alexy wrote:

B A R R Y wrote:

On Fri, 20 Oct 2006 19:41:45 +0000 (UTC), Andrew Barss
wrote:

RayV wrote:

: Andrew Barss wrote:

: Latest issue of Wood magazine rates biscuits as _barely_ stronger than
: butt joints in all directions. Dowels were second in strength to M&T.

: http://store.woodstore.net/november173.html

Interesting. There have been two previous studies (first one
in FWW, second maybe also there) which showed M&T at the top, with
biscuits very closely behind. Dowels, if I recall, were nowhere near as strong.

"Wood" tested the joints two ways, shear strength and pullout
resistance. As I remember, biscuits did OK in pullout resistance, the
comparison to butt joints was in the shear test portion.

M&T came out on top in both.

"Wood" also included pocket screws in the tests.

Question on this: Other than seat rails, bed rails, and maybe table
rails, how important is shear strength? It seems that for many of our
joints, including the cabinet door frame, the forces acting on the
joint are angular. And what is important to the joint integrity is
that the joint not pull apart at the side of the joint under tension.

As another poster pointed out, the strength added by a biscuit is
concentrated on the center, so only has 1/2 the "arm" of an attachment
at the end of the joint.

Thinking this way also points out one reason that M&T is so much
stronger in actual use--the M&T provides no only additional resistance
to pulling out of the side of the joint under tension, but additional
mechanical w00d-to-wood contact from the shoulders of the joint.
^^^^
e.g., even a relatively loose unglued M&T provides massively more
resistance to a joint opening out at an angel than does a biscuit.
^^^^^

Good grief! I think it's time for another cup of coffee!
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.