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From: leeper@ahutb.UUCP (m.r.leeper)
Newsgroups: net.puzzle,net.jokes
Subject: Re: Manhole covers (interview question)
Message-ID: <564@ahutb.UUCP>
Date: Mon, 18-Mar-85 18:13:09 EST
Article-I.D.: ahutb.564
Posted: Mon Mar 18 18:13:09 1985
Date-Received: Tue, 19-Mar-85 06:05:23 EST
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REFERENCES:  <462@nbs-amrf.UUCP>, <1282@amdahl.UUCP>

Curves of constant breadth came up during WWII.  The British were
trying to mill hulls of submarines to have perfectly circular
cross-sections.  They tried rolling molten cylinders between parallel
forming sheets, much like you would roll clay between your hands to
make a solid cylinder.  The problem was they were not getting circular
cross-sections.  They eventually discovered that the process gives you
only a constant breadth curve, not a circle.  The triangle described
elsewhere in a response is called a Rouloux Triangle.  One of its
applications is in a special drill bit that cuts square holes.  Placed
inside a square frame, one side of which is the length of the breadth
of the triangle, a Rouloux shaped drill bit can be made to follow the
edges of the square.  (It is amazing how many interesting things you can
learn from one really good high school math teacher!)

				Mark Leeper
				...ihnp4!ahutb!leeper