I’m having a strange issue with my Bambu Lab P1S and I’ve already tried many troubleshooting steps, but the problem remains.
Problem
During printing I get periodic bands / pulsing extrusion.
The pattern repeats across the entire print surface and is visible in the first layer and infill.
It looks like extrusion becomes weaker and stronger in a repeating rhythm.
Important observation
Manual extrusion from the printer menu is perfectly smooth and constant.
However, during actual printing the extrusion becomes periodically unstable.
What I already tried
Installed a brand new 0.4 hotend
Performed cold pulls and hot flush before replacement
Cleaned extruder gear
Installed new PTFE tube
Tested with filament fed directly (no AMS)
Tested with default slicer profile
Ran vibration calibration
Ran printer calibration
Checked filament path
Manual extrusion test is smooth
Despite all this, the issue is exactly the same.
Question
Has anyone experienced something similar with the P1S?
Could this be related to:
extruder assembly
stepper motor
belt / motion system
toolhead board or driver?
Any suggestions on what else I could test would be greatly appreciated.
To my eye this looks like an Extruder problem. I’m imagining a gear that has some of it’s teeth stripped and/or plugged with shredded plastic. Every time it rotates around completely it has a small area that slips by. Or the tension is off and it just lets go occasionally.
You mention you cleaned the gear, perhaps the gear tension is too low after reinstallation? Couple pics here. Did you also get eyes on the extruder’s gear’s health, the one that drives the replacable gear?
In addition to what @Bullocks mentioned, the 45° artifacts you are seeing make me wonder if the right-hand stepper motor or belt is being interfered with.
Your suspicion of a belt or stepper motor issue is worth investigating.
Try the following test, but make sure the printer is powered off.
Because the P1 series uses a CoreXY motion system, each stepper motor actually moves the printhead along a 45° diagonal. This can seem counterintuitive at first.
With the power off, move the printhead manually. It should move freely. When you move the head along a 45° diagonal you will notice that only one motor turns at a time. Check the movement of the belt and motor in each of the four diagonal directions.
Listen carefully while doing this. The motion should feel smooth and sound the same in each direction. If one direction feels rough, makes a different sound, or binds slightly, that area should be investigated.
The belt is usually the easiest thing to diagnose. Unfortunately the stepper motor itself generally cannot be serviced and would need to be replaced if faulty. Perhaps someone with more experience can suggest additional ways to confirm a bad motor.
Slow moving is okay and fast has a bit of tension?
I also printed different patterns to check but it really seams extrusion to me?
Bullock, the gears were cleaned because od this issue but this did not solve the issue
This latest picture points to a a layer adhesion issue. I say that because you can see evidence of filament flow but not sticking. At this point I would investigate for build plate contamination. One effective method is to do a first layer test. Right-click and add a Cube Primitive on the build plate. Size it to 250x250x0.4mm and center it which should produce a solid sheet of one layer filament. If there is any contamination on the build plate, it will readily show. Ideally you should get a solid translucent sheet of filament without gaps.
Here’s an example of a build plate I contaminated with finger prints. You can see that the filament is smooth overall except for where the plate was contaminated.
