The web is filled with tempting DIY dual extrusion builds that, unfortunately, don’t always deliver. Who hasn’t dreamed about 3D printing fantastic multiple colored objects? The reality, however, is that most FDM 3D printers operating with a dual extruder set-up suffer from the dreaded ooze: a leakage of filament from the extruders, causing colors to drip on places where you never wanted them. Others, meanwhile require a lot of additional electrics and electronics that take up more build space and drive the costs way up.
You can imagine our amazement when we learnt of a fascinating new dual extrusion DIY project that simply seems to avoid all these problems. It’s called the Twin Extrusion Project (rather than dual extrusion, because they look the same but function separately), and has been developed by veteran maker Tim Edwards who has found a way to strip down the dual extrusion mechanics to create a system that is relatively easy to construct, requires almost no additional electrical or electronic components, requires no firmware changes and can be applied to almost every FDM desktop machine. Most importantly, it doesn’t drip on your precious building projects.
It almost sounds too good to be true, but it really seems to work. As Tim Edwards explains, its secrets are a magnetic coupling system featuring two extruders on one single belt drive, which switches the extruders in a simple passing sequence. To put his money where his mouth is, Tim implemented it on his own MakerGear M2. One of the many things he liked about the MakerGear M2 is the open hardware and firmware it comes with and the encouraging tinkering atmosphere provided by MakerGear. “The good folks at MakerGear are very friendly toward people who tinker with their M2s, providing encouragement and even the occasional piece of extra hardware,” he says. “In July of 2014, MakerGear offered an experimental dual extruder kit to those of us on the forum who were interested. I was one of the first batch of beta testers.”
The problem with that MakerGear set, however, is that it still oozed – though MakerGear cleverly protected the bed area perfectly. “It became clear that this general architecture of having two extruders fixed side by side has its limitations. For one, I usually print using PETg plastic, which tends to ooze and drip a lot more than the PLA plastic,” Tim says. “Also, the right extruder does tend to drag across the print, and if the print ever warps or curls up the slightest bit, it is in danger of catching on the other extruder and ripping the print off of the bed (among the worst-case scenarios).”
While working on a few alternatives, Tim recently came up with a clever solution: two separate single extruders working on the same linear rail. “I had firmly in mind that whatever solution I came up with must keep the restriction of requiring no additional motors, actuators, or switches, but should be able to be wired up with the existing wiring to the electronics box. Other dual extruder ideas I had seen consisted of additional hardware, and that required additional wiring, additional electronic components, and a good deal of firmware writing, leading to incompatible and non-upgradeable firmware,” he says. In fact, you’ll only need some tinkering equipment and some 3D printed parts. What’s more, you don’t need to be an expert engineer to install this solution, and will only take a few days.
But the real question that remains is: how does this mechanism work? The Twin Extruder completely revolves around a simple magnetic coupling mechanism. “There are two extruders, left and right, which are bolted onto mount plates that hold them firmly to the X-axis linear rail, but critically, not to the belt. Instead, there is a printed piece, the belt grip, that is the only thing attached to the belt,” Tim explains. Both extruders have a parking space on either side of the belt, where they are magnetically coupled to the side of the 3D printer with a single magnet. There, they can drip to their hearts content and one can stay there while the other 3D prints.
To activate one of the parked extruders, Tim simply relies on the power of the X-axis motor. “[It] pulls the left extruder to the right. Because the belt grip connects to the extruder with two magnets, it is stronger than the magnet holding the extruder to the left side, and pulls it off. The left extruder is now active and printing,” he explains. And by passing the extruder over a wiper, any oozing filament is wiped off.
To switch the extruder from one to the other, the active extruder moves all the way to one side – pressing against the inactive one. “Although the left extruder cannot move any further, the belt grip can. By continuing to move the X stepper motor further right, the belt grip is yanked off of the left extruder, breaking the magnetic connection. By carefully calibrating the distance to the right side, the belt grip can continue until it magnetically engages the right extruder. The left extruder is now free-moving,” he explains. The other extruder is now pushed all the way to the other side, ‘parking’ it again. Now the roles are reversed.
It is, in short, a bit of a complicated switching process, but a very impressive one. Most importantly, you don’t need extra electronics, extra wiring, extra motors, solenoids, or other electromechanical systems, or special firmware or software to run. All you really need is some regular making tools, a 3D printer and all the software scripts provided by Tim already. And with the help of a very detailed tutorial, which you can find on Tim’s blog here, it isn’t even beyond the reach of regular makers. While it will take some time and effort, it is definitely worth checking out.