figuring the width of staves

[cal thelen]

anybody know the formula for figuring out the width of staves to get the desired diameter? trying to figure how wide to make the staves if i want a 3-1/2 inch outside diameter circle. and I want to use 6 pieces to get it. i am figuring 60 degree angles but how wide does each piece need to be. or if i wanted to use 8 pieces i was figureing 22.5 degree angles but again who wide each piece to get desired diameter. thanks
cal

[Wally Wenzel]

Cal, I don't know for sure what you are after but try typing in "fisher wood craft" the click on tips and see a calculater for figuring segments for making circles.
Wally

[Richard Allen]

As a rough estimate I use (Diameter*pi)/number of staves. This ends up being slightly off. There is also the question of how the stave angle are cut. I use a router table and a champed bit. I let the bearing of the router bit ride near the top of the board. This actually makes the apparent stave slightly larger. The joints on the outside will all be turned away so having the stave bevels going to the edge of the stave is not needed.

If I need to have a precise diameter then I start off cutting a long board to the width described by the formula above. I then bevel both sides of the board at the router table. Next cut the board into stave lengths. Dry fit the staves together and use a hose clamp to hold it all together. There is usually some taping with a hammer to get all the staves to line up. Measure the distance outside flat to opposite outside flat. This will be the absolute maximum diameter than could be expected. Measure the distance at each of the opposing flats. Next I measure from inside corner to opposite inside corner. This is the absolute max inside diameter. Measure each of the opposite inside corners. The difference between the measured outside diameter and the measure inside diameter is the max wall thickness. Given that the stave ring is not likely to be perfectly centered when turning allow at least 1/2" diameter loads (1/8" lost on the outside which is 1/4" of diameter and 1/8" lost on the inside which is 1/4" diameter on the inside.

The diameter i am looking for will fall within the measured diameters given the allowances. If the ring of staves is to small you can insert thin strips of wood at the joints to increase the diameter. You can decrease the width of each stave by various means (table saw the re-cut the bevel angle, use a jointer to remove a small amount and then re-cut the bevel angle.)

If I am going to make a bunch of these same stave rings which need to end up a precise size I will write down the measurements.

3 1/2" is a small stave ring.

BTW you can bevel just one side of the stave. Then the bevel angle doubles. So a bevel on one side of 45 degrees would be used for an 8 stave construction. This works fine for a constant diameter. If there are contours turned into the outside the glue line will curve.

[Jason Roehl]

Well, you picked a very, very simple one to figure. Since you're using 6 segments, the outside face of each segment is one leg of an equilateral triangle whose 3 sides are equal to the large radius (the small radius being at the midpoint of each segment). So, if you want the large diameter to be 3.5", then the width of each segment will be 1.75".

But, if you want the small radius to be 1.75", then the width of the segment would be 2x[1.75/sqrt(3)].