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 Post subject: Geometry Problem
PostPosted: Thu Mar 25, 2010 6:29 pm 
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Location: University City, MO
I have to confess that I did pretty good in plane geometry back in H school a long time ago, but didn't go on to solid G. Big regret.

I'm making a pyramid (actuall the top is cut off and it will become a lamp shade...art glass will be framed by my work) I've made four trapezoids that will form the sides of the pyramid. The base and top must, of course, form a square. But, right now the face of each trapezoid is 90* to the edge and I can't glue that.

Here's the problem: Is the bevel angle 45* on the edges? If so, it just doesn't look right. When I clamp an edge of one trapezoid to the face of the adjacent one the angle where they meet is less than 90* :confused:

Am I over thinking this or is there something I'm missing?

What's really agravating is that I did one of these a few years ago from plans in a mag. Can't fine the plans and can't remember how I did it! The shade turned out really well. My second attempt is turning into a nightmare :mad: .

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PostPosted: Thu Mar 25, 2010 7:14 pm 
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Location: London, England
Joe,

Take a look HERE

Ralph :wink:

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PostPosted: Thu Mar 25, 2010 7:25 pm 
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Location: Forest, Ontario, Canada
There is a compound angle calculator on the home page of this site. Here is a link directly to it: http://www.woodworking.org/WC/mitercalc.html

I seem to remember seeing a calculator for hopper miter angles somewhere a few years ago, but I can't find it now. If your lampshade was upside down it would be a hopper.

Good Luck!
Bob


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PostPosted: Thu Mar 25, 2010 7:26 pm 
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Ralph was typing while I was still looking for that hopper calculator.... :D

Bob


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