Polished edge retainsion

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fujita yuji

Joined
Jul 12, 2008
Messages
1,397
I have one question for some time.
Polished edge cuts better than unfinished coarse edge.
That is trivial. There is no question. That is what higher grit stones are for.

What I cannot understand is, why polished edge lasts better?

Of course, better cutting edge can do some amount of job
by the time it gets as dull as inferior one.
But I feel there is something more.
I mean, for example, used polished edge lasts better than unpolished one.

Does anybody share something like this ?
or have some explanation for this ?
 
I agree that generally a sharp and fine edge will cut most materials using less force than a sharp and coarse edge, and keep it's sharpness longer. A polished edge will have less friction in slicing (and less sawing action) and less friction (and correspondingly less wear) perpendicular to the edge in push cutting. I don't know that it applies equally to every type of cutting, though.

There is the carbide tear-out theory where a nice coarse edge will have its edge "renewed" by carbide tear-out wear keeping the edge slicing nicely for a long time - usually brought up in with D2.

It is up to the user to determine whether ease of cutting (maximized generally with a fine sharp edge) or control of cutting (maximized generally by a sharp coarser slicing type edge) is more important. I have polished edges on most of my EDC's, but I talk occasionally with butchers at work, and I haven't found one yet that uses a polished edge - control of cutting & safety are more important to them than cutting force and edge retention.
 
Ya, just10minreader. Less friction, more pleasure. Absolutely.
That's what I wanted to say, and you know.

Thanks, Broos. I've always admired your technically sophisticated posts.
While I must confess that I think optimal edge for ease of cutting is also very controllable,
I agree that there are different things to be cut and different corresponding edges.
Anyway, you mentioned D2 and its relatively coarse carbide.
Do you think each type of steel has its own preferable type of edge?
I usually use M2 and I think polished edge is better for this steel.
 
fujita yuji said:
Polished edge cuts better than unfinished coarse edge.
That is trivial. There is no question. That is what higher grit stones are for.
Click to expand...
Just remember that you need the lower grit stones to do their job of CUTTING before you can play with the higher grit. Serrations of all sizes have their place in cutting different materials. Friction can be a good thing.
 
fujita yuji said:
While I must confess that I think optimal edge for ease of cutting is also very controllable
Click to expand...

I also prefer the sharpest edge possible, but after a rash of slicing my fingers lately I think there is some danger involved with having edges that will cut your flesh with any coincidental contact. :eek:

fujita yuji said:
Anyway, you mentioned D2 and its relatively coarse carbide.
Do you think each type of steel has its own preferable type of edge?
I usually use M2 and I think polished edge is better for this steel.
Click to expand...

Hard to disagree that there are preferred types of edges (or preferred angles) for different steels, but I am not holding my breath for a formula that can calculate it, and I'm not experienced or knowledgeable enough to match the finish and angle with the steel. There is some good anecdotal info here about this. Some say coarse edge is best for S30V, some say polished edge works best. I have had varying experiences with the same steels in different knives (I can get 2 of my D2 knives real sharp, can't get the others there), further complicating the issue.
 
I do not really see how initial edge on D2 may differ from initial edge on 52100 - right after sharpening and polishing. May be in time they will react differently on wearing out - one may chips another may bends. But D2 get polished as well as any other steel. This is huge misconcept that D2 can not be sharpened to high extent - it whittle hair as any other steel, which means that those huge carbides get sharpened as well as surrounding them steel.

Polished edge stay longer may be because it has less or smaller tooth to be broken. Polished surface has less weak points to apply force to take it out or affect it some other way, rough surface make more contact with cutting material and so it's particles can be riped out. Fact that it has less friction not only make it more pleasant to cut, but also cause less damage to the edge.

Thanks, Vassili.
 
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No matter how well you "polish" the edge of the blade, under a microscope it will appear to be minutely serrated. It is sharper and easier to cut with with the smallest serations posible.(POLISHED).It's like trying to cut with a buck saw (large serrations) or a hack saw(small serations). The width and breadth of the bucksaw teeth make it difficult to drag the blade through the material you are cutting. Also, the smoother the edge is polished, the less likely it is to corrode and get ugly, nasty and dull.
 
Understanding micro-teeth will not explain everything about how an edge dulls, assuming the wear causing mechanism for micro-teeth would be frictional wear. There are other mechanisms of failure involved in dulling - micro-chipping & deformation being a couple. Different types of cutting and different steels will have different combinations of the various failure modes that cause dulling.

There are a lot of people here who have commented pretty extensively on the phenomena of D2 being impossible to get to a razor sharp edge that is comparable to other steels that will take a finely polished razor edge. That said they are nevertheless great cutters at a 600 grit DMT finish. Maybe that one reason why D2 isn't used in razor blades, but finely grained steels are...
 
Broos said:
Understanding micro-teeth will not explain everything about how an edge dulls, assuming the wear causing mechanism for micro-teeth would be frictional wear. There are other mechanisms of failure involved in dulling - micro-chipping & deformation being a couple. Different types of cutting and different steels will have different combinations of the various failure modes that cause dulling.

There are a lot of people here who have commented pretty extensively on the phenomena of D2 being impossible to get to a razor sharp edge that is comparable to other steels that will take a finely polished razor edge. That said they are nevertheless great cutters at a 600 grit DMT finish. Maybe that one reason why D2 isn't used in razor blades, but finely grained steels are...
Click to expand...

I am personaly, first hand, sharpened D2 to hair whittling sharpness - Benchmade Ares with D2 in particular.

