removing a back bevel

[Corneel]

No, it's just randomly picked from the internet. The right hand shows how the metal on the edge deforms in front of a sharp tool. A grinding stone is in fact just a lot of very small edge tools.

I still don't know what happens exactly when a burr forms. And a bit of googling around didn't really give me an answer either. All research in this direction has been done with rotating grinding stones anyway, not with flat stones. Not that it really matters, just curiosity.

 

[Jacob]

No, it's just randomly picked from the internet. The right hand shows how the metal on the edge deforms in front of a sharp tool. A grinding stone is in fact just a lot of very small edge tools.

I still don't know what happens exactly when a burr forms. And a bit of googling around didn't really give me an answer either. All research in this direction has been done with rotating grinding stones anyway, not with flat stones. Not that it really matters, just curiosity.

But with normal sharpening the edge would be to the left. I can see that if you reversed the process and ground away from yourself and the tool handle, you would move metal and possibly form a burr at the edge, but that's not what we do (most of the time anyway).

 

[woodbrains]

Hello,

The grains of metal at the sharp end are supported by progressively thicker, layer upon layer of more metal grains. The ones that are not abraded away have to move somewhere and it cannot be backwards into the rest of the steel, so has to be forwards and upwards; it is simply the only way it can go. The energy from the system has to be dissipated somewhere, it will not go away. The deformation of the metal moves along the path of least resistance. Particles unsupported at the front can and do move forwards. Think of cuing a snooker ball into a tightly formed pack; many of the balls will shoot forwards.

Also, it is commonly asserted that sharpening with, and especially fine oilstones, steel is abraded and consolidated. Consolidate suggesting moving steel around to fill in voids in the grain structure. Metal will move, and in all directions.

Mike.

 

[Jacob]

Hello,

The grains of metal at the sharp end are supported by progressively thicker, layer upon layer of more metal grains. The ones that are not abraded away have to move somewhere and it cannot be backwards into the rest of the steel, so has to be forwards and upwards; it is simply the only way it can go. .....

That's close to what I was saying in the first place, which was that the metal not abraded away stays in place and/or bends upwards to form a burr. No metal is added on to the edge, it is simply not all removed.
Though I can see it might be added if you were grinding towards the edge rather than the heel.

 

[woodbrains]

Hello,

If it stayed where it was, it would not form a burr, would it? There would just be scratches on the surface and the mean height of the surface would remain the same. Subsequent passes on the stone might eventually abrade away these high points, but this does not explain how a burr forms. This is likely the main part of the story with a brittle material like chalk, say, but steel is ductile. Corneel's diagram with a plastic phase, is an understandable explanation. I don't understand the opposition to the displacement of steel. Burrs form, this is undeniable and they tend to be larger than you would expect from the removal of such tiny amounts of steel.

Mike.

 

[Corneel]

In a scientific article (google for "burr formation grinding") where they study surfface grinding, I read that the burr is mostly formed by plastic deformation. The metal is pushed ahead in front of the tool (grit particle) in a plastic deformation zone. At the edge the deformation zone isn't supported anymore and the metal is pushed "over the edge". A bit like the right hand part of the picture above.

I can't read the entire article at home, but tomorow at work I'll be able to read all of it.

Mike, where did you get the knowledge about fine abreassives? Do they do something different from coarser abrassives? And about what size are you thinking?

BTW, when sharpening I put most pressure on the backstroke, allthough my 1000 grit waterstone is quite hard. The 8000 is much softer and would easilly dig in the edge when i put a lot of pressure on the forward stroke. The picture above is about an "exit burr". An entry burr is also being described, but they are usually much smaller.

 

[Corneel]

I think Mike and Jacob are in agreement! Just another way to describe the same process.

 

[Jacob]

Hello,

If it stayed where it was, it would not form a burr, would it? ....
..

It stays in place as a thin bendy little filament, which may curl up or spring back. "Wire edges" are not round they are flat and thin. Many variations of course.

You can simulate the process by sanding off a bevel on the end of a piece of timber at say 30º, on a belt sander. When you get close to completing the bevel up to the top surface it may well spring up slightly and form a bit of a nib which doesn't get sanded off but instead rides up the face of the sander. Depends on the material and the sander.

 

[Corneel]

You mean like in the pictures at the end of this article? Very nice thin wiry burrs, some are curling others are quite straight and the extend quite a bit beyond the egde of the metal.

http://www.wpi.edu/Pubs/E-project/Available/E-project-050908-095350/unrestricted/CAD1106.pdf


These are on a square block of 440C toolsteel. So it is not so much the fine curring edge that is the culprit, it happens on a square edge just the same.

EDIT: But that looks like it not JUST plastic deformation of the edge, but also swarf which was grinded and pushed beyond the edge.

 

[woodbrains]

I think Mike and Jacob are in agreement! Just another way to describe the same process.

