Lost Art Press

“Der Narzissmus der kleinen Differenzen (The narcissism of small differences).”

— Sigmund Freud, 1917

The topic of sharpening is plagued by Freud’s “narcissism of small differences,” and the best example of this is all the noise about the shape and angle of the tool’s bevel.

Almost every word written about this topic is nonsense, at least from a practical perspective. Let’s talk first about the shape of the bevel.

Convex, Concave or Flat?
All the wood can see is the tiny intersection of the bevel with the back. It cares only about two things: the angle at which the edge is cutting and whether or not the edge comes to a zero-radius intersection.

The wood doesn’t care if you hollow-grind your bevel and hone it flat on stones. It doesn’t care if you have a dead-flat bevel. It doesn’t care if you add a secondary bevel. Or if your bevel is convex.

The wood never sees the bevel – only you can.

So from a practical standpoint, the shape of the bevel is unimportant (I’ve worked extensively with all of these shapes). Unfortunately, theory and speculation cloud what is – at the bench – dead simple.

A hollow-ground edge is not weaker than other edges. You might draw diagrams that show how the cutting edge isn’t as well-supported by the iron atoms behind the edge, but you are only making noise. Please stop that. A hollow-ground bevel works very well.

A flat bevel that is fully polished is not particularly difficult to sharpen. Yes, it might take a little longer to polish the scratches out because you are polishing a lot of iron and steel. But the time difference is not significant enough to warrant discussion. If it were, entire woodworking cultures wouldn’t have done it for thousands of years. So a flat-sharpened bevel also works very well.

A secondary bevel works very well. The wood has no clue you are using one.

And a convex bevel isn’t any more robust or easier to sharpen than any other bevel. Yes, there is theory that our human brains might ponder, but the wood doesn’t care about your theories. Bottom line: A convex bevel works very well.

Animosity Toward Angles
Another source of intense noise is the exact angle of the bevel. I’ve written about this red herring before. It seems logical that low sharpening angles are best for end grain, and high sharpening angles are good for mortising.

What’s is far more important than the angle, however, is the zero-radius intersection. You can pare end grain with a sharp chisel honed at 35°. I do this all the time. In fact, almost every tool in my chest is honed at about 35°, which keeps my sharpening regimen simple.

Pre-industrial woodworkers didn’t seem to care much about angles, either. In the old texts, a wide variety of angles are acceptable (check out Joseph Moxon’s discussion in his ‘Mechanick Exercises’” for a good example). The advice of the dead: If the edge crumbles easily, raise the sharpening angle. If the tool becomes too hard to push or won’t take a shaving, lower it.

So pick a practical angle – somewhere between 20° and 35° – and see what the wood and steel tell you. Soon you’ll forget the sharpening angle you’re using (I certainly do) and focus more on that zero-radius intersection and less on the shape of the bevel or its angle.

— Christopher Schwarz

Read the other installments in the “Sharpen This” series via this link.

Read the other installments in the “Sharpen This” series via this link.

Let’s pretend I want to break one of your fingers. The job would be easy if you held up your fingers in the air with them spread apart.

It would be more difficult to harm you if you clenched your fingers in a fist. And it would be almost impossible if you stuck your fist inside a shiny and hard vase.

Violent fantasies aside, this exercise demonstrates one benefit of polishing your edges. A steel edge breaks down quickly when the iron atoms aren’t well connected to one another. So when there are deep abrasive scratches in your tool’s edge, those act like the space between your fingers. Without good support among the atoms (or your fingers) it’s easy to break them off – making a dull edge and a howling reader.

Clench your fingers in a fist, and you have created a durable structure that can keep your fingers intact. Sheathe your fist in something, and it’s going to take me a while to punish you for the naughty things you’ve done.

In sharpening, the act of polishing removes the deep scratches that separate the iron atoms, which are in a matrix with carbon. The fewer and shallower the scratches, the more durable the edge. This is, I think, easy to understand.

But what makes some people do silly things is the idea that they can create the ultimate cutting edge by polishing to finer and finer grits using particles that are less than 1 micron across.

In theory, sure. Polishing can refine an edge to an incredible degree. But it’s unlikely in the real world using real-world abrasives.

I’ve used sub-micron sharpening equipment (less than half a micron) that costs a stupid amount of money. I worked with these stones and slurries for months to get comfortable with them and improve both the sharpness of my edges and the finish on the wood. I concluded it was a fool’s errand.

In a real workshop, there are just too many abrasive particles on every surface to make this sort of crazy sharpening a practical thing. And the purity of the sharpening media itself – despite the manufacturer’s claims – plays a big role in the results.

Also, these super-fine abrasives cut so slowly that you might want to have “Heaven’s Gate” on your shop’s TV while you polish that one holy edge.

