Four-Axis 3D Printing with an Innovative, Completely Unique Kinematic System

The vast and overwhelming majority of 3D printers in existence utilize kinematics that support planar, Cartesian printing processes. In layman’s terms, that means that they print stacks of layers in the shape of flat horizontal slices with a head that moves linearly in the usual Cartesian X, Y, and Z axes. But 3D printers don’t have to work that way and, in fact, some challenges would be much easier to overcome if they didn’t. With that in mind, Joshua Bird created something I didn’t think I would see again: a four-axis 3D printer with an innovative and completely unique kinematic system.

Unusual kinematic systems are actually pretty hot right now, as makers flex their mechanical engineering muscles and look for promising new concepts. CoreXY is one example that exploded in popularity in just a few years. But most of those, while interesting and often beneficial, follow the same planar, Cartesian processes as the conventional printers we’ve seen since the beginning of the RepRap Project.

This printer is completely different. It isn’t planar or Cartesian. Instead of a Cartesian coordinate system with X, Y, and Z axes, it uses a polar coordinate system. We have seen a handful of polar 3D printers over the years, but the concept never gained much popularity. This design, however, takes it another step further with non-planar printing. Rather than a big stack of horizontal slices, this prints radial slices. That yields a part that is more like an onion than a lasagna.

What’s the point of that? Aside from looking cool, it handles overhangs much better than regular printers. The tree part Bird shows in his video illustrates that well. As the printer reaches the outer branches that are horizontal—or even at a negative angle — it continues extruding well because the hot end is pushing material inward onto the existing limb. That’s very dependent on geometry, but it can do some parts that would simply be impossible on a regular 3D printer without supports.

For any of that to work, Bird had to invent a new kinematic system that he’s calling “core-RΘ.” It moves in four axes, starting with a belt that rotates the circular build plate (the C axis). Then there is a vertical rail with a lead screw (the Z axis) and a horizontal rail with a belt (the X axis). A rotating print head (the B axis) sits at the end of the X axis rail above the bed. Therefore, the print head can move to any point above the bed, while also tilting on the XZ plane to form those radial layers.

As you might expect, most firmware and slicers aren’t compatible with this printer. Bird ended up using Duet3D firmware that did let him configure the unusual set of axes and built his own Radial Non-Planar Slicer to generate the g-code.

Both the printer itself and the slicer are open source if you want to give them a try. Bird reports that it should cost $300-400 to build the printer.