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    Need some math help

    I am to old to remember how this is done, so hopefully someone else can..

    I have a 13" diameter circle in which I want I want 15 equal slices (24 degrees each). What is a good way to determine the layout (please show your work to get extra credit)

    Thanks in advance

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    Re: Need some math help

    I would step off 15 equal spaces with dividers.

    or set my Starrett protractor to 24 degrees and mark it out.

    or do a print on the computer

    or

    or
    Last edited by Mike Davis; 05-08-2018 at 06:52 PM.



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    Re: Need some math help

    the chord for 13" dia circle with a central angle of 24 is 5.4056"

    Just set your dividers to exactly 5.4056" and step off the circle

    Hope this help

    Sorry I misread and calculated this for a circle with 13" radius instead of a 6.5 radius


    The real answer is 2.7028"

    Formula is (Sin 12 * 6.5)*2
    Last edited by Phil S; 05-08-2018 at 08:30 PM.

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    Re: Need some math help

    Somehow I came up w/ a different number than Phil. Using SketchUp, I came up w/ 2 11/16" for the dividers.
    I'll gladly tell you how I do something. Just please don't confuse that with the right way to do it, and almost certainly not the only way.


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    Re: Need some math help

    Sanity check, 5x15 is 75 that seems larger than the circumference if a 13 inch diamiter circle.

    3x15 is 45 I’d say that’s closer.
    Last edited by Mike Davis; 05-08-2018 at 08:33 PM.



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    Re: Need some math help

    I'd also do it graphically with SketchUp's Pie tool to set up dividers. If I really wanted it to be accurate, I'd print it full size so I could set the dividers off it directly.
    Screenshot - 5_8_2018 , 9_12_50 PM.png
    Last edited by Dave Richards; 05-08-2018 at 10:22 PM.
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    Re: Need some math help

    13 x 3.1416 = 40.8408 / 15 = 2.72272 will get you close.

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    Re: Need some math help

    Quote Originally Posted by Dave Richards View Post
    I'd also do it graphically with SketchUp's Pie tool to set up dividers. If I really wanted it to be accurate, I'd print it full size so I could set the dividers off it directly.
    If you want it in fractions instead of thousandths, I came up w/ 2 45/64" using Dave's method. SketchUp is a wonderful tool.
    I'll gladly tell you how I do something. Just please don't confuse that with the right way to do it, and almost certainly not the only way.


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    Re: Need some math help

    Quote Originally Posted by Bill Clemmons View Post
    If you want it in fractions instead of thousandths, I came up w/ 2 45/64" using Dave's method. SketchUp is a wonderful tool.
    I started with fractions and got 2-45/64, too. That would be 2.765625. Probably close enough for government work.
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    Re: Need some math help

    The best that you're probably going to get is setting your calipers to 2.70" (2.703" = 2 45/64", +/- 1/64") if you can get that close in the real world. Our pure math carries the decimal beyond what's practical in the shop.



    https://www.mathopenref.com/arclength.html
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    Last edited by Jeff; 05-09-2018 at 10:43 AM.

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    Re: Need some math help

    Of course printed out to full size, you could pick up the divider setting right off the drawing.
    24 degrees.pdf
    Last edited by Dave Richards; 05-09-2018 at 01:13 PM.
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    Re: Need some math help

    A math problem? No problem for me, I'm just gonna go back to bed.........
    Experience is a hard teacher; she gives the test first, and the lesson later.

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  21. #13
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    Re: Need some math help

    Thanks Dave. How do you get a full size PDF file printed? Where?

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    Re: Need some math help

    Jeff, that one is just 8-1/2 x 11 so you should be able to print it on your printer at home. When you get set to print it from Adobe Reader or Acrobat make sure you select the correct setting.

    Screenshot - 5_9_2018 , 12_08_09 PM.png
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    Re: Need some math help

    Quote Originally Posted by Jeff View Post
    Thanks Dave. How do you get a full size PDF file printed? Where?
    For that particular print 8.5x11 will fit, Most small print shops and even the office supply stores have large format printers now. They charge a lot for a full size 36x48 or some can do even larger but when you really need it...



    One machine can do the work of 50 ordinary men. No machine can do the work of one extraordinary man." -Elbert Hubbard

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