Flexible Filament (and buying a printer from Craigslist)

October 2018, I listed a bunch of filaments and my experiences with them. It was an older post than that, but had never gotten around to posting before then...and it was correct for the time. I had picked up some flexible filament earlier in 2018 as well as a toolhead to print flexible filament...but didn't get around until this past month.

The Craigslist Printer from February 2018

When I bought my (used)backup Lulzbot Mini from Craigslist, it was $1000 for the printer, and a spare flexystruder head (which at the time was about $300, designed for TPU use). I paid the guy an extra $40 or so for the remains of his two Ninjaflex (TPU) spools. He had been posting the printer locally for several months without buyers, and I had negotiated the flexystruder head in with his original price of $1000.

Was it a good deal?

Kind of. New retail for 1.04 at the time was $1250, plus tax. The Flexystruder head at the time was $275 — it was the only way a Mini could print flexible filament. The Ninjaflex, was probably break-even, maybe trending towards not. Within 4 months, the glass bed cracked. I also noticed that the "scrub" phase of warmup, it would knock into the plastic frame that held the scrub pad. (And he must have printed a replacement frame.)

Fixing up the Craigslist printer

My 1.03 Mini was 18 months in, and its glass was still good. (I actually stole that bed to the Craigslist one, because the 1.03 was out of commission. It's now over 30 months in use, so maybe the seller didn't treat his 1.04 right. I printed a new scrub pad frame, and manually edited the startup gcode to rub on the pad correctly. (This is awkward, because I have to check a text file every time I tamper with the printer's settings.)

When I bought the printer from Craigslist, I did have the guy run through a sample print, so I could see warm-up and first layers. I just missed the scrub issue. (And forgot the printer came with a putty knife, single-ended pick.) It wasn't the worst deal, but 4-5 months later, Lulzbot announced the Mini 2, and I picked up a refurbished Mini 1.04 from them for $1000. No issues with that one.

I guess I still have the Flexystruder head. And the Ninjaflex. I never got around to swapping out a head to print it. I wasn't really sure what I wanted to print, that would be worth the time to swap the head in and out and change settings around.

Remember the Micro .25 SL toolhead from three months ago (December 2018)? In addition to printing normal filament, it can also print 3mm flexible filament. (I have two 1.04 machines, the refurbished "standard" machine, and the other with the Micro toolhead. The original 1.03 is still in the closet, waiting for me to fix the z-axis.)

Trying out Flexible Filament aka TPU

The orange "Cheetah" line of Ninjaflex was nothing short of magic. 230 degrees, just like PETG. The bed was 40 degrees. Printed very easily, with a little bit of extra stringing. With two shells, and 20% infill it was spongy but firm (for a solid object). The filament feels similar - it has a slight give, but firm overall. If you flick it, there's a bit of bounce as it returns to its semi-rigid state.

I printed a voronoi-style ball, about 3.5cm across - it bounces a little. The TPU also made for an excellent 20-sided die, with just the right amount of bounce.

The white Ninjaflex was probably a more generic TPU. It was much more flexible. Printing a solid object like the orange TPU, you could definitely tell it was a soft version...you could gently pinch the same model and it would collapse all the way through. It was still solid — I couldn't tear it apart with my fingers. The solid object would still stand upright and not deform. More stringing occurred than with the orange.

Swapping out TPU seemed problematic. It felt like it was harder to get the initial flow correct, and also difficult to swap back out to PETG. Normally switching from one PETG color to another PETG, is usually 60 mm of extrude to flush out the previous filament. After 120, there were still bits of PETG in the TPU. I probably won't be going back-and-forth between the two often, but it's much easier than swapping in toolheads (maybe a 30-minute process, and then another 30 to verify all of the settings are correct.)

Overall, the Cheetah was really good. I could see using that in designs. The more basic white was flimsy feeling. I'm sure it has a purpose, but something to design for.