Dieter Schmid's Fine Tools
Sharpening tools, water stones

Sharpening tools, water stones


Sharpening your tools is an important part of your job as a woodworker
– do not look on it simply as a necessary evil!

Should you grind wet or dry?

Never use a dry grinding wheel to sharpen your good carbon steel plane and chisel blades. The heat developed leads to loss of hardness and a much reduced tool life. It is a common misconception that this will not happen if you stop soon enough, before the blade starts to turn blue, and take it away from the still-whizzing wheel to plunge it into water. Changes to the microstructure will occur even at much lower temperatures and you have no way of monitoring what is going on. Complaints about the allegedly poor steel quality of blades, whose quality was known to me, could generally be traced back to their being sharpened on dry grinding wheels. Low-speed (90 to 120 rpm) wet grinding wheels prevent heat build-up. Sharpening will take longer, but you have the peace of mind that comes with knowing you’re treating your tools with the respect they deserve. The best wet grinding wheels on the market are based on a sophisticated system and are made by Tormek in Sweden. The initial purchase price, however, may well exceed some budgets.

On the other hand, with a good whetstone, a grinding guide and a certain amount of practice, your results will be perfectly adequate. Sharpening by hand teaches you the most about your tools and has the advantage that you can do it anywhere, while a machine is fixed. Besides, a grinding wheel is useless when it comes to sharpening the back of your plane blades and chisels. For this, you need a flat surface and this is not available on a rotating wheel.

Opinions differ as to whether it is better to grind the bevel on a blade hollow, as happens on a grinding wheel, or flat, as happens in manual sharpening with a whetstone. Hollow grinding simplifies the subsequent honing but the more acute angle that results will make the cutting edge weaker and more liable to be damaged. This detrimental effect is especially noticeable on the very hard, laminated Japanese plane blades and chisels. In Japan it is unthinkable to grind the bevel of a blade hollow. The German manufacturer E.C.E gives a clear warning against hollow grinding. So if you decide on a flat bevel for your plane blade, you are in the best of company.


Water stone or oil stone?

Many stones will give a good performance with either water and oil. However, once the choice has fallen on oil, water is no longer an option. Because contact with the mineral oil one has to use is not particularly healthy, I prefer water stones. Japanese water stones are becoming more and more popular because of their superb quality.

Among the Japanese water stones the soft ones make for efficient sharpening, as their loose composition means that new abrasive particles are constantly exposed. The stones only need to be soaked for five or ten minutes before use. It is not wise to leave them in water all the time, because that will result in a slimy surface. On some stones the surface will decompose.

These stones do, however, become concave with use more quickly than harder stones and must therefore be dressed more often. The quick method of doing this is a flattening stone. A cheap alternative is to take wet-or-dry sandpaper (grit grade 80 or so), a flat surface to rest on, (a sheet of glass is best), a splash of water for the sandpaper to cling to the glass, and – if you want to speed things up even more – a packet of silicon carbide powder, grit grade 60 or 120.

Your basic kit should be: a sharpening stone of grit grade 700 to 1200, a honing stone of grit grade 3000 to 6000, and a honing guide. A coarse stone of grit grade 120 to 400 is a useful complement to restore blades or to grind down notches. If the grinding guide is used for working on plane blades the stone should be a few millimetres wider than the widest blade. A combination stone is available, which offers a sharpening stone on one side and a honing stone on the other.

Many tools made of stainless steel alloys, particularly stainless steel knives, are very difficult to sharpen. Even Japanese water stones will not work consistently in sharpening these knives, and will load up. All is not lost, however, because the stones can be quickly and easily dressed following the method described above. If you have stainless steel knives or chisels, you may wish to visit our page showing Missarka synthetic stones.

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