segmenting question

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triw51

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I was asked to make a six sided box that is 13" tall and 5.5" inside diameter. My question is how wide do I make the sides so the inside diameter is 5.5" What would the formula be? I know the angles on each side are 30 degrees (360 divided by 6 [number of boards] the divide by two for each edge). Any help would be greatly appreciated William
 
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magpens

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How wide you make the sides depends on the thickness of the sides.
Let's say the thickness is T.
Also, when you use "diameter" do you mean from flat-to-flat, or corner-to-corner ?
Let's assume you mean flat-to-flat.
Then, from the center axis to the outside flat surface will be 2.75" + T.

The outside corner-to-corner distance across the flat surface is:

2 x (2.75 + T)/(tan60)

= 2 x (2.75 + T)/1.732

= 1.155 x (2.75 + T) inches

Of course, you have to cut the sides with your table saw blade tilted 30 degrees, as you said.

The total circumference will be 6 times that value, or ... 6.93 x (2.75 + T) inches

I hope that I have done the trigonometery correctly !

As an example, suppose your thickness is 3/8" = 0.375". Your cut board width will be 3.609", and circumference is 21.654".

Does that seem right ? (Comparing circular cylinder with same wall thickness would have circumference of 19.635".)
 
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Charlie_W

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Nov 16, 2011
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Sterling, VA USA
William, I know I am late in posting to your inquiry..... but the easiest way to me is to simply dray it out on paper. You know how many sides and the degree.... just need a compass and protractor. This will not only show you the width of each stave but also the thickness needed to make the wall thickness what you want.
Good Luck and post pics when done!
 
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