“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.