3D printing is all well and good for making low numbers of units, so long as they’re small enough to print in a reasonable time, but what if you want to go really big? Does a 35-hour print time sound like a fun time? Would it even make it that long? [Nathan] from Nathan Build Robots didn’t fancy the wait, so they embarked on a project to build a huge parallel 3D printer with four independent print heads. Well, kind of.

The premise seems obvious at first glance: More print heads mean more plastic is laid down per unit of time. As long as you can maximise the nozzle diameter and machine speed, it should theoretically be possible to speed things up massively. But it doesn’t work like that. The custom machine they constructed utilises a polar coordinate system, with a rotating bed (the ‘theta’ axis) and four radial axis gantries arranged at 90 degrees to each other. Each gantry has its own independent extruder, so multilateral printing is also an upfront option. [Nathan] laments that the problem with constructing such a beast is not so much the mechanical aspects but the limitations in the current firmwares out in the wild. There are also more complex considerations at the slicing level, so getting the machine to operate as desired is quite a large programming task! Right now, this means that each radial axis must operate in lock-step, meaning objects to be printed must be rotationally symmetric of order four. Another option is to print four copies of a much smaller object in parallel, which has its use cases, but that’s not their end goal. [Nathan] says he was going for a record-breaking 20kg print. However, multiple issues with alignment over height and bed adhesion, not to mention keeping the extruders fed with fresh filament, scuppered this first attempt.

There are some large hurdles regarding alignment. The four corner verticals can be out of alignment with each other in all sorts of ways, causing the radial axis to shift as the Z axis moves. We suspect that’s just one glaring problem, and other more subtle issues are waiting in the wings to cause problems in the future, but we’ll keep an eye on this and see where it goes!

We covered a few projects turning up the 3D printing knobs lately. Here’s a big printer, for big prints. Our thoughts about speed printing and, lastly, a fascinating machine mod that optimises colour swapping by having automated hot end swapping.