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Thread: math help

  1. #1
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    math help

    I need to build a octagon, outside diameter of 12 inch. I know the cut will be 22.5 but what is the length? I know how to do this, but for the life of me I am drawing a blank this morning.

    I am getting 4.97 inch, guess I should throw that out as well. Sound right?
    Last edited by Steve Southwood; 11-25-2010 at 03:11 PM.

  2. #2
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    daaaaaaa I draw a blank
    I dream a lot. I do more painting when I'm not painting. It's in the subconscious.
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    colonialrestorationstudio.com

  3. #3
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    draw a circle 12" in diameter, divide it by 8, and connect where the circle and lines intersect. that way, your outer points are at the 12" diameter mark.
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  4. #4
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    just ran it through sketchup, and i get 4 7/16".
    benedictione omnes bene

    www.burroviejowoodworking.com

    check out my etsy store, buroviejowoodworking

  5. #5
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    Thanks Dan, probably right on the money. One more thing to add to my to do list.

  6. #6
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    I'm drawing a blank too, but I want to say you're looking for the hypotenuse of an acute triange (one which all angles are less than 90 degrees). Haven't found a good example of the forumla or a calculator. All calculators I've found for hypotenuse are based on one side being 90 degrees.
    Darren

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  7. #7
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    Well then we will call this the turkey day challenge

  8. #8
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    SU is your friend:
    Attached Thumbnails Attached Thumbnails octagon.jpg  
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  9. #9
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    No lets see it been 40 years since I had to do this but as I recall This is a SAS problem. Side Angle Side. You take the length of the two side squared and add them together multiply the by the sine of the included angle and take the square root of the result.
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

  10. #10
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    Oh and the reason the pythagorean theorem works as A^2=B^2+C^2 is because the sine of 90 degrees is 1.
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

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