Sharpening Basics
“A dull tool is a dangerous tool.” This old woodworking adage simply means that a sharp tool is easier, more predictable and safer to use, so let’s talk about sharpening.
What Is Sharpening?
Sharpening is the act of putting an edge on a tool the will cut wood. In most cases it will be a steel tool, but in some cases it will be carbide. In order to do this, you need an abrasive harder than the material being sharpened in a matrix that holds the abrasive in a manner you can use. In other words, rubbing a powdered abrasive on the edge of your tool with your fingers might eventually sharpen the tool but there are better ways.
Forms of Abrasive Used
The most common forms of abrasive in a usable matrix would be stones such as Arkansas or Japanese waterstones, coated metal such as a diamond coated plate, and abrasive paper. The actual abrasive used can vary, but the abrasive has to be harder than the material it is used to sharpen.
Abrasive Size and Consistency
It all comes down to particulate size of the abrasive. This is what determines how aggressive the abrasive cuts and what you use it for. “Big rocks” make big scratches, cut fast and are great for taking chips or nicks out of a tool or reestablishing the bevel. “Small Rocks” make really small scratches and cut slow –a must in finishing the cutting edge and usually the last stop. “Medium rocks” are in between and a bridge between the other two. The size of the rocks is referred in several different ways dependent upon the system you choose, but in most cases the smaller the rocks, the more expensive they are in whatever form you choose.
Consistency of size is important in sharpening. You certainly don’t want some errant big rocks cutting big furrows in your edge when you’re trying to polish. Companies spend lot of money for this consistency. They also spend a lot of money making sure their products work as intended, which is harder to do as the particle size gets smaller. This small problem is all about making sure the abrasive in whatever form you choose works.
What Do You Need?
What you need is dependent on what you’re sharpening and how. A woodturning tool doesn’t require as fine an edge as a bench chisel or plane iron, and how you sharpen determines what is available.
In General Terms:
Grit 80-400:
Coarse work – shaping, bevel fixing, removing nicks, etc. Woodturners usually start and finish in this area.
Grit 800-2000:
Medium work – smoothing or refining the finish left behind by coarse work. Removing very small nicks and correcting minor flaws in the edge or shape of the tool.
Grit 4000-6000:
Polishing – refining and polishing the edge. A good edge can be had here, and quite a few people stop here.
Grit 8000-30,000:
Super Polishing. Not happy with simply polishing, this is the fine-tuning of the cutting edge. What’s left here is polishing the polish. A lot of folks advocate going into this area to finish … very notable folks. It is true the finer polishing you do to an edge, the sharper and longer the edge will last.
A Final Word about Sharpening.
Sharpening is very personal pursuit. I know people that hone on the cardboard sheet that comes in a commercial laundered shirt, others that flatten waterstones on cement driveways, and some that pay a lot of money for the best of the best. None of this makes them a better sharpener. That takes time and practice.
