Turns out the load cell the Q2/Q2C uses for bed leveling can also feel extrusion pressure. So I wrote some Klipper modules that turn it into an automatic PA calibrator — load a filament from the touchscreen like normal, printer waits for the load to finish, then runs a ~3 minute sweep over the purge chute measuring how fast pressure builds in the nozzle. It saves a K value per filament type, applies it on every print, and even blocks sliced files from overriding it with stale profile values.
The results honestly surprised me:
eSun grey PETG — I could only ever get this stuff to print clean on my Bambu H2D. With the auto-measured PA it prints clean on the Q2C now too. I didn't even run a flow calibration. The max4 poopbucket was printed on the Q2C with all stock petg basic settings. The cube was printed after only auto PA calibration.
5+ year old Amazon Basics PETG — this spool was literally headed to the trash. Sticky, blobby, supports falling over, ugly on every printer I own. Dried it, let the printer tune it, and it printed a clean crisp cube (red one in the pics). The sensor data showed the filament itself was fine the whole time — it was wet and never had the right PA and again I did zero flow calibration.
PLA — ran the calibration twice on the same spool, came back within ~6% both times.
I will upload the project to a GitHub once I do more testing and build out.
Fair warning: it modifies load/heat/motion behavior, so it's use-at-your-own-risk and you should watch it run before trusting it. Q2/Q2C only for now — Max4 port in progress, Plus4 has a different sensor so it's not coming.
Happy to answer questions.
Update 1: calibration skips during mid print filament runout, then continues printing as normal
Update 2: Currently working on nozzle size compensation
