woodworker?

[azhuntnut]

Do we have any woodworkers on this site? I am trying to determine the angle of my cuts to build a pentagon shaped pedistal. I know its 72 degrees on the inside of the box at each corner, but for some reason I am having a hard time determining the cut angle for all the boards to match up together. David

[scoutm]

 

 

[Snapshot]

An octogan is an easier one, as all angles are 45 degrees. Just a thought.

[tomgobbler]

the corners are 108degrees, so your cut's on each piece would be 54 degrees, so that when put together it would be the 108.... were are you getting the 72?

on the diagram apove, you can not cut 1 piece 72, and the other one 36 to get your 108, yes they would fit together BUT the lenght on the angle would be different for each piece....and so not fit together very well.

 

good luck

tommy

[Non-Typical Solutions]

Set the saw at 22.5 degrees and let er fly.....for a six sided one that is....easy to keep track of too.......

[azhuntnut]

I am using some old 1x10s I found and will be cutting the long side of the boards. So I would need to run them through a table saw and set the saw at a 22.5 degrees. Is this correct? David

 

http://www.k6-geometric-shapes.com/pentagon-shape.html

[Non-Typical Solutions]

I am using some old 1x10s I found and will be cutting the long side of the boards. So I would need to run them through a table saw and set the saw at a 22.5 degrees. Is this correct? David

 

http://www.k6-geometric-shapes.com/pentagon-shape.html

 

If you are agreeable to change to a six sided pedestal 22.5 is the correct angle, I have never done the pentagon shape, but lots of work with the six sided configuration.

 

Make sure you have a dang sharp blade on that tablesaw which by the way should have a tick mark for 22.5 on it as well.

Good luck and holler if you need, if your lumber is warped at all it makes that cut really tough to get accurate but I guess that is a DUH. I use alot of old thrown away resawn lumber and I have to cull through a bunch of it when I am making cuts like you are talking about.

[Gr8 White Jr]

TomGobbler is correct. The angle is 108 degrees which means that your miters need to be 54 degrees. Now you have to keep in mind that when your table saw is set at ZERO that the blade is actually making a 90 degree cut. With that in mind when you need to make a 54 degree cut you have to go 54 degrees off of the 90 degree blade which means you need to set you table saw at 36 degrees.

 

-Tracy

[Outdoor Writer]

There's a real simple formula I use when figuring the miter angles for different shapes. Start by dividing 360 by the number of sides, subtract that from 180 and divide by 2.

 

Let's start with a simple square where most of us know that each corner has to be 90 deg. So you have 360 divided by 4 = 90 and 180 -90 = 90 divided by 2 = 45.

 

For a pentagon: 360 divided by 5 = 72. Then, 180 - 72 = 108 and 108 divided by 2 = 54. So each miter is 54 deg.

 

For a six-sided shape (hexagon): 360 divided by 6 = 60. Then 180 - 60 = 120 divided by 2 = 60.

 

For an eight-sided shape (octagon): 360 divided by 8 = 45. Then 180 - 45 = 135 divided by 2 = 67.5

 

Now, since both a miter or table saw is set at 90 deg. to the table, you then must subtract the above miter angles from 90 deg. to get the angle for setting the blade, Thus, it's 45 deg. for the square, 36 deg. for the pentagon, 30 deg. for the hexagon and 22.5 for the octagon.

 

The real key to getting tight fitting joints is to be sure every piece is the exact same length or width. Otherwise, you'll end up with gaps.

[Non-Typical Solutions]

There's a real simple formula I use when figuring the miter angles for different shapes. Start by dividing 360 by the number of sides, subtract that from 180 and divide by 2.

 

Let's start with a simple square where most of us know that each corner has to be 90 deg. So you have 360 divided by 4 = 90 and 180 -90 = 90 divided by 2 = 45.

 

For a pentagon: 360 divided by 5 = 72. Then, 180 - 72 = 108 and 108 divided by 2 = 54. So each miter is 54 deg.

 

For a six-sided shape (hexagon): 360 divided by 6 = 60. Then 180 - 60 = 120 divided by 2 = 60.

 

For an eight-sided shape (octagon): 360 divided by 8 = 45. Then 180 - 45 = 135 divided by 2 = 67.5

 

Now, since both a miter or table saw is set at 90 deg. to the table, you then must subtract the above miter angles from 90 deg. to get the angle for setting the blade, Thus, it's 45 deg. for the square, 36 deg. for the pentagon, 30 deg. for the hexagon and 22.5 for the octagon.

 

The real key to getting tight fitting joints is to be sure every piece is the exact same length or width. Otherwise, you'll end up with gaps.

 

Great math lesson there Tony which pointed out that I didn't have enough sides for my 22.5 I was writing six and thinking eight I stand corrected on my number of sides. All my years of playing with wood and you had that simple formula all the time??? I really need to get out more often, thanks!!!