On Thu, 03 Mar 2005 20:01:05 -0500, Guess who
wrote:

On Thu, 3 Mar 2005 14:33:26 -0800, "J" wrote:


What about the cross section of two dowels in the same space a biscuit
would
occupy?

Do the math.
Cross section of dowel = PI x r^2
Cross section of biscuit = length x thickness (#20 is 2.375 x 0.147)
So it would take three 3/8" diameter dowels to match the shear strength of
a #20 biscuit or two 1/2" dowels.
Assuming the same strength of materials.

Do more math: The dowel has the same cross-section throughout the
penetration into both pieces of wood, and the biscuit cross-section
lessens away from the joint. And, with today's glues the joint will
be the last to go. That makes the dowels the winners. Also there is
no comparison with strength of materials; a solid hardwood dowel wins
hands down over pressed paper.

1) shear happens at the joint. that is the measure that matters for
shear. other modes of failure vary, but the section at the joint is
the relevant one for most of them.

2)biscuits are made from beech, not paper. most dowels are made from
birch. anybody with hard data about those species? I'm betting beech
has better strength than birch....



We can theorise all we want until there is solid scientific
[experimental results] evidence one way or another to back up "common
sense". The point is that if you drop a ton weight on it, it won't
matter either way, and barring that, either is "strong enough", and
the important factor is ease and accuracy of assembly and cost, not
strength.


ease of use favors biscuits, unless you're talking about using big
dollar multi-spindle dowelling machines. strength data goes either
way, depending who you're talking to...