removing a back bevel

[DannyEssex]

So ... Danny, how are your chisels coming on?

I got lost by page 7 :| I am going to get a bench grinder and do as suggested. Im in no rush though

 

[Corneel]

That's a pitty, it just started to become interesting after page 7!

 

[bugbear]

Just thinking out loud, as it were.

I wonder if the particle shape of the abrasive has a significant effect?

Yes - particle shape is probably second in importance to particle size.

What's surprising is how non-edged the particles are, and yet how effectively the cutting action
is. Counter-intuitive, which is always interesting.

BugBear

 

[woodbrains]

Just thinking out loud, as it were.

I wonder if the particle shape of the abrasive has a significant effect?

A stone made up of hard, sharp-edged particles would tend to act mostly as a cutting tool, shearing metal off the sharpened surface, leaving gullies and peaks on the abraded surface. A stone made of hard, rounded particles wouldn't cut so much, it would burnish a sharpened surface by smearing metal (plastic deformation) - perhaps tending to compress the high points left by the previous stone into the gullies it leaves as well.

So, whilst the abrasive particles of the two stones may be of similar size, the two stones would behave very differently in sharpening, and give different edge qualities. One rather cut and ragged, the other more burnished or polished.

Hello,

This is part of what I've been driving at; the fact that some stones sharpen finer than their particle size would suggest. Cal it burnishing, consolidation or whatever, there is obviously a movement of the steel and a smoothing element in the sharpening with such stones.

I have thought about it some more, and my idea of this causing work hardening might not be the only explanation as to why there might be a better edge retention to the tool. There might be some sort of healing effect. I have said in previous posts, and bugbear on this thread has highlighted an article which says the same; but micro fractures at the sharp end is the cause for the edge dulling in use. Essentially these fractures are stress raisers, which allow the steel to further break down in use. The reason finer stones give a longer lasting edge is due to the fact that these fractures are smaller than ones produced by the less fine stone. (After a little use of the tool, the sharper one will get to the same level of less-keenness as the one which was slightly less sharp to begin with, but the finer fractures on the first will keep it lasting longer from this point onwards)

Now what if the stone with rounded abrasive, giving the consolidation effect, actually moves the steel to fill in some of these fractures, essentially healing the stress raisers somewhat, and this is what imparts the longevity. Consolidation is the perfect word for the effect, if this is the case.

Mike.

 

[Corneel]

I'm not so sure about the fractures being the major cause for edge dulling. As far as I can see, a worn edge is very rounded. When you get nicks in the edge, you should enlarge the sharpening angle. A well wearing toolsteel in a handplane with a large enough sharpening angle shows very rounded shapes after using it a lot. In my opinion, abrasion is the main cause of edge dulling.

 

[Cheshirechappie]

Danny started the thread to ask a perfectly sensible question, which received some perfectly sensible and satisfactory answers. The conversation then morphed into a 'my method of sharpening is better than yours and you're an idiot for not doing it my way' phase (which didn't interest me) and then further morphed into a 'we know it works, but why and how does it work?' phase which is rather more interesting.

Mankind has evolved his knowledge fast since the stone age. Part of the reason for this, particularly in the last couple of centuries, is that some people were prepared to ask 'why'. Through that questioning and investigation, they often found better ways of doing it. If everybody had been content to just accept what works with no care as to why, we'd still be in the stone age.

I fully accept that some people have a way of honing edge tools that works for them to their satisfaction, and they really don't particularly care why or how it works. Fine - don't bother reading this thread, then. But I'm quite interested in why it works, and how. I think it's a legitimate subject for discussion, even if we don't answer all the questions.

 

[woodbrains]

I'm not so sure about the fractures being the major cause for edge dulling. As far as I can see, a worn edge is very rounded. When you get nicks in the edge, you should enlarge the sharpening angle. A well wearing toolsteel in a handplane with a large enough sharpening angle shows very rounded shapes after using it a lot. In my opinion, abrasion is the main cause of edge dulling.

Hello,

There is plenty of documentary evidence to explain that the fractures are the cause of edge dulling. Unless you are talking about exotic timbers with significant silica content, there is very little in wood which is abrasive enough to dull steel. It is the steel failing due to stress which is part of the reason. Once the steel fails a bit, heat will build up and as I understand it the steel actually loses hardness locally ( the temper is actually drawn) and then the dulling becomes more rapid. The sharper the tool initially, the less heat is generated and the edge lasts longer. The rounding over is the last phase in the dulling process. But then again, you are reinforcing the fact that steel will move in a plastic state , it is just not as helpful during blunting the tool as when sharpening.

Mike.

 

[Corneel]

What documentary? The stuff I have been reading is quite universally agreeing about abrassion. In some kinds of wood chemical abrassion plays a role, especially with carbide cutters, but that is hardly interesting for us.

A good summary of a lot of research in the fireld of wood cutting and tool wear is: Klamecki, A review of wood cutting tool wear literature.
Edge wear is all about abrasion, yes, even in wood which seems to be so soft compared to steel.

Catastrophic edge failure with cracks and nicks is the result of poor tool selection or use.

 

[Corneel]

Another reference:
http://www.ncsu.edu/bioresources/Bi...y_Review_Wood_Machining_Focus_Sawing_3847.pdf

"Abrassive wear plays the largest role in the edge recessionof tools"
"Further study has shown that the silica residue within the wood cell walls plays a very small role"

If you can't read these documents, then send me a PM with your email and I'll send you a copy.

