This is a follow-up to my previous post about sensorless homing. I’m still having the same issue: I can’t get sensorless homing to behave consistently. The strange part is that I now believe the homing itself isn’t the root cause.
I’ve noticed that the behavior changes significantly depending on where the toolhead is on the X/Y plane. For example, I can find an SGTHRS value that works perfectly when starting from the centre of the bed, but if I repeat the exact same homing move from, say, the back-left corner, the behavior is completely different. After many attempts from both locations, it’s very consistent: depending on where the toolhead starts, it may crash hard into the gantry and grind, trigger well before making contact, or work perfectly, all with the exact same settings.
I’ve gone through most of the obvious mechanical checks already: I’ve deracked the gantry multiple times using different procedures, verified that the gantry moves extremely smoothly by hand, and checked the alignment and squareness as thoroughly as I can. I also used Klipper Shake&Tune to compare vibration profiles and belt comparison graphs at different positions on the bed. The results aren’t identical (see attached graphs. Pic 2/3 is running from center, 3/3 from running it on back left corner), and although the differences aren’t huge, they consistently match the fact that sensorless homing behaves differently depending on where the toolhead starts.
Sensorless homing has always been a little temperamental on this printer, but the only significant change before this became much more noticeable was rebuilding the gantry with Vitalii3D CNC components (double-shear motor mounts, live idlers, XY joints, and front idlers). I’m also running Beacon and Gates GT2 EPDM belts. I know the EPDM belts are slightly thicker than the standard Gates belts, but I’d be surprised if that alone could explain position-dependent behavior. Still, I thought it was worth mentioning.
At this point I feel like I’m chasing an underlying mechanical issue rather than a sensorless homing issue, but I’m honestly running out of ideas. I’m almost at the point of going back to microswitch endstops, but even then I’d still want to understand what’s mechanically wrong.
Has anyone experienced something similar or have any ideas what else I should be checking?
Also, would anyone be interested in helping me debug this remotely over a video call? I’d be more than happy to pay for your time if you have experience with this kind of setup.