Reply to message from laurent@c... of Fri, 24 Jul
>
>alan ferrency[SMTP:alan@l...] said:
>
>
>>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.
>
>Okay, here's where I'm really confused.  I've heard this theory before
>(probably from Mike Dunbar's newsletter), but I don't yet understand it.
>Could someone explain to me how the stretchers of a Windsor chair
>are under compression?   I don't deny that it's true, I just don't understand.
>My more-or-less intuitive analysis indicates just the opposite.  Perhaps
>I should have paid more attention to vectors in high school Physics class.
>

I'll take a stab at this.  Since the stretches are longer than the
actual distance between the non-stretched legs they bow the legs outward
when installed.  The springyness of the legs then pushes back on the
stretcher holding it tight.  If the legs splay too much, or the person
sitting on the chair is two heavy then I think that the stretcher might
come loose.  Over time, I tend to think that the wood would creep and
the compression on the stretcher would gradually lessen.  Maybe 'over
time' is several hundred years, though.

Also, since the legs are splayed when the seat is pused down on the legs
the splayed legs will be ever so slightly drawn closer together, also
putting compressoin on the stretcher, though I expect that is a trivial
effect.