On Thu, 24 Dec 2015 12:41:08 -0600, dpb wrote:

On 12/24/2015 9:53 AM, OFWW wrote:
On Thu, 24 Dec 2015 09:04:52 -0600, wrote:

...[preceding discussion elided for brevity]...

I don't think there's anything wrong with the tests themselves such as
they were; it's simply trying to draw too many conclusions from the
results that the amount of testing doesn't support.

(*) Confounding -- when an uncontrolled or unknown variable other than
the one under test has an effect on the result of the device under test,
the result of the test cannot be shown to actually have measured the
desired effect of the intended variable. The example easily seen here
is that between the M&T, F-M&T and the Domino the sizes of the tenons
aren't controlled; only the type used. Hence, one had _no_ controls in
place for the confounding variable and there's nothing that can be said
specifically about the effectiveness of the joining _system_ at all;
only that for the three specific cases with the specific dimensions that
the results were in the order observed.

After nearly 40 yr of consulting in the area for which I coined the term
"statistical engineering", being called in after the fact to try to make
something of results from such tests as the above was all too common
what a client was wanting. Unfortunately, in almost every instance, it
was too late in the process to salvage the work done to date other than
to try to complete an actual design for a series of experiments in which
the tests run could be used to fill in the necessary test matrix.

Brings to mind large laminated beam, what if one of the variables was
mid point in the beam?

Ya' lost me there...no idea how is intended to relate to current discussion.


Sorry, I was watching some lamination jobs and some Japanese big beams
and how they were jointed. Just thought some of it was common to
WWing.

One of the questions nagging me is, the amount of pressure used on a
glued joint. Is it really possible to squeeze out too much glue and
render the project worthless a few years down the road?

US FPL (Forest Products Lab) has performed extensive tests on the
question and concluded "no"; in fact, the test data shows that the
higher the clamping pressure, the stronger the joint up to the point of
physically crushing the material. I've posted links to this in the
(fairly distant) past and unfortunately don't seem to have a bookmark at
hand so will leave it at that for now, other than to point out the
specific testing (as is virtually all work by the lab) was done in
support of the production manufacturer of wood products, and doesn't
really reflect a home-shop rec woodworker environment. Consequently,
the pressures achieved at the upper limit there exceed what generally
would be found in work rec.wooodworking participants shops. Which
simply supports the bottom line answer of "No" is why I included the
discussion. (Leon may be the one exception here with his known
penchant... )

The key limitation in a quality glue joint as far as material prep
causing poor adhesion (other than that of ill-fitting joints) is have a
fresh, unburnished surface. If one were to, for example, joint the
material with a set of dull knives it's possible for them to "hammer"
the edge rather than cleanly slice the fibers. In this case the
micro-pores that are critical for the bonding to occur can be closed and
thus the glue simply lays upon the surface instead of actually forming
the bond. I forget, it may be that Hoadley in his tome on wood
discusses; I'm virtually sure it's in the FPL Handbook (all again I've
not looked recently to confirm).

Hmmm, the same pores for bonding that are also important for finishes
and stains to adhere to. I think I understand that, so an overly
"finished" joint can be a disadvantage and coarse sand paper the best
when fitting?