Thread Rating:
  • 1 Vote(s) - 5 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Edge Rolling in High Vanadium Knives
(03-16-2019, 03:23 PM)grepper Wrote: As far as rolling goes I wouldn’t think honing with diamond would be much different than honing with some other abrasive.  Diamonds may cut steel a bit differently than AO for example, but how much difference could that really make?  For all intents and practical purposes I would think that finished sharpness and bevel angle would be of much greater consequence.  

Maybe I’m just lazy, but I’ve come to worry less and less about tiny differences in edges because I know in real-world use I wouldn’t even notice any difference.  As I blunder through chopping some carrots or onions would I even notice if some edge stayed, say, 10% sharper?  For me at least, the answer is no.  

I’ve gotten to the where now I sharpen general use knives to somewhere around 125-200, call it good enough, and use the knife.   When it get’s dull enough that I care I’ll sharpen it again.  

But that’s just lazy me and my requirements for an edge.  I’m sure that there are applications where minute differences require more attention

Check this video grepper. Smile
Cool video Mr. Sharpco.  As presented, he seems like a thoughtful guy who is really trying to understand sharpening.  He could be right or he could be wrong, but he says it in such a convincing way you’d have to think he’s right... Right?

Even a burry, gnarly edge can whittle hair because it’s “catchy”, but from his method I’d think he is working with a very sharp polished edge.   That is one guy who REALLY needs to buy an edge tester so he could numerically quantify and share what’s actually happening with his edges.  It takes a very sharp polished edge to whittle hair like he shows.  Sure would like to see some numbers.

Is it your understanding that what he is saying is that using the wrong abrasive causes carbide particle tear out resulting in an edge less resistant to wear, but using diamonds actually sharpens the carbide particles leaving them intact in the edge resulting in a stronger chip resistant edge?  Is he inferring that AO rips carbide particles from the edge but diamonds do not?  Is that your take on this video?

He speaks about not completely sharpening an edge resulting in not removing fatigued steel.  That makes sense to me especially if the edge is maintained by “steeling” to straighten rolling.  I guess he is saying that diamonds will cut better and remove the fatigued metal where AO will not.  If that is true, well then, OK, maybe it is.  Or, is he saying that some steels cannot be sharpened with AO or the edge will be fatigued?  

His stated method was, cut cardboard, strop it.  Cut cardboard strop…”  That’s vague, but OK, whatever.

Honestly, carbine particle tear out is way beyond my pay grade to comment on.  I would think that only SEM imagery could verify carbide tear out, but he says that “I’m not real concerned with what somebody in a lab says”, and that he is absolutely convinced it exists.  Well then, I guess it must be absolutely true.

The video states that he cut 4046 in (~337’) of cardboard before the blade would not whittle hair as demonstrated in the video, presumably due to honing with special diamond sauce.  I’m curious, what do you think of that?  IMHO, I’d sure like to see before/after 337’ of cutting cardboard sharpness numbers and some verification of the results by independent testing.

"That is one guy who REALLY needs to buy an edge tester so he could numerically quantify and share what’s actually happening with his edges.  It takes a very sharp polished edge to whittle hair like he shows.  Sure would like to see some numbers."
>>> I agree. Maybe he doesn't know the existence of Edge tester?

Actually I don't know exactly about carbide tear out. But I think many people, including KG, are making the same argument and we should not ignore it.
This is an interesting industry and subject. Don't know about you but we already have visions of embedded chunks of carbide sticking out from a metal surface and then an abrasive particle sweeping past and uprooting the carbide from it's metallic foundation. This is, of course, strictly, the creation of our imaginations and nothing more. A long time ago, this subject was touched on in a previous thread . At that time, the physical size of carbides was touched on and in particular, how the subject related to so-called "super steels" and the powders they are made from. We're not going to try to find the thread but as we recall, it was reported in that thread that carbides are several microns in diameter and we know that the edge apex is sub-micron in width. If the carbide isn't ripped out by the roots then that brings another vision to  mind; that of a golf ball sitting on a tee with the golf ball representing the carbide and the tee, the edge apex. 

