble high speed machining routers... My Nema 34 stepper will fit easily on the gantry, and the weight will still be under 50 pounds for the whole moving assembly. I'm actually considering a step UP on the pulley system, as my system resolution is far in excess of requirements with my .166 lead screw. Six turns per inch. I'll use some LARGE preloaded double row bearings to translate the linear motion, as the speed will be limited to about 2000 RPM