# Box Joints vs. Dovetails for strength



## LeeBarker (Aug 6, 2010)

Before you get into a big bar bet, better check this out.

Beyond the obvious interest in the subject, I am really impressed with how he set the whole test up. Just enough science to make it pretty reliable, with still some room to exercise your woodworking muscle instead of paying someone to weld up something fancy!

Kindly,

Lee


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## richgreer (Dec 25, 2009)

That was interesting. Thanks for sharing.

I've always felt a good box joint was as strong as a dovetail joint, but a dovetail joint can be a little showier.

This confirmed that.


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## jusfine (May 22, 2010)

Thanks Lee, you are right, an impressive simple test.

If I hadn't read Rich's comment, I would not have thought the dovetail would have been weaker.


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## beckerswoodworks (Dec 26, 2009)

Not a very fair test when he's got nearly twice as many finger joints as dovetail joints which means nearly double the glue surface.


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## SCR0LL3R (May 28, 2010)

But if you tried to put that many dovetails on the same piece, would it be any stronger? I wonder what the optimal number of dovetails would be in that example. Also, even with more fingers, the box joint was quicker to make.

The way I see it is that I would expect the optimal number of fingers in a box joint would be stronger than the optimal dovetail joint.


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## childress (Sep 14, 2008)

I remember this test he did a while ago….


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## Viktor (Jan 15, 2009)

Box joint is obviously stronger than dovetail (given sufficient glue area in both cases). No need for testing here. 
In finger joint cross sectional area of all fingers at their base, where failure occurs, on one piece (A1) = cross sectional area of all fingers on the other piece (A2), and both =0.5 of the total cross section (At). 
A1+A2=At
In dovetail joint regardless of the number of pins and tails or their arrangement either A1 < 0.5At or A2 < 0.5At.
A1+A2 < At
This happens because tails have sloping sides, i.e. portion of the grain is undercut.


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## Viktor (Jan 15, 2009)

In fact, finger joint has a threshold after which failure occurs in fingers rather than along glued surface. After this threshold increase in number of fingers does not compromise strength.
In dovetails, after optimal number and proportion of pins and tails is reached adding more pin/tails will weaken the joint.


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## Greedo (Apr 18, 2010)

i believe i saw this on his site long time ago.
for me dovetails are something of the past when all was done by hand, and when modern glue wasn't available.
but today it's purely for visual effect, since a glue joint today is more solid than wood, it's the wood that will fail first. so with dovetails you put all the stress in the narrowest part of the dovetails.

but then this is kind of pointless, both methods almost overengeneered anyway, theres 100+ year old drawer chests here that have huge drawers joined by simple nailed rabbets, and they hold up just fine!


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## Viktor (Jan 15, 2009)




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## richgreer (Dec 25, 2009)

Viktor - I find your graft interesting and insightful. THank you.

Can you comment on the optimal number of pin/tails?


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## IrreverentJack (Aug 13, 2010)

Matthias Wandel is impressive. Fine WoodWorking did a more exten$ive joint test. -Jack


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## beckerswoodworks (Dec 26, 2009)

Great points Skarp. I'm also in the "Does it look nice, and still remain strong?" camp. They're both strong enough and making anything stronger than strong enough is wasted effort. So deciding which to use should be based primarily on how nice you want something to look and how much work it takes. I don't think that means dovetails will always win though. Green and Green style has some pretty nice looking finger joints.


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## Viktor (Jan 15, 2009)

Rich, optimal number will depend on glue strength and wood properties (compression vs tensile strength, etc.). In other words I don't know  May be someone cares to conduct an experiment?


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