Just curious here. What happens when a chisel with a hollow is sharpened down to the hollow over time. Is it now useless? Would that ever happen?
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Just curious here. What happens when a chisel with a hollow is sharpened down to the hollow over time. Is it now useless? Would that ever happen?
You can tap the metal down from the top or wear back the bottom to the point where the edge is straight again. Wearing (grinding) down the back is safer.
Mike
Not being a user of Japanese chisels, this has never made sense to me. How does hardened steel fill the area without cracking?Quote:
You can tap the metal down from the top
What mysterious metallurgical malleability have I missed?
jtk
Read this article: http://giantcypress.net/post/931326880/hatful-of-hollow
In addition to explaining how you manage the hollow of a Japanese chisel when sharpening, it will also explain why you tap out Japanese plane blades, and why you don’t have to do that with a Japanese chisel.
Thanks for that Wilbur. It seems odd that the hard steel in Japanese blades is malleable enough to not break when tapping it with a small hammer.Quote:
Originally Posted by Wilbur Pan
People squawk about flattening the back of western chisels and plane blades. I guess it all depends on the maintenance routine to which one becomes accustomed.
jtk
Jim, you don't tap on the steel but I instead the soft iron.
Thanks Gents!
A Japanese chisel with the hollow (or Ura, as it is called) sharpened away to nothing will work just fine, so long as the back is kept reasonably flat. It will just take a bit longer to sharpen, and will require more caution to keep flat. Perfect flatness must be the goal, and makes sharpening faster and chisel work more precise, but is not absolutely critical for anything but paring operations. The flats on Western chisels, for example, are frequently not very flat, but they do an excellent job anyway.
Once the flat has been trued and polished the first time when the chisel is new, avoid working it on anything but your finest grit finishing stone afterwards. This will preserve the hollow as long as possible, and aid greatly in maintaining the flat flat.
A contradictory problem arises when the hollow and the cutting edge intersect as the bevel is ground away. Here you have a choice of either "tapping out" the flat (by gently and cautiously tapping on the softer layer of steel at the bevel with a small hammer, never the hard high-carbon steel layer), or grinding the hollow down.
As Wilbur's article says, the flat can be "tapped out" on wider chisels. But don't attempt this casually since the steel laminations in Japanese chisels are constructed different from those in Japanese plane blades. Tapping out chisels takes a lot more skill and precision with the hammer, and the risk of damaging the blade is high, so I don't recommend newbies try it right away.
Grinding down the hollow to restore the flat at the cutting edge can easily be done using a "kanaban" with abrasive powder or a diamond plate.
But I am only adding detail to what Mike said so succinctly above.