Robert wrote:
>Can you folks recommend a good set of sharpening stones? I need to know
>the exact grits that work the best. I saw the set available in the Baren
>mall and they looked very small to me. Does size matter? (haha) Thanks, Rob
EVERYone will have their own favorites, tried and true, I think... Here
are mine...
http://www.deltamachinery.com/index.asp?e=180&p=44080 is a good article on
machine sharpening and 'modern' methods (I've used an inexpensive motorized
"Reliant" horizontal 1000 grit stone with water drip for years -- much
faster and easier to get a true bevel than by hand, but you need
electricity and the machines are heavy and not very portable -- I use a
Reliant horizontal 1000 grit stone with water drip for shaping the bevels
and then touch the tools against a cheap cloth buffing wheel (attached to
same machine) with honing compound to produce an accurate mirror-finish
razor edge)... Adhesive aluminum oxide sandpapers stuck to glass work
well by hand, too, I've found.
Japanese tools have two layers of steel -- a thin very hard layer on the
edge-side backed up by a thicker softer and more flexible layer on the
other side (back side). The flatness or contour of the back isn't too
important (thicker tools are stronger, but thinner tools are easier to push
through the wood), but on the hard side (edge side) the flatness or
smoothness of the contour is critical! The edge side must be as smooth and
flat (preferably polished) as possible in order to produce a true edge (if
it's rough or wavy, the tool can't easily be sharpened and the edge will
appear to be forked like a saw or mezzotint tool under magnification) -- if
you deform (by abrading) this side, you won't be able to sharpen your tool,
but if your tool is a poor one, you can vastly improve it by surfacing this
side truly flat (or round for gouges). So if you remove the inside of
gouges or V-chisels or the tops of flat chisels or tohs (skew chisels) or
curve them, you won't be able to produce an accurate edge. Good tools
should come with these surfaces already perfectly prepared -- be careful
not to mess up this surface. Think of 'sharpening' as cleanly slicing
through from the soft side to that perfect inside edge at the 'right' angle
-- the right angle (usually 23 degrees for Japanese tools) is a compromise
between ideal and practical... Ideally, I suppose, the angle would be 0
degrees, producing an infinitely thin tool so there would be no resistance
regardless of how deeply the tool was driven. Practically, the 'chip' to
be removed has thickness (more as you go deeper) and resists moving out of
the way of the tool -- that's why it's so easy with a sharp tool to remove
a very thin shaving, but very difficult to push the tool in 'too' deeply'
-- the chip just doesn't want to get out of the way! So in order to reduce
the tendency of the hard edge to snap during carving, the angle of the
bevel has to be much greater than 0 degrees. I suppose the strongest tool
for any given thickness of steel would have a 90 degree bevel, but then it
would be possible to remove only minute shavings (this would be more like a
'scraper', not a cutter, and the back would interfere with the edge ever
touching the material to be carved). For soft woods, some hundreds of
years of practical experience have demonstrated that 23 degrees is a close
to optimal trade-off between tool strength and ease of carving.
The "traditional" approach is with waterstones and moving the tool by
hand. Takes some time to learn to produce the clean and accurate bevel
which is key to sharpening. With a broken tool, first re-create the
correct ~23 degree bevel (a bit shallower is OK for very soft woods, a bit
steeper is better for very hard woods to avoid chipping the tool edge
during carving) on a coarse stone, then flatten the grooves on a fine
stone, then hone to create a very flat and true mirror-polished
edge. There are some clever tool-holders available which can assist in
keeping the bevel angle constant during hand sharpening.
DMT double sided (coarse one side and medium the other) diamond-stones are
terrific (and expensive), but last forever and NEVER lose their dead-flat
surface like a natural or composite stone. Great for shaping broken edged
tools!
http://www.japanwoodworker.com/product.asp?s=JapanWoodworker&pf_id=45.018.3&dept_id=13103
Fine stone --
http://www.japanwoodworker.com/product.asp?s=JapanWoodworker&pf_id=04.003&dept_id=13119
(this is cheapest natural, grade 3 stone from an old Kyoto manufacturer --
higher grades are same stone, I think, just larger and much more
expensive... This one should work for you for a long time.
Honing -- you don't want too fine a honing compound (jeweler's rouge is WAY
too fine, IMHO and cuts too slowly). During carving, pause frequently to
hone the tool with a few firm strokes away from the edge to keep it razor
sharp and ~double the carving time between stone sharpenings -- when you
can't easily hone the tool to sharp, then re-sharpen on the fine stone and
re-hone and continue. Here's a very good honing compound
http://www.japanwoodworker.com/product.asp?s=JapanWoodworker&pf_id=01.098&dept_id=13100
and a decent strop
http://www.japanwoodworker.com/product.asp?s=JapanWoodworker&pf_id=49.201&dept_id=13100
-- it's easy to make your own strop, too -- sole leather (vegetable tanned)
works well -- use the grain side for stropping (not the suede side).
Sometimes it seems like honing isn't 'doing' anything. It's easy to
demonstrate to yourself that the honing compound is actually 'cutting' away
metal -- take a piece of paper and rub your tool firmly on the paper
(stroking away from the cutting edge) a few times. You may see the paper
get shiny, but it doesn't change color at all -- no metal is being
removed. Now rub the paper with a little honing compound and repeat the
experiment. You'll see that the tool now makes dark marks (like pencil
marks) when you stroke it across the honing compound embedded paper. The
dark is the steel which has been removed!
After sharpening, a few strokes with honing compound parallel to and
against the hard side of the tool (stroke away from the cutting edge) will
remove any burr (as you sharpen the bevel, the last few molecules of steel
tend to curl up away from the stone and resist being cut off -- like a tiny
bit of foil clinging to the edge -- these final strokes will remove them
without much altering the hard side of the tool). If you don't remove the
burr, it sorta folds back against the hard side of the tool so you're
cutting with a 'dull' edge -- remove it and the tool will cut the block
like it's made of butter!
Now I'm feeling exhausted from trying to describe sharpening with all these
words! :)
Mike
Mike Lyon
Kansas City, Missouri
http://mlyon.com