On 12/23/2015 2:48 PM, Leon wrote:
On 12/23/2015 2:24 PM, John McCoy wrote:
Leon lcb11211@swbelldotnet wrote in
:

On 12/23/2015 12:09 PM, Jack wrote:

For example, a floating M&T is
way, way stonger than a Domino?

I thought a domino WAS a floating
M&T???

My thoughts exactly Jack, a Domino is a floating M&T.

In fact a Domino or floating tenon may ever be better than a plain
M&T.
Often the end of a board that you are going to form into a tenon
might
not be suitable if it has a knot or strange grain.

Well, as I recall the article (and as I posted above), the
two joints broke in different ways. The M&T, all varieties
including floating, sheared the tenon. The domino (and
dowelmax, etc) all broke the mortised board.

I have no idea why that difference would exist, and I don't
recall that the article went into any analysis of it.

It does seem to me strange that the mortised board should
break at a much lower strain with the domino than with a
floating tenon (where the mortised board didn't break at
all).

Especially since a Domino is a floating tenon. BUT wood is not perfect
and the pieces could have been weaker for one of the tests.

As I said in an earlier response, "the results have no bearing as a
general rule; they _only_ represent the actual joints as tested".

Of course a Domino is a floating M&T but you can see precisely why the
two are so disparate in results in the test and in the order they are if
you go look at the pictures. While the actual dimensions of the F-M&T
in the test aren't given, it is obviously at least twice the width of
the (single) Domino used giving it 2X the surface area each side plus
twice the vertical dimension from the midplane (vertically) to resist
racking force mechanically.

As so much of the other discussion, it's obvious just looking that it'll
win; precisely how much I'd have guessed at the roughly 2X factor shown.

The problem with both the cope and stick and stub tenon in this test is
there's no material left on the sides of any significance -- look at the
failure mechanism, it split the two skinny sides while the glue joint
remained intact. This is certainly going to be true as far as it goes,
but one would never use such a joint in the case of the example
justification in the leadin for the test of wracking forces like a chair
rail; such a joint would only be found in a panel door or the like and
there the panel would be there and provide the wracking resistance.
I'll note the biscuit suffered a like fate--the glue is so strong it
simply fractured the two remaining long-grain sides of the slot in the
stile as their cross-sectional areas are so small given the depth is,
like the stub and cope, so short there's no area over which to dissipate
the concentrated tension force. That's the reason (besides that the
tenon itself has bending moment resistance) the M&T does well, there's
the full depth of the tenon over which the force is spread.

I think if one were to do similar actual geometrical comparisons of the
rest there would be clearly recognizable reasons for them as well.

It's a case of comparing things that for the most part, shouldn't be
compared in the overall rankings; only the minor differences between the
similarly-sized and purposed joints should actually be compared against
each other within a set of classes, perhaps.

--