>ssalb@l... writes:
><< So this raises the obvious question:  What is "sprung"?

To throw in my two-bits on this perennial topic, among the reasons I've
heard for spring --all of them reasonable-- are:

1] Economy
(Since quarter-sawn wood --with its radial grain-- is prefered for a wooden
plane, spring gives you a wider sole for the same width of the expensive
wood.)

2] Consistency of the mouth
(The throat on a wooden plane gets wider away from the sole.  As a result
at the bottom of a "deep" groove in the sole the mouth will be wider than
it would be at a "shallower" point in the sole.  The spring is choosen to
give the narrowest "average" width of the mouth.)

3] Restricted by the shape.
(Some complex profiles would be hard, if not impossible, to cut if the
plane were held vertically.)

4] Ease of use #1
(Easier to hold a plane of this type against the wood by pressing down at
an angle.)

5] Ease of use #2
(Easier to hold the fence against the edge of the work, given the possible
weird shape of the sole.)

In short, I don't think there's "a" answer.  Also, the reason probably
changes for different types of planes and different sole-profiles.

N