Chisel sharpening

[Jacob]

So why are Japanese chisels deliberately very concave?

Makes them very easy to sharpen. The edges of the chisel are 'co-planar' or flat, but the middle is hollow. I don't know much about them but I believe that when the hollow gets sharpened away it's put back in with a few hammer blows from a blacksmith. Something I read - could be wrong!
English chisels similarly are often (always?) slight concave for the same reason. See OP's first photo for a very typical example.* Hence a new chisel is very easy to sharpen but gets progressively less easy as it gets honed convex ('bellied' as the toolies say. :lol: )

PS* I've no idea if this is deliberate or not but it's something I've often noticed - I did a thread a few years back when I first noticed it on a new Marples chisel.

 

[Wend]

Just to respond to a few things that a number of people mentioned:

This is one of a set of 3 cheap chisels I've had since I was a teenager, and while they haven't been used much, most of their use has been DIY abuse, so they all have bits missing from their corners. I don't have a grinder, nor the ambition or space to own one, but I don't think the missing corners are affecting what I'm currently using them for, nor my learning how to sharpen them, so I haven't worried about it. By the time I care, perhaps I will have eroded them down to a better shape, or perhaps I will just invest in a better chisel or two.

When I said "work on the back", I didn't mean "flatten it" - I've mostly been working off of a couple of Paul Sellers videos, where he starts off by making the bit of the back near the tip flat, but leaves the rest concave. That said, it does look like I've ended up flattening it. In the first photo I think it's actually convex: Before that photo I'd done some vertical then horizontal movement on the coarse stone, and the horizontal hadn't reached the tip. In fact, I suppose the vertical movement would make it convex, as the metal near the tip is in contact with the stone for longer. I shall make sure to only use horizontal movement in the future!

Finally, as for paper cutting, it seems to me that this is a simple test that I can do, to give me an indication of how well I'm sharpening. I'm sure that once I get some experience I'll be able to tell from the way it goes through wood, the sort of shavings I can make with it, etc, but right now I don't know how to interpret those results. Whether or not it cuts paper cleanly is at least something I reckon I can objectively measure.

Oh, and I don't have to worry about having paper around to test with. A number of companies send me some updating me on things like the availability of cabal TV in my street, and local furniture sales, on at least a weekly basis :wink:

 

[Phil Pascoe]

... Severely concave could be a prob but you could probably get away with it the other way up, even with a rounded bevel. Anything from flat to convex would be fine...

So why are Japanese chisels deliberately very concave?

Makes them very easy to sharpen.

:? :? :?

 

[D_W]

Japanese chisels are a little bit different in this case - if they're full hardness, you wouldn't be able to flatten the back with traditional stones.

Historically, they would've been maintained with natural stones, which are notoriously bad at working a polished flat surface (they don't have enough cutting power to dig in on a wide hard flat surface, and are better at knocking down ridges left by a coarser abrasive).

There have been japanese carpenters relatively recently who still believe that using a synthetic stone on a good japanese chisel is a recipe for permanent damage to the chisel (a user on another forum relayed that to me - potentially could've been an interaction that he had with said carpenter 20 years ago, but that's relatively recently in the world of hand tooling).

 

[Jacob]

... Severely concave could be a prob but you could probably get away with it the other way up, even with a rounded bevel. Anything from flat to convex would be fine...

So why are Japanese chisels deliberately very concave?

Makes them very easy to sharpen.

:? :? :?

I meant curly chisels, not just hollowed out like the Japanese ones, which are effectively flat in use.

 

[Jacob]

Do you need the back of the chisel to be perfectly flat?

Well, it'll help if at least a couple of your chisels are in that shape. The reason is that you'll often reference from the back of a chisel, and that's true even in simple DIY jobs. Take for example if you've used some iron-on edging on a piece of laminated chip board, or if you've got a protruding dowel or peg that you want to cut down flush. Neither of these tasks are exactly Guild Mark level cabinetry, but you'll perform them both better with a flat backed chisel....

