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Duet: Calibrating Z Probe

Difficulty Level: Advanced

Reading Time: Minutes

Test and Calibrate a Z Probe

Static Test of the Z Probe

Static Test Using the Web Interface

  1. Apply power to the printer.
  2. Connect to the printer from a browser.
  3. If the probe needs to be deployed before use (e.g., BLTouch), test the deploy and retract functions using M401 to deploy and M402 to retract.
  4. With the Z probe deployed but not close to the bed, check the Z probe reading in Duet Web Control (DWC) is zero or close to zero.
  5. Trigger the probe using a surface and check the DWC reading is correct (e.g., ~537 for Mini Differential IR probe, ~1000 for others).
  6. For probes producing a short pulse (e.g., Smart Effector, BLTouch), proceed to the dynamic test as the pulse may not be visible.

Static Test Using PanelDue or USB Connection

As above, but monitor the Z probe reading in PanelDue or send G31 via USB.

Dynamic Test

  1. Apply power to the printer and connect via browser or USB.
  2. Home X and Y axes (or all axes if a Delta printer).
  3. Position the print head well above the bed.
  4. Send command G30 to initiate a Z probe.
  5. Hold a surface under the print head to trigger the probe; ensure Z movement stops upon triggering.
  6. If Z movement doesn’t stop, cut power immediately to prevent a crash.

Calibrate the Z Probe Trigger Height

  1. Ensure the dynamic test is successful.
  2. Cancel any active mesh compensation with M561.
  3. Position the nozzle over the center of the bed using X and Y jog controls.
  4. Jog the nozzle down until it touches the bed or grips a piece of paper. Use M564 S0 if limits prevent further movement.
  5. Send G92 Z0 to set the current position as Z=0.
  6. Jog the nozzle up by 5-10mm and send G30 S-1.
  7. Record the reported trigger height and repeat steps to ensure consistency.
  8. Edit the config.g file in DWC to update the G31 Z parameter with the trigger height.
  9. Check and remove any conflicting G31 commands in config-override.g.
  10. Restart the Duet with M999 or Emergency Stop to apply changes.

Fine-Tuning the Trigger Height

During a test print, adjust the Z position using baby-stepping. Update the G31 Z value based on adjustments.

Measuring Probe X Y Offset

  1. Measure the distance between the probe and nozzle using a piece of paper and marker for reference.
  2. Record the X Y offsets following the right-hand coordinate system conventions.

Additional Resources