Misterious filament breaking

Bambu Lab H2 Series
1

Hello,

Recently I’ve been experiencing the following issue:

I’m using Siraya Tech PPA-CF Core filament on my H2S, fed via the external spool holder. During filament loading—before the actual print even starts—the filament breaks inside the PTFE tube, shortly before the extruder.

The tube is not kinked, and I even replaced it with a brand-new one as a test. The external filament path forms a smooth, gentle curve. The filament can be threaded through the tubes very easily; there is no visible kink, tight bend, or constriction.

As another test, with the motors disabled, I moved the print head multiple times across the entire build plate to all possible positions. In this scenario, the filament did not break a single time. A further successful test was printing without the feed tube at all—feeding the filament directly from the spool into the extruder.

Previously, I was able to print at least 10 spools of the same filament without any issues. I also tried a second brand-new spool and encountered the exact same problem. Extensive drying did not help either. I initially suspected a defective batch, but even so, I don’t understand why the filament breaks at all when it otherwise moves freely.

I’m aware that this filament is on the brittle side, but I’d really like to learn and understand how such a break can occur in this situation. Has anyone experienced something similar, or does anyone have a tip or explanation?

Thanks in advance.

2

First post initially stated it’s an issue with the H2C:

Which nozzle side do you use?

I was printing Siraya PPA-CF none core version using the left nozzle and I detached the PTFE from the holder closest to the nozzle. However I did this on my H2D before the H2C upgrade. I do not know if it will behave differently in the H2C since it does move much more on the outer right side during print preparation, if the left nozzle is used. (I was using the PPA-CF with Bambu PC as support.)

I usually print it from an AMS HT using the bypass and setting the AMS HT to 80 degrees C.

3

I only have one nozzle side, because i am printing on a H2S. Do you mean you don’t have a tube inside the printer from the inlet to the extruder carriage? Only the Filament without a tube there?
In my case i just wonder how it can break if it doesn’t break durig “test movements” all around the build plate. Maybe something inside the extruder has changed wich couses some “shock waves” to the filament, because the movement itself seems not to be the reason…

4

bambu lab wiki has this guide on printing pps-cf on the h2s and it involves twisting the tube to avoid snapping th filament

PPA/PPS-CF printing guide | Bambu Lab Wiki

1 Like
5

@user_505837330

Ah ok, then you may correct your first post, since it states H2C in bolt.

1 Like