Building a FlexyStruder

We recently got our hands on some flexible filament samples, kindly provided to us by the guys at FormFutura. One commonly encountered problem with these filaments is their tendency to bend, buckle and loop between the extruder’s hobbed bolt and the top of the hotend. Enter the FlexyStruder, an extruder made by LulzBot to deal specifically with flexible filaments.

The FlexyStruder is based on Jonas Kuehling’s Greg’s Wade extruder, but the idler that pushes the filament into the hobbed bolt has disappeared. Instead, to guide the filament there is a teflon tube running from top to bottom, with a half-round cutout half-way down, where the hobbed bolt grips the filament. This ensures that the filament has nowhere to go but down into the top of the hotend. There is a bolt going into the side of the teflon tube that can be tightened to push the filament into the hobbed bolt, increasing the grip.

Initially, we were thinking about just ordering the complete FlexyStruder toolhead from LulzBot, but it was sold out. But LulzBot, being the awesome crew that they are, published the 3d model and all the instructions, allowing us to build our own! We already had a Budaschnozzle 2.0 and the right size teflon tube, so all we had to do was print the chassis out of ABS. Of course we acetone-vapor-treated it for strength (we do this with all our printer parts). We ran into problems trying to find a heat set insert for the ‘side bolt’, though. In the end, we were able to ‘hack around’ the problem by using a regular m5 nut, melting it into the plastic with a soldering iron and securing it with a nylon spacer (the black ring around the side bolt in the picture) that we glued into place with a generous helping of ABS juice. So far it is holding up well.

The FlexyStruder parts, after acetone vapor treatment. The chassis already has the teflon tube and side bolt installed.

The FlexyStruder uses the same gears as the regular Greg’s Wade extruder and all the mounting holes are the same as well, so we could easily mount it on our existing Prusa i3.

Our home-built FlexyStruder on our Prusa i3.
Our home-built FlexyStruder on our Prusa i3.

Time to print! Loading the filament into the FlexyStruder turns out to be much easier than loading a conventional Wade extruder. It is nothing more than feeding the filament into the top of the teflon tube until it hits the hobbed bolt and then extruding for a few cm while pushing down gently on the filament until the hobbed bolt grips it. That’s all, no messing around with bolts and springs.

The first filament we tried was some FlexiFil, which is extremely bendy. The FlexyStruder handles this material very well: we can print at full speed (up to 70 mm/s) without a single jam. We talk more about this material in this post.

The FlexyStuder handles conventional filaments pretty well, too. We tried some PLA and it feeds it just as reliably as the flexible filaments. All in all we are very happy with the FlexyStruder, we don’t think we’ll go back to a conventional extruder on this printer any time soon.