[MattKellett]

It using two processes to make the square hole. Basically rotating and chiseling, but the thing is moving so fast that we can't see the tool doing the chiseling.

I suspect it pauses rotation for a fraction of a second, while it chases out the corner with the chisel part of the cutting tool, similar to a hammer motion.


Edited - Basically as Reg says above, the wood working tool for this has been around for ages. Still a cool cnc process.

2 nd edit, if I'd bothered to watch the end of the video, I would have seen this!