> After Jeff's reply, what else is there to say except that the theoretical
> deflection calculations wouldn't apply to  the tool in use, ie with
> something under it!

   It's a multi-step thing, this plane-performance stuff.  There are
   a number of different things to consider.  So far we've looked at
   cast-iron flexibility, the effect of planing pressure on the 
   flatness of the worksurface, and we've seen a simple estimate of
   what the plane-sole flatness requirements would be if all there
   was to it was geometry.  But there are a number of other issues
   to consider as well.  None of these things can be taken in 
   isolation as saying anything one way or the other.  It's about
   understanding what's going on physically when you plane.  One can
   be forgiven for being curious about that, of course.  The things
   that have shown up in this thread so far are just preliminary,
   nothing is definitive there.  It's the system as a whole that
   rules the outcome.

   BTW, there's some of this stuff that every woodworker should
   know, regardless of whether they're even into handtools or not.
   The behaviour of boards under load, etc..  It's useful.

   Doug Dawson
   dawson@p...