Delta calibration point triggering (way) before reaching the bed

I've been trying to recalibrate my printer recently as it acted up the last few times I printed with it - the very last time it didn't even lay plastic on the bed.

My printer is a self-built Kossel Mini Delta. I'm driving it with a Duet2Wifi, and for a Z Probe I'm using the nozzle with a PrecisionPiezo Orion.

I've followed the calibration procedure here (https://docs.duet3d.com/en/User_manual/Tuning/Delta_calibration) including setting trigger height corrections. Most of the points that my head probes work just fine, but one of them (nearest the Z tower) reliably triggers long before it reaches the bed - almost immediately. At the moment I'm starting my probing quite high up, but I don't think that would have any effect on it. It feels to me like it ought to be a mechanical issue - like some sort of strain that only occurs close to the Z Tower cause for rigidity or vibration or something - but I really don't have a sense of why this would happen. Has anyone seen something like this before or have any ideas on how I could try to address it?

thanks

I agree with your diagnosis. What sort of rod end joints are you using? Perhaps one of the joints between the effector and the Z tower rods is hitting its limit and stressing the effector and then the piezo module.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
I agree with your diagnosis. What sort of rod end joints are you using? Perhaps one of the joints between the effector and the Z tower rods is hitting its limit and stressing the effector and then the piezo module.

The rod end joints are RC Ball linkages. The have M3 screws through them to mount to the carriages on the tower and the effector in the middle. The rods are 288mm carbon fiber center-to-center. I assembled them on a jig many years so I feel pretty confident that they're reliably the same length. I removed a belt-tensioner print I made a month ago and the printer can now successfully hits that point on the bed. After calibration and mesh-leveling, however, the filament is not laying down on the bed.

I now suspect that there may be more play in the top frame than I previously thought. Removing the belt tensioner may have relieved pull on the tower, and it may have previously been non-parallel. I will continue to investigate. Thank you!