On Thu, 03 Mar 2005 17:57:23 -0700, s wrote:

On Thu, 3 Mar 2005 15:52:16 -0500, "Mike Marlow"
wrote:


"J" wrote in message
...

And is much wider. The cross section of the typical biscuit is much larger
than the cross section of the dowel.
A #20 biscuit has a cross sectional area of 0.35 sq in. You would need a
dowel 2/3 inches in diameter to match that cross section.
Not easy to use that size of dowel in 4/4 stock. :-) This is why the
loose
tenon was invented.


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


shear is a direct function of section. a dowel with a given section is
much thicker than a biscuit of the same section, so it weakens the
board it's in more. dowel joints often fail by blowing out the wood
surrounding the dowel rather than breaking the dowel itself.

Ahh, I've been waiting to see if anybody raised that rather practical point!
I've also seen whole dowels pulled out of a joint, but I've never seen a
biscuit do so, as it breaks instead. Part of this may be the dowel having a
weaker glue joint, due to the relatively large amount of end grain. Once it
starts to fail, it either pulls out of the joint, or acts as a lever to blow
out the side of the wood.

Now, has anybody compared the difference between dowels, from smooth to ridged
to ringed? I've heard said that a ringed dowel is far stronger, but haven't
tried it or seen any data. Similarly, we now have the Miller dowel system as
another variable.
GerryG