Hand Tools Archive

Re: 58-62
Response To:
Window of hardness ()

David Weaver
I've had some tools tested in the past and would put the window around 58-62.

It sounds narrower than a beginning woodworker might suspect. At 58, anything will form a fairly large wire edge on an oil stone. At 62, an oil stone is starting to struggle.

More than half of the difference that people perceive with a2 vs o1 is a difference in spec hardness

What I found hardness testing is that I had a chisel that I couldn't get anything out of
It was a witherby parer, and I tried to give it to a friend. He had it and a bunch of other stuff tested on a version three strikes and averaged them. The chisel tested 53. I had another witherby socket chisel that had a nice profile, and it tested 59. It was decent, but not great compared to older tang chisels.

Ln's mortise chisel and an iyoroi mortise chisel both tested 61. I didn't have any good quality Japanese chisels back then, but they're carbon steel so I can get a pretty good guess now based on japanese stones that I have, or if I get some well made Japanese chisels that are several points soft, they will sharpen wonderfully on a washita alone (too hard for much removal, but they can be kept in shape indefinitely). Because they're at the stone's limits, they'll take a very fine edge whereas the witherby chisels will take something that I'd call serviceable.

I've found over the years that Japanese makers who advise that they have a very easy sharpening plane iron made of some kind of specialty steel, often swedish, the real difference is that they're usually tempered software.

When Japanese makers stick to some of the book specs and go way up in hardness, natural Japanese stones struggle with them, too, despite being fifteen percent or a little more aluminum oxide.

The other thing I found is that when a tool is marginal, it'll usually go from very poor performing to fine in just two or three degrees. Ultra hard Japanese chisels tend to have a more spectacular type of failure
....like loss of corners until you find where they hold up.

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