I haven’t seen this situation before so I figured I would post my solution and let folks critique or suggest alternative ideas. I recently found myself needing to mill an 18 mm deep pocket in aluminum on my Nomad 883 Pro. Programmed with MeshCAM. The MIC6 arrived and I tried a few 1/4" end mills before giving up and going with the 1/8" Flat Endmill (#102).
Speed: 300 mm/min
Plunge: 20 mm/min
RPM: 10k
Stepover: 1.5875 (50%)
Stepdown: 0.20 mm
Contour Offset
This was going well and I creeped up the speed to ~500 mm/min while monitoring. At a depth of ~5 mm the corners began to struggle. They sounded awful and I could see the end mill halting and restarting as it tried to navigate two corners in particular. I manually dropped the speed to 100 mm/min to improve navigating those two local corners until reaching a depth of 6 mm exactly.
Knowing that I needed to reach 18 mm I figured I would just add terraced steps into the design each 6 mm. MeshCAM allows me to set the Program Zero 6 mm above my new geometry and to NOT machine top of stock. This allows me to keep my part in the vise, maintain my program zero, pause the program and upload a new program with the new geometry and continue along without having to start over from the beginning and waste the hours it took the Nomad to cut a 100 mm x 85 mm x 6 mm pocket.
Except that didn’t work at all. The Z-level dropped down to the top of the new geometry and then moved to the center to begin pocketing. It crashed at the SW Zero corner and caused the X-axis stepper motor to miss count. The pocket began cutting off-center.
So I stopped the program and went back to CAD to put the 3rd terrace level back to restore the original height.
I realized that I needed to manually delete the G-code for the first terrace level but MeshCAM V7 saves in .EGC encrypted file format so I couldn’t access it. So I launched MeshCAM V6 which saves to a .NC extension and found the correct depth.
Kind of a hassle, but it finally worked as expected.
Just posting for future reference in case anyone else finds themself in a similar situation. If this has been posted before, sorry but I couldn’t find it.