A month off, Day 3: The Devil in the Ductility


For a while now I've noticed cracks developing in a lot of the parts of the Voron 0.1. While this was concerning at first, the parts seemed to be holding together so I dismissed them as something that normally happens. After all, no many make a printer out of transparent material, so such stress fractures would be hidden by the outer perimeters of the prints, right?


Putting that aside for the moment, I decided to tackle the next part of the assembly for the printer: the hotend. The "mini-afterburner" hotend on the Voron is a clever piece of printed design and integration with conventionally manufactured pieces. The hotend isn't in one big piece, but several smaller ones making it easier to print. Toothed gears, small bearings, and a drive shaft from an extruder kit provide the key functional pieces.

While the default design of the Voron 0.1 uses a Dragon Hotend, it turned out to be difficult to get one. The problem, as it turned out, was patents. A competing -- and more expensive hotend -- had the patents in the US, and successfully sued to keep US-based retailers from selling the hotend. You can, however, still buy one direct from China.

After removing the included bracket, it was fairly straightforward to mount the hotend into the fan cowl I had printed earlier. Once installed, the change of heft was profound. It felt more real than before, funny how that works.

Assembling the rest of the hotend was fairly straightforward, even if fiddly.

Once all the pieces were together, I used a piece of nylon filament (really, cleaning filament) to check the flow path of the hotend. Without the nozzle installed, the filament can be pulled straight through. Even better, light could be see through the entire filament path through the hotend. That all went amazingly well for such a complex component.

Once installed, however, a problem did develop. The drive shaft I had was slightly too long and protruded out the back of the hotend. This is a problem as it would rub against the stepper motor once installed, creating additional resistance and wear. I marked the exposed part with a sharpie and disassembled the hotend.

I repeated this process several times until I realized that I also had to file down part of the plastic boss on the drive gear as well to make the components flush. That was more concerning to me, since it was closer to the gear which wasn't 3D printed and any damage would require me to purchase a replacement. Still, I think I managed to get it all fitted.

This is where all those cracks in the printed pieces started coming home to roost. On the fourth disassembly, the "glider" -- the part that holds the unpowered extrusion gear -- broke in half. I had no replacement on hand, so I would need to spin up the Ender 3 to print a new one. This prompted a question:

Do I need to print this in something else?

You see, I had printed nearly all of the parts for this printer in transparent red ABS. The plans and the materials guide strongly suggest using a temperature resistant material such as ABS for all parts. PLA+, ProPLA, or other materials simply didn't have the correct mechanical properties. I was printing with ABS, though, so what gives?

Thinking back, I've always had a problem with transparent filaments. They had a tendency to snap in printing, resulting in failed prints when the connection back to the spool was broken. I had assumed that this was more a problem with transparent PLA, but transparent ABS also has similar issues.

The materials guide stresses that it's not simply heat resistance needed for the Voron's printed parts. You also want something with an amount of ductility. The plastic has to be able to give a little so as not to...break or crack under stress. While I cannot be sure of this, anecdotal evidence suggests that whatever is done to the plastic to make it transparent also results in it having lower ductility and making it more prone to cracks and breaks. A solid color filament wouldn't have these issues.

So now I have a problem. Not only do I need to reprint a lot of parts, but I also don't have any ABS on hand in the proper color. I used the red transparent ABS initially as it was what I had on hand. A later, black ABS roll I ordered appeared to have quality issues and I had difficulty getting it to print as cleanly. I could order a new roll, but I'm out of project budget for the moment.

I'm hoping that the problem with the black ABS I have is less an inherent problem and more I'm printing with the wrong settings. I'll try a few calibration tests this morning to see if I can pin down the issue. Sure, I'd rather not replace all the pretty red parts I already have printed, but parts in a neutral color are better than broken ones.