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 process.

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

If 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.

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.

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 stone.

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

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

• Heavy metal removal 80 - 400 grit • Moderate metal removal and touching up 700 - 2000 grit • Honing and polishing 3000 to 8000 grit

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.

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.

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