M851 - XYZ Probe Offset

none Set the Z probe XYZ offset from nozzle HAS_BED_PROBE

Description

Set the XYZ distance from the nozzle to the probe trigger-point. These offsets are required for the firmware to know how to probe the bed and where probed points are in relation to the nozzle, and vice-versa.

For LCDs that support MarlinUI you can enable PROBE_OFFSET_WIZARD and follow a guided process to set the probe Z offset.

If the Probe Wizard is unavailable, the easiest way to get the Z offset value (assuming your homed Z = 0.0) is to:

Home the Z axis.
Raise Z and deploy the probe.
Move Z down slowly until the probe triggers.
Take the current Z position (as reported by M119) and negate it. (5.2 => -5.2)
Set with M851 Z-5.2 and save it with M500.
Configure with #define Z_PROBE_OFFSET_FROM_EXTRUDER -5.2.

For the X and Y offsets you have to measure the distance with a ruler or caliper.

The probe offsets don’t modify the current coordinate system or existing leveling data in any way, but will apply on subsequent uses of the probe.

Notes

The default (factory) values are set by

(version 1.x)
- X_PROBE_OFFSET_FROM_EXTRUDER
- Y_PROBE_OFFSET_FROM_EXTRUDER
- Z_PROBE_OFFSET_FROM_EXTRUDER
Where the X and Y offsets must be integers.
(version 2.x)
- NOZZLE_TO_PROBE_OFFSET

X and Y offset: Use a caliper or ruler to measure the distance from the tip of the Nozzle to the center-point of the Probe in the X and Y axes.

Z offset:

For the Z offset use your best known value and adjust at runtime.
Common probes trigger below the nozzle and have negative values for Z offset.
Probes triggering above the nozzle height are uncommon but do exist. When using probes such as this, carefully set Z_CLEARANCE_DEPLOY_PROBE and Z_CLEARANCE_BETWEEN_PROBES to avoid collisions during probing.

Assuming the typical work area orientation:

Probe to RIGHT of the Nozzle has a Positive X offset
Probe to LEFT of the Nozzle has a Negative X offset
Probe in BACK of the Nozzle has a Positive Y offset
Probe in FRONT of the Nozzle has a Negative Y offset

Some examples:

#define NOZZLE_TO_PROBE_OFFSET { 10, 10, -1 } // Example "1"
#define NOZZLE_TO_PROBE_OFFSET {-10, 5, -1 } // Example "2"
#define NOZZLE_TO_PROBE_OFFSET { 5, -5, -1 } // Example "3"
#define NOZZLE_TO_PROBE_OFFSET {-15,-10, -1 } // Example "4"

   +-- BACK ---+
   |    [+]    |
 L |        1  | R <-- Example "1" (right+,  back+)
 E |  2        | I <-- Example "2" ( left-,  back+)
 F |[-]  N  [+]| G <-- Nozzle
 T |       3   | H <-- Example "3" (right+, front-)
   | 4         | T <-- Example "4" ( left-, front-)
   |    [-]    |
   O-- FRONT --+
 (0,0)

Usage

M851 [X<linear>] [Y<linear>] [Z<linear>]

Parameters

[X<linear>]

Z probe X offset

[Y<linear>]

Z probe Y offset

[Z<linear>]

Z probe Z offset

Examples

Set a reasonable offset for an inductive probe

M851 Z-2.0

A probe that is triggered by the nozzle itself

M851 Z1.2

Set the XY distance (probe left front of nozzle)

M851 X-1.70 Y-1.30

Set the XY distance (probe right back of nozzle)

M851 X0.20 Y.40