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I need some help from you woodturners

1593 Views 10 Replies 7 Participants Last post by  jake36
I THINK that somewhere I have seen a formula which will allow me to make a staved cylinder of a certain diameter. I cannot seem to find it anywhere. If any of you know where I might find and copy this information I would sure appreciate it. I am trying to make some birdhouses for Christmas.

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you take the number of staves you want to use and diviide it into 360, then take that number to get the degree of angle you need to cut, for example, I use twelve sides for alot of my segmented turnings, you would take 360 divided by 12=30 degrees, divide that by 2 which equals 15, that is the number of degrees that you need to set your saw for. An improtant thing to remember is that the fewer sides the more forgiving the tolerances, the more pieces the greater chance that even being off a fraction of a degree can add up fast to being off by several degrees at the end.
I did a little searching and couldn't find anything so I decided to try to figure it out.

Disclaimer: I have only tested this on paper and I'm no mathematician but here's what I came up with. Use with care!

d = diameter of vessel
n = number of staves
s = stave length

d • sin(180/n) = s

For example if you want a 4 inch diameter vessel with 12 staves each stave would be:
4 • sin(15) = 1 inch
pi x R (radius) squared will give you the circumference.

3.14×4 = 12.56 / 12 = 1.04"

Looks like ignoring that .035" in the trig calc is going to leave you about 1/2" short on the circumference. :))

I doubt if the birds will ever know, As long as the staves are cut with the correct bevel, it will still come out.
Bob.. Pi R squared equals area.. for the circumference.. it is 2 x Pi x R
Btw barlow is closest to the answer.. 12 staves need a 15 % angle on each side,
so ergo a 4" diameter is near enough 12 and a bit circumference aso as the outer width need to be a little over the 1 inch mark IFN u use 12 bits.,
I almost understand what I just typed.
Larry from downunder,,
You're right!! :-(( Guess I'd better use pi x Diameter, eh? :)) I wonder why the 2 calcs are .14" off?
Thanks for all your help. Barlow seems to have one I can understand. Jake
Sorry I couldn't miss the opportunity for a little pun

The roundest knight at King Arthur's round table was Sir Cumference. He acquired his size from too much pi.
I've used this reference for a couple of items - which pretty much says what Barlow did
That 's a handly little table, Thanks.
Gota thank you Reggick this is solving all my problems. Be sure to take your flea meds. Its a hot summer.

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