More about steel grades and edges

[matthewwh]

He's cutting downwards at at least ten degrees.

'Plunging' on a cabinetmakers chisel would be a deviation from a perfectly straight cut of a fraction of a mm over the length of the cut - you wouldn't be able to see it on a video.

Aside from the issue of a convex blade getting progressively more so with each sharpening, how would you pare with it without having the opposite problem of the edge riding up out of the cut?

I appreciate that you are talking about a very mild convexity, similar to the degree of concavity that I and others suggest, I'm just curious about the mechanics of how it would work.

 

[Jacob]

...
Aside from the issue of a convex blade getting progressively more so with each sharpening,

Why? Almost the whole point of the convex bevel as I describe it here is that after every sharpening it ends up exactly the same as the previous sharpening. As you dip the handle you also apply max pressure so that you back off the bevel as you go. Difficult to describe, easy to do.

how would you pare with it without having the opposite problem of the edge riding up out of the cut?

I appreciate that you are talking about a very mild convexity, similar to the degree of concavity that I and others suggest, I'm just curious about the mechanics of how it would work.

Do you mean chisel with convex face (flat side)? If you pare face down you steer the chisel to rise , stay level or plunge, by lifting/lowering the handle. Same as any carver would do with a gouge. Seems basic to me, have I missed something?

 

[matthewwh]

Hi Jacob,

I understand the convex primary, but controlling and maintaining a mildly convex flat side is not something I have tried or even considered trying. I suppose you could ruler trick the bevel and maintain the rest of the flat side as 'normal' (if that expression still has any meaning in this thread).

Surely if you have a flat flat side that jigs the blade against the surface and produces more of the same on areas that the cutting edge has passed over then you are paring. If you are riding the heel of a bevel against the surface and controlling the cut with up and down movements, you are carving. Yes, you can carve a reasonably flat surface but I'm not confident that it would be as accurate as a pared one, and if you wanted to carve it why not just turn the chisel over. Perhaps that is an advantage of the Japanese full flat bevel?

 

[Jacob]

Is there a difference between carving and paring? Paring is just a particular form of carving isn't it?

 

[matthewwh]

Not quite.

With carving you maintain direct control over the direction of the cut at all times, with paring you are perpetuating an existing surface by referencing directly off it. The existing surface is guiding the edge and all you are doing is managing that relationship to ensure that everything goes according to plan.

Hence the preference for a substantially flat surface on the underside of the chisel.

 

[Jacob]

....
Hence the preference for a substantially flat surface on the underside of the chisel.

Well yes but not concave I'da thought

 

[bugbear]

Is there a difference between carving and paring? Paring is just a particular form of carving isn't it?

Well, a "muntin" is a particular form of a "bit of wood". It's specialised and different.

BugBear

 

[matthewwh]

The concavity is too slight to be significant in regard to working tolerances. Our Ashley Iles and Narex chisels are only concave by a couple of thousandths of an inch when new.

A top end professional cabinetmaker will work to a tenth of a mm, so they are technically flat enough for making exhibition grade furniture straight out of the box.

You only really notice it when you come to sharpen them and find that the underside of the cutting edge gets shiny first.

 

[Jacob]

The concavity is too slight to be significant in regard to working tolerances. Our Ashley Iles and Narex chisels are only concave by a couple of thousandths of an inch when new.

So if they were convex by a thou or two this would also be too slight to be significant in regard to working tolerances?
Marginally better than concave though - would there not come a point with concavity where a chisel would become difficult to use?

A top end professional cabinetmaker will work to a tenth of a mm, ....

Really? Who says? I don't believe it.
They are a bit mythical these 'top end professional cabinet makers' and not necessarily very interesting IMHO.
There's a lot more to woodwork than 'top end professional cabinet makers' thank god!

You only really notice it when you come to sharpen them and find that the underside of the cutting edge gets shiny first.

Then if it's convex you use the 'without a ruler' trick to achieve the same thing.

PS and what is exhibition grade furniture? We have all seen appalling crapp at exhibitions (amongst other things of course).

 

[matthewwh]

If the chisel were convex by a thou or two then that wouldn't make much difference to the cutting performance either, it might cause it to ride up through it's own shaving on longer cuts, which would be irritating, but certainly for chopping work it wouldn't be an issue. The real difficulty would be how to maintain that very small amount of convexity without increasing it.

