Archive for August 29th, 2019

Printer Filament Millifiori

I finally decommissioned my old Thing-O-Matic, as it’s been far surpassed by the current generation of dirt-cheap Prusa-style 3D printers, and must now figure out what to do with about 10 kg of 3 mm ABS filament. Yes, 3 mm filament from back in the Bad Old Days.

Also back in the day, our Larval Engineer made millifiori creations in glass (at school) and polymer clay, building up the final piece from murrine canes, which suggested a similar technique using filament strands:

Filament Millefiori - 160C pipe - slice detail
Filament Millefiori – 160C pipe – slice detail

Well, maybe it’s not exactly art

Just to see how it might work, I packed a random length of conduit with filament snippets and jammed a thermocouple into the middle:

Filament Millefiori - packed conduit
Filament Millefiori – packed conduit

Which went into the shop’s sacrificial Dutch oven over low heat:

Filament Millefiori - conduit heating
Filament Millefiori – conduit heating

For lack of anything smarter, I slowly heated it to 250 °C, well above what the Thing-O-Matic used for extrusion, let it soak for a few minutes, then let the tube cool on the counter.

Some persuasion with a hammer and drift punch extracted the fused filament:

Filament Millefiori - 250C results
Filament Millefiori – 250C results

Obviously, the concept needs more work, but the bottom side looks promising:

Filament Millefiori - 250C results - bottom
Filament Millefiori – 250C results – bottom

Wrapping the bundle with silicone tape should keep the filament from sticking to the tube and provide uniform compression:

Filament Millefiori - 235C silicone wrap
Filament Millefiori – 235C silicone wrap

I forced it into the tube and wrapped the whole affair with aluminum foil to confine the hot ABS stench:

Filament Millefiori - 235C heating
Filament Millefiori – 235C heating

I held this one at 235 °C for a few minutes, cooled, unwrapped, and discovered the silicone wrap worked as expected:

Filament Millefiori - 235C thermocouple blob
Filament Millefiori – 235C thermocouple blob

OK, the blob on each end wasn’t expected, but at least the thermocouple came out with gentle persuasion. The compressed filament looked like it should be edible:

Filament Millefiori - 235C results
Filament Millefiori – 235C results

The molten filament oozed out of the wrap inside the tube, over there toward the right.

The filament snippets have a distinct curvature, brought on by years spent snuggled around a spool’s core, so I wondered if they could be straightened by application of somewhat less heat. Wikipedia lists the glass transition temperature for various ABS compositions as around 105 °C, so I packed the tube with more snippets and affixed the thermocouple with silicone tape:

Filament Millefiori - 100C setup
Filament Millefiori – 100C setup

Wrap with foil, heat to 100 °C, let cool, and they’re definitely straighter than the unheated white strand at the bottom:

Filament Millefiori - 100C results
Filament Millefiori – 100C results

Having learned my lesson with a thermocouple inside the strands, the straightened strands get a looser silicone wrap with the thermocouple secured to the outside of the bundle:

Filament Millefiori - 160C setup
Filament Millefiori – 160C setup

Heat to 160 °C:

Filament Millefiori - 160C setup
Filament Millefiori – 160C setup

Let cool and (easily!) slide the compressed bundle out of the tube:

Filament Millefiori - 160C cooling
Filament Millefiori – 160C cooling

The silicone wrap definitely mushed the strands together, as shown by the larger diameter on the uncompressed end:

Filament Millefiori - 160C results
Filament Millefiori – 160C results

Bandsawing the bundle reveals nicely fused filaments inside, along with melty ends that stuck out of the wrap:

Filament Millefiori - 160C cut end
Filament Millefiori – 160C cut end

Thinking shorter lengths might pack better without straightening, I faced the ends of a thick aluminum pipe and stuffed as many snippets into it as would fit. This is the point where a real artist would arrange the filaments in a pleasing pattern, if not a picture, but I was content with a random layout:

Filament Millefiori - 160C pipe - cable in pipe
Filament Millefiori – 160C pipe – cable in pipe

That’s what the ends looked like after heating to 160 °C: somewhat glazed, reasonably fused, but certainly not compacted. The other end pointed upward and definitely felt the heat:

Filament Millefiori - 160C pipe - cable melty end detail
Filament Millefiori – 160C pipe – cable melty end detail

With a PCV pipe “collet” holding the cable / cane / murrina in the chuck, I faced the end:

Filament Millefiori - 160C pipe - cable facing
Filament Millefiori – 160C pipe – cable facing

After taking this picture, I came to my senses and bandsawed the slice instead:

Filament Millefiori - 160C pipe - cutoff tool
Filament Millefiori – 160C pipe – cutoff tool

Parting the slice in the lathe might have worked, but it just seemed like a really really bad idea when I looked at the setup.

A PVC pipe spacer kept the slice lined up in the chuck jaws while facing the bandsawed end:

Filament Millefiori - 160C pipe - slice facing
Filament Millefiori – 160C pipe – slice facing

The slice and the cable:

Filament Millefiori - 160C pipe - slice and cable
Filament Millefiori – 160C pipe – slice and cable

Although the filament snippets fuse together without a silicone tape compression wrap, the gaps collect plenty of swarf during the cutting & facing:

Filament Millefiori - 160C pipe - cable end detail
Filament Millefiori – 160C pipe – cable end detail

The snippets along the outside, closest to the pipe, obviously got hotter than the ones in the middle and fused more solidly.

The pipe has a 35 mm ID for an area 136 times larger than a 3 mm filament. I packed about 100 snippets into the pipe, a 0.73 packing fraction, which looks to be in the right ballpark for the high end of the Circle Packing Problem. If they were straighter, maybe a few more would fit, but twisting the lot into a cable seemed to align them pretty well.

Perhaps filling the gaps with pourable epoxy before cutting the slices would help? A completely filled interior might require pulling a good vacuum on the whole thing.

A hexagonal pipe would produce slices one could tile into a larger sheet.

All in all, a useful exercise, but … it ain’t Art yet!

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