Edge retention comparison : Sharpmaker CBN, Diamond, Medium (+ steeled edge)

[Jax]

Cliff
I ment I would like to see a chart showing TCE and initial sharpness for a test run on a used blade that was re sharpened by first using the Bester 700,then finished on a medium rod.
Or using a medium rod to finish a edge after the CBN.

[The Mastiff]

Cliff, don't want to side track this thread but is there any noticeable difference in the HSS Bi Metal blades when it comes to either cutting or amount of cardboard cut compared to the regular HC blades? I'm not asking you to cut several KM's of cardboard but just wanting to know if you can reasonably notice a difference to make the upgrade (?) worth getting?

I'm just guessing but I'd think the Bi Metal blades would not really show differences until the medium changed to something like dirty old carpet padding, which is some of the worst stuff I've cut when it comes to dulling blades. That is what initially got me to go to actual commercial quality razor blades for carpet and setting my EDC blades aside. The Geometry made the lower carbide HC type blades last longer than steels like D2 on my regular carry blades.

Joe

[Cliff Stamp]

Cliff
.... showing TCE and initial sharpness for a test run on a used blade that was re sharpened by first using the Bester 700,then finished on a medium rod.

That is the last bar in the chart.

Or using a medium rod to finish a edge after the CBN.

Yes, this would have been much more sensible, I did the Bester 700 out of habit and only after I had a few rounds done did I realize it didn't make sense to throw a waterstone into the mix. I would have done the CBN+Medium as well but I ran out of that type of cardboard and since I was not random sampling I can't add to it now, that is the problem with doing runs on a particular type of cardboard.

However it is an interesting question and I might look at it in the future because while I am fairly confident in what will happen it is always nice to do the work so you can know.

[wrdwrght]

Instructive, as usual, Cliff.

[Jax]

Ok thanks Cliff.
I reread post #1,I must have missed or didn't absorb the part where the medium rod finished the Bester edge.
:)

[Cliff Stamp]

Video overview :

https://youtu.be/5ZyI-fOaYDA

[Sir Joe]

I checked this as I was curious and the CBN has the same steeling effect. If I just do 2 passes on the CBN rods the edge is very sharp, but at that point while it did remove metal it also pushed a lot of it back into place.

does this mean that the cbn are less coarse than the diamond?
I, like many other people, am trying to decide which one to buy.
The aim use would be reprofile new knives with too wide angle of edge.
My understanding was that cbn and diamond were both hard enough to do the job similarly well and similarly fast.
But if the cbn is less coarse, this means it also is slower in reprofiling?
Would it make sense to start the reprofiling with a metal file?

PS.: I am reading your old thread on your Website. Somebody asks you why not using a low carbide steel for your comparison of CBN vs diamond.
You say they both are much harder than steel.
I am reading elsewhere that Diamond is better for carbides, and actually cbn is not good at all for carbides. So people prefer cbn for steel and diamond for carbide. This was about grinding wheels but still valid in this case.
I am an ignorant newbie so my supposition may be very wrong, but I am supposing that cbn would not do well with steels which form hard carbides.
What do you think?

[Bodog]

CBN is only slightly softer than diamond. Both are harder than vanadium. Do a search here for "polycrystalline" and a thread should pop up explaining the difference between diamonds and CBN.

Here ya go, found it:
//forum.spyderco.com/viewto ... e#p1037565" onclick="window.open(this.href);return false;

[HarleyXJGuy]

Excellent thread Cliff with a lot of great information.

All that cardboard cut but utility steel and for it to still be shaving sharp. Guess I can sell my 204P and Cruwear knives.

[Cliff Stamp]

But if the cbn is less coarse, this means it also is slower in reprofiling?

The Diamond and CBN rods I have are near identical in grit.

Would it make sense to start the reprofiling with a metal file?

If it can be cut with a file then a file is faster than even very coarse stones.

I am reading elsewhere that Diamond is better for carbides, and actually cbn is not good at all for carbides.

There is a bit of confusion here because this is true in industry but they don't mean the same thing by the terms. In industry Diamond would be used over CBN for grinding carbide, but by that they mean actual solid carbide/ceramics. In that case the g-ratio or efficiency of Diamond is 100:1 meaning Diamond removes 100X the amount of material as CBN for a given rate of wear. However you won't see Diamond being used to grind steel generally and it will be behind CBN because it has rapid diffusion based wear from the carbon/carbon interaction (there is carbon in steel and Diamond is essentially carbon).

Now for hand grinding, diffusion based wear can't be just assumed because the temperature/pressure is much less. I have not seen a lot of data on wear rates in hand sharpening, but from what I have seen the rates of wear are so slow that damage is likely to set in before the tools wear out. Just think that the Spyderco stones are alumina which is much softer than CBN and Diamond and how long does it take to wear out a Spyderco medium stone? Used properly with lubricant and low force they last a long time, used dry with heavy force you could damage either the CBN or diamond in literally seconds.

[Cliff Stamp]

All that cardboard cut but utility steel and for it to still be shaving sharp. Guess I can sell my 204P and Cruwear knives.

Ha, I have as many, or likely more duper steels than most people. However angle/finish play a larger role in performance. Roman Landes was the first knife maker I saw really make this argument. He broke performance down in to various factors and he ended up making the argument that the steel used was ~1% of the performance when you consider all aspects. Now you can always debate/argue over