Recommendations for super-stiff filaments to prevent breakage in Nextruder
I'm trying to print some CF stiffened filament - both PET-CF (NOT PETg-CF) and PPA-CF* - and both filaments are breaking as they pass through the extruder path, right at the center of the extruder gear. In the unannealed state, these filaments have low fracture toughness and as they pass around the gear they tend to break. Retraction makes it worse, but even without it and lowering volumetric rate ramping I'm seeing breaks. I've tried PPA-CF both through the bowden as well as testing it directly fed from above the tool without any bowden tube. I'm curious if anyone else has encountered this and, hopefully, to find strategies or recommendations you have used to successfully print these materials. I'll note that PA-CF prints well on my XL as its fracture toughness in filament form seems a bit higher than the two mentioned above.
Thanks!!
*Yes, I know that this is a higher temp filament, generally (300-320C), than is available on the Nextruder, but it DOES print at low/moderate speed with a 295C head and I will soon have an annealing oven. I have an application for which a 150C+ HDT is desirable and if I can get PPA running it would be convenient, even with the unheated/low heat enclosure limitations. Although I appreciate everyone's willingness to help, please don't comment or make recommendations unless you are actively printing with one of the two filaments above. I've been in aerospace and structures as an engineer for over 3 decades and I've been printing with FDM for 15 years. Please also skip recommendations about a lack of a high temperature OEM enclosure, or of drying the filaments unless they directly relate to your success in printing one or both of the filaments above. FWIW, all of my high temp filaments are dried for 24 hours at 85C in a commercial dryer prior to printing and are fed from the drying enclosure to the printer directly, with active humidity control after drying. You may also skip recommendations that printing these filaments is not practical/possible in the XL - that is already my observation pending some sort of mitigation techniques.
RE:
Hi,
have you looked at the extruder, whether you can fine-tune the mechanism? The first thought that comes to my mind is the springs on threaded screws. You'll feel them scratch when you open the idler - it works but it can be done better. I've filed the threads off and (lazily) polished the screws. Needless to say, no more scratching.
Then, have you minimized idler spring tension? Don't forget to recalibrate. And I wonder, whether scavenged (softer) springs from ballpoint pens would do a better job here, as the original ones feel quite stiff (which arguably makes assembly-by-the-book easier but is not necessarily the optimum, mechanically).
PS my comments are based on core One but I think the XL head looks similar.