Bisecting a circle into five segments

[Jonathan Spool]

All cleaned up. Thanks

[James Watson]

Unless I'm missing something (which is very likely), couldn't you just use dividers around the circumference, just like you would do to divide a straight line?

Start with a guess of the chord length between two points. Walk the divers around the circle. Adjust the dividers by 1/5 of the error. Repeat until you can't see the error.

No math or measuring needed.

[lowell holmes]

That works.

It can take a while to get there.

If you multiply the width you want to end up with by 0.525731 will give you the radius of the circle you need to divide.

As others have stated, a protractor works. I probably woud use an adjustable triangle.

Frank Stazza makes a star inlay by sawing the points of the star at an angle of 18 and 36 degrees. They are cut from 3/4" thick board. It yields a star that is 3 1/4" wide.

Check heritagewoodschool.com

[hank dekeyser]

Am I missing something or did we forget simple math ? Circle = 360 degrees : 360/5=72 degrees between points.

[ray hampton]

YES , the math is simple but drawing a pentagon and star is not done quickly

[Pat Barry]

I agree with Hank - that's what a protractor is for.

[Thomas Canfield]

If you can strap the circumference, you can divide it by 5 and that locates the 5 sections. Close enough for most work, and probably closer than the level of your floor.

[Steve Schoene]

Surely the measurement guys jest. A compass that can be adjusted and locked plus a straight edge can give a very precise star and hence pentagon. Surely, to achieve the same precision with a protractor and ruler calls for rather more sophisticated versions of those tools than are likely in a wood working shop. Measurements have inherent problems with error that are much less with direct comparisons with a simple devise like a compass.

[Pat Barry]

I don't see the compass method as being very obvious at all. In fact, unless you knew the trick, I bet you could sit for days on end with a compass and never figure out how to make a pentagon or a star. For the intended task you would be far better off taking the time to go to the nearest store and buy a simple protractor and lay out the 72 degree angles.

[Frank Mussenden]

Just use the math. Any amount of sided polygon 10, 13, 3, 27, 8, 5, so on. The cord length on any size of circle you wish go 360 divided the number of sides you want. Lets say 10 sides. 360/10 =36 =Cosine D = 36deg 24" diameter =12" radius
36deg use this as your cosine internal angle. Your radius is the length from center of circle to out side of circle. The arrays from the center we will call Radius Asq and Radius Bsq which are the same length with 36 degrees between them both. For a 2' diameter circle = 12" Squared and 12" squared.
Ok this is real easy. The Cord length to step off around the circle with only the circle drawn= C Which = the square root of (A squared + B squared) -2x AxB X Cosine D Which is your internal angle. This gives you the cord length. Program this into your calculator. Very handy for Segmented work.
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[Pat Barry]

Frank - the only people that math is easy for is rocket scientists and math professors.