Is a Threadless Ball Screw Right for Your 3D Printer?

Lead screws are common on machine tools, but they have significant backlash and that is an issue for CNC-controlled machine tools — especially those without positional feedback. Ball screws eliminate most backlash and are the usual solution for CNC mills, but they’re expensive. For that reason, 3D printers tend to rely on belts for the X and Y axes. What if, however, you could save money by making inexpensive threadless ball screws?

This isn’t a new concept, but we don’t often see threadless ball screws used in real products. The big advantage is that they’re very affordable to make. All you need is a smooth hardened steel rod and three ball bearings. You can get those components at low prices these days. In theory, you could build a threadless 500mm threadless ball screw for something like $10 — maybe even less if you shopped around a bit. In comparison, even the cheapest 500mm ball screws, which aren’t very good, cost about $50. They’re usually several times that much if you want decent quality.

Angus Deveson of Maker’s Muse explains how a threadless ball screw works in his video. A special carriage holds the three ball bearings against the steel rod, but at an axis angle slightly tilted from that of the rod. When something like a stepper motor turns the rod, it forces the bearings to “drive” like wheels along the length, achieving linear motion.

The bearing carriage is easy enough to 3D-print, so this has a lot of promise. You could even put two carriages on the same rod and have them move at different speeds or in opposite directions, which has some cool potential.

So, what is the downside? One word: slip. It relies entirely on friction between the bearings and the rod, which means slip is a very real problem. Deveson tested that and found that within a few minutes of back-and-forth motion, it had already drifted by a few inches, which is very dramatic.

Deveson was able to get a huge improvement by adding a second mirrored carriage to counteract drift. But even then, it did still lose position over time. On top of that, the bearings slip too easily to handle much torque.

That all paints a pretty poor picture and you probably wouldn’t want to use threadless ball screws on your 3D printer — certainly not on a CNC machine. However, it is still a very interesting mechanism and one that does have some potential for niche applications. If positional accuracy isn’t important (or you actively monitor position) and slipping under torque is desirable for the use case, then a threadless ball screw may be exactly what you want.