Coopered Calculator?

[Jared Cuneo]

Anyone know where to find a calculator to figure out the angles and number of staves for coopered panels?

I can't seem to find any info on this..

Thanks!

JC

[Jon Knauft]

Jared,

I found this with a quick google search:

woodworkforums dot com thread 17973

-Jon

[Jared Cuneo]

I thought I was pretty good at 'the Google' :)

Thank you!

JC

[Todd Bin]

I did a quick back of the envelope sketch and geometry and came up with the angle you want to cut off the edge of each board is:

Angle = Inverse Tangent of (L divided by 2 W) where

W is the width of each board and R is the radius of the arc of the cooper.

This assumes that all of the boards are the same width. For example. If I have boards that are 4 inches and an arc radius of 20 inches then the angle I would set my table saw to would be 5.7 degrees.

BIG DISCLAIMER: I have not verified this but it seems pretty reasonable. You would need to verify my math.

[Todd Bin]

That should have read:

Inverse tangent of (W divded by 2 R)

[Brian Dormer]

It's not surprising that there is little information.

Last time I was in Williamsburg, VA, I spent some time watching and talking to the coopers - they told me that they DO NOT use any gauges, jigs or mechanical widgets to shape the staves. There is no formula. It's all done by look and feel. Of course, you need a master cooper and probably 2-3 years of apprenticeship to get good enough to make even a small bucket or barrel that won't fall apart or leak.

They also told me that they make about 120 variations of "barrel" - but in the 1700's - coopers were expected to be able to make over 300 types.

They cut "billets" with bowsaws, rough it with a small axe and then shape the stave with a drawknife. I watched one lady (yes, a female cooper) make a small bucket (I forget the proper term) - when she was done - it didn't leak a drop. It's humbling to watch that kind of expertise at work.

Food for thought.