Hello,

Don't quite see how you come to that conclusion, I'm saying the steel will move to form a burr, as I think your diagram shows. Jacob does not think this is the case.

Anyway, years ago I bought a Welsh mica slate polishing stone. There was in the literature info on honing with the stone and there was reference to steel consolidation. I seem to have read similar about Translucent and Black Arkansas stones also. Over the years of using these, I have noticed that there seems to be a finer edge attainable than the grit size of the abrasive should logically allow. This must be due to steel consolidation. It is a phenomenon that I have not observed with Japanese waterstones. I would contend that friable abrasives 'cut' to a fine edge and non-friable ones consolidate to a fine edge. There is an amount of both going on, of course, but coarser oilstones abrade more and have little if any consolidation taking place, the finer the oil stones the more significant the consolidation becomes. There are references in books, to taking longer on the finest oil stone being a good thing. I interpret this as to allow the movement of metal to take place.

I wanted to put this forward on a post a long while ago, but obviously sharpening threads get sidetracked, and I didn't want to waste my time getting lots of abuse. My conclusion to my experiments would be a question, since I cannot be certain without fancy test equipment, to a pool of knowledge such as here to find some sort of consensus. I hold faint hope for this, but here goes: 'do edges formed from consolidated sharpening such as I have observed with FINE oilstones last longer than finely abraded ones, due to micro work hardening of the edge?

To have any hope of finding an answer, there needs to be Input from woodworkers who actively use both methods and have the objectivity to tell if there is any difference to edges made in these ways. Reliable, measurable consistency will be needed, if any conclusions can be made.

Mike.

 

[Corneel]

Would you strop after the fine oilstone? How do you remove any remnants of the burr?

Oilstones seem to have carser grit then the manmade ones, but the shape of the grit is quite different. It is not so much the grit itself that does the grinding, but its sharp corners. In manmade stones, AlOx for example, these edges are larger and more agressive. A Belgium hone has a quite large grain size, but these grains are very round, so they don't act like large ones. Grit with very sharp edges can really cut the steel, while the rounder ones are more or less plowing through the steel. All this makes oilstones acting finer then their gritsize suggests, especiallywhen they wear in and the grit particels get rounded over more and more.

Is this plowing effect in the steel what you mean with consolidated sharpening?

 

[woodbrains]

Is this plowing effect in the steel what you mean with consolidated sharpening?

Hello,

Yes, I think we are talking about the same thing. However, I do maintain that the oil stones need to be fine (as they can be for oilstones) as abrasive particles that are too large will leave big sctatches, just with rounded bottoms, if you pardon the expression. At some point, the particles will be fine enough to make fine enough scratches that the roundness of the abrasives will then fill in the ploughed furrows, if you like, with steel in its plastic state. There is only so far the plastic state can be moved, so over a certain grit size, this will not happen and the abrasion is more significant than the consolidation.

Mike.

 

[Corneel]

I think I understand what you mean. A plowing particle will create walls of steel ahead of the particel and to the sides. If the particle is small enough these sidewalls could fill in the groove, behind the particle, they just spring back. At least, that would be a hypothesis. Pretty difficult to prove without a scanning electron microscope.

Regaring your idea about a test, it's worthwhile to experiment a bit. But I am not sure yet how you would measure wear. If there is a difference at all between fine manmade and fine oilstones, the difference will be small, I guess. And which ones do you compare? Black Arkansas against which grit of waterstone?

 

[woodbrains]

Hello,

I don't think we need be too specific, just a subjective test, from a lot of people would show some sort of consensus. I think hard Arky is about 9 micron and 8000 Japanese stone is about 1.2. But is my contention (yours too, I guess) that the consolidation of the oilstone gives an apparent level of finer sharpening, then I think comparing the two would be fair enough. I do not know what my slate is particle size wise, but. Think it is comparable to fine Arkansas. Stropping after the oilstones would have to be a separate sub test. I think off the stones is a good start, to give a feel as to if there is a greater longevity to edges, or not, attained by oilstone consolidation. If there is, it is likely to be due to micro work hardening, I could not think what else it could be, but I'm open to suggestions.

Obviously the test would need to be done with the same brand if tools, too.

Mike.

 

[Cheshirechappie]

Couple of things.

Firstly, an observation. A few months ago I bought a 'Dragon's Tongue' hone fron Inigo Jones - a Welsh mica slate stone. It's given me the finest edges I've ever been able to produce; better than a stropped edge. The technique I used was to hone on a fine Norton India until I had a good wire edge, then move to the slate (lubricated with the same oil as the India) and using a very slightly higher honing angle than on the India stone, draw the edge back along the stone five or six times. Then turn over, back off by drawing the tool backwards once, then turn over again and draw the edge back again once, then the flat face once, then the bevel once and repeat about six times in all. That's it. I can't explain the theory, but by heck the edge is keen after that.

