On a guitar, you have to join the two pieces of the back
and the top with a joint that will not pass light.  These
pieces of wood are less then 1/10" thick and with the top -
the glue is all ya got.

On one of the forums, someone posted about an English
builder who says do this:  On these 22" or so pieces, get
close, then start about 2-3" in from the end and take a
pass or two til 2-3" from the other end - in other words,
create a tiny hollow.  Now take 1-2 passes over the full
length and you will be flat.

Got to thinking about this and came up with an explanation.
 Am I
1) Spot On
2) Partially Right
3) Full of Horse Hockey

The hand plane is not at all like a power planer - the
*l*ctr*c tool has 2 beds that stay parallel (hopefully) as
you raise and lower one, so the workpiece travels smoothly
from the infeed to the outfeed tables and remains parallel
to the bed.

Think about the toe of the handplane laying flat on the
piece as you start the cut.  Start pushing the plane and
the blade then removes a little bit of wood and this causes
the back end of the plane to be lowered (we are talking
tiny amounts here) to a new level lower than where the toe
is, so the plane is now tipped up a tiny bit - the tool and
the workpiece are no longer parallel.  Until the bed of the
plane is totally on the workpiece there is a slight
thinning of the cut.  Once the end of the bed is on the
piece of wood, the angle of the raised toe stays the same
and the cut continues flat.  Then at the end, your tendency
is to push on the toe which causes a little bit of of over
cutting at the very end.  The result is a very slight hump
in the center of the board.  The numbers are very small.

This supports the notion of scooping out a tiny amount of
material in the center before a final pass or two.

My belief is that when craftsmen made their living with a
plane, it didn't much matter if the bed was absolutely flat
because they learned how to compensate during the length of
the cut to make it flat - that's why we rarely find flat
plane soles on well used older planes - it didn't much
matter.  He could put downward force on different parts of
the plane at different times to compensate for the
difference.  We are told to do this, but we are told in a
generic fashion, not in a way that might help with
different lengths and flatnesses of plane beds.

But we mere mortals don't use our hand tools enough to be
that proficient, so every ounce of advantage we can muster
is helpful.  Flatten that sucker!

And one of the amateur luthiers uses a #7 - 22" of plane on
a 22" piece.  Is this making it easier or more difficult to
get a flat surface?

Food for thought - did I get it right?

Ed Minch
I think we did something like this 10 years ago.
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