Threadless Ballscrew - 3D Printed

OK, so I found this on thingiverse and made a little testprint myself.

Basically you take at least three ball-bearings and group them around a plain steel rod - but skewed.

That skew will generate a linear motion when the rod is turned.

Pros of this approach are:

+ Almost no backlash.

+ Use stuff that you have laying around / can obtain for cheap to make something you usually have to order.

+ Travel-per-turn is variable! It depends on the skew angle and the diameter of rod and bearings (not sure on the exact math here). It seems that 20° will travel about double the same bearing-rod-combo would at 10° skew.

+ You can use multiple "speeds" on one rod at the same time.

+ Travel-direction is determined by nut-orientation. You can have multiple nuts with opposing directions on one rod.

Cons are:

- Holding-force is obviously much lower than with a thread-based system.

I made two different ballnuts with what i had laying around.

Shaft is a 4mm Fischertechnik axle, the bearings are 3x7x3mm and 4x8x3mm RC-hobby bearings.

I printed the centerpieces on my UP! mini at 0.25mm layer-height. Threads for the screws are cut directly into the PLA.

The purple one has a skew angle of 10°, the transparent one 20°

Here's a little video on YouTube.

Embedding videos here is crap by the way…

Step 1: Some Files…

OK, by popular demand - the STLs for the three ballnuts you see above…