Charley wrote:

The latest issue of WOOD Magazine (issue 177 July 2007) has an article
comparing the strengths of joints that you might find interesting as it
shows the Domino and how it compares to other methods of joinery.

--
Charley

Got the magazine, read the article and while I agree with their
conclusion that the DOMINO was their choice - mainly because of
the ease, accuracy and speed of use.

BUT - the test methods - and their conclusions - well let's just say
they were less than ideal. On both their "pull apart" and "shear"
tests, it was the wood that the dowels/loose tenons/biscuits were
in that failed, not the dowel / loose tenon / biscuit.

They were testing THE WRONG THING - the strength of the stock
the joint was in - AND the glue bond.

Had they skipped the glue entirely - then maybe they'd produce
some results that would provide indications of how well each
joining method does - for furniture applications. And had they
included the total cross sectional area of the dowel, beadlok
or DOMINO loose tenon - that would give you a better idea
of how "equal" the methods are. OH - and if you're going to
test a glued joint - whats the common surface area for the
joined parts.

They also skipped over a significant shortcoming of dowels.
UNLESS you orient the dowel grain with the parts grain - it
will expand and contract differently than the wood it's in -
going from round to oval and back with changes in moisture
content - which we know WILL happen.

You want your joint to prevent SIX types of movement. You're
probably saying "SIX!? Yup - SIX - you forgot rotation - about each
of the three axis (we'll leave time out of this discussion). Look
here if that's still not clear.

http://web.hypersurf.com/~charlie2/MT/MtPrimer4.html

A more meaningful test - for "shear" (though I'd call it "torque")
would be to assemble the joint - without ANY glue - and apply
a constant downward force, beginning right at the joint and
moving it away from the joint slowly - until the joint a) began
to open - or come apart completely.

THAT's the test Festool did. They applied 145 Kg (319 pounds)
of downward force on the horizontal member, starting at the
joint and moving away from it.

Their results
Biscuit - 2.1mm to joint opening
Dowel - 2.2 mm to joint opening
Loose Tenon - 14+mm to joint opening

If you do the math (25.4 mm/inch, 2.2 lbs/Kg) the torque
in foot-pounds come out to 2.20, 2.30 and 14.65 foot-pounds
for Biscuit, Dowel and Loose Tenon. The loose tenon
required six time the torque that the other two did - with
NO GLUE.

And lets get real - "resitance to shear" is what you're
after, NOT resistance to "pull apart". If you were sitting
in a chair, joined by one of the four joinery methods
evaluated in the article - and you're one of those people
who like to tilt the chair back on its rear legs - which
method would you trust your ass to?

Bad science is worse than no science. And I won't even
get into Intelligent Design.

charlie b