screws_tilt_adjust: Add MAX_DEVIATION parameter for bed level invariant.

This is useful when a saved bed mesh is used to ensure that the bed level
has not drifted too far from where it was when the mesh was created.

Signed-off-by: Johannes Stuettgen <johannes.stuettgen@gmail.com>

docs/Manual_Level.md

@@ -191,3 +191,10 @@ it has an X or Y offset) then note that adjusting the bed tilt will
 invalidate any previous probe calibration that was performed with a
 tilted bed. Be sure to run [probe calibration](Probe_Calibrate.md)
 after the bed screws have been adjusted.
+
+The `MAX_DEVIATION` parameter is useful when a saved bed mesh is used,
+to ensure that the bed level has not drifted too far from where it was when
+the mesh was created. For example, `SCREWS_TILT_CALCULATE MAX_DEVIATION=0.01`
+can be added to the custom start gcode of the slicer before the mesh is loaded.
+It will abort the print if the configured limit is exceeded (0.01mm in this
+example), giving the user a chance to adjust the screws and restart the print.

klippy/extras/screws_tilt_adjust.py

@@ -19,6 +19,7 @@ class ScrewsTiltAdjust:
         self.config = config
         self.printer = config.get_printer()
         self.screws = []
+        self.max_diff = None
         # Read config
         for i in range(99):
             prefix = "screw%d" % (i + 1,)
@@ -51,11 +52,13 @@ class ScrewsTiltAdjust:
                                      "of turns to level it."
 
     def cmd_SCREWS_TILT_CALCULATE(self, gcmd):
+        self.max_diff = gcmd.get_float("MAX_DEVIATION", None)
         self.probe_helper.start_probe(gcmd)
 
     def probe_finalize(self, offsets, positions):
         # Factors used for CW-M3, CCW-M3, CW-M4, CCW-M4, CW-M5 and CCW-M5
         threads_factor = {0: 0.5, 1: 0.5, 2: 0.7, 3: 0.7, 4: 0.8, 5: 0.8}
+        screw_diff = []
         # Process the read Z values and
         for i, screw in enumerate(self.screws):
             if i == 0:
@@ -71,6 +74,7 @@ class ScrewsTiltAdjust:
                 z = positions[i][2]
                 coord, name = screw
                 diff = z_base - z
+                screw_diff.append(abs(diff))
                 if abs(diff) < 0.001:
                     adjust = 0
                 else:
@@ -87,6 +91,10 @@ class ScrewsTiltAdjust:
                                         "Adjust -> %s %02d:%02d" %
                                         (name, coord[0], coord[1], z, sign,
                                          abs(full_turns), abs(minutes)))
+        if self.max_diff and any((d > self.max_diff) for d in screw_diff):
+            raise self.gcode.error(
+                "bed level exceeds configured limits ({}mm)! " \
+                "Adjust screws and restart print.".format(self.max_diff))
 
 def load_config(config):
     return ScrewsTiltAdjust(config)

test/klippy/screws_tilt_adjust.test

@@ -5,3 +5,4 @@ DICTIONARY atmega2560.dict
 # Simple script to test
 G28
 SCREWS_TILT_CALCULATE
+SCREWS_TILT_CALCULATE MAX_DEVIATION=0.01