Calibration works good but when printer starts printing it crashes into the bed

Hey everyone, I’m new to 3d printing and I bought myself a vertex delta to start.
Unfortunately when I first booted when the build was complete the printhead kept crashing into the bed.
I have fixed the issue by tightening the motor bands and setting the potentiometer to max sensitivity. anything lower than max would result in crashes again.
now it calibrates as it should, it all looks to be working perfectly. that is until I start the print. the calibration goes smoothly and when it goes to the back to clean nozzle there are no issues there.

but then comes the problem. once it starts printing it scrapes over the bed and then tries to print like a slope the lowest point under z0 and the highest point about 5 to 7mm form the bed.
(it managed to print “ok” on the first time I printed it, still the same issue but only with 1 layer off height)

Does anyone know or even have a slight idea how to fix this issue?

This seems to be a calibration problem.

Check this guide very precisely and step by step.

Set the potentiometer just over the center position.
On Max. setting is not optimal.

Best Regards,
Velleman Support

Hello, same issue for me. I follow guide, no result.

@grasseelsp, @epoxy32

Please also check the 3 piezo sensors. It’s not normal that the potentiometer must be set to max. sensitivity.

To check to correct working of the piezos, see manual here:
4. Checking the calibration sensitivity (

Normally, the LED lights up every time you gently tap with 2 fingers on the black circle of each piezo sensor, remove the bed (glass) to check this.

Also check whether the timing belts are cut straight.
If these are S-shaped, this can also suffer from calibration problems or falter. if these are S-shaped, it is best to replace them.

Best Regards,
Velleman Support