

How to Drill a Square Hole - hhm
http://mathworld.wolfram.com/ReuleauxTriangle.html

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jws
The angle of attack of the cutting edge appears to vary by about 90 degrees.

But I'm sure it works for spherical chickens in a vacuum.

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frankus
A lot of countries use related curves of constant width for their coins. It
makes it easy to tell, say, a Loonie from a Toonie by feel, yet they can still
be automatically sorted by sliding them through a slot without them needing to
be oriented in a particular way.

I've never seen a triangular coin like that though. That would be pretty cool.

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iamdave
Never before has 'looked good on paper' carried more weight.

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sosueme
you can buy a drillbit that does this

[http://www.drill-
service.co.uk/Product.asp?Parent=0206200400...](http://www.drill-
service.co.uk/Product.asp?Parent=020620040000&Tool=347)

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miratom
Also, how to build a Wankel Rotary Engine:

<http://en.wikipedia.org/wiki/Wankel_engine>

~~~
skittles
Does anyone happen to know why the Mazda RX7's and 8's keep using this type of
engine? It makes no sense that all their other cars don't.

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LogicHoleFlaw
They burn oil like mad to keep the tip seals of the rotor lubricated. They
suck down gasoline - the RX8 gets maybe 15mpg if you drive it hard. 20 if you
are careful. And it has to be premium. You have to be careful not to flood the
engine - never run it for less than 30 seconds, or without revving to at least
3K RPM.

The upside is that the engine itself is _tiny_ and mounted almost exactly in
the middle of the car - under your feet. Rotary's get about 3x power for the
same displacement as a reciprocating piston engine. They're great in
airplanes.

I've spent a lot of time in an RX8 and it's a blast to drive if you're willing
to deal with the cost and finicky nature of the beast. When the engine spools
up and it just starts whirring... that's a beautiful thing.