It'd have to be a very strange chisel for the shape to cause a problem trimming a dowel, and no 'normal' chisel (like the OP's) would need specially flattening!
Severely concave could be a prob but you could probably get away with it the other way up, even with a rounded bevel. Anything from flat to convex would be fine, as long as sharp.

PS I forgot to say - the ideal tool for trimming Custard's dowels is the block plane. This is more or less its principle function. It's what it's for. It's what I've used one for from day one, and also for arrisses and general fettling.
Trimming a dowel with a chisel is possible of course, but difficult done face down as they tend to dip and dig in, however flat they are. Easier done bevel down - or with one of those notoriously "bellied" chisels face down but with more control. Bevel down easier with a slightly rounded bevel - it gives more control, flat bevel would be problematic.
It's all a bit of a myth much of this flat stuff! Interesting though - and the "meme" process by which these myths come about.

 

[nabs]

another anti-flattener here (discovered while wading through the length 'blue spruce chisel flattening' thread):

https://logancabinetshoppe.wordpress.co ... p-lapping/

He argues that rather than going to the bother of removing high points/pitting etc from a big area of the face, using (the obviously quicker) method of flattening a small 'back-bevel' (by lifting the chisel as mentioned earlier) does no harm to the tool's use in practice (and in any case replicates the long term effect of using a dished stone, which would have been true for many tradesmen of old).

you can see the end result here:

personally I would still have flattened the first inch or so to remove the pitting, but that's just how I roll, man.

I admit I stopped reading when it got to the chisel geometry bit, but he has clearly given it a bit of thought! Anti-flatteners should note that this article contains the term 'belly'

 

[Jacob]

another anti-flattener here (discovered while wading through the length 'blue spruce chisel flattening' thread):

https://logancabinetshoppe.wordpress.co ... p-lapping/

He argues that rather than going to the bother of removing high points/pitting etc from a big area of the face, using (the obviously quicker) method of flattening a small 'back-bevel' (by lifting the chisel as mentioned earlier) does no harm to the tool's use in practice (and in any case replicates the long term effect of using a dished stone, which would have been true for many tradesmen of old).

you can see the end result here:

personally I would still have flattened the first inch or so to remove the pitting, but that's just how I roll, man.

I admit I stopped reading when it got to the chisel geometry bit, but he has clearly given it a bit of thought! Anti-flatteners should note that this article contains the term 'belly'

In fact all chisels and plane blades are going to be a tiny bit like this otherwise it would be impossible to remove the burr without flattening the whole face every time. No doubt some have attempted this - nothing worse than having a great fat bellied chisel! :lol: :lol:
Dished stones don't come into it - it's the same problem with a flat one.

One of the worst flattening myth makers is at it here
He burbles on about imaginary problems and comes up with pointless solutions. At no point does he explain or demonstrate why he needs this perfect flat face, it just so looks a good idea! I wouldn't buy a second hand car from him!

 

[bugbear]

In fact all chisels and plane blades are going to be a tiny bit like this otherwise it would be impossible to remove the burr without flattening the whole face every time.

Simply not true.

The burr (to be a burr) must project beyond both the bevel plane and the back plane.Therefore it can be removed without any lifting being required.

If the burr is flexible and/or the pressure is too high, it may bend out of the way, but the (traditional ) switching between bevel and back will address this. Lifting is not required, one might even say wrong.

BugBear

 

[Jacob]

In fact all chisels and plane blades are going to be a tiny bit like this otherwise it would be impossible to remove the burr without flattening the whole face every time.

Simply not true.

The burr (to be a burr) must project beyond both the bevel plane and the back plane.Therefore it can be removed without any lifting being required.

If the burr is flexible and/or the pressure is too high, it may bend out of the way, but the (traditional ) switching between bevel and back will address this. Lifting is not required, one might even say wrong.