Second, a bit of engineering theory, which might inform the debate. Most metals behave like elastic up to a point (the yield point) and plastically beyond it to the point where the metal breaks - 'fails catastrophically' - at it's ultimate point. In the case of hardened tool steels, the elastic range is large compared to the plastic, but there is still a plastic range. That range will be greater the more the steel is tempered back from full hardness, though will not be anywhere near the range of the same steel in it's annealed (soft) condition.

So in sharpening a tool using an abrasive (which is effectively lots of little very hard cutting tools) some plastic deformation of the steel will take place between abrasive and abraded surface. The exact nature of that deformation will in all probability vary greatly depending on the particular conditions.

 

[Trafalgar]

At some microscopic level I'm sure that even the type of stone lubricant matters. That's a bridge a bit too far for me. I do know what a burr looks like when peeled off and laid onto a stone as a whole. It doesn't happen often but when it does it looks more like Jacob's description than anybody else's.

I do know that the resulting edge is very sharp (by use, not microscopic examination) as long as one doesn't strop too much or too heavily and ruin it. Two or three strokes down the strop is enough in this instance.

 

[Vann]

Anyway, years ago I bought a Welsh mica slate polishing stone. There was in the literature info on honing with the stone and there was reference to steel consolidation. I seem to have read similar about Translucent and Black Arkansas stones also. Over the years of using these, I have noticed that there seems to be a finer edge attainable than the grit size of the abrasive should logically allow. This must be due to steel consolidation. It is a phenomenon that I have not observed with Japanese waterstones. I would contend that friable abrasives 'cut' to a fine edge and non-friable ones consolidate to a fine edge. There is an amount of both going on, of course, but coarser oilstones abrade more and have little if any consolidation taking place, the finer the oil stones the more significant the consolidation becomes. There are references in books, to taking longer on the finest oil stone being a good thing. I interpret this as to allow the movement of metal to take place.

I interpret what you've written as suggesting a burnished finish. Very interesting.

So a consolidated (burnished) finish from a slower cutting stone would give a better wearing edge than the raw abraded edge from a faster cutting waterstone. That would give a whole new outlook to fine sharpening :idea:

So finally, after ploughing through 8 pages of bickering (I was about to give up on the thread - only visited for the entertainment (hammer) ), I've learnt something new. Thanks.

Cheers, Vann.

 

[woodbrains]

So a consolidated (burnished) finish from a slower cutting stone would give a better wearing edge than the raw abraded edge from a faster cutting waterstone. That would give a whole new outlook to fine sharpening :idea:

Cheers, Vann.

Hello,

The better wearing edge is only a feeling I've got, but not a theoretical one entirely. Over more than 30 years of sharpening, I have a notion that there is some sort of longer lasting edge from a consolidated sharpening than a purely abraded one. It is just that there are so many variables from blade to blade and in working characteristics from wood etc. etc. that I think it has yet to be conclusively proved. Could even one woodworkers lifetime be a big enough survey to prove a point, unless one goes down the route of making the test the sole objective. I want to work wood not test steel exclusively, which is why other perspectives might show a trend.

The dragons tongue stones, I suspect, are the same as the one I have used for many years. They are very good indeed. They give a keen edge, quicker than translucent Arkansas and without the rapid wear of the Japanese waterstone. It is a happy medium of speed and low maintenance and I think gives a really long lasting edge.

Mike.

 

[bugbear]

I seem to have read similar about Translucent and Black Arkansas stones also. Over the years of using these, I have noticed that there seems to be a finer edge attainable than the grit size of the abrasive should logically allow. This must be due to steel consolidation. It is a phenomenon that I have not observed with Japanese waterstones. I would contend that friable abrasives 'cut' to a fine edge and non-friable ones consolidate to a fine edge.

It would (surely?) require a very careful and subtle experiment to tell the difference between a fine abrasive making a smooth surface and a fine compound(?) consolidating a surface into smoothness, especially since the resulting shiny surfaces are difficult
to micrograph without very special lighting or a SEM.

It is common experience that finer abrasives make smoother surfaces (no **** Sherlock!). To prove that a fine abrasive is making a smoother surface than expected from the grit size would require a quantitative experiment, which sounds (and I use a technical term) "tricky". It is well known that while grit size is the most important factor in edge generation, many other factors have an effect (particle shape, bonding, lubricant etc)

BugBear

 

[bugbear]

So a consolidated (burnished) finish from a slower cutting stone would give a better wearing edge than the raw abraded edge from a faster cutting waterstone. That would give a whole new outlook to fine sharpening :idea:

It's interestingly analagous to what chefs and butchers (in Europe) do with a coarse sharpening stone and a smooth(*) steel.

BugBear

(*) a proper steel is NOT a file. Don't be fooled by some of the crud offered in the cookware section of your local department store