Not all Japanese chisels are great

In January I got a batch of chisels after deciding that there should be a wide, large chisel in the jobsite array.

Now there is one (two, actually) & working well.

Four of the six are partially restored/sharpened. One was ground to a very low angle & I honed it steeper but still maybe 20˚.

After working it longer than normal, it still didn't polish up, or take a shaving sharp edge. Then, after shaving a couple of edges off of a piece of fir, the edge was trashed.

It shows considerable use, but I'm not sure how it made it this far in life. It's a timber chisel, but with the low angle, I only did shallow paring cuts- no hammer blows.

Sometimes, the edge of a new chisel will not perform well until after a few sharpenings but that's not the case here.


Attachment 518004Attachment 518005

This one took some work but is looking very promising:

Attachment 518006

Just a report from the field- carry on...

You may have run out of steel and/or hardened steel that close to the shoulders of the chisels.

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Originally Posted by Rafael Herrera

You may have run out of steel and/or hardened steel that close to the shoulders of the chisels.

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Or it could have been ground on a machine, overheated, and lost its heat treatment.

20 degrees is a pretty low angle for some steels to maintain, simply too brittle to hold up.

How hard would it be to re-harden it?

Yes, it could have been overheated, the extreme low angle would be easy to overheat.

I could grind off 1/8" & see if that helps.

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Originally Posted by Cameron Wood

Yes, it could have been overheated, the extreme low angle would be easy to overheat.

I could grind off 1/8" & see if that helps.

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You might try testing the hardness with a scratch awl or a file. My dad showed me this once when he wanted me to see the difference between regular chain and case hardened chain.

jtk

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Originally Posted by Eric Brown

How hard would it be to re-harden it?

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Not too hard, given how small they are. You'd probably want to remove the handles first so they don't catch fire (just in case). I've done it with a MAP torch and a tin can of used motor oil (and gloves, vise grips, eye protection, an all of that safety stuff). Ron Hock has a video on YT about it for Popular Woodworking. That's a good place to start. To do it really well, you have to control temperatures very precisely. But to do it "good enough to work", you can usually guess the temperatures by the color of the glow. Sometimes people will use ceramic fire bricks to help trap heat for larger items, as it can be hard to evenly heat up larger areas with a small torch. But I bet you could get away without that in this case.

Either way, test it with a file first. Make sure that's the problem before spending more time or money into it.

I ground about a 1/16" flat on the edge, and then honed back at a more normal bevel, and it seems much better, so I guess there's hope.

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To do it really well, you have to control temperatures very precisely. But to do it "good enough to work", you can usually guess the temperatures by the color of the glow.

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This is a color chart of heats and temperatures found on line:

Attachment 518049

jtk

Are those the kind that one has to "tap out" on a special anvil? Or, is that just for the Plane irons?

Maybe your last pic is deceiving me?
Your chisel doesn’t look sharped all the way to the edge. I have one kanna it’s blade is way too hard for my liking. The steel has large grains of carbide or whatever the smith used. I didn’t pay much for it so I don’t use it on serious work. It is fun to mess with though
Good Luck

Edward is correct. 20 degrees is too low for this steel. Remember, oire nomi are designed to be used with a gennou - the edge needs to be beefy.

Grind back until you have sufficient steel to support the edge, and then hone it at 30 degrees. If it is sharp and does not then work and hold an edge a decent amount if time, then look to take action. But I would be surprised it the regrind and correct angle does not perform a miracle.

Regards from Perth

Derek

In practice, chisels are rarely tapped out since they are narrower and made more beefy.

The chisel is sharp, but not perfectly polished. It will take a couple of arm hairs, but not a swath of them. It's quite difficult to get good pics of cutting edges, & shiny objects in general, IME.

The re-grind did work (in limited test), but ordinarily, a too shallow edge will chip, but in this case it immediately folded over, making a substantial burr after paring a couple of inches of wood.

Thanks Derek.
If it indeed is a Timber chisel, (Tataki Nomi) as the OP said, I would suspect a 30 degree angle is what should be used. It's possible someone sharpened it as some type or paring chisel sometime in the past.