Originally Posted by
dharmic
At the moment you're taking baby steps down into the sheet and repeating the whole pattern. What I'm suggesting is you ramp in a helix or, if you can't do that, just plunge down slowly (100mm/min maybe) into the middle of each hole so the cutter's full depth, then spiral outwards taking a thin slice of the wall each pass until you reach the full diameter of the hole. Thinking about it you'll probably need to do your current approach for the external wall, especially if you're leaving tabs to keep the thing in place with clamping and whatnot.
Which means back to square one or looking at the other things. Sorry, red herring. Try lubrication if you aren't already, and try tweaking the feed rate multiplier to make the machine as quiet as possible through the cutting process.