BLTouch Mesh Adjustment Tool

[April 10th: Updated to better reflect using the 4-point levelling positions as references]

This tool will help you to calibrate your BLTouch sensor and additionally produce the required GCodes to adjust for twisted x-carriage rails and resulting probe errors. See here for a detailed explanation of the issue you can address with this.

Please enter at least your BLTouch Z-readings for the left and right probes in the form below. In most cases you should be good with the default values for the other settings if you have a standard Anycubic Mega S setup with the BLTouch mounted in the hotted housing and followed the below calibration routine. Otherwise please don’t forget to change them as required, or the adjustments will not work properly.

We use the front left and right positions from the preceding manual 4-point levelling, which for this calibration we consider to be the gold standard for the perfectly levelled bed (because of course we did that very carefully 😊 ). If you have a different setup, please launch the 4-point levelling from special menu, go to points A and B and use M114 to read your positions and change them accordingly below in steps 6, 13 and 24, and set them in the calculation form.

Use a terminal interface for your printer (OctoPrint, Pronterface) to execute the following commands to setup BLTouch probe and adjustment data:

1. Make sure you have a properly 4-point manually levelled bed and that the bed is either cold or warm now, but not still cooling down from manual levelling.
2. Heat up the nozzle to preferred printing temp. (e.g. 200°C). The bed doesn’t need to be heated for the following calibration.
3. G28 (homing)
4. G90 (absolute positioning)
5. G1 Z10 (lift printhead to height 10mm)
6. G1 X17 Y40 F4000 (move BLTouch tip to front left 4-point levelling point <15,15>, i.e. X=15-(-2) and Y=15-(-25))
7. M280 P0 S10 (release BLTouch probe)
8. G91 (relative positioning)
9. Slowly lower the probe with G1 Z-1 or G1 Z-0.1 or G1 Z-0.02 until the BLTouch sensor is triggered (blinking red). NOT FURTHER! Otherwise start all over!
10. M280 P0 S160 (pull probe back)
11. M114  (Read and note current z position of the nozzle, e.g. Recv: X:17.00 Y:40.00 Z:2.20 …)
12. G90 (absolute positioning)
13. G1 X15 Y15 F4000 (move nozzle to front left 4-point levelling position)
14. G91 (relative positioning)
15. Place a sheet of paper under the nozzle
16. Slowly lower the nozzle with G1 Z-1 or G1 Z-0.1 or G1 Z-0.02 until the paper scratches when dragging
17. M114 (Read and note current position of the nozzle, e.g. Recv: X:15.00 Y:15.00 Z:0.02 …)
18. Subtract this Z value from the reading from step 11 -> 2.20 – 0.02 = 2.18 mm -> This is the Z offset between the nozzle and a triggered BLTouch probe on the left side.
19. M851 Z-2.18 (set probe/nozzle offset)
20. M500 (save data)
21. Now we need to determine the correction value for the x-carriage twist impact on the right side
22. G90 (absolute positioning)
23. G1 Z10 (lift printhead to height 10mm)
24. G1 X207 Y40 F4000 (move BLTouch tip to front right 4-point levelling point <205,15>, i.e. X=205-(-2) and Y=15-(-25))
25. M280 P0 S10 (release BLTouch probe)
26. G91 (relative positioning)
27. Slowly lower the probe with G1 Z-1 or G1 Z-0.1 or G1 Z-0.02 until the BLTouch sensor is triggered (blinking red), like you did above already
28. M280 P0 S160 (pull probe back)
29. M114  (Read and note current z position of the nozzle, e.g. Recv: X:207.00 Y:40.00 Z:2.35 …)
30. Use the values from step 11 and 29 (i.e. here 2.20 and 2.35) and enter them in the form below for the left and right BLTouch Z fields..
31. Press “Generate GCode” and apply those adjustment commands after each G29 automatic bed levelling. You can do it now once using e.g. OctoPrints multi line terminal command plugin, but a better way is to create one printing profile for your slicer (Cura, Prusa) that will do a bed levelling ahead of printing. After the G29 for the bed levelling procedure, add the below GCodes to apply them right away. Another option is an OctoPrint custom bed levelling command button that heats up the bed, does the levelling procedure and then applies the generated fix commands.

Note: if you don‘t apply this to an Anycubic Mega S printer or have a different position for your BLTouch, you will likely need to adjust the other parameters also, like finding an appropriate right side x-coordinate close to your bed edge and the left and right corner x-coordinates of the mesh. See also the note above on using the correct 4-point levelling positions. If your BLTouch position does not allow you to move the tip to the exact 4-point levelling positions, use the closest possible position instead.