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Thread: Bisecting a circle into five segments

  1. 02-10-2011, 2:17 PM #1
    Jonathan Spool
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    Bisecting a circle into five segments

    When installing 5 casters on a circular base, I realized that I did not know how to locat 5 equally spaced locations other than using a protractor, or measuring, or calculating the diameter and dividing by 5. Is there a method to bisect a circle into 5 using a compass?
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  3. 02-10-2011, 3:00 PM #2
    Jonathan Spool
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    I found instructions how to draw a pentagon which will in effect divide the circle into five.
    http://www.youtube.com/watch?v=nXqDg7FD9nM
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  4. 02-10-2011, 3:56 PM #3
    Fred Belknap's Avatar
    Fred Belknap
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    That is good information to know, wonder how long I can remember that?..........remember what??????????
    Fred
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  5. 02-10-2011, 6:14 PM #4
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    Brent Ring
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    Quote Originally Posted by Fred Belknap View Post
    That is good information to know, wonder how long I can remember that?..........remember what??????????
    Does anyone know how to bisect a circle into 5 segments? (Ok I could not resist!)
    Sawdust is some of the best learning material!
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  6. 02-10-2011, 6:31 PM #5
    Jonathan Spool
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    I'll post a quiz in around a week to see if anyone retained this!
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  7. 02-10-2011, 9:21 PM #6
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    glenn bradley
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    Quote Originally Posted by Brent Ring View Post
    Does anyone know how to bisect a circle into 5 segments? (Ok I could not resist!)
    Quint-secting???
    "A hen is only an egg's way of making another egg".


    – Samuel Butler
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  8. 02-11-2011, 3:20 PM #7
    ray hampton
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    the first test is to draw a five-point star by using this information
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  9. 02-12-2011, 10:36 AM #8
    lowell holmes
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    CONSTRUCTION OF A STAR.JPG

    Here is a slick construction. I thought it would have been presented by now. I hope it can be zoomed up. If you want, PM me and I will send you a pdf, jpeg, tiff, or dwg file of it.
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  10. 02-12-2011, 5:32 PM #9
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    Out of curiosity, why would you do such a thing if you have a protractor available? Theoretical/educational quests are great and all, but if you're trying to create a design, a protractor is going to be 10 times more accurate than using arcs and intersections...
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  11. 02-12-2011, 6:55 PM #10
    ray hampton
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    drawing a pentagon for a 5 point star is easy with the use of a
    protractor but drawing the pentagon the right size for the star
    is a hit or miss proceed----do anyone know a formula for drawing
    the pentagon for the star size
    Last edited by ray hampton; 02-12-2011 at 6:58 PM. Reason: line break
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  12. 02-12-2011, 10:21 PM #11
    lowell holmes
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    The circle sizes the pentagon and the star. The points on the circle defines both shapes.

    Jonathon ask how to lay out a star. I showed him just one of many ways to do it.

    IMO, the compass and dividers are more accurate in the shop than a protractor. I typically calculate the chord length with trig and lay it out, or lay it out with autocad.

    The method above was used by Frank Strazza when he conducted an inlay class at Homestead Heritage. There was nothing theoretical about it. No trig was used and the star was perfect. It was layed out in about 5 minutes.

    Brent, take the distance between the two points of the star opposite each other times 0.5257 to determine the radius of the circle.
    Last edited by lowell holmes; 02-12-2011 at 10:42 PM.
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  13. 02-13-2011, 1:42 PM #12
    ray hampton
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    If I want to cut a star out of metal 2 ' from tip to tip
    how big of a pentagon will I need to start with ?
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  14. 02-13-2011, 2:21 PM #13
    Jonathan Spool
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    Thanks Lowell,
    Thats exactly what I was looking for.
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  15. 02-13-2011, 4:50 PM #14
    lowell holmes
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    Ray,

    A circle with a radius of 12 5/8" will yield a pentagon measuring 24" point to point.

    Lowell
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  16. 02-13-2011, 4:58 PM #15
    lowell holmes
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    Jonathon,

    Your PM mailbox is full.

    I tried to respond to you and couldn't.

    Lowell
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