So What is a Practical Polish?
Believe it or not, the cutting edges of woodworking tools haven’t gotten insanely better in the last 200 years. That’s because we have always had abrasives that get the steel to the same approximate level of sharpness and polish. The pre-Industrial craftsman might have had stones that were inferior to modern stones, but he or she also had a strop, which is the great leveler among the sharpening cultures.

Strops are charged with fine abrasives – a micron or so – that break down to even finer particles with use. And so a fine polish and a wicked edge have been available for many generations. We know this from books, of course, but also from the furniture record. Visit the Winterthur Museum some time and observe the pieces made using ribbon-stripe mahogany that are nicely planed. Those cutting edges were plenty sharp.

In my experience, the sharp edge that can handle anything in woodworking is made with an abrasive that is about 1 or 2 microns – give or take. After that point, the time and care required to take the edge to a noticeably higher level simply isn’t worth it (unless your hobby is sharpening or you participate in Japanese planing contests).

If you want to polish beyond 1 micron, you’re not hurting anyone. So feel free. But for people who want to get back to the work as soon as possible, 1 or 2 microns is the sweet spot for an edge that is sharp and durable.

— Christopher Schwarz

Read the other installments in the “Sharpen This” series via this link.

I roll my eyes when people talk about the superiority of their chosen sharpening media, whether it’s waterstones, oilstones, diamonds or cinderblocks. To my ears, it’s like you’re boasting about the superiority of the oxygen molecules that you breathe compared to those in your neighbor’s lungs.

Sharpening comes down to abrasion with small rocks. Some rocks cut steel faster but break down faster. Other rocks cut steel slower but are sturdier. Some rocks are expensive; others are cheap.

The practical differences among the systems are minimal. As a result, there is no clear winner among the rocks. Anyone who tells you different is either an evangelist or sells little rocks for a living.

I can say this with confidence because I wallowed in every sharpening system for about 15 years. I used them to sharpen tons of chisels and plane blades for tool tests at Popular Woodworking Magazine. And I listened to every snake oil salesman’s speech and put their assertions to the test.

We all want to believe that there is a superior system out there. It’s human nature to compare, contrast, contest and cajole. But the truth is that the best system is the one you have mastered.

So when I talk about sharpening media, I don’t give two figs about the type of media – oilstone, sandpaper, diamond, gallstone. Instead, what is far more important is the actual size of the little rocks you are using (which are best measured in microns when talking about sharpening).

Big rocks remove material quickly and leave deep scratches. Little rocks remove less material but leave smaller scratches. Tiny rocks remove little baby mousy bites of material and leave scratches the naked eye cannot see.

So the competent sharpener uses big rocks to create the zero-radius intersection. Then he or she uses the little rocks and then the tiny rocks to refine and polish the edge so it’s more durable.

That’s why the most important questions when it comes to sharpening media are: How big are my big rocks? And how tiny are my little ones?

Measuring Rocks
Here’s the useful information: The world of practical sharpening media ranges from rocks that are about 200 microns in size down to rocks that are 1 micron (or smaller). A rock that is 200 microns is about .008” – that’s about the size of a thick plane shaving. A rock that is 1 micron across is about .00004”. By way of comparison, a human blood cell is about 5 microns across.

I separate the rocks into three different sizes, each with a different job in sharpening. The biggest rocks (200 to 40 micron) are used for grinding edges. Grinding is for fixing damaged edges or changing the shape or angle of the edge.

In my shop, this job is handled by an #80-grit grinding wheel, which has 192-micron rocks.

The next size rock is what I use to sharpen an edge that has become dull from normal work (not abuse). This rock is usually between 20 microns and 7 microns in size. This rock removes metal quickly and leaves scratches that are easy to polish out with smaller rocks.

You need only one grit in this size (unless you love to fund the sharpening stone industry). In my shop, this is a #1,000-grit waterstone, which has 15-micron rocks in it.

Lastly there are the rocks used for polishing. These are from 6 microns down to a fraction of a micron. Polishing an edge helps make it more durable (more on that in a future post). Deciding on your polishing rocks is all about how much patience you have. Some people have three or four grits for polishing. Others have one polishing grit. Neither choice is superior to the other.

The more polishing you do the longer your edge will last. But there is definitely a point of diminishing returns. Finding that point is up to you.

In my shop, I use two polishing grits. A #4,000-grit waterstone (4 microns) and an #8,000-grit waterstone (2 microns).

Those are my rocks – 192, 15, 4 and 2 – and they are no better than yours.

— Christopher Schwarz

P.S. You are going to hear people challenge the above information with words such as “mesh,” “polycrystalline” and “binder.” When they do this, let your eyes glaze over and build a motorcycle in your frontal lobe. Then, when they are out of breath, ask to see their edges. I haven’t found that high-level abrasive knowledge leads to superior edges. If they won’t show you their rocks, then ask them to “sharpen this.”