Sharpening Part 10 – The Ura 浦 – Covington & Sons Tools

Chisel Ura. The term “Ito-ura” refers to the narrow land located immediately behind the cutting edge.

If a craftsman wants to do good work, he must first sharpen his tools.
Confucius, The Analects

We talked about the Ura in the previous article in this series (Part 9).

It is a defining detail in most Japanese woodworking blades, and one we must understand if we are to efficiently sharpen them, so in this post we will examine this important feature in more detail.

What is the Ura?

Japanese plane and chisel blades have a unique and intelligent design feature at what is called the “flat” on Western plane and chisel blades, and is called the “Ura” (pronounced oo-rah) in Japan.

Ura translates into the English language as “bay,” as in a protected area where the sea meets the shore. At the center of the ura is a hollow-ground, depressed area in the hard steel hagane layer called the “Uratsuki,” meaning the ura hollow, that serves two purposes.

One purpose of this design is to make it easier to keep the blade’s “flat” (the shiny areas surrounding the depression) planar (in the same plane).

If you pay attention when sharpening your wide Western chisel and plane blades lacking the Ura detail you will notice that, after many sharpening sessions, the blade’s flat, which was once planar, tends to become convex with a high point at the flat’s center making it difficult to keep the extreme cutting edge, especially the corners of the blade, in close contact with the sharpening stone. Yikes!

This doesn’t occur because you don’t know how to sharpen your blades, or because of pernicious pranks by pesky Pixies, but simply because your sharpening stones/platens/paper tend to abrade the blade’s perimeter more aggressively than the center. The resulting curvature makes it more difficult to polish the flat’s extreme cutting edge. Major buzzkill.

Because of the most excellent Ura, Japanese woodworking blades are quickly fettled initially and tend to stay planar without a second thought for many years of hard use, an important benefit if you count your time worth anything.

Another purpose of the Ura is to reduce the square inches or square millimeters of hard steel you must polish during each sharpening session. As you can see from the photo above, the shiny perimeter land is all that touches the sharpening stone. Compare this with the black area which doesn’t touch the stone. That’s a lot of hard steel you don’t have to deal with. Besides making the job easier, it also saves a lot of time when sharpening and helps one’s expensive sharpening stones last longer. Time is money and stones ain’t cheap, as my old foreman scolded (lovingly, I’m sure).

Even if you don’t use your tools to make a living, you should at least recognize that time spent sharpening is time making wooden objects lost.

The Downside Of the Ura

Despite my poetic praise, the Ura detail is not all blue bunnies and fairy farts, because it does have one unavoidable downside: Over many sharpening sessions the Ura unavoidably becomes gradually shallower, and the lands surrounding the Ura on four sides become correspondingly wider. Nothing lasts forever except regrets and taxes.

It is not uncommon to see old chisels and plane blades with the hollow-ground area of the Ura almost disappeared. You can postpone this day by sharpening the Ura wisely. However, in the worst case where the Ura disappears entirely, you will still be left with an entirely usable Western-style flat, so not all is lost.

In the case of plane blades, unless the plane’s ura is subjected to a brutal sharpening regime, the land that forms the cutting edge (called the “Ito ura” meaning “strand” as in a flat area on a riverside, in Japanese) tends to gradually become narrower, and even disappear entirely after numerous sharpenings. Of course, when this happens, the blade loses its cutting edge, and the land must be restored by “uradashi” (oo-rah-dah-she) aka “tapping out” or bending the cutting edge towards the ura side, and then grinding it flat to form a new ito-ura land. Tapping out a blade requires some caution, but is not difficult. We will discuss the how-to of this aspect of blade maintenance in a later article in this series.

In the case of chisels, which have smaller and shallower ura compared to wider plane blades, the land at the cutting edge does not typically require tapping out, although it’s certainly possible to tap out wider chisel blades. Narrow chisel blades, on the other hand, are difficult to tap out without damaging them due to the rigidity produced by the hard steel layer (detailed in the previous post in this series) wrapped up the blade’s sides.

Mitsuura Chisels

Ichimatsu Nomi Ura (by Kiyotada). After many years of hard use, the multiple ura (aka “mitsuura”) on this oft-sharpened chisel used to pare precision joints has become shallower and the planar lands have become wider. Still entirely useful, it now takes more effort to sharpen than when new.

Some chisels are made with multiple ura, typically called “mitsuura” meaning “triple ura.” Mitsuura chisels are more difficult to sharpen than chisels with a single ura because the total area of hardened steel that must be polished is comparatively larger. The ura of mitsuura chisels also tend to wear-out quicker than single-ura chisels because each individual uratsuki is shallower in depth than standard uratsuki. They look cool, but I am not a fan of multiple ura except in a few specific applications.

In the next stage of our journey into the mysteries of sharpening, we will wander through the metaphysical realms of the “Fae.” A word of caution: Be sure to have a brass bench dog in your pocket when you leave the well-lighted pathways and accept neither food nor drink from anyone’s hand until we return, not even a cheeseburger with fries. ☜ (◉▂◉ )

YMHOS

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