3D Printing with Cheap Nylon Trimmer Line

Short answer: yes it can work, but only for some part geometries, and forget bottom layers' flatness. At least with the cheap trimmer line I got... 😅

Now, of course it's possible. After all, it's in part how DIY 3D printing started: melting weed wacker lines. Noobs like me, who started printing only once it became a "just works" experience, are just rediscovering archeological evidence from circa ~2012.

Anyway, after seeing a few recent successful attempts by others (links at the end), I got a cheap roll and decided to single-handedly change the future and economics of the 3DP market.

Or so it felt at the time. Fast forward to today, and what remains of the roll has been given away, and I now print much more expensive for-3D-printing Nylon filament. And I'm happy about it !

What follows is the short story of that attempt. For the curious, or more enterprising 3DP tinkerers than I am.

Bottom line: even with a 65°C chamber, 110°C bed, engineering plate and glue, parts lifted from the bed. So, short of constantly body slamming each part onto the bed, being cheap with filament ended up being expensive for my wallet 😞

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It all started with buying a $34 5lbs (ie $15/Kg) spool of 0.065" nylon string used on weed eaters. Much cheaper than the usual ~$25/Kg ripoff for basic PA6 filament. Its diameter is 1.65mm rather than 1.75, and the print quality is probably questionable. But my plan is just to make gears, not shiny detailed figurines, so don't care about stringing, voids and blobs. Hopefully it'll be good enough ?

First step was to transfer some filament from the 3Kg trimmer drum to a 1Kg Bambu spool thanks to The Lazy Winder

Before optimizing any filament parameter in the slicer, I started with the generic PA profile in Bambu Studio and tried a first print on the H2S. The crackle & pop noises coming from the nozzle immediately woke me up: telltale sign of excessive humidity in the filament. Forgot to take a pic, but pretty much looked like that:

So, in the West3D filament toaster (great drier!) it went. Where, after a few hours at 70°C, the spool... 'exploded' ! Wait, whaaaaaat ?

See how much larger the left spool is, compared to a regular one ?

Yeah, the humid trimmer line expanded so much with temperature in the oven that it broke the connector tabs on the Bambu reusable spool:

Should have only loosely wound the filament on the 1Kg spool, and only partially filled it. Oh well, no problem, I re-wound the now-dry filament on a new spool, and off to the first print: temperature towers.

Layer adhesion was bad below 260°C, stringing showed up at 275, so 270°C was picked.

Next, printed a simple 35x35x10mm cube primitive from the slicer. Didn't go anywhere, kept peeling away like it wanted nothing to do with the bed surface. No matter the bed temp (up to 110°C), no matter the chamber temp (up to 65°C), no matter the cleaning method (IPA, Dawn...):

Ok, no big deal, let's spread some liquid glue on the bed. That worked:

Fortune and fame, here I come ! Time to calibrate the shrinkage factor before moving on to real parts. For that I simply printed a 200mm long bar:

Which resulted in a 100 x (1 + (197.3 - 200) / 200) = 98.65% shrinkage value in the slicer.

Was pretty pleased by how straight the bar was. Virtually no warping, except in the very corners which only slightly lifted up:

Man, this is going to be a slam dunk. Onward to real parts, let's print a real sunless Wolfrom gear train and see how many Kilotons cheap Nylon can lift !

Answer: zero ton, zilch, nada. Despite a 10mm brim with zero spacing, none of the parts, except the small planets, would stick to the bed, glue or not.

So, time to get a Bambu engineering plate to replace the PEI textured plate. That plate sounds awesome as it is "Optimized for high-temp filaments" and "Its smooth, dependable surface guarantees stable adhesion every single time".

Made absolutely zero difference, what a waste of $70:

And that's the point where I decided to try Nylon filament actually made for 3D printing. So I got some Sunlun easyPA Nylon filament. Mais par mes ancêtres, at $35/Kg it's over 2X the trimmer line's cost, so it better deliver stellar results.

Calibration resulted in a 99.35% shrinkage factor:

Printed the same parts on the same plate, with the same slicer settings except for EasyPA's filament profile, and they printed superbly.

First try, low bed temp, no high temp chamber, no drama, no fuss (discard the blobs on the large chamfered round piece in the bottom right corner, happens with all filaments, overhang is too steep):

Those gears then easily passed a 40Kg (87lbs) load test that PLA had miserably failed at. See that post for the results (scroll down to the "Updates" section), which also includes the Sunlu EasyPA filament's technical data and materials composition.

So yeah, story time is over: that trimmer line is not worth it in my case. Seems to work only with specific geometries, like a long bar, but anything with a round shape and over a few centimeters large will lift from the bed like crazy.

So that spool found a new home and I'll forever bear the stigmates of abject failure... C'est la vie.

Don't care, though. Discovered that EasyPA is surprisingly easy to print and has amazing mechanical resistance. Wallet be damned !