BugBear

If you use a chisel much at all you get wear on the face as well as the bevel. It soon becomes difficult to remove the burr face down on a flat stone unless you remove the wear, either by flattening the whole face, or, as done most commonly, by slightly lifting the handle; usually imperceptibly - you are merely putting slightly more pressure towards the edge and effectively adding very slight bevel to the face. Same but even more so with a plane blade
If you look at nabs's picture above you can see the problem - a burr on that edge would not be removed by the flat on flat stone process - you'd have to lift it to match the bevel.

The only advantage of the tedious flattening process is it stops you having to think about it! :lol:

 

[bugbear]

If you use a chisel much at all you get wear on the face as well as the bevel.<much else would logically follow>

I agree with the reasoning, but not the Axiom. Simply not my experience, and I can't really see a mechanism for causing it (other than lifting to remove burrs, which is a circular argument).

Anyone else?

BugBear

 

[Beau]

Never understood how you can pare properly with a bellied chisel. Love to see a demo Jacob

Flat back all the way here. Never had problems keeping it that way during subsequent sharpening on some water stones which occasionally get dressed flat. Plenty of good advise already been given on how to sort the back. If mine are really bad I grind the back on a horizontal wetstone grinder to get the worst off. Then get it true with a DMT 1000 grit diamond stone and polish it up on a flat water stone to 6000 grits but the 1200 is quite good enough for most work IME.

 

[Jacob]

Never understood how you can pare properly with a bellied chisel. Love to see a demo Jacob

Flat back all the way here. Never had problems keeping it that way during subsequent sharpening on some water stones which occasionally get dressed flat. Plenty of good advise already been given on how to sort the back. If mine are really bad I grind the back on a horizontal wetstone grinder to get the worst off. Then get it true with a DMT 1000 grit diamond stone and polish it up on a flat water stone to 6000 grits but the 1200 is quite good enough for most work IME.

You must get through a few chisels with all that grinding! I've never flattened any of mine and I've no idea why you think paring should be a problem.
As a matter of interest - what do you mean by 'paring' and when do you yourself do it?
NB I know what I mean by paring - it's equivalent to using a chisel in place of a plane, typically across the grain in housings or shoulders, less typically along the grain e.g. easing the edge of a door where a plane can't reach etc - long paring chisels particularly handy there (that's what they are designed for), but usually any old chisel will do, bevel up or down, bellied even!

 

[Trafalgar]

Never understood how you can pare properly with a bellied chisel. Love to see a demo Jacob

Flat back all the way here. Never had problems keeping it that way during subsequent sharpening on some water stones which occasionally get dressed flat. Plenty of good advise already been given on how to sort the back. If mine are really bad I grind the back on a horizontal wetstone grinder to get the worst off. Then get it true with a DMT 1000 grit diamond stone and polish it up on a flat water stone to 6000 grits but the 1200 is quite good enough for most work IME.

Carvers pare all the time with No. 1 sweep chisels almost invariably set up and maintained with a bevel on both sides. A chisel so arranged won't 'dive' into the work, move lines back, etc., etc.

That said, I have bench chisels with flat backs, but in truth aren't nearly the equal of a carving chisel or two I own when doing fine paring. And I am in no way an accomplished carver.

The notion that you must have a flat back in order to pare to an incised line is vastly a overstated one as well. Took me some time to figure this out.

 

[Ttrees]

At what point do you back lifters say, that's enough of a back bevel ...
Do you grind it off ?

Paring long grain, flat/back side down , do any of you find there is a difference in angle
to get the chisel to engage into the wood ?
I find with my flat backed chisels, I still have to raise the chisel to about 10 degrees(ish).
I wonder if there would be any difference if it was back beveled.

I'm surprised that no-one has mentioned double bevel sharpening..like Brian Burns (hammer)
Kind of hinting with the carver talk, at the one useful thing I've read about a back beveled chisel ...
(a fairly well honed back bevel)
That it can be used to scoop timber like guitar braces instead of getting a curved paring chisel.

