It's been a few years since first dabbling with a 3D printer, and one thing I've always wanted to do was experiment with soft materials. Knowing that they can be a bit finicky to print, especially with a Bowden-style extruder as found on the Ender 3, I had been a bit hesitant. However, recently I finally took the plunge, and the result was... surprisingly good!
The material I chose, to make it not too difficult, was a higher shore hardness (91A) TPU. I chose this wanting to try something soft, but also not too challenging to print as it is very easy for softer materials to bunch up on Bowden-style (remote) extruders where there is a long filament travel path past the extruder gears. One thing that made it slightly easier was that my Ender 3 already has the newer version which has a bit of a wedge that reduces the gap past the extruder gears. This meant that I didn't need to print out this upgrade :).
One thing I've been wanting to make for a while now is a bellow system for pushing out the retained grinds of my espresso grinder. Being a shop grinder, the Mazzer Mini is designed for constant high volume operation, and a number of design choices make it less ideal for the home enthusiast. Some of these I had tackled in the past and includes a 3D printed "mini" hopper, and doser replacement seen here:
This allowed the grinder to fit well under the counter. However, one other major issue was that the grind chamber exit is quite large and horizontal, and tends to hold a lot of grinds, which makes it hard for
Single Dosing. Some people deal with this with a paint brush, but a more "elegant" way involves a bellow on top of the grinder throat. This not only allows you to clear the grinds from the exit without opening up the chute cover, it can also potentially blow out more of the grinds that are stuck deeper inside the chamber itself.
So I made a new filament profile based on recommended settings for TPU (all speeds set to 15mm/s, with reduced retraction (2mm instead of the 5mm default) and 230C/225C first and subsequent layers). After one failed print due to filament bunching, I raised the remaining layer temperature to 227 and it printed fine.
However, there were a two issues with this particular model:
- Super thin walls: this results in a shell of just 2 layers which had trouble holding its shape during the print. The result was airtight, but a bit rough looking.
- The actual throat diameter, even though it was labeled for the Mazzer Mini, was a tad on the small side.
Therefore, I decided to make a fully parametric version in OpenSCAD (
linky here). I chose this over Fusion360 for the simple reason that you can quickly edit this using the "customizer" on Thingiverse, or just generate the STL locally by downloading the .scad file directly. For many people this is more accessible, and potentially faster than getting the project loaded up in F360 ;)
The main trick here is the "rotate extrude" command that generates the cylindrical shell around a centre point from a zigzag vertical line. I had to experiment with different bellow sizes to improve the "squishability", as the cleaner result of having 3 perimeters meant the accordion part was a bit firmer than I liked. Making each zig (or zag) a bit wider seem to help...
The following image shows the three printed results - the leftmost is the
existing Thingiverse model I tried, and the two on the right are iterations of my
parametric one.
The TPU I used was the 91A hardness
house branded one from filaments.ca. Before setting on 230/227C I used 230/225 for the very first print, which bunched up at the extruder gears. After bumping up the temps to 227 everything worked great. I'm pretty happy with getting 3/4 for the first ever TPU prints! (fingers crossed).
Here's what it looks like on the grinder:
Right after the bellows, I tried out a
thin bracelet that also came out pretty cleanly. Overall, I'm quite excited by the possibilities opened up by this new material and look forward to trying out more interesting applications!
