Showerthought: I spent a full shift chasing a chatter that wasn't there.
Had a job last month on an older VMC, making a simple aluminum bracket. The finish looked awful, like bad chatter. I checked the tool, the speeds, the holder, even the coolant mix. Spent about 6 hours on it. Turns out, the vise jaw had a tiny, almost invisible burr from a previous crash, so the part was vibrating ever so slightly. A five-minute file job fixed it. Has anyone else been fooled by something that simple?