I hear a lot about one or other steel hard to sharpen. To my opinion in all this cases it is not matter of steel being hard or impossible to sharpen, but sharpening skills of whoever made those statements, because I did not see so far any steel I was not able to sharpen to whittle hair.

So once again D2 get sharp as good as any other steel.

Thanks, Vassili.
 
nozh2002 said:
I am personaly, first hand, sharpened D2 to hair whittling sharpness - Benchmade Ares with D2 in particular.
Click to expand...
Way to go. Did you muster up the courage to try any of those dangerous sharpening demonstrations with it? And I'm not real sure cutting a big thick hair meets my criteria for really sharp. Can you tell me the thickness of the hair? And I'll bet if you practice, that someday you might be able to sharpen well without that wedge thingy. ;) sorry I just couldn't help myself...

nozh2002 said:
I hear a lot about one or other steel hard to sharpen. To my opinion in all this cases it is not matter of steel being hard or impossible to sharpen, but sharpening skills of whoever made those statements
Click to expand...

Maybe you are right having had all that experience with the one Benchmade Ares in D2.

Maybe you're right, and all other D2 knives made by everybody else will be just like that Benchmade Ares you have. Maybe all those knifemakers heat treat it the same. And maybe all the batches of D2 used to make knives for the last few decades have been so close in composition and impurity levels as to not make any difference. Or maybe not....
nozh2002 said:
This is huge misconcept that D2 can not be sharpened to high extent
Click to expand...
Or maybe it is a "huge misconcept" to think that your experience with a Benchmade D2 Ares applies to every other D2 knife ever made.

Just a theory.
 
Let me summarize my understanding at this point.

Sticking out part of edge suffers more load
which result in scratched off (in case cutting fiber like substance),
chip (cutting heterogeneous materials) or bend (cutting hard substance).
While in case of cutting fibre like substance,
peaks and valleys of edge have some role.
 
Broos said:
Way to go. Did you muster up the courage to try any of those dangerous sharpening demonstrations with it? And I'm not real sure cutting a big thick hair meets my criteria for really sharp. Can you tell me the thickness of the hair? And I'll bet if you practice, that someday you might be able to sharpen well without that wedge thingy. ;) sorry I just couldn't help myself...

Maybe you are right having had all that experience with the one Benchmade Ares in D2.

Maybe you're right, and all other D2 knives made by everybody else will be just like that Benchmade Ares you have. Maybe all those knifemakers heat treat it the same. And maybe all the batches of D2 used to make knives for the last few decades have been so close in composition and impurity levels as to not make any difference. Or maybe not....

Or maybe it is a "huge misconcept" to think that your experience with a Benchmade D2 Ares applies to every other D2 knife ever made.

Just a theory.
Click to expand...

Which D2 knives you were not able to sharpen to whittling hair sharpness (I assume you have first hand practical experience as well?).

Mathematically speaking one example - as it is here "BM Ares with D2 whittling hair", makes statement - "D2 is impossile to sharpen to high sharpness" not true any more. To be correct now you have to say that this and that maker can not HT D2 so it may be sarpened properly (which is IMHO bad HT). Or you may say all D2 expect one used by BM is not suitable for sharpening...

However I guess if you know how to sharpen - any steel can be sharpened.

Thanks, Vassili.

P.S. I have record page:
http://playground.sun.com/~vasya/SharpeningRecords.html

let see how many D2 I have here:

Microtech Manus (D2)
2 x Benchmade 710 (D2)
Benchmade 705 LE: D2

So seems like it is not an issue for people who know how to sharpen.
 
Is this kind of controversy about D2 sharpness common?
I personally have very little experience about this steel,
which is generally a good one. Quite easy to sharpen and holds edge well.

I found some disagreement exists about chipping resistance of M2.
As far as M2 is concerned, I think heat-treatment causes this diversity.
Differently heat-treated M2 was a completely different steel for me.
Work required in sharpening, edge holding, toughness, corrosion resistance, all were
different. If I had no idea what kind of steel I am handing, I should have recognize
them as a different type of steel.
 
D2 has very big carbide particles - 50 microns. Some people just looking into micrograph came with idea that because this hard carbides sticking into edge it can not be sharpened to very fine edge. It may looks reasonale, but on practice it is not true and those carbides get sharpened as well as surroubded steel. Iron Carbides are not harder then Diamods, as well as Chromium Oxidea as well as ceramic (Aluminum Oxides).

So this is just some wrong theory based o some pictures which many support just as an excuse for their bad sharpening skills.

It is true however for Vanadium Carbides in steel like CPM S90V. They are harder then Aluminum Oxides. So those carbides can not be sharpened by ceramic and for this reason CPM S90V can not be sharpened with Spyderco Fine Ceramic where abrasive size is same as size of Vanadium Carbides. But with diamonds it is not a problem.

However it is 9% of Vanadium Carbides in CPM S90V steel, while same carbides does not make any significant impact in CPM S30V.

Thanks, Vassili.
 
I'm another guy that hasn't had a problem getting D2 to a sharp polished edge. Queens, Benchmades, and a few customs. However, I disagree that a polished edge will always last longer or perform better than a less polished edge. Edge performance is highly dependent on how and or what your cutting.
 
The OP spoke about the edge lasting longer. Most applications are a slicing motion. Ridges left from a course sharpening stone will grind off quicker in this motion. A smooth edge will offer less resistance (sharper) and wear less (last longer) all else being equal.

TF
 
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