Tom Banes wrote:

On 13 Dec 2005 23:13:39 -0800, "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.

DJ:

I suspect (tho' can't prove) that the deflection of an 18" long hunk
of 1/2 (or 3/4) MDF under any reasonable hand pressure is so minimal
that it's not in the equation. Is MDF flat - well it sure seems to be.
My 1/1000 DI doesn't wiggle when I pass it across a clean piece
(actually passing the piece under the DI). You're not going to put a
heck of a lot of weight on it when sanding, at least not if you want
the paper to survive.

As I said in my original response, the twisting that causes the
rocking is far more of a problem than the absolute flatness of the
sole. And, as other posters have noted, good enough is good enough.

You can read Jeff's notes at

http://www.amgron.clara.net/planingp...g/fettling.htm

He's kinda considered an authority on "fetting" a plane.

Anyone know the origin of "fetting"? I've assumed it was a translation
from the Scots brogue, but maybe there's another reason for the term.

Regards.


It is 'fettling'. Here's a good explanation:

http://www.worldwidewords.org/qa/qa-fet1.htm