# Help on calculating angles for barrel/drum making?



## bobkberg (Dec 26, 2009)

I'm looking to make a drum, and was hoping to find some chart or guide to show how to calculate what angle to cut the staves to make the initial X-agon.

I imagine that the number of staves would depend on the size of the intended drum, but don't know how to go about that.

Any advice would be appreciated.

Bob


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## Loren (May 30, 2008)

Are the drums to be tapered?

I know a lot about this topic. Today's electronic gizmos
make it a lot easier than it used to be. You'll definitely
want to get one of those gizmos that stick to your
table saw blade with magnets.

If you're planning to make congas, you have no
idea what you're getting into I bet, but you'll learn
a lot if you persevere and figure it out. Ashikos
are WAY easier.

Assuming the drum is not tapered much off straight-sided,
like a djun-djun, then you decide on the number of
staves it's going to have and use that as a divisor of
180. This will give you the angle for the table saw
blade to rip the staves. A 24 stave drum has each
stave beveled to 7.5 degrees.


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## bobkberg (Dec 26, 2009)

Hi Loren,

I'm actually intending to make a round cajon. My plan is to start by practicing with scrap fir just to get the cutting and joining techniques right. I never start anything potentially complex without working up some prototypes just to learn what's involved. My post the other day on slivers of plywood is an example. All scrap material - nothing serious lost if I make mistakes.

Bob


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## InstantSiv (Jan 12, 2014)

Sketchup.


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## Loren (May 30, 2008)

I found pinch dogs useful in making straight drums.

Tapered drums can be clamped up by ramming
steel hoops down on the drum form. Band
clamps alone are awkward.


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## bobkberg (Dec 26, 2009)

I can see now that I failed to ask the right question.

For example, if I intend to start with an 8 or 10 or 12, etc. sided figure, each piece will look a little like this:

/__\

How do I calculate what angle to cut the staves so that the assembled piece forms an even roundish shape?

Bob


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## Loren (May 30, 2008)

180/x = saw blade angle

x= number of staves


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## NoThanks (Mar 19, 2014)

Bob,
You need to give the final size that you want the drum and the thickness of the walls of the drum. 
You also need to know what the thickness of material you have to work with.
Then you can figure how many staves you will need to make the circle and then you can figure the angles on each stave.


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## bobkberg (Dec 26, 2009)

Thank you Loren, Iwud4u. I appreciate the help. I've already started playing with it.


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## Finn (May 26, 2010)

If you want a rounded shape to the sides of the barrel you will have to change the angle a bit as the stave approaches each end. I think this is why coopers (barrel makers) would hand shape each stave with a draw knife. I imagine coopers would soak the staves in water a day or two before assembly so that the wood would bend well and the joints would crush a bit to shape as the staves were forced together with iron hoops. I have tried to make this rounded shape with poor results. Straight or slanted sides of baskets is a lot simpler to make. After doing the math as to number of staves and angles to cut I always make one or two extra staves so that while assembling I can add or subtract a stave to get the best fit.


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## bobkberg (Dec 26, 2009)

Wow Jim! Those are great!

I'm not about to take up a new career as a cooper, but the idea of adding curved sections this way opens up a bunch of possibilities!

The chest on the bottom with the curved top makes me think of the chest that pirates supposedly buried their treasure on some lonesome desert island.


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## MC73 (May 7, 2013)

is this what you are looking for?
http://www.woodworkersguildofga.org/ShopHelpers/MiterCalculator.htm

You have a pdf at the top that you can print.


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## wormil (Nov 19, 2011)

Here is another resource:
http://woodgears.ca/miter/

I want to build a drum too some day, an ashiko as mentioned by Loren.


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## ArlinEastman (May 22, 2011)

I am pretty sure a 6 stave is 30* 8 stave is 22.5* 10 stave is 18* I think 12 is 15*.


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## davezedlee (Feb 22, 2016)

try here:

http://www.quest42.co.uk/woodwork/Segment/Seg-Calc.htm


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