Sharpening a well-worn chisel

[ryanjg117]

I inherited some old Japanese chisels and have purchased a honing guide to go about sharpening them. Some of these chisels have been well worn--and my guess is, sharpened on a bench grinder  :'(--so some of these chisels have been reduced down to a point where the back (dished) part of the grind is now almost at the cutting edge. Here's a little graphic example of what I'm talking about (see my imaginary red line):

[attachimg=1]

When it gets to this point, should I just toss the chisel, or try to grind flat the ENTIRE back to get it to be flat? I did just get an Atoma 140 grit diamond plate so I'm sure with some elbow grease I can get them flat pretty quick, but I will be losing a good amount of material.

 

[RKA]

The idea is you grind the back every so often so the edge doesn't end up colliding with the hollow section.  I think it won't take long on the 140 to grind it back so you have a little room between the two.  I wouldn't toss the chisel without at least trying, assuming it's of value in working condition.

 

[Rob Z]

Raj,

I don't know much about Japanese chisels other than they often are of extremely high quality. What is the function of the design with the scalloped/dished area on the back of the chisel?

 

[CeeJay]

The idea of the scalloped back is that you can easily flatten it each time you sharpen without needing to work on the whole surface area. Also helps with grip for fine work I have found.

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[ryanjg117]

Makes sense - kinda like having a secondary bevel, just makes it easier to resharpen so you don't have to hone it all down. I'll get to work on the backside!

 

[RKA]

And bear in mind, only the lead working edge of the chisel is hardened.  The rest of it is comparatively soft so grinding the back should be easier than a western chisel.

 

[macrutt]

Hi ,

You need to tap out the back .Here is a link .
https://brianholcombewoodworker.com/2017/04/05/on-ura-dashi-ito-ura/

Take care George

 

[sg1011]

Hi ,

You need to tap out the back .Here is a link .
https://brianholcombewoodworker.com/2017/04/05/on-ura-dashi-ito-ura/

Take care George

This is the best way. It’s quicker and it keeps the hollow in tact for easier flattening in the future. Also check out this video from Andrew Hunter on YouTube.

 

[Svar]

Hollowing the back made sense in the old days when abrasive options were limited. Today it's just a nod to tradition. If you are not a purist who enjoys this king of things, an aggressive diamond plate, not to mention a machine, will take care of it for you in a matter of minutes if not seconds.

 

[Rob Z]

CeeJay--thanks for the explanation. 

The idea of the scalloped back is that you can easily flatten it each time you sharpen without needing to work on the whole surface area. Also helps with grip for fine work I have found.

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[Wooden Skye]

The idea of the scalloped back is that you can easily flatten it each time you sharpen without needing to work on the whole surface area. Also helps with grip for fine work I have found.

Sent from my iPhone using Tapatalk

I have to disagree, you don't need to flatten the back after it is done initially, provided it was done right.  The scalloped backs do allow for a quicker flattening process. I would say the chisels and question is because the bevel has been reground several times and most likely incorrectly.

 

[RKA]

I would say the chisels and question is because the bevel has been reground several times and most likely incorrectly.

That's a good point!  There may not be any hard steel left if it was ground down this much.

 

[CeeJay]

I have to disagree, you don't need to flatten the back after it is done initially, provided it was done right.  The scalloped backs do allow for a quicker flattening process. I would say the chisels and question is because the bevel has been reground several times and most likely incorrectly.

I’m just describing the method I was taught to sharpen Japanese chisels.

Each time a new micro bevel is put on (or bevel), you need to take the burr off the back of the blade, so a light run over the stones for the back of the blade achieves this. The scalloped back means much less surface area requires work for this step.

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[waho6o9]

Move the edge down by tapping. 

Flattening Chisel Backs: Sharpening 1 by Japan Woodworker

 

[Jiggy Joiner]

Get the back of the smaller one down, then sharpen both in the normal ways.

I use diamond stones, water stones and still sometimes an oil stone.

 

[Sourwould]

The scallop on the back is as much for tradition and looks as it is for practicality. If you tap it out, you'll still have to flatten it. Those atoma stones cut stupid fast. I think it depends on if this is a passion project or if you're just trying to get them usable.

