Hollow backs on Japanese chisels

[Paul Chapman]

Something I've never been able to fathom is the hollow backs on Japanese chisels. In particular, it seems to me that there's only a few millimetres of metal between the edge of the chisel and where the hollow starts. So what happens when you have honed the chisel several times and you reach the hollow :? Do you just throw it away and buy another one :? Do you keep flattening the back to move the hollow (but end up with a very thin blade) :?

Frankly I'm baffled. Grateful if someone could explain.........

Cheers :wink:

Paul

 

[Philly]

Paul
I believe the idea is you polish the back as well as the bevel every time you sharpen - this then moves the hollow progressively further back.
Cheers
Philly

 

[Paul Chapman]

Thanks Phil. That's what I guessed - but you'd have to do a lot of polishing :shock: It only takes about one swipe to remove the wire edge when honing a blade but it would take a lot more to move the hollow back.

Seems to me that Japanese woodworkers like to make life difficult..... :lol:

Cheers :wink:

Paul

 

[Karl]

Hi Paul

Below are two pics - the first shows the backs of a 24mm and 18mm paring chisels. The 24mm required work to flatten the back, the 18mm minimal work.

You can see how much the hollows on the 24mm have moved up the back of the chisel.

Below is a side on pic of both blades - the 24mm is on the LHS.

Although the 24mm is thinner (due to the back flattening), it is not substantially so. This is because the hollows are actually quite shallow, so metal removal quickly moves the hollow up the blade.

Hope this makes sense.

Cheers

Karl

 

[Paul Chapman]

Thanks Karl, that makes it very clear. I suppose Japanese tools are an acquired taste - I think I'll stick to the Western style :wink:

Cheers :wink:

Paul

 

[ByronBlack]

The thing that puts me off with these, is the offset when holding them upright, there's always that angle to consider - whereas a western chisel is usually perfectly perpendicular and can be 'trusted'. I don't know if that is the case with all Jap chisels, but I could never get on with mine.

 

[Ironballs]

Glad it wasn't just me that was unclear about this, it does seem a lot of work each time you need to sharpen it

 

[jimi43]

Well I am totally sold on these thing....

I don't even bother picking up my other chisels and they all had the same treatment on the scary board!

The Japanese one I used the entire week on a number of projects on hardwood and it only needed a few swipes to rehone it....it is great!

Jim

 

[Modernist]

Another reason I got rid of mine was that it was difficult to register the back on narrow shoulders because of the hollow. You could easily have the thing rocking making it difficult to pare square which is the last thing you want.

 

[jimi43]

Anyone want to ditch these since they are "so bad"....I will take 'em off yer hands cheap like!

Jim

 

[woodbloke]

Anyone want to ditch these since they are "so bad"....I will take 'em off yer hands cheap like!

Jim

Jim...not If I get to 'em first

The honing is really quite easy because I've now realized that a single bevel needs to be honed on Jap chisels...not a ground bevel and then honed secondary bevel, as on Western chisels.
This is very easy to do by having a good selection of 3M papers (in my case) and simply moving from one grade to the next, finishing with .3micron, which if I understand correctly is around 18,000g. Then the same on the back.
This single bevel sharpening (to produce a dead square edge) would be very, very hard to do accurately without the best honing guide out there :wink:
Fortunately I have one :lol: - Rob

 

[SBJ]

The honing is really quite easy because I've now realized that a single bevel needs to be honed on Jap chisels...not a ground bevel and then honed secondary bevel, as on Western chisels.
This is very easy to do by having a good selection of 3M papers (in my case) and simply moving from one grade to the next, finishing with .3micron, which if I understand correctly is around 18,000g. Then the same on the back.
This single bevel sharpening (to produce a dead square edge) would be very, very hard to do accurately without the best honing guide out there :wink:
Fortunately I have one :lol: - Rob

That's interesting Rob, i've been thinking of getting some Jap' chisels myself.

Why do you think they work better with a single bevel? Is it because it gives you more "meat" behind the cutting edge? Surely its having a larger surface to register on the sharpening medium would make it easier to sharpen? Decent pressure at the tip of the chisel should keep it in place.

