"George" george@least wrote in message
...

"David" wrote in message
...
We're talking Fuji apples vs McIntosh apples. g

M&T, when glued, need to be less than "as tight as you can get them".

NOW I find out you were talking pegged...


Nope, you just need to think of how the M&T joint works. In load
direction,
the tenon takes the force. At right angles to load, the shoulders resist
movement when they register against the other piece - thus the pegs or
draw
boring, which substitutes for a clamp in assembly. The glue may be
omitted
or may crumble, leaving the joint mechanically sound.

If you want to know what happens to unshouldered tenons, look at the loose
rungs on any chair.


Tenons are subject to two loading conditions and hopefully not three . The
third a longitudinal load ,would call for a dovetail joint as opposed to a
modern mortice and tenon.[non pegged]. A pegged tenon would even take some
longitudinal load .

An unpegged tenon basically is subject to bending and shear loads . The
shear load is applied at 90 degrees to the tenons length, thus the load will
crush the glue film [which has thickness with a sloppy tenon /mortice.fit]
between the bottom of the tenon and the bottom mortice surface until the
shear load is resisted . this will result in a compression in the lower glue
thickness and a tension in the upper one with commensurate strains
[movement].

The second loading is due to the moment the load causes . This load results
in a point loading of the lower outer edge of the mortice and the upper
inner edge of the mortice . The former results in even more deformation of
the glue layer [in addition to that resulting from the shear load ] and a
reverse deformation at the upper inside of the tenon/mortice .

This loading condition occurs whether the tenon is pegged or not. The pegged
haunched tenon does somewhat better as the effctively the peg keeps the
tenon "engaged" and tight allowing the haunch to spread the bending loads..

The bottom line is in the case of a tight fitting mortice and tenon the glue
joint thicknesses are mininized resulting in the basic wood taking the loads
directly rather than allowing the loads to be transferred through the glue
thicknesses for which it is ill suited to do . Wood to wood contact results
in less flexure and longer joint life .

having a sloppy joint is akin the having a poor edge to edge joint and
hoping in the poorly fitting sactions that the glue will take the load ,we
all know how that works ....mjh