Author Topic: Sharpening a well-worn chisel  (Read 1548 times)

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Offline ryanjg117

  • Posts: 257
Sharpening a well-worn chisel
« on: June 19, 2020, 03:26 PM »
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):



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.

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Offline RKA

  • Posts: 1980
Re: Sharpening a well-worn chisel
« Reply #1 on: June 19, 2020, 03:34 PM »
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.
-Raj

Offline Rob Z

  • Posts: 1007
Re: Sharpening a well-worn chisel
« Reply #2 on: June 19, 2020, 03:36 PM »
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?

Offline CeeJay

  • Posts: 209
Re: Sharpening a well-worn chisel
« Reply #3 on: June 19, 2020, 03:42 PM »
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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Offline ryanjg117

  • Posts: 257
Re: Sharpening a well-worn chisel
« Reply #4 on: June 19, 2020, 03:45 PM »
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!

Offline RKA

  • Posts: 1980
Re: Sharpening a well-worn chisel
« Reply #5 on: June 19, 2020, 03:47 PM »
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.
-Raj

Offline macrutt

  • Posts: 32
Re: Sharpening a well-worn chisel
« Reply #6 on: June 19, 2020, 03:55 PM »
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

Offline sg1011

  • Posts: 39
Re: Sharpening a well-worn chisel
« Reply #7 on: June 19, 2020, 04:05 PM »
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.




Offline Svar

  • Posts: 2238
Re: Sharpening a well-worn chisel
« Reply #8 on: June 19, 2020, 04:19 PM »
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.

Offline Rob Z

  • Posts: 1007
Re: Sharpening a well-worn chisel
« Reply #9 on: June 19, 2020, 04:40 PM »
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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Offline Wooden Skye

  • Posts: 1171
  • My little girl was called home 12-28-15
Re: Sharpening a well-worn chisel
« Reply #10 on: June 19, 2020, 06:02 PM »
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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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.
Bryan

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Offline RKA

  • Posts: 1980
Re: Sharpening a well-worn chisel
« Reply #11 on: June 19, 2020, 06:43 PM »
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.
-Raj

Offline CeeJay

  • Posts: 209
Re: Sharpening a well-worn chisel
« Reply #12 on: June 19, 2020, 10:40 PM »
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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Offline waho6o9

  • Posts: 1569
    • Garage Door Handyman.com
Re: Sharpening a well-worn chisel
« Reply #13 on: June 19, 2020, 10:51 PM »
Move the edge down by tapping. 

Flattening Chisel Backs: Sharpening 1 by Japan Woodworker


Offline Jiggy Joiner

  • Posts: 1111
Re: Sharpening a well-worn chisel
« Reply #14 on: June 20, 2020, 04:48 AM »
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.

Offline Sourwould

  • Posts: 120
Re: Sharpening a well-worn chisel
« Reply #15 on: June 20, 2020, 06:22 AM »
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.

Offline derekcohen

  • Posts: 504
    • In The Woodshop
Re: Sharpening a well-worn chisel
« Reply #16 on: June 20, 2020, 11:58 AM »
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):

(Attachment Link)

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
Visit www.inthewoodshop.com for tutorials on joinery, hand tools, and my trials and tribulations with furniture builds.

Offline Svar

  • Posts: 2238
Re: Sharpening a well-worn chisel
« Reply #17 on: June 20, 2020, 01:03 PM »
@derekcohen
Derek, I think the discussion here is not how to sharpen, but what to do then the edge reaches the scalloped area.

Offline derekcohen

  • Posts: 504
    • In The Woodshop
Re: Sharpening a well-worn chisel
« Reply #18 on: June 20, 2020, 01:50 PM »
@derekcohen
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
Visit www.inthewoodshop.com for tutorials on joinery, hand tools, and my trials and tribulations with furniture builds.

Offline HarveyWildes

  • Posts: 950
Re: Sharpening a well-worn chisel
« Reply #19 on: June 20, 2020, 03:24 PM »
@derekcohen'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.
« Last Edit: June 20, 2020, 03:27 PM by HarveyWildes »

Offline derekcohen

  • Posts: 504
    • In The Woodshop
Re: Sharpening a well-worn chisel
« Reply #20 on: June 20, 2020, 08:46 PM »
Thanks Harvey. There are varying views on sharpening Japanese chisels.

