"Bill Clouser"  wrote:

> > In his early stages, Mike Dunbar used to recommend that the
> > tenon material be very dry so that it would swell to lock the
> > joint together.  But later, he said that was a mistake, because
> > he realized that, as it swelled, the super-dry tenon would
> > compress the wood fibers around the mortise which would lead
> > to a looser joint during subsequent wet/dry cycles where the
> > tenon and mortise might shrink away from each other.  I
> > believe this is his current thinking anyway.
>
>
> As for real-world experience... does anyone have a wooden post and
> rung chair more than a few years old that doesn't have loose tenons?
>
Only the Dunbar chairs...

Then Alan who has been doing his homework sez:
>
> I don't really want to speak for Mike Dunbar, but as I understand it,
> the main reason he stopped doing wet/dry locking tenon construction of
> his chairs was because he realized it was unnecessary.  The stretchers
> in a Windsor chair are compression members, not tension members (in
> his book he makes the stretchers 1/4" longer than they should be, to
> make sure they're pushing the legs out).  Since they work to push the
> legs apart, it doesn't help much to construct them to resist a
> pulling-out force.  If the mortices and tenons are well constructed,
> the bottom half of a Windsor will stay together with no glue at all,
> and sitting on the chair only strengthens the joints.
>
>
Bingo!!!

Tension vs compression is the key here.  Glue is an attempt to keep
the tension, the Dunbar system is under compression, the your weight
on the chair produces an opposing force.  Or course no one seems to
have figured out how to automate this yet, which is why you need a
"bench made"  (real person with brain in gear) chair to get the effect.

I am not "speaking for Mike" but it's in his classes and his newsletters.

Esther eoh@k...