Hardness is relative and in general you can get chatter in anything depending on the weak point in your system. If you take a deep enough plunge and feed fast enough in something like maple you will get chatter. But maple is going to be vastly softer than any grade of aluminium.
Not sure what you mean by cutting the aluminium with a knife. Ran a quick test of it just now to see though. The 6061 I had to use much more force and the knife wanted to skip. The 5052 I could cut deeper and was a much smoother cut. Wouldn’t want to rely on this as a method for testing though. Pics attached for reference anyway.
5052 top 6061 bottom
(sorry for the bad pics. Just did it real quick on my phone.)
As long as you’re clearing the chips you should be good. I’m wondering though if the cut starts to degrade at the bottom because your air can’t clear it that deep. The corner of your cut looks a lot like a soft grade with chips getting recut.
Glad they have something. Keep in mind though, this is a feed guide for those tools, with a 611 (or close by RPM), on a Shapeoko 3. Not sure what tools Mike is using, he’s on a Nomad, and can only hit 10k RPM.
Tool geometry, tool material, RPM, runout, machine rigidity, spindle power, etc all can have a profound effect on feeds, speeds, and DOC.
Not trying to be a downer Will. I love how much time you spend helping everyone and all the good information you give out. Just want to make sure people understand that chart in context relative to their setup.
Think & Tinker / PreciseBits