Freecad Gcode issues

[angrysamsquanch (s)]

I modeled a simple coaster in freecad and am having an issue where I set the z height in carbide motion to the top of the work surface beings machining at double that height.

(Exported by FreeCAD)
(Post Processor: grbl_post)
(Output Time:2024-04-26 14:59:39.687253)
(Begin preamble)
G17 G90
G21
(Begin operation: Fixture)
(Path: Fixture)
G54
(Finish operation: Fixture)
(Begin operation: TC: 201 1/4" Flat Endmill Generic)
(Path: TC: 201 1/4" Flat Endmill Generic)
(TC: 201 1/4" Flat Endmill Generic)
(Begin toolchange)
( M6 T1 )
M3 S18000
(Finish operation: TC: 201 1/4" Flat Endmill Generic)
(Begin operation: Pocket_Shape)
(Path: Pocket_Shape)
(Pocket_Shape)
G0 Z22.200
G0 X26.039 Y26.039
G0 Z20.200
G1 X26.039 Y26.039 Z14.700 F1496.000
G3 X-4.065 Y36.599 Z14.700 I-26.039 J-26.039 K0.000 F1500.000

[mhotchin (Michael Hotchin)]

Are you absolutely sure that the Z Zero in FreeCAD matches the Z Zero you set on the machine? The behaviour you describe is consistent with a design Z Zero of bottom-of-stock.

[gdon_2003 (Guy Donham)]

Usually in CC if you get an air job you set Z zero on the bottom in CC but set the Z zero on top of the material. Then you get an air job twice as high as the material thickness. I dont know that software but the behavior fits setting Z zero in the CAD and setting a different location in the CAM.

[angrysamsquanch (s)]

That’s it. In Freecad a copy of the model is created which is then used to create the tool paths. This model has to be translated below z0 so that it will match the z0 set in carbide motion.