Not had the chance to do it to a chisel yet
Tom

 

[Beau]

Never understood how you can pare properly with a bellied chisel. Love to see a demo Jacob

Flat back all the way here. Never had problems keeping it that way during subsequent sharpening on some water stones which occasionally get dressed flat. Plenty of good advise already been given on how to sort the back. If mine are really bad I grind the back on a horizontal wetstone grinder to get the worst off. Then get it true with a DMT 1000 grit diamond stone and polish it up on a flat water stone to 6000 grits but the 1200 is quite good enough for most work IME.

You must get through a few chisels with all that grinding! I've never flattened any of mine and I've no idea why you think paring should be a problem.
As a matter of interest - what do you mean by 'paring' and when do you yourself do it?
NB I know what I mean by paring - it's equivalent to using a chisel in place of a plane, typically across the grain in housings or shoulders, less typically along the grain e.g. easing the edge of a door where a plane can't reach etc - long paring chisels particularly handy there (that's what they are designed for), but usually any old chisel will do, bevel up or down, bellied even!

I see my spelling is out as usual I am talking about pairing. Had a quick search on youtube and this best explains best why I would look to have flat backed chisels https://www.youtube.com/watch?v=LM-uQZUyraE Trying to do work like this with a chisel with a belly I would have thought would be near impossible. I would pair like this ie just taking small bites per cut on many hardwoods on jobs like mortise and tenons. As for grinding the backs that is a once only deal to get the worst bumps and lumps off and careful polishing off the burr in sharpening is all that the backs see after the initial set up.

I should add in the video the chisel is clearly a bit blunt I would not generally use a jig as a guide but once I had established a land at the height required would use this finished area as the guide for subsequent cuts

 

[ED65]

I think one thing that needs to be stressed here is that how you prep a chisel is partly down to how you use it. This might have been addressed already and it got lost in the noise; there is a high noise-to-signal ratio in this thread which unfortunately started on page one.

Some chisels, in the hands of some users, it won't be a problem if they have even a fairly significant dubbing of the back, what amounts to a back bevel but not deliberately created, an artefact of honing technique. But those same chisels in the hands of another user who works with his chisels differently that will be a big problem indeed.

So it brings us back to the thing that has to be said out loud far too frequently: horses for courses. There's no one way that a chisel must be prepared and works best. It's entirely down to the individual.

 

[Beau]

Paring long grain, flat/back side down , do any of you find there is a difference in angle
to get the chisel to engage into the wood ?
I find with my flat backed chisels, I still have to raise the chisel to about 10 degrees(ish).
I wonder if there would be any difference if it was back beveled.


Tom

If it's sharp and the back is flat it should not need raising at all IME. As per the video in my previous post.

 

[Ttrees]

I must confess that I probably don't get the chisels as sharp as my plane irons
My most used one for this job is a new Chinese 2", 2 quid chisel.
It can't get as sharp as my plane irons and I do them by hand instead of in a honing guide like my
plane irons.
I still think I will have to lift a chisel in this instance, to engage it into the wood.
Even with my better Stanley chisels honed with the help of a guide .

I will have to show you guys what I mean, I'm not gonna test this out with a back bevel though
so its probably not so interesting.
Maybe I'll get a tip from you guys
Tom

 

[Jacob]

At what point do you back lifters say, that's enough of a back bevel ...
Do you grind it off ?

Never give it a thought. Sharpen to get a burr, turn over and take the burr off as necessary.There may or may not be a trace of a back bevel. Not bothered either way!

....
I'm surprised that no-one has mentioned double bevel sharpening..l....

One thing at a time!

Re paring video. Personally I'd saw off dowels, tenon ends etc with tenon saw, and finish with a block plane. If plane not available then any old sharp chisel would do instead. No magic flat tools required here! In fact you could what he's doing with a sharp knife if you were stuck. Or a sharp anything.
NB 'flush cutting saw' is another fairly unnecessary gadget though I have used one for sawing down through tenons when trying to dismantle stuff with as little damage as possible.