 

[woodbrains]

Hello,

Not 'a documentary', evidence in document form, there is plenty on the Internet.

The word micro fracture is salient here, I'm not talking about ones that can be seen because of too low a sharpening angle, or whatever. I mean fractures in the grain structure of the steel.

What do you think abrasion means? There is a mechanism to it on the microscopic level. A soft material can only abrade a harder one if there is some defect in the hard one to allow the particle failure. The micro fractures being stress raising points is part of the mechanism. Abrasion is just a word unless you define the mechanism that is causing it.

Mike.

 

[woodbrains]

Hello,

I was not talking of silica in the cell walls, either, I was referring to exotics that actuall have silica crystal inclusions throughout the wood itself. I had already inferred that the wood we normally see is too soft for that to be significant.

Mike.

 

[Corneel]

Do you have any pointers?

 

[Corneel]

A quick search reveals load sof studies to cemented tungsten carbide tools. The main wear mechanism seems to be removal of the cobalt biner between the carbide cristals, indeed through mechanical wear and micro cracking. In wet wood chemical attack of the steel plays an important role. And high silica content increases the mechanical wear. High temperatures are weaking the steel, but I don't think that plays a role in handtools

But I can't find anything yet about carbon tool steels. Handtools don't use cemented tungsten carbide.

 

[woodbrains]

A quick search reveals load sof studies to cemented tungsten carbide tools. The main wear mechanism seems to be removal of the cobalt biner between the carbide cristals, indeed through mechanical wear and micro cracking. In wet wood chemical attack of the steel plays an important role. And high silica content increases the mechanical wear. High temperatures are weaking the steel, but I don't think that plays a role in handtools

But I can't find anything yet about carbon tool steels. Handtools don't use cemented tungsten carbide.

Hello,

You just wrote this, why do you not believe it. You can't just write a whole load of stuff, which is all I have been saying, and decide it does not apply. Why do you not think it applies to hand tools? You can't just have doubts without foundation, we are not dealing with magic here. The forces and temperatures generated at the tiny cutting tip of a hand plane or whatever is absolutely immense. In the order of tons or even hundreds of tons per square inch. Just because some cutting tools are attached to spinny things is really not that relevant. Nor is the braze on TCT tools. That is completely out of any context here.

Mike.

Translated from hedgehog to something approximating English in the edit!

 

[Corneel]

Wait a moment, I'm completely confused at the moment. Not arguing, just looking for information. Micro cracking is indeed a mechanism in cemented tungsten carbide tool wear. But carbon tools teel isn't the same. So I am looking around trying to find all the documentary evidence you wrote about.

(But I have to do some real work first).

 

[Jacob]

Wait a moment, I'm completely confused at the moment. ...

Really?

..... The forces and temperatures generated at the tiny clotting tip of a hand plane or ........
re attached to spiny things ....
Mike.

Wos this "clotting" tip?
"Spiney things" - are we talking hedgehogs?

We have arrived at another planet! I knew we would. It's planet Steampunk.
Seriously though, "steampunk" is 90% of modern sharpening. The other 10% is hedgehogs.

Have you seen the Veritas Mk III yet? Being demo'd here by woodbrains:

 

[woodbrains]

Hello,

He is using his eye lenses to detect micro fractures on a newly sharpened edge. :lol:

Jacob, you should like steampunk. They have a preference for red metals over iron. They truly are in the Bronze Age.

Mike.

 

[G S Haydon]

I think context is very important. I'm not sure you can make the leap of saying spindle moulder or router tooling, their uses and steels translates to hand tools. It might but evidence would be useful.

 

[woodbrains]

Hello,

Sorry that I don't keep a bibliography of everything I have read all my life, so I can prove what I say, but there it is. I have read things about carbon steel having micro fractures which is the point at which abrasive wear begins. I do not make stuff up, so I don't see why my word is not good enough. Fine to find stuff out for yourselves, but the assumption that I am wrong without offering reasons why is argumentative. For the sake of the discussion, we could just just assume that I have read and relayed the info and we can get back with the idea that sharpening media can affect the longevity of cutting tools.

I still don't see why a spindle cutter will dull any differently than anything else. Perhaps a variation in degree, but a completely different mechanism altogether is not likely. Micro fractures in the grain structure of metals exist, the wood is the same, the colossal forces at the cutter tip are of similar order. Why do we feel that hand tools will behave differently? And if so, someone else prove it, I have read what I have read.

Mike.

 

[Corneel]

A handplane excerts something like 0.5 kgf per mm on the cutting edge. We are happy if we can take a 0.1 mm thick shaving at 1 meter/second.

A router rotates at 14000 rpm. Say, we have a bit with a 4 cm circumference. That translates to 10 meter/second. You can easilly take a shaving 10 times as thick. So the total force at the cutting edge might be 100 times as large.

No idea how that translates to pressure at the micron level.
Tungsten carbide is quite a bit more wear resistant then carbon steel of course.

So, who knows, Mike might be right after all!
Cracking tool steel. And when the grooves made by sharpening are less deep and less abrupt, that means less stress on the carbides.

I still would like to see all the evidence on the Internet though.