JPagona@a... said:

snip...

> I'm not really sure what the true benefit of a sprung plane is, but
> according

The reason they are srung is to keep the profile as low in the throat
as possible.  For illustration, imagine a hypothetical molder used to
make a profile on a 45 degree bevel in a 1-1/2" thick board.  If you
hold the plane perpendicular to the face of the board (not the bevel),
the topmost bit of the cutting edge will be 1-1/2" up from the lowest
part.  The throat of the plane is quite wide that far up from the
sole, so the mouth at the high point will be really gaping.  Somewhere
along the line, Joe planemaker realized that if you hold the plane
perpendicular to the bevel insted, the high point of the iron will be
governed by the highest feature from the bevelled edge.  Because that
point is pretty much guaranteed to be less than the thickness of the
board, the resulting mouth will be tigher and the resulting profile
more kick-ass.
        One thing to keep in mind is that the amount of spring is
limited by the steepest feature on the profile.  This is because it is
very difficult (maybe impossible) to make a plane that will undercut a
profile.  So, for example, if you have a nice wide molder whose
profile contains an astragal, it probably isn't sprung...

Hope I didn't cloud thins up too much...

/Tad