Shipwright's compass

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charangohabsburg
Blackwood
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Joined: Sat Oct 16, 2010 1:25 am
Location: Switzerland

Shipwright's compass

Post by charangohabsburg » Fri Apr 25, 2014 7:08 am

Nothing really new here. Instead of using stretchy ropes or heavy beams as a compass for drawing a curve with a huge radius, or being dependent on the radius of someone else's template a shipwright's compass may be the way to go.

This is the sketch which shows how it works:
a.jpg
The angle ACB is always the same.
a.jpg (58.51 KiB) Viewed 3875 times
In any case the radius is kind of an odd measurement to use when designing a dished workboard. But the setting parameters of a shipwright's compass are exactly the data points we are interested in! (Lower bout width and dish depth respectively doming height).
However, here goes the math part ready to use:

radius.xls
radius.ods (the same in OpenOffice format)

(For those who own the Gore/Gilet book: I used a different approach than Trevor did to calculate the same thing, so the formula in his book looks different than the one I ended up with in my spreadsheet. But the formulas do exactly the same!)

And this is the tool itself:
2014_P7700_1470.JPG
2014_P7700_1470.JPG (69.48 KiB) Viewed 3875 times
I glued on a piece of 80 grit sandpaper to increase friction when tightening the screw.
This is important because otherwise the compass would change its opening too easily while drawing the curve!
2014_D70_8062.JPG
2014_D70_8062.JPG (61.81 KiB) Viewed 3875 times
And here even more pictures about how to use the compass.
Markus

To be stupid is like to be dead. Oneself will not be aware of it.
It's only the others who suffer.

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wadkin
Wandoo
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Location: Colchester,Essex,England
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Re: Shipwright's compass

Post by wadkin » Sat Apr 26, 2014 12:22 am

great post :cl I'm sure to use this handy method in the future cheers
Alf

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