Our experience tells us that our imaginations are only rarely correct when it comes to visualizing these microscopic sized events. We'll wait for the video that shows AO uprooting and diamond slicing through, a carbide particle.
I have read an interesting paragraph about carbide tearout in a review by Cliff Stamp:
Carbide tearout during sharpening in detail
As a point of clarification, carbides can be cut by a suitable abrasive, i.e., one which is harder than the carbides so it is not immediately obvious that a lot of carbide would so limit the ability to polish the edge. However as the abrasive cuts through the carbide there is an action/reaction force pair between the carbide and abrasive generated which in turn generates an action/reaction force pair between the carbide and the surrounding steel matrix, i.e., the non-carbide portion of the steel. As the edge angle of the cutting tool is reduced the carbides will be contained by less matrix volume and at some point there will no longer be enough matrix to sustain the action/reaction force pair and the carbides will get torn out of the cutting edge. Thus a steel with a higher carbide volume and larger carbide size requires a greater volume of steel matrix around the carbide to form a highly polished edge and keep that edge stable. A higher matrix volume around the carbides requires a greater angle as shown by Landes, Johnston and Elliot. As the abrasive is both harder and sharper there will also be less of an action/reaction force pair so the greatest edge stability will be found by using the hardest and sharpest abrasive as noted by Elliott.

Interesting Jan and thanks for the above but it spawns a couple of questions for us. It would seem that a fair amount of force/time would be required in order for an abrasive particle to grind the surface of a carbide down. This would seem antithetical to a few other conversations that have been conducted on the BESS Exchange with regard to heat generation during the grinding process. What would be your opinion with regard to this? Secondly, it would seem then that high carbide content knife steel then shares some similarities in construction to an abrasive wheel - A matrix and an abrasive particle (carbide). Since the abrasive particle in the wheel is more abrasion resistant than the matrix, the matrix wears away more quickly exposing new abrasive particles. Seems as if, then, that any attempt to "grind down" a carbide particle embedded in softer steel might become an exercise in tail chasing. What say ye?
Mike, you are asking good but tricky questions. Wink

Diamond abrasive, thanks its hardness, is suitable for machining all carbides, but is not suitable for machining steel. The reason is following: at high temperatures produced in high speed grinding process, steel extracts carbon atoms from the diamond abrasive, which results in eroded diamond grit.
CBN abrasive, in contrast to diamond, contains no carbon atoms which could be extracted, and for this reason is CBN better suitable for machining hardened steel and HSS.
There is another advantage of CBN over diamond abrasive. Diamond is at room temperature about two times harder than CBN, but losses the hardness very rapidly with temperature rising above 700⁰C (1290⁰F).  For temperatures above 1000⁰C (1830⁰F) CBN performs better than diamond.
P.S.: IMHO Tormek offers diamond wheels and not CBN wheels because at low temperatures (water cooled grinder) they perform better than CBN wheels.

I think that what EOU was getting at is that if hard particles (carbide) are embedded in a softer substrate (steel), grinding with an abrasive hard enough to grind the carbides would cause the softer substrate around the harder particles to be removed at a faster rate than the carbide particles are ground down.  As grinding continued, the harder particles would be torn away as they are no longer supported because the substrate around them is removed.  This would in turn expose more substrate and the process would continue until the knife was reduced to a tooth pick.  

Of course I have no idea if anything like that really happens, but it makes sense and is fun to imagine.
Yes Mr. Grepper you are correct. Mike’s questions were tricky for me, so I have posted consideration which is only vaguely relevant and which reflects what I was just thinking about. Wink


Thank you Grepper and Jan. Now, why didn't I phrase the question, in the first place, just as you have Grepper?

Forum Jump:

Users browsing this thread: 1 Guest(s)