The traditional way is to hone a flat bevel. A hollow grind is considered negatively as it is believed by many to remove the support behind the hard cutting layer and so weaken the bevel. I do not believe this having hollow ground some if the cheaper bench chisels (nomi) over many years. Jim Krenov used to add a secondary bevel as well.

I believe that the real reason is probably that the bevel just looks nicer with the laminations standing out, hard steel against soft iron, and on the more expensive chisels this can be quite beautiful.

Here are three different types I own. Kiyohisa slick (paring) and bench chisels (white paper steel) along with a PM-HSS bench chisel.



The Kiyohisa are very special, even if they do not look fancy. No longer available, and when they were there was a 6 year waiting list.

Note that the slicks are only pushed and never struck with a hammer (gennou). The bevel is 25 degrees. Bench chisels are generally at 30 degrees. I try and use these chisels in the traditional manner, and only sharpen with waterstones. In my case, Shapton Pro 1000, and Sigma 6000 and 13000.

Somewhere here are Koyamaichi dovetail chisels as well. :)



Bench chisels are designed to be used with a hammer (gennou), hence the hoops to reinforce the handle. This creates a tool with great precision.





To the OP: I recommend that you do some research on the use of Japanese tools and chisels before going any further. Be patient :)

Regards from Perth

Derek
Visit www.inthewoodshop.com for tutorials on joinery, hand tools, and my trials and tribulations with furniture builds.

Offline Jiggy Joiner

  • Posts: 1111
Re: Sharpening a well-worn chisel
« Reply #21 on: June 20, 2020, 09:16 PM »
I think the OP is asking what happens, which could be sooner or later, when the hollow is reached when honing the bevel, I think?

I cannot remember the Japanese term for the hollow, “Uri” maybe?
Anyway, if/when the hollow is reached at the bevel, the hollow needs bringing back some.
This can be done with a ball pein hammer and anvil, or similar. The chisel needs to be upright, (bevel at top, and hollow underneath) then the bevel needs to be carefully/skilfully beaten with the ball pein or similar hammer. Done properly, this will strengthen the hollow, and give some more meat up front, to re hone the bevel.

A lot depends on the amount of use and honing the chisels receive. My Japanese chisels are respectful but, not top end in the world of Japanese steel and blades but, they get used regularly, and hold a nice edge for a good while.

Offline derekcohen

  • Posts: 504
    • In The Woodshop
Re: Sharpening a well-worn chisel
« Reply #22 on: June 21, 2020, 04:17 AM »
For the final word on Japanese blades, read Stanley Covington's blog. Stan has lived in Japan for many years and lives and breaths woodworking ...

https://covingtonandsons.com/about-covington-and-sons-tools/

On chisels ...

https://covingtonandsons.com/tag/sharpening-japanese-chisels/

On preparing the back of the blade, the hollow (indeed, the ura, not a scollop) ...

https://covingtonandsons.com/2019/10/04/sharpening-part-10-the-ura-%e6%b5%a6/

Regards from Perth

Derek


Visit www.inthewoodshop.com for tutorials on joinery, hand tools, and my trials and tribulations with furniture builds.

Offline Jiggy Joiner

  • Posts: 1111
Re: Sharpening a well-worn chisel
« Reply #23 on: June 21, 2020, 05:42 AM »
Great links Derek, I’m not too shabby when honing but, always ready to learn, even at my age.
I keep promising myself some nice top end Japanese chisels but, in honesty my modest grade collection has done me proud over the years.




Offline RKA

  • Posts: 1980
Re: Sharpening a well-worn chisel
« Reply #24 on: June 21, 2020, 09:27 AM »
I misread the OP and thought the chisels he inherited were already ground past the scallop on the back.  Upon re-reading, he says “almost” to the scallop.  There is a big difference.  Ryan, sorry about that.  Derek is right, if it’s close to the scallop, it’s fine.  Take some time to read up on Japanese chisels and give them a go.  If you have a question about a particular chisel that may have been improperly sharpened, post a picture of the actual chisel (front and back) close up so we can give you better advice.
-Raj