Japanese Chisel Question

[gregbois]

I have read contrasting views about tapping out Japanese chisels to maintain the hollow-ground section on the back.  Some suggest that one should only tap out wider chisels, without saying what ought to be done to maintain the hollow on a narrow chisel.

If a narrow chisel's bevel is approaching the point where there would be nothing left of the hollow on the back upon sharpening the bevel, what is one supposed to do?  Flatten the back to or tap out?  I am wondering this only about a narrow chisel.

Thanks.

Greg

[Howard Pollack]

I don't know the answer, but you could try posting the question here: https://www.woodworkforums.com/f111  it is an Australian Japanese Tool forum.  -Howard

[Aram]

SMC thread with a link to an article by Wilbur Pan, and a response from Stan Covington, among others.

[adamcherubini]

This just seems like a terrible idea to me. I don’t see how this helps the edge. It’s just a lot of internal stress. They bend the hardened back down away from the bevel.

This really sounds like the grandma sawing the end off the ham story. Assuming the tool is differentially hardened, I don’t know what you would get if you ground out the hollow. Maybe the ruler trick would be a better approach.

[Wilbur Pan]

This just seems like a terrible idea to me. I don’t see how this helps the edge. It’s just a lot of internal stress. They bend the hardened back down away from the bevel.

This really sounds like the grandma sawing the end off the ham story. Assuming the tool is differentially hardened, I don’t know what you would get if you ground out the hollow. Maybe the ruler trick would be a better approach.

The reason for tapping out the edge of a Japanese plane blade is to maintain/reestablish the flat area between the edge and the hollow as it gets sharpened and the flat area gets smaller and smaller.

The reason for the hollow is so you don't have to flatten a lot of very hardened steel on the back side — just the perimeter. Tapping out maintains the hollow, so you don't grind it away and are left with a lot of work on the back going forward.

Using the ruler trick could work, but then you're changing the geometry of the cutting edge, and I'm not sure how consistent the new cutting angle would be over time. This may or may not be a big deal.

Tapping out is not as hard as it seems. I think part of the problem is that most of the descriptions out there on the tapping out process include something about how you can crack the blade, and that freaks people out. I figured out how to do this, and I think that if I can figure this out, anyone can. The only dexterity you need is the ability to accurately hit something with the pointy end of a tack hammer.

[hbmcc]

SNIP>>> The only dexterity you need is the ability to accurately hit something with the pointy end of a tack hammer.

Well, that puts me out of the game! Have you ever hammered tacks without a magnetic end? 

One thing always bothered me about the hollow (urasuki) on Japanese cutting tools. Why bother grinding one into the cross-section of chisels smaller than 3/4-inches? The bulk of material removed isn't that significant. I suppose it could define alignment a little easier.

[adamcherubini]

The reason for tapping out the edge of a Japanese plane blade is to maintain/reestablish the flat area between the edge and the hollow as it gets sharpened and the flat area gets smaller and smaller.

The reason for the hollow is so you don't have to flatten a lot of very hardened steel on the back side — just the perimeter. Tapping out maintains the hollow, so you don't grind it away and are left with a lot of work on the back going forward.

Using the ruler trick could work, but then you're changing the geometry of the cutting edge, and I'm not sure how consistent the new cutting angle would be over time. This may or may not be a big deal.

Tapping out is not as hard as it seems. I think part of the problem is that most of the descriptions out there on the tapping out process include something about how you can crack the blade, and that freaks people out. I figured out how to do this, and I think that if I can figure this out, anyone can. The only dexterity you need is the ability to accurately hit something with the pointy end of a tack hammer.

I get it. Just wondering what this does to the edge. I mean, it’s plastically deforming. I would think it work hardens it and may leave residual stress. I get that the bevel side is soft. But the back is hardened, sometimes very hard.

Also curious about why Japanese craftsmen would do it? I suspect it was a faster way to sharpen when good coarse abrasives weren't available. Now that they are, is this an obsolete technique? I think the hollow ground feature is a cool idea. I just think I would sooner hone it out, as that’s better for the edge. Tapping seems both risky and potentially damaging.

Last: the fact that Japanese craftsmen have been doing this for a long time tells me whatever damage is done to the edge is probably minor/imperceptible. One thing I’ve learned studying and recreating old woodworking is that our ancestors were smart and practical.

[AHill]

Tapping is something that the Japanese have been doing for at least 200 years, so I think it's well understood. That said, I don't think it should be done unless you have some experience with the process. Japanese woodworkers served pretty extensive apprenticeships and the knowledge and technique to do this was passed along by masters of the trade to their apprentices. It would be very easy to tap too hard and ruin your chisel. Repeated light tapping is work is also inducing surface stresses that could increase the probability of failure. I'm not saying not to tap the chisel, but proceed with caution, and with the realization that you may end up with a broken chisel.

Another point is that Wilbur Pan doesn't own your normal factory-made Japanese chisels. His are Fujihiro, made by an independent chisel maker. The steel is probably the same as most factory made chisels, but the technique is different, which can change the way the steel behaves when tapping.

[gregbois]

Thanks everyone for all of this information.  I'm reading up more before I try tapping out -- if I do.

[Wilbur Pan]

I have read contrasting views about tapping out Japanese chisels to maintain the hollow-ground section on the back.  Some suggest that one should only tap out wider chisels, without saying what ought to be done to maintain the hollow on a narrow chisel.

If a narrow chisel's bevel is approaching the point where there would be nothing left of the hollow on the back upon sharpening the bevel, what is one supposed to do?  Flatten the back to or tap out?  I am wondering this only about a narrow chisel.

Thanks.

Greg

Flatten the back. That will reestablish the flat area between the edge and the hollow.

Here's the link to my write up as to why tapping out is needed for Japanese plane blades, but not for chisels. 

Overall, it is possible to tap out a wider chisel. But I don't know why you would do that when flattening the back is a much easier way of achieving the same result, and even if you do tap out a wider chisel, you're still going to have to work the back of the chisel.