So, the license for MeshCAM that came with my Nomad was my first experience with CAM. And while I agree with people who claim that MC is a great entry point into CAM, I really want to take advantage of some of the features that Fusion 360 CAM offers.
But, since I don’t really know what I’m doing, I decided to start with training wheels. So, I mounted a slab of 2x6 (soft pine, cheap, easy to work with) and tweaked a deep hogging/roughing operation in MeshCam until it was working smoothly. My cutter was a .250" 2-flute up-cut, flat-end mill, at 10k-RPM (everyone who talks about Fusion CAM seems to agree on using max RPM).
Then I changed my origin point, and tried running the same model, but with Fusion’s 3D-Adpative CAM. Same chunk of wood, same cutter, very different cut path.
The helical “plunge” was beautiful – very nearly whisper-silent, I probably could have pushed it a lot harder. Since that was the part I was most worried about, I thought I was past the hard part… but then I hit the bottom of the plunge, at ~90% flute-length engagement of the cutter, and started into the flat outward spiral. And that’s where things got… weird.
I immediately started getting rythmic “pulses” of chatter – very loud chatter for about 250-500ms, followed by 250-500ms of quiet cutting. This kept repeating, very regular.
So, I went back to Fusion and started reducing the Chip Load (which had the side effect of reducing the feed rate), then re-generating the G-Code. But I kept getting this rythmic chatter, on/off. And the rythm didn’t seem to change much, even when I threw my hands up and turned the feedrate down to 10mm/min (no, that’s not a typo). The chatter was so loud, I honestly thought I might be skipping steps on the axis motors, but didn’t have a good way to confirm that.
So… I’m confused. This cutter, in this wood, does good hogging with MeshCAM-style roughing paths, and mostly cutting with the tip of the end mill. My research on 3D-Adaptive suggests that going deep and then cutting outward with the side of the cutter should be easier on the cutter, improve tool life, and give better surface finishes, as long as your chip load per flute isn’t excessive. And at the stupidly low feedrate of 10mm/min, I should have been shaving the wood away a micron at a time. But I still got the darned chatter.
Given how well this cutter/wood combo works on this machine under MeshCAM, I’m inclined against thinking it’s a hardware issue. So obviously there’s something I’m badly misunderstanding about the Adaptive settings. But slowing down (even enormously) didn’t help at all, and I’ve been too much of a chicken to try getting more aggressive yet. The rythmic nature of the chatter also puzzles me – if nothing else, I would have expected the “beat frequency” to change when I made large changes to my feedrate, but it didn’t really seem to have much effect.