"djs" wrote:

It sounds like flattening it down to less than 0.005 should be pretty
easy as you suggesty, but is that good enough? Flattening it down to
0.001 would require a better flat reference than my table saw top.

I would question how flat a piece of MDF is. It seems like it would
depend on how flat the tabel top the MDF is resting on. A little
pressure down on the MDF or any other flat plate of glass or marble,
while pushing down on the sand paper, would also force the MDF to
conform to the supporting table, which is probably not all that flat.

On the other hand this plan has two high spots, one at the toe and one
at the heal, and both are limited to about 1 to 1.5 inch from the end.
It seems like all I would have to do is work on one end of the plane on
the sand paper at a time.



Heel, Toe, and Mouth should be flat and co-planer. And flat enough that you
are satisfied with the output - no flatter.