From: walt@eng.clemson.edu (Walter B. Ligon III)
Subject: Re: Hand Plane Question
Reply-To: walt@eng.clemson.edu
Organization: College of Engineering, Clemson Univ.
Date: Mon, 5 Oct 1992 22:25:41 GMT

In article 4633@linus.mitre.org, jdobbs@mwunix (John Dobbs) writes: 
>My understanding of the theory of operation of a jointer is that with a 
>flat and level outfeed table, blades set at the same height as the outfeed 

just to be picky, the outfeed should be just a tad lower than the blades, to
account for compression of the wood ...

>I have been trying to make an analogy between a jointer and a hand 
>plane.  In the case of a hand plane, the "infeed" portion (the front of the 
>sole) and the "outfeed" portions (the back of the sole behind the blade) 
>are the same level (or are supposed to be in a properly "fettled" plane).  
>The question is which portion of the plane is acting as the register as the 
>outfeed table acts in a jointer (the apparant answer is that the entire 
>body of the plane is acting in this way).  It seems that the material under 
>the back part of the sole of the plane is lower than the material under 
>the front part of the plane because material has been remove by the 
>blade.  How does material become flat if this is the case?

well, first of all, since the iron is not as wide as the body, the body won't
neccesarily ride down in the cut - but if you're talking edge planing, it will.
All in all that won't really matter.  When you are edge planing, the sole will
register between the front edge and the back edge at an angle, which will give
you a consistent cut over the length of the sole.  If the board is concave,
you'll get  a deeper cut at the ends - if it's convex, a deeper cut in the
middle.  If its flat, you'll get a even cut the whole way.  One pass won't
make the board flat, but with each stroke you gradually flatten the board.

This is a different process than on a power jointer.  On a power jointer,
you essentially draw a straight line on the board at a minimum depth and then
take off material to that line. The areas cut with each pass are flat, and when
the cut occurs along the length, you have a flat board.  In theory, if you
could take a deep enough cut, you could make it flat in one pass.

With a hand plane things are different.  Even if you COULD take a cut as deep
as the largest variation in the board, you would not get a flat cut.  Rather,
each pass with a hand plane simple increases the radius of arc in the board
until it is negligible.  I suppose in theory it never gets flat, its just that
the curvature is so slight you don't really care anymore.  Actually, this
process occurs on a power jointer too when the board you are working is longer
than the bed.  There was a bit of argument a while back as to how to deal with
this - but the answer is it deals with itself, it just takes more material.

Of course, one nice thing about hand planes is you don't have to stroke the
entire surface of the stock.  Once you know where the high parts are you can
work on them until it is "mostly" flat, and then finish up with full length
strokes.  If you are lucky enough to have a plane you can dedicate to that
task (typically termed a "scrub" plane) you can tune it to improve bulk stock
removal at the expense of accuracy, and then tune up your jointer to give you
that final cut.  An old jack plane is great for this.

Anyway, if you're still unsure about this, draw yourself a picture, side view,
concave board, and the plane sitting in there making a line from just before
the cutting edge back to the heel of the sole.  The line is slanted, but the
depth of cut is limited by the toe of the sole.  If the cut is uphill, the depth
of cut is reduced, so that a deeper cut is made on top of the hill.  When you
get to the end of the board, you get full depth of cut because the plane registers
entirely on the heel of the sole.

If that STILL doesn't help, just pull out your plane and nice warped board and
spend a few hours getting to know it ... it should become clear eventually ...

Walt




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