 

[derekcohen]

I inherited some old Japanese chisels and have purchased a honing guide to go about sharpening them. Some of these chisels have been well worn--and my guess is, sharpened on a bench grinder  :'(--so some of these chisels have been reduced down to a point where the back (dished) part of the grind is now almost at the cutting edge. Here's a little graphic example of what I'm talking about (see my imaginary red line):

[attachimg=1]

When it gets to this point, should I just toss the chisel, or try to grind flat the ENTIRE back to get it to be flat? I did just get an Atoma 140 grit diamond plate so I'm sure with some elbow grease I can get them flat pretty quick, but I will be losing a good amount of material.

Good Grief!!! I really cannot believe some of the stuff written here!

I use Japanese chisels like these all the time, for the past 30 years.

You do not tap out the hollow. Leave that for plane blades.

The backs of these chisels are fine as they are. Leave them alone!

The bevels are ground at 30 degrees, and then honed at the same angle. Single bevel, no hollow and no secondary bevel.

Ideally, you learn to do this freehand, but you can use a honing guide (not ideal).

Do NOT use a 140 grit diamond stone on these blades! The idea stones are 1000/6000/13000 grit, such as Sigma or Shapton Pro water/ceramic stones.

If you are new to chisels, then put these away until you are more experienced. Practice on some cheap Western chisels first. You will thank me later.

Regards from Perth

Derek

 

[Svar]

[member=4358]derekcohen[/member]
Derek, I think the discussion here is not how to sharpen, but what to do then the edge reaches the scalloped area.

 

[derekcohen]

[member=4358]derekcohen[/member]
Derek, I think the discussion here is not how to sharpen, but what to do then the edge reaches the scalloped area.

You are very far from the hollow (it is called, simply, a hollow) creating any issues. It only becomes a factor when the hollow reaches the edge of the blade.

When one sharpens, a little bit of steel is wasted away, and the blade gets shorter. Eventually, it will reach the hollow, and it cannot go further. Generally, this is not a problem since one polishes the back of the blade, which lowers the hollow and moves it away from the edge.

What most here do not appear to recognise is that someone has been over-enthusiatic with flattening the back of this chisel, and the hollow is already very large. Here is a new chisel for comparison ....

As you can see, there is not much flat steel at the back behind the edge. The hollow is to aid with sharpening. Japanese blades are laminations of very hard steel and a soft top layer, which adds shock absorption and ease of sharpening. The hard layer is so hard that it would be difficult to sharpen if it did not have the hollow. So, try and maintain as large a hollow as possible. Do not grind the back of this chisel!

In the usual process, one simply laps to back of the chisel, which is done when honing the bevel. This would wear the hollow down. Too much of this has already been done.

Feel free to ask questions.

Regards from Perth

Derek

 

[HarveyWildes]

[member=4358]derekcohen[/member]'s advice on hand tools is always spot on.  If he disagrees with anything I'm adding below, believe him .

If you start with a western chisel, you can practice good sharpening technique without ruining the back of the chisel.  Good sharpening technique includes flattening the back, polishing the back to the same grit you will use to create your secondary bevel, then setting the bevel angle, and then removing a minimal amount of steel to set the secondary bevel.  After the initial set up, all you need to do is hone the secondary bevel for quite a long time before additional work on the primary angle is needed again.

Another detail - don't regrind the primary angle frequently to change it.  That will just remove a lot of metal and push the edge back to the scallop that much sooner.  My recommendation is to use the angle that the chisel came with.  If you need a variety of angles for some reason, buy additional chisels.

If you do manage to work back into the scalloped area, my recommendation would be to start flattening the back at 1000 grit until you have somewhere between 1/16" and 1/8" (I'd go for closer to 1/16" than 1/8") of distance between the edge and the scallop, then polish it with 4000-6000 and then 10000- 16000.  Use your final polishing grit to hone the secondary bevel.  When flattening, remember that the hard steel layer is being removed, so don't be any more aggressive than you have to be.