✨ G34 MECHANICAL_GANTRY_CALIBRATION (#425)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

_gcode/G034-mgc.md

@@ -0,0 +1,51 @@
+---
+tag: g034b
+title: Mechanical Gantry Calibration
+brief: Modern replacement for Průša's TMC_Z_CALIBRATION
+author: thisiskeithb
+
+requires: MECHANICAL_GANTRY_CALIBRATION
+group: calibration
+
+codes: [ G34 ]
+related: [ M422, M906, M907, M915 ]
+
+notes:
+  - Requires `MECHANICAL_GANTRY_CALIBRATION`.
+
+parameters:
+  -
+    tag: S
+    optional: true
+    description: "Current value to use for the raise move. (Default: `GANTRY_CALIBRATION_CURRENT`)"
+    values:
+      -
+        unit: mA
+        type: int
+  -
+    tag: Z
+    optional: true
+    description: "Extra distance past `Z_MAX_POS` to move the Z axis. (Default: `GANTRY_CALIBRATION_EXTRA_HEIGHT`)"
+    values:
+      -
+        unit: linear
+        type: float
+
+videos:
+  - 3jAFQdTk8iw
+
+example:
+  -
+    pre: 'Mechanical gantry calibration:'
+    code:
+      - G34
+---
+
+The command aims to align the ends of the X gantry. Here's a [video demonstration](//www.youtube.com/watch?v=3jAFQdTk8iw&t=684s).
+
+- The carriage moves to `GANTRY_CALIBRATION_SAFE_POSITION`, also called the "pounce" position.
+- If possible, the Z stepper current is reduced to the value specified by `S` (or `GANTRY_CALIBRATION_CURRENT`) to prevent damage to steppers and other parts. *The reduced current should be just high enough to move the Z axis when not blocked.*
+- The Z axis is jogged past the Z limit, only as far as the specified `Z` distance (or `GANTRY_CALIBRATION_EXTRA_HEIGHT`) at the `GANTRY_CALIBRATION_FEEDRATE`.
+- The Z axis is moved back to the working area (also at `GANTRY_CALIBRATION_FEEDRATE`).
+- Stepper current is restored back to normal.
+- Finally the machine is re-homed, according to `GANTRY_CALIBRATION_COMMANDS_POST`.

_gcode/G034.md → _gcode/G034-zsaa.md

@@ -1,5 +1,5 @@
 ---
-tag: g034
+tag: g034a
 title: Z Steppers Auto-Alignment
 brief: Align multiple Z steppers using a bed probe
 author: shitcreek
@@ -9,7 +9,7 @@ experimental: true
 group: calibration
 
 codes: [ G34 ]
-related: [ M422 ]
+related: [ M422, M906, M907 ]
 
 notes:
   - Requires `Z_STEPPER_AUTO_ALIGN`.