 

[woodbloke]

The honing is really quite easy because I've now realized that a single bevel needs to be honed on Jap chisels...not a ground bevel and then honed secondary bevel, as on Western chisels.
This is very easy to do by having a good selection of 3M papers (in my case) and simply moving from one grade to the next, finishing with .3micron, which if I understand correctly is around 18,000g. Then the same on the back.
This single bevel sharpening (to produce a dead square edge) would be very, very hard to do accurately without the best honing guide out there :wink:
Fortunately I have one :lol: - Rob

That's interesting Rob, i've been thinking of getting some Jap' chisels myself.

Why do you think they work better with a single bevel? Is it because it gives you more "meat" behind the cutting edge? Surely its having a larger surface to register on the sharpening medium would make it easier to sharpen? Decent pressure at the tip of the chisel should keep it in place.

I think that's probably it. The steel is brittle (or can be) so if a double bevel is produced (aka Western style) then there's less steel behind it...a single bevel seems to be stronger.
Derek of Oz gave me a good tip for the parers. He recommends that they have a single bevel of 25deg (which I've done) so that they can be used bevel side down (if required) and still register. This also gives a shallower angle for hand work...also the parers should never be struck

I wouldn't like to sharpen one freehand and be confident that the bevel had been maintained. There'd be a danger of it rocking out of true and ending up with a rounded bevel...which would be a bit grim 8-[ - Rob

 

[SBJ]

I wouldn't like to sharpen one freehand and be confident that the bevel had been maintained. There'd be a danger of it rocking out of true and ending up with a rounded bevel...which would be a bit grim 8-[ - Rob

In all honesty, it would be exactly grim!!! Funny how things work out.

 

[jimi43]

Actually...I have come to the conclusion who everyone that says they don't like them is spot on.

I couldn't recommend them to anyone....they are rubbish...

I'll force myself to take them off your hands at decent scrap rates....


:wink:
Why didn't I not just keep my mouth shut...I could have got some serious bargains...now they ALL blinkin' well want one!

Jim

 

[Ironballs]

Don't worry Jimi, I don't want them, I'm still happy enough with my AI dovetails and LNs, they take and hold an edge sharp enough to shave a mastiffs scrotum without getting your head bitten off

 

[dh7892]

I think there is a bit of a misunderstanding about the hollow back on Jap tools.

First a caveat: I'm not an expert so take everything I say with a pinch of salt.

The hollow at the back (it's called an Ura or Urasuki when hollow like this) is NOT ground, it's forged. To understand the reason for it, you need to know that Jap blades are not made out of only steel. They are laminated steel and iron.

The steel is only a very thin section on the back of the blade. The rest is iron. This allows the steel to be hardened more than if it were solid steel because the iron is soft enough to stop the whole thing shattering. It's also a more economical use of the (more expensive) steel.

So, if you've got only a thin layer of steel on the back, repeated flattening of the back will soon remove the vital hard steel needed to form a good edge.

For this reason, the Urasuki is forged into the back. This means that flattening the back only removes material near the cutting edge.

Once you have had the blade a few years, and repeated sharpenings will have erroded the cutting tip back to the Ura, you do NOT just flatten the back by abraiding it. You need to use a pein hammer on the top (bevel) side to push the hollow down thus reforming the Ura and giving you a flatter back. No doubt you will then need to do a bit of flattening on the back but mainly you will need to re-grind the bevel (which should be easier as it's just iron).

I hope this helps.

 

[paulm]

......or, just get yourself some decent AI, LN or BS chisels and just get on with your woodworking :shock: :lol: :lol: :lol:

Cheers, Paul

 

[Paul Chapman]

:lol:

 

[ByronBlack]

......or, just get yourself some decent AI, LN or BS chisels and just get on with your woodworking :shock: :lol: :lol: :lol:

Cheers, Paul

Amen - why go to all that bother? I rarely have to touch the backs of my AI's, and they hold an edge as good as anything I've used.