Selecting a Coarse Stone for the Woodworking Shop
What is a coarse stone and how is it used?
Coarse stones are sharpening stones in the 150 to 325 grit range, with abrasive particles of about 45 to 100 microns in size. These stones provide aggressive cutting action allowing for fast material removal, setting the stage for efficient honing on finer stones.
A coarse stone is essential for tasks such as establishing an edge on a very dull or damaged tool. Using a coarse stone is the first step to changing the bevel angle or shape of a cutting edge, as you would when adding a skew to a chisel or changing the angle of a block plane iron. A coarse stone also provides a fast and efficient method for flattening the backs of chisels and plane irons.
What are the options in coarse stones?
There are a variety of stones to choose from at the coarse end of the spectrum. Oil stones, water stones and diamond stones all have coarse options worth considering.
Oil Stones such as the Coarse India, Coarse Crystolon or Medium Crystolon are the slowest cutting of the options. While they do a good job of removing metal and wear less quickly than water stones, they are the hardest to flatten when the time comes.
Diamond Stones such as the DMT Extra Coarse are available in a number of sizes. They are used with water, and are easy to clean. Diamond stones offer outstanding value as they are long lasting, cut quickly, are flat and do not lose their flatness. Indeed they can even be used to flatten waterstones.
Waterstones are available from Norton and Naniwa. Waterstones are fast cutting, but do require regular maintenance. They are available in multiple grades with the higher grades like the Naniwa Sharpening Stone or the Shapton GlassStones being harder and therefore not wearing as quickly.
See the article Difference in Sharpening Stone Materials for an in depth look at the different types of stone materials.
What is the best choice?
Many woodworkers find that the low maintenance, speed and flatness of diamond stones make them the best choice, offering the most value for the money. Often, these coarse diamond stones are paired with finer waterstones to create an excellent system covering the whole range of grits.
Whichever type you choose, there are some important considerations:
What size blades are you sharpening? Ideally, the stone should be larger than the blade you are sharpening. For instance, trying to sharpen a 2 5/8” wide plane blade on a 2” wide stone is counterproductive at best.
What shape blades are you sharpening? It is often assumed that woodworkers are sharpening blades that they would like to keep flat and straight, but this is not always the case. If you are sharpening carving gouges for instance, the tendency of water stones to wear is not necessarily a problem, as the stone will conform to the shape of the tool. Conversely, keeping the cutting edge of a chisel or plane blade dead flat on a fast wearing stone can be difficult.
How much maintenance do you like to do? While the higher maintenance stones such as water stones do cut faster, they have a tradeoff in the amount care they require. If you are using them frequently, you will be spending more time flattening your stone.