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Have you tried a spade bit? I know they're designed for wood, but if you're willing to burn a few up, I think that would be the easiest. Spade bits have a pilot point that might end up going all the way thru your sheet, depending on thickness, is that permissible for your application? Other than the small pilot hole, the bottom should be nice and flat.
If that won't work, your router is the best bet. Is it a plunge router, or do you have a router table for it?
Another option would be to cut all the way through with a hole saw, use a band saw to cut the plug to the desired depth, then weld or epoxy the plug back into place.
Can You use counterbore bits?
Why not just use a centre-cutting endmill?Easy enough to just chuck one up in a drill press, a hand drill would also be possible if you're careful enough.
A brad point drill with give you a decent hole with a little dimple in the middle. http://www.wlfuller.com/html/brad_point_drills.html You should still be able to glue OK even with the little dimple (I would think)
Would it work to drill a hole with a standard bit and then inject a small amount of epoxy or other non shrinking glue/resin in the bottom of the hole and let it dry? With the right kind of glue, it should find it's own level and dry relatively flat.
Yes, but unfortunately they are all at the same place as the mill (who said "get off your lazy butt" )
Just ensure enough back clearance on the flattened cutting edge and grind in the drill's web to have the flat cutting edge go all the way to the center (like an 2-fluke end mill).
Quote from: Soeren on August 21, 2012, 09:22:11 PMYes, but unfortunately they are all at the same place as the mill (who said "get off your lazy butt" )That's the origin of so many regrettable decisions in robot building