K2 Plus Printing Issues with PA6-CF

[melmath315]

Hey guys,

I have a K2 Plus Combo, purchased it about a year ago. The printer has acted bipolar since I purchased it, bouncing between printing amazingly and printing horribly with little in between. Most recently, I have been facing issues with printing Creality-brand Hyper PA6-CF. I have printed around 200 hours of this material previously with mixed but ever improving results. Up until the issues described below, I had it printing pretty well.

I printed a part (~27 hours, ~600 grams) that came out beautifully. I needed a second one (mirrored part) immediately after, so I didn’t change any settings and ran the second part. I have been unable to successfully complete this print, as anywhere between 10-20 hours in (ish), it clogs the nozzle. Most recently, it also under extruded for quite a few hours before clogging. Of course, when it clogs the printer doesn’t notice and continues the print, even though it has clog detection.

I’m looking for possible issues that may be causing this. When printing, the filament is pre-dried at 65C (Space Pi Plus) for a minimum of a day and a half ahead of time, as well as printed directly out of the still-drying Space Pi with PTFE tubing routing the filament directly to the extruder (skipping CFS entirely). The Space Pi reads the humidity as 13%. Running the setup this way has previously yielded extremely positive results. I have also tried using a new spool of filament compared to a spool opened 2 weeks prior (though it was kept in a drybox) and saw no difference.

When it clogs, I heat the nozzle and manually clear the clog from the nozzle, as well as clear any jams from the extruder gears, followed by cutting off all filament that was sitting in tubing and starting from the dryer again. I swapped to a brand-new nozzle (it was also recommended by the built-in maintenance tracker) and saw no difference. I am printing with a 0.4mm nozzle, which I know it may not the highest recommended option, but it has worked in the past. I’m currently thinking that my next step would be to swap to a 0.6mm nozzle, but it baffles me that it has worked so well in the past and decided to give up on me now when printing with the same settings. Did I just get extremely lucky with all previous successful PA6-CF prints when using the 0.4mm nozzle?

For reference, I am running it with a 300C nozzle, 60C bed, 60C target chamber (though it rarely gets above 55C).

Below, you can see two previously failed parts. These were mostly okay up until the clog point, with a little evidence of under extrusion.

Below, you can specifically see the most recent failure, which seems to have severely under extruded for a good chunk of time before eventually clogging.

And here, you can see the same part (mirrored, though) that I printed successfully. In my non-expert opinion, I’d say my settings must be dialed in pretty well because it came out really good.

Looking for any insight anyone may have, as this is continually wasting a large amount of not-so-cheap filament.

Thanks
Melmath315
(first post)

[JoeFriday]

There could be a number of reasons why a normally reliable print suddenly started going rogue. Since this is PA-CF, my first suspicion would be added resistance somewhere in the filament path. PA-CF is abrasive, and over time it can wear the nozzle, PTFE tubing, and other contact points enough to create drag or inconsistent flow.

Here is what I would try, in this order. For troubleshooting, I would avoid changing slicer settings at first. Otherwise, you may fix the symptom without knowing what actually caused it.

1. Run a contrasting color filament through the printer, such as white, yellow, or pink. Avoid black or gray. Print a simple cube or flat test piece about 1 mm high and see whether the old filament clears cleanly. If the extrusion still looks contaminated, inconsistent, or restricted, I would start suspecting the nozzle.

2. Replace the PTFE tubing, or better yet, bypass the CFS and feed from the side spool using new PTFE tubing. That shortens the filament path and removes the CFS from the equation, which makes it a better diagnostic test.

3. If the problem remains, replace the full nozzle / hotend assembly. I used to replace only the nozzle, but I found that created other problems. The nozzle alone may be $3 to $8, while the full nozzle and heater block assembly is usually around $23 to $28, but the full assembly has been easier and more reliable for me. After breaking enough nozzles while trying to remove the so-called quick-swap nozzle, I stopped treating it as quick-swap at all.

[melmath315]

Hey JoeFriday,

Thanks for the advice and time spent to help me solve my issue. Unfortunately, these things seem to be items I have already thought of and tried.

1. After the nozzle clogs, I generally do clear the nozzle and run white or red PLA filament through it until black stops carrying through from the PA6-CF. I do this before reloading the PA6-CF and attempting another print, which generally prints well for the first ~10 hours before all bets are off.
2. As mentioned in my original post, I am already bypassing the CFS and printing directly from the SpacePi Plus filament dryer. There is a new length of PTFE tubing connecting the dryer to the back of the printer, replaced within the last 100 hours.
3. As I started having these issues, the nozzle clogged so badly I was unable to clear it using conventional methods while installed. I ended up swapping the 0.4mm nozzle (installed stock from Creality) for a brand new 0.4mm nozzle (Creality brand). This new nozzle lasted the entirety of ~8 hours before partially clogging, and ~17 hours before fully clogging. Also being unable to clear this clog, I replaced the nozzle yet again but installed a 0.6mm instead. I am in the process of trialing this larger, more recommended nozzle (As Creality says, the recommended list goes: 1. 0.6mm 2. 0.4mm 3. 0.8mm 4. 0.2mm). When installed, all nozzles were properly coated in thermal paste where instructed by Creality. Also, the quick-swap Unicorn nozzles work well for me as quick-swap.

Thank you!
Melmath315

[daveyk]

I find the K2 Plus is not a reliable printer. I did fix it recently by replacing the filament buffer (which could not grip the filament, which passed through and the sprint level never moved). Still I must kiss its ass to print some days. A BQ Build plate helped a LOT.

Still the printer was more or less replaced with a H2S and ultimately will be replaced with an H2C. And, the K2 Plus probably will head to recycling, or as extreme backup fourth printer, if I find room for it.