Monday, March 22, 2021

Everybody Must Get (Whet)Stoned

In a previous article, I talked about files and said I’d get to stones later. Well, I checked and it’s later now. 

Also called lapping, sharpening, or whetstones, stones are used for polishing and honing, i.e. to produce a smooth finish, while files are generally considered to be tools for removing material. There are many different types and grades of stones to choose from, especially when working metal, but some are designed to be used for other materials such as glass. 

For this article, grinding wheels, although technically stones, are grouped with files as they are primarily used for metal removal.

Stone Types
The first division in stone types is natural versus artificial. As the name implies, natural stones are mined as found and then processed to their final form, while artificial stones come in a variety of bonded abrasives.

Natural stones are frequently named after their source location, such as Arkansas stones. Most Americans who’ve use a sharpening stone have probably used an Arkansas stone; they’re mined primarily in the Ouachita Mountains of Arkansas, but smaller outcrops can also be found in western Texas, Oklahoma, Japan, Syria, Lebanon, and Israel. Arkansas stones are a form of Novaculite, a Latin word  meaning "razor stone," which gives you an idea how old the use of stones for sharpening is. Arkansas stones are something of an industry standard, as they are very consistent in hardness and contain few impurities that affect their use.

Artificial stones are a combination of some type of bonding material (such as epoxy) and one or more abrasive grains (such as aluminum oxide, zirconium oxide, or silicone carbide). The material chosen and the specific size of the grains will determine both its cutting speed and finish quality.

For the casual user, the main difference between the two types of stone are price, as artificial stones are generally less expensive than  similarly-sized natural stones. However, there are some very cheap natural stones available that are often not worth even their very low price, and these low-end stones will usually break easily, cut poorly, and produce a poor finish.

Wetting a Whetstone
While some stones can be used dry, most will benefit from the application of a liquid, usually water or some form of thin mineral oil. This fluid serves several purposes: 
  • It causes stone particles to “float” on top of the surface, forming a slurry that can improve surface finish; 
  • The fluid also limits particles from being caught in the grain of the stone which can reduce the cutting ability or cause scratches;
  • Wetting a stone (not to be confused with a whetstone) can simplify cleanup. 
Most stones will work equally well with either oil, water, soapy water, or even spit.

Please don't ever do this. 

Care and Cleaning
After use, stones should be cleaned to remove any cutting residue, which includes particles of stone or metal as well as leftover lubricating liquid. (I generally wash mine with dish soap, water, and a scrubby sponge, then pat dry.) Once cleaned, stones should be stored so they aren’t damaged by other objects, many quality sharpening stones come with their own cases or boxes, but wrapping them in a clean cloth before putting them in a drawer can work as well.

As with any tool, proper care is essential for longevity. Unlike many other tools, stones are a consumable item. I’m sure most people have seen an old sharpening stone that has become almost bowl-shaped over time. When a stone is no longer capable of doing its intended job properly and easily, don’t hesitate to demote it and purchase a replacement.

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