Waterstone vs. Oilstone
Japanese waterstones have a reputation for fast
and efficient sharpening. As the supply for natural stone fades
away, man-made stones are becoming more available and important.
Oilstones are another choice that the woodturner has, but they don't
compare to the waterstone's speed. One
reason that waterstones out perform oilstones is that waterstones
are made up of soft abrasive particles that break off during use.
Each stroke across the stone breaks loose a small amount of particles,
constantly exposing new and sharp particles. The loose particles also
build up a muddy abrasive slurry that helps to speed up the sharpening
Oilstones on the other hand do not have the same
characteristics as waterstones. Instead of the abrasive particles
breaking off, they round over and become dull. At the same time,
oil residue and metal particles can fill up the stone's pores, reducing
the ability of the stone to produce a sharp edge.
Understanding the grit
Japanese waterstone grades fall under three major
groups: very coarse grits for fast removal of metal; medium coarse
grits for refining the edge and removing the burr; and finish stones
for the final honing and polish. These grades cover a range of 150
to 8000, and they don't exactly match up with U.S. grades. For example,
the abrasive action of a 1000 grit Japanese stone is the equivalent
of US 500; and the Japanese 4000, a US 1000.
In comparison to the Arkansas stones, the Japanese
800 grit is equivalent to a Natural Soft Arkansas; the 1000 to a
Hard Arkansas; and the 1200 falls between the Hard Arkansas and
the Black Hard Arkansas.
Here are some tips for buying Japanese waterstones.
- If you need to remove a lot of metal fast, restore the damaged
edge of a tool, or change the bevel on a blade, you'll want a
stone in the 80 to 400 range.
- For general purpose sharpening, a stone between 700 to 2000
will do the job. The finer stones, 1200 and 2000, are preferable
if your tools don't have an nicks or other defects. The 800 is
an good all-around choice if you sometimes need to sharpen nicked
or heavily used edges.
- For honing and polishing an edge, choose a stone in the 3000
to 8000 range.
- Often you can get by with just a pair of stones: a medium grit
stone (800, 1000, or 1200), and a finish
stone (6000, 7000, or 8000). If you have
to deal with damaged blades a lot, toss in a more aggressive coarse
grit stone (240, 280, or 360).
- Waterstones can cost on average from $20 to $40, with some finer
grit stones up to $80. You can often buy combination stones with
a coarse grit on one side, and a finer grit on the other side
for $20 to $50.
- For sharpening turning gouges, there are special stones that
are concave to fit the shape of the gouge.
Wet stones are better stones
The driving force behind waterstones is of course,
water. To keep the stones reliable wet during use, they should be
thoroughly saturated before use. Soak times vary between grits.
The very coarse stone stones are so porous that five minutes should
be sufficient. Medium coarse stones will take about ten minutes,
with the larger sized stones taking up to twenty minutes. Finishing
stones are so dense that it takes them fifteen to twenty minutes
to become saturated. Occasionally the slur on top of the stone might
get dry during use. Just sprinkle a little bit of water on top of
the stone, and that should suffice. Be careful though not to wash
away the slur as it is very important to achieving a sharp edge.
The coarse and medium coarse stones, can usually
be left in water so that they are always ready for use. Plastic
boxes with lids are an excellent way to store them. However, do not
leave the finish stones in water. They should be stored dry. If you
do store your stones in water, you will want to periodically change
the water as smelly bacteria can grow, making your sharpening an unpleasant
experience. The best practice for storing stone in water is to rinse
them after a day's use, and store them in fresh water. This will prevent
the growth of bacteria, and keep the stones from being contaminated
with muddy waste containing different grit sizes.
you live in a cold environment take care not to store
your wet stones where they can freeze. If they freeze
they will be reduced to a pile of useless rubble. You'll
find that your stones might take a few days to completely
dry, so during that time, they should be stored in a warm
environment to prevent freezing.
How to flatten those stones
After repeated use you might notice that a small
valley is forming in the middle of your stones, or that it's no
longer as flat as it was. There are a couple of ways to restore
your stones to their original flatness.
The easiest way to flatten a coarse stone is to
rub it against a piece of wet/dry sandpaper. Place a 120 to 220
grit paper (depending on the flatness of the stone) abrasive side
up on a piece of glass or other flat surface. Wet the sandpaper
and rub the stone in a figure 8 across the paper. Check for flatness
with a straight edge. Finishing stones are easily flattened by rubbing
them against a previously flattened coarse stone. It is also a good
idea to rub a 45° bevel on the four top edges of the stone.
This will prevent "pressure flaking" on the sides of the
The only way to properly flatten the very coarse
200 grit stones is to rub it on a slurry of coarse silicon carbide
abrasive grit. Sprinkle a pinch of the grit on a piece of glass
(6" x 18", or approximate size). Wet the stone, and begin
to rub in a figure 8 pattern. Stop and check your progress frequently
to prevent wasting any of the stone.
Ultimately, the best practice is to flatten your
stones before or after every use. This way only a few seconds of
flattening is required to keep your stones in their proper condition.
Nagura stones are a useful accessory to 6000 and
8000 grit finishing stones. They serve two purposes: to develop
a slurry, and to flatten high spots on
finishing stones. Creating a slurry on your finishing stones before
actually sharpening your tools on them is a good practice because
it will greatly speed up the sharpening process. To create the slurry
first soak both the sharpening stone and the Nagura stone until saturated.
Then rub the Nagura stone over your finishing stone until a good slurry
has developed. If during the use of the finish stone you notice a
high spot developing, you can rub it out with the Nagura stone. It
should be noted that the Nagura stone is only useful with the 6000
to 8000 grit stones, they won't accomplish anything with coarser stones.
OK, lets sharpen those tools
Now that your stones are saturated with water and
flat, you can begin to sharpen your tools. The first thing that
you will need to do is to find a flat, stable surface to put your
stones on. There are many different models of stone holders that
you can buy that will do the job. You
can also place your stones on your bench top on a piece of sandpaper.
Or you can build your own wooden stone holder. The choice of what
grit to use depends on how much work needs to be done on your tool.
Begin sharpening your tool by rubbing it back and forth on the stone.
A figure 8 pattern is also good to use. Allow the slurry to build
up and remain on the surface. If the top of the stone gets dry, wet
it down with a few drops of water. Take care not to wash the slurry
away. As soon as you've developed a wire edge or "burr",
change to a finish stone and complete honing the bevel and back side
of the blade. Use the same sharpening technique on the finish stone
as you did on the coarse stone. With the finish stones you won't see
much of a burr. Let the quality of the shine at the cutting edge tell
you how close you are to optimum sharpness. As you feel you are getting
close to completion, apply less and less pressure with every stroke.
Finish up with two or three light strokes on the back of the tool,
and then a couple more on the bevel.
Heavy metal removal 80 - 400 grit
Moderate metal removal and touching up 700 -
Honing and polishing 3000 to 8000 grit
If your tool requires a lot of sharpening, periodically
check the stone to ensure that it is flat. If not, flatten as described
earlier. Using the entire stone will help to minimize any valleys
or high spots from forming.
As a final step to sharpening, use a leather strop
to buff and further hone the tool edge. Running the tool up and
down the strop 10 or so times will do the job.
After all that, you're now ready to get down to
the real work, creating beautiful works of wooden art.