With a slight concavity you can produce many sharp edges with considerable ease before you need to reinstate it. The bit that touches the abrasive is the bit that needs polishing and it gradually gets closer and closer to flat each time you hone the chisel.

With a convexity, you could lift the handle to achieve contact at the edge but that would gradually and progressively increase the convexity - moving it further away from flat each time.

Alternatively you could remove material over the entire flat side of the blade (lots of work so far without touching the edge at all) and then reinstate the convexity by lifting the handle to polish the edge.

So it either progressively ruins your tools or generates lots of unnecessary work, or both - and I'm still struggling to find any potential advantages at all.

I'll let the mythical 'cabinetmakers' know that you now believe they are imaginary - I'm sure it will come as a great relief.

 

[Jacob]

How many angels on the point of a needle?
Basically a chisel, whether convex or concave by a few thou here and there, can be made to cut perfectly well. You will even find a way with a severely bent chisel (if that's all you have). Progressive sharpenings can make things worse - but only if you let them! It's entirely up to you.

 

[matthewwh]

Going back to the original point, Brian is quite correct that edge retention is significantly influenced by the honing angle. The grinding angle could, within reason, be lower or higher and it wouldn't make a lick of difference. A low grinding angle can help to reduce penetrative resistance, which I believe is what Rob Cosman is after with his very shallow ground chisels. It looks from the photo as though the edge has failed by very slight chipping and a little bit of bending - this means that LV have got the heat treatment absolutely perfect. Too soft and it bends, too hard and it will chip, but if you've got a little bit of each under extreme workload then they have struck the balance point between the two precisely.

It is also worth noting that going steeper still with the honed angle significantly increases edge longevity, albeit at the expense of a little bit of sharpness. I remember reading a metallurgical analysis that said that the wear resistance of A2 is only 6 percent higher than O1, I only wish I could find the source again. This would suggest that most of the perceived longevity of A2 blades actually comes from honing them at 35 rather than 30, so Brian's observation of how much difference there is between honed angles of 27 and 30 is only part of the story.

 

[Jacob]

Right. Yawn.
Done any woodwork lately? Come to think - does R Cosman make things? I often wonder abt our gurus and priests - they talk the talk but what do they actually make? DC - WIP?

PS IMHO these meandering conversations about bevels, flatness and hardness never really come to much of a conclusion as in reality there isn't that much difference in use between the various extremes, as long as the thing is well made and the metal hasn't been softened by over heating etc.
Even then it's not the end of the world, convex, concave, flat you just adjust your technique as necessary.
I guess the biggest difference is malleability. A hard steel is more likely to chip and paradoxically make hard work more difficult, and vice versa. A malleable edge is going to get reshaped in use but will be easier to sharpen.

 

[jimi43]

Going back to the original point, Brian is quite correct that edge retention is significantly influenced by the honing angle. The grinding angle could, within reason, be lower or higher and it wouldn't make a lick of difference. A low grinding angle can help to reduce penetrative resistance, which I believe is what Rob Cosman is after with his very shallow ground chisels. It looks from the photo as though the edge has failed by very slight chipping and a little bit of bending - this means that LV have got the heat treatment absolutely perfect. Too soft and it bends, too hard and it will chip, but if you've got a little bit of each under extreme workload then they have struck the balance point between the two precisely.

It is also worth noting that going steeper still with the honed angle significantly increases edge longevity, albeit at the expense of a little bit of sharpness. I remember reading a metallurgical analysis that said that the wear resistance of A2 is only 6 percent higher than O1, I only wish I could find the source again. This would suggest that most of the perceived longevity of A2 blades actually comes from honing them at 35 rather than 30, so Brian's observation of how much difference there is between honed angles of 27 and 30 is only part of the story.

I believe the test results which showed that A2 was not that much superior to 01 was part of the new PM-V11 data:

Veritas Test Results Here

Of interest is the ease of sharpening table...which shows that A2 is almost twice as hard to sharpen vs 01...which kind of negates the tiny bit of extra wear resistance.

Whilst I realise that they are trying to promote PM-V11 as others have tried to promote A2 in the past....even if these results are a bit out it puts the new steel in that ideal category...easy to sharpen and twice as hard wearing.

Or did I interpret the results wrongly?

Jim