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mooseye
10-21-2007, 09:40 PM
Ever tried to lay out a big one? I had to do some serious head scratching on this one.
Wife(read boss) wanted a small garden work area so we decided on a gazzabo type thing. I decided on the pentagon. What a headache. I was just wondering if there is any kind of formula or method for laying out one about 8 feet in diameter?

William McCormick Jr
10-21-2007, 10:54 PM
http://www.Rockwelder.com/WeldingWeb/Five/Five.html

I made a movie of how I would do it with Cadd.

You can see in the movie that I created a four foot radius inscribed pentagon. And got the measurements between each of the legs of each angle. And the length of each side for you.

The length of each side would be 56.427" or 56 7/16" and the length between both legs of each angle would be 91.301" or 91 5/16" long.

If I was out in a field. I would create a circle with a string or rope to hold the radius from a stake in the center.

Knowing that each side is 56 7/16" long you can use that measurement. And go from one point on the circumference of the circle to the next. Until you come back to the first point. Then you can just draw the straight lines between those points.

But if you are cutting stone, you can use the 54 degrees as the miter angle for the 108 degree pentagon corners.

Sincerely,

William McCormick

Brett
10-22-2007, 03:38 AM
The length of the sides will be 0.588 of the diameter you want.
ie 8 ft diameter = 4.072282018ft :)

(sine 36° x 2 x radius)

As William correctly pointed out external angle of 108°,
but miter angle to set saw is (180-108)/2=36° which will give you an angle of 54° on your material
(saws say what your cutting off not resultant angle)

Brett
10-22-2007, 05:19 AM
To set it out on site,
a)I would choose where I the center of the structure and put a peg there.
b) Choose my radius (4' ft?) and with a 4 ft piece of string on the center peg scratch a circle.
c) Choose where you want a leg (any one) and put a peg there on your scratched circle.
d) A piece of string 56 7/16" to first on perimeter peg , scribe an arc , where that arc crosses the perimeter is your next leg.

Dont be surprised if your a bit out as there is a margin of error with string lines and arcs,

Good luck it is easy

mooseye
10-22-2007, 08:06 AM
http://www.Rockwelder.com/WeldingWeb/Five/Five.html

I made a movie of how I would do it with Cadd.

You can see in the movie that I created a four foot radius inscribed pentagon. And got the measurements between each of the legs of each angle. And the length of each side for you.

The length of each side would be 56.427" or 56 7/16" and the length between both legs of each angle would be 91.301" or 91 5/16" long.

If I was out in a field. I would create a circle with a string or rope to hold the radius from a stake in the center.

Knowing that each side is 56 7/16" long you can use that measurement. And go from one point on the circumference of the circle to the next. Until you come back to the first point. Then you can just draw the straight lines between those points.

But if you are cutting stone, you can use the 54 degrees as the miter angle for the 108 degree pentagon corners.

Sincerely,

William McCormick

That is bad to the bone! I want one!

steve45
10-22-2007, 11:20 PM
Funny, my wife wants to build a small outdoor kitchen near the pool. I thought a hexagon would be more artistic than a square building. The inside will be divided to provide room for a small kitchen on one side, pool equipment room on the other.

I decided to make the sides about 8 feet long. In order to see how it would really fit into our yard, I made a hexagon out of 1/2" PVC pipe. With a 4 foot wide overhang, it's a pretty large structure. At least with the pipe, I can try moving it around to see the best place to put it, as well as layout where my sprinkler lines will have to be moved to, etc.

William McCormick Jr
10-23-2007, 09:54 PM
The length of the sides will be 0.588 of the diameter you want.
ie 8 ft diameter = 4.072282018ft :)

(sine 36° x 2 x radius)

As William correctly pointed out external angle of 108°,
but miter angle to set saw is (180-108)/2=36° which will give you an angle of 54° on your material
(saws say what your cutting off not resultant angle)

You may have input something into the calculator by mistake.

I get 0.588 * 8 = 4.704 and in inches that would be 56.448

You probably hit a wrong key on the calculator. I do that occasionally, and then I catch it an hour later as I am reading through the posts, and can no longer change it.

Sometimes I use the computer calculator. And when I have a bunch of programs running, it will cause a slight delay in taking input. Especially for decimal points. I go through some long calculation to find out that one of the numbers did not register the decimal place. That is annoying.

I had never used that formula before. It gives a slightly different answer, but surly for what we are talking about doing more then accurate enough.

Sincerely,

William McCormick

Brett
10-24-2007, 03:27 AM
You may have input something into the calculator by mistake.

I had never used that formula before. It gives a slightly different answer, but surly for what we are talking about doing more then accurate enough.

Sincerely,

William McCormick

Opps..:laugh: (4.70228 is the correct one thanks WMC)

I sorta make that formula up : 5 sided figure is 1/5 of 360° =72°, halve it ,get the sine and you have half of your inscribed length .

For the super scribed size 2x the inverse of the Cos x radius.

Use them often .

As a side note thankyou for picking up my error as it protects other posters.

Brett

William McCormick Jr
10-28-2007, 06:06 PM
That is bad to the bone! I want one!

They are a pretty cool company. The owners/programers will actually customize the product if you find a real need for something. Sometimes they do it in hours.

Last time I checked they charge about \$450.00 dollars for the most current version. But they sell the older versions that do almost everything the newer versions do for less. It is better to just get the latest version. Especially with Vista taking over.

I have to draw up some pretty insane things for work. And I often only have a few minutes between all my crazy experiments and side projects. So I got the program that really lets you fly.

It starts up in about three seconds.

If there is a down side it is their security key. Sometimes I forget to take it out of my home computer and then cannot save drawings on my laptop. Other then that, it is pretty cool.

Sincerely,

William McCormick