Ball Screw Rack (aka Driven or Rotating Ballnut) Prototype

Quick update video of revised design here: https://youtu.be/6VC_oVYWeBk
And same config milling aluminum: https://youtu.be/ihivT0f9ifU
Longer screws suffer from sagging under their own weight, which gets translated into "whipping" when rotated at high speeds. It's worst when the driven carriage is at either end and less of the screw is supported.

Conventional means of combatting this are to add high tension to the screw. This can complicate installations in terms of screw alignment and requires high rigidity of the frame for larger format machines, creating a situation where cost can increase sharply as machine work envelope increases.

Industry has answered this problem by rotating the ballnut instead of the screw. This is a more complex assembly than simply turning the screw and usually built into large format industrial machines as part of machine design. Not typically available for the high end hobbyist or "prosumer" type user in kit form that's compatible with off-the-shelf ballscrews. I'm in the process of developing just such a kit for entry level commercial and high end hobby and prototyping shops.

Below are the Fusion 360 design files appropriate for a typical SFU/DFU2005 ballscrew, NEMA23 stepper and integral GT2 48T pulley. It is designed to work with a pair of 6809 radial bearings (they are cheap). I will convert it for 1605 use at some point. The number of pulley teeth and many other paramters can be adjusted using the parameters sheet. Please inspect the model carefully after doing so as I'm not sure how durable the design is in response to these changes. Please note these files are only to serve as a starting point for your own efforts at this point, and should not be treated as production ready. Please inspect before attempting fabrication.

The weak part of this design is definitely the mounting bracket (which fastens the whole assembly to the gantry or driven part of yourvmachine) , but I have made this a separate part so it can be customized to get the most rigid shape for your machine's clearances. I had a very tight fit and was limited with what I could fit here. The design file has the part completely containing the ballnut (a ballnut representative model is in the design but not intended for you to fabricate this, only to see hwo it all fits together). Note that the part labeled as "driver" is designed to be made in duplicate (or triple) to use like a locknut against each other between the bearings (this takes up the lash). The other pulley piece I fixed in place by drilling and tapping for a setscrew. You could also make a 3rd "driver" part as the thread is all the same pitch here.

I made the driver and related assemblies from 3d printed nylon, which seems plenty strong for a router intended to carve wood and non-ferrous materials. The rest I made from mild steel and this is the material I'd recommend. Aluminum may not be quite strong enough at these thicknesses, but if you do use aluminum probably you want at least 6061/6063 or better.

Fusion 360
https://a360.co/3Ap20rt

These files are made free to the community to help hobbyists, emerging small businesses and those in developing economies. Just participating in the adoption of the design and giving feedback is a good way to help the effort. But If you can afford to donate monetarily to these efforts, any amount helps and goes directly towards me being able to spend more time making these designs (and eventually products) available. There is a Paypal link on the channel banner's lower right corner.

Purchasing crafted items from my Etsy store also is way to contribute while also receiving tangible product. Thanks for looking and supporting! Have fun crafting!

https://www.etsy.com/shop/WizardofOverallCreek

Видео Ball Screw Rack (aka Driven or Rotating Ballnut) Prototype канала The Wizard of Overall Creek