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“Unsolved Mystery. Weird Z0 behavior around the perimeter”

Posted by JJ Johnson on

Here at SeeMeCNC we are constantly working to improve our products and we take notice when our users experience difficulty. This week, we focused our attention on investigating the issues relating to the “Unsolved Mystery. Weird Z0 behavior around the perimeter” discussed on our forum. The issue is not observed by all, it depends on where you position your prints or the overall size the objects printed. Those who experience it most, are makers who print objects close to the perimeter of the build plate. What occurs is that users experience difficulty, typically limited to the first layer, due to nozzle not traveling at a consistent height above the printbed. We discovered an error in the firmware pertaining to the Carriage Horizontal Offset value. The value that was in place was 35 while the value should be 37.5. We believe that this difference in offset values for the carriage is and has been enough to cause many of the printing height issues near the edge of the bed between the towers.


Once the changes to the firmware were made and a Rostock Max V2 was calibrated with a digital dial indicator, the result was an accuracy of +/- .004”  (Roughly the thickness of one Post-It note) for the print nozzle to bed height in six equidistant positions located around the perimeter of the bed.  (Editors Note: Later in the evening I was also able to apply the firmware change to my own Rostock Max v1 and was pleased to see these changes make a positive effect on printing large objects near the perimeter of the glass build plate, without a dial indicator.)


This affects only those using the Repetier firmware for the Rostock Max kits, not the Orion Delta printers. You can tweak the Carriage Horizontal Offset value yourself in the Repetier Firmware or download the most current version from the SeeMeCNC Github.


Video of resulting change and calibration:



 

You can find the .stl for the dial indicator mount at http://repables.com/r/344/


The calibration gcode used:


G28

G1 Z10 F15000

G1 Z0 F3500

G4 S1.5

G1 Z10

G1 X0.000 Y115.000

G1 Z0

G4 S1.5

G1 Z10

G1 X-99.593 Y57.500

G1 Z0

G4 S1.5

G1 Z10

G1 X-99.593 Y-57.500

G1 Z0

G4 S1.5

G1 Z10

G1 X0.000 Y-115.000

G1 Z0

G4 S1.5

G1 Z10

G1 X99.593 Y-57.500

G1 Z0

G4 S1.5

G1 Z10

G1 99.593 Y57.500

G1 Z0

G4 S1.5

G1 Z10

G1 X0.000 Y115.000

G1 Z0

G4 S1.5

G1 Z10

G28

 

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