Long post as my first post here,

3D Printing
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Long post as my first post here, sorry!

I’ve recently developed some problems with printing black Taulman 910 on my Folgertech i3 2020.

During the winter, I would print 910 no problems. Spool would sit inside my filament dryer for a couple hours at about 160F and then i’d feed it into my printer. Total exposed length was around 40cm, but the print would go fast enough that there would relatively no moisture absorption during the print. No crackling or hissing or popping of the filament during printing. I’d extrude at 245C (no idea if this is true temp of the hot end, never confirmed with a thermal imager) but parts would look and feel good. RH of my house was around 40% at the time.

I stopped printing it for awhile and recently dug it back out again to print. RH of my house is the same, around 45%. Dried the same exact spool of filament and started printing, except this time, it won’t stop crackling. It stops when it’s quickly extruding the perimeter, but returns as soon as it starts laying down support. Decreasing the temp down to 230C helped a little. Wish I took a video, but it’s very strange given similar RH, drying procedure, identical filament and identical settings.

Not sure if relevant: Print speed is at 50mm/s. Sliced using cura engine in Rep Host.

Couple of thoughts:

  1. Overheating the filament. When I manually extruded plastic at about 2mm/s before the print, there was no crackling but as soon as it stopped, crackling resumed. Seems to match up with actual print behavior too. During perimeters, there is no crackling but it immediately returns when printing support (which i assume is using less plastic? or am i wrong?). Decreasing temp seems to have helped, but 230C seems awfully low for 910. The final part felt strong and layer adhesion seemed good though. One explanation is that my hotend is actually way hotter than the thermistor is reading, but I don’t have a thermal imager to confirm.
  2. I’m technically printing with the stock extruder, which is PTFE lined. I haven’t had issues with the PTFE noticeably degrading over time, but maybe it’s degraded enough that now it’s burning? Also skeptical about this because it’s able to print without crackling when laying down perimeters.
  3. Residual PETG in hot end. I printed PETG for awhile so maybe I didn’t clean it out enough before printing Nylon so the PETG is burning. I’m skeptical this is the issue since the hotend should have cleaned itself out after awhile but crackling happened all the way until the last layer.

Any thoughts?

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It’s moisture. Relative humidity isn’t the whole story. Colder air can hold less moisture than warmer air. Relative humidity is the percentage of the maximum the air can hold at that given temperature.
Nylon is often super hard to dry. Either try drying longer, find a different method of drying, or try printing slower. Most slicers have different speed settings for supports and perimeters, and the software I’ve used do allow you to adjust the speed of these different operations.

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@Jeff_DeMaagd thanks for the input. I only noted RH as extra data since it will affect drying times. In both cases, I always dry the nylon for long enough (5+ hours) to get to about 10% humidity (or at least, that’s the lowest my hygrometer reads) so i’m pretty sure it’s dry enough (even if it isn’t perfectly dry). I futzed around some more yesterday and noticed a burning smell. Took my IR gun and stuck it right up against the nozzle. I know emissivity probably isn’t properly calibrated on the gun but it was already reading 15° higher than what cura was set to. Did couple cold pulls until the filament looked clean. Lowered hot end temp until IR read around 240C and the crackling largely stopped.