Is it possible to drill a square hole using drill of special pattern? I have known one of the solutions which uses Reuleaux triangle as the drill, however the hole actually is a "square" with four round corner (brief info about this solution).
However, in another post, someone claims to improve the approach and gives a pattern which, as he claims, can make a "square" without round corner(the pattern). But he didn't give any further explaination, and barely the picture can't get me across.
I am now confused whether it is possible to make a "square" without round corner using drills.Or is it impossible theoretically?

Square-Hole Drill in Three Dimensions
