Hi revered Galoots !

After weeks of sitting here (and at work - shshsh) reading some
of the most amazing & learned prose I could ever imagine to see,
especially as some of it (by statistics alone) could have been
written by SUV drivers ...

I've gotta say some things about:

Flatness of planes - I once spent considerable time hand
scraping a straightedge - roughly 1 X 2 X 24 inches if
anyone's interested - to fit a granite surface plate.  I
had gotten to a pretty good bearing - perhaps 15 to 20
spots per square inch - when I decided the pattern would
look better if I draw filed it.  I made one pass with the
file and then, not wanting to squander all that effort
expended in the hand scraping, I spotted the bearing
again (with the customary Prussian Blue - obtainable from
most art supply stores) only to find that it was now about
one spot per square inch.

So a scraped surface is flat to the standard of your surface
plate - within 0.00005 to 0.00010 inch of a mean plane - that's
1/20th to 1/10th of a thousandth (0.001) of an inch.  Optical
flats are better than that, but let's be real.  You can make
your own surface plate as good as that, but you don't hand scrape
an optical flat.  Filing takes a lot of strokes to remove even
0.001 inch from a cast iron surface, and that one stroke nearly
ruined my hand scraping job.  You might achieve 0.001 inch flatness
by draw filing, but then only if you use a surface plate and
Prussian Blue so as to know where the high spots are.  Sanding
on top of a surface plate (or a Blanchard ground jointer table)
probably is intermediate between filing and scraping, assuming
that your technique and the sandpaper don't add their own little
errors.

I adjusted one of my smoothers to a minimal mouth opening and then
used it to plane a shim I wanted to reduce from 3/64 inch to 1/32
inch.  That took about 30 strokes (pushing the shim across the
bottom of the upended plane) so the plane was cutting sub-mil
chips.  Doing that on a board therefore requires flatness better
than 0.001 inch.  So scraping's not such a bad idea.  Especially
when you consider that the plane is not clamped when you spot it
on the surface plate - you just push down much like you would
while planing - but in surface grinding 90% of the hassle is
finding out how to affix it to the table of the grinder without
distorting the plane.

Norm Abram - has the best presentation manner of any DIY show
host that I ever have seen - and I watch in awe of his ability
to sound natural, even when uttering memorized (!) lines.
Lawyers in court do not reach that standard of assuredness. And he
actually shows us the hard parts of some of the projects. Sure -
the PT mfgr's pay for the show - it's fun to imagine how much
easier some of those steps would be with hand tools - but not all
of 'em.

Sources of steel for bottom feeders - screwdrivers make decent
pry bars but are terrible for chisels because they do not have
enough carbon to form & hold a sharp edge. Also, the chisel-
shaped screwdriver then makes a lousy tool for doing any more
than scraping the paint out of a screw slot.  And chisels make
lousy screwdrivers because of their high hardness and concomitant
brittleness. A screwdriver might make a temporary (and very
narrow) scraper blade, but that's about it.  Same goes for
hex keys.  There is a product called Kasenit which can easily be
used by anyone to case harden even a nail, and that is the best
way of making cheep & dirty cutting tools.  A two-inch-wide chisel
made from an old cold chisel (with much heating & hammering) is
a distinct possibility with Kasenit.  Don't make aircraft landing
gear or carabiners out of old scrap steel, however, because the
composition & cleanliness (freedom from sulfur, phosphorus, oxygen
& inclusions) of tool steels and alloy steels are carefully
controlled to maximize strength & ductility, whereas nails and
unidentified steel bars generaly aren't so well pedigreed.  So your
DIY chisels might just snap if used too aggressively; on the other
hand, you can't through-harden a Kasenit treated piece of steel,
so there will nearly always be a tough, unhardened interior, and
my fears of the brittle DIY chisel may be unfounded.

Oil- and air-hardening tool steels - aren't really necessary unless
you are making tools which have to sustain heroic loads - such as
punches and dies.  A water-hardening steel will be hard deep enough
to sustain a sharp edge, and that's all you need for chisels,
plane irons, and the like.  J**nt*r blades need to be hard (and
tough) clear through because of the much higher forces applied by
impacts with knots, dig-ins, and centrifugal force - those are
better made of more highly alloyed steel, so there won't be so much
chance that undetected cracks occur during the quench cycle - the
gentler the quench, the less likely that cracks will form.

The several explanations I've read for why steels distort during
quenching are as good as any I have read in textbooks - mebbe
better.  During the transformation from austenite to martensite
(the hardening itself) there is a volume expansion and a shearlike
distortion that are both violent and substantial.  If the chunk of
steel has a big temperature gradient across it, the transformation
will propagate across the piece as it cools, and the distortions
will be concentrated in a narrow zone, maximizing the damage.  If
the entire piece is cooled uniformly, then the distortions will be
spread out both in time and in space, and the distortions will all
tend to cancel each other, with minimal net effect, except for
that volume increase, but even that will occur uniformly.  If you
don't need to harden clear through, then you don't need a hardenable
steel, and the W1 will work just fine; better, actually.  If you need
the whole cross section to be hard (usually tough like a wrench or
an aircraft landing gear) then the oil-hardening or air-hardening
steel is the better choice.  Even W1 works pretty well for small
wrenches - and it makes quite good drills.

The alloy steel plane blades are for people who aren't willing to
re-harden their blades every so often.  A cast steel blade (meaning
the archaic equivalent of W1 tool steel) will be hard clear through
only near the original edge, so after that's been ground off, the
metal behind it might not be nearly as hard.  Just heat 'er up
again, quench in water, and run to SWMBO's oven for a toast at
about 300 to 350 F.  Just the edge.  You can do that over and
over again as the blade is sharpened away, because the metal behind
the edge hasn't been heated very hot since it was forged, and then
it ought to have been annealed afterwards.  I'd do the re-hardening
each quarter to one-eighth inch of blade life.  Or go by the time
between sharpenings - reharden when it's noticably less.

If you back-bevel a cast steel plane iron, the wear life might go down
dramatically if the blade wasn't hardened clear through.  The usual
geometry places the edge quite near the original surface of one side
of the blade, but a back bevel might place the edge in the middle of
the thickness of the blade.  Especially so for thick irons.  You can
restore a back-beveled blade by hardening & tempering it after forming
the back bevel; save the final sharpening for after the heat treatment,
so you'll remove the small amount of surface decarburization.

Whew.  Now I'm caught up. Back to dreaming about the inverse jointer,
replacement EB chuck springs, and simple copy lathes.

Best regards,
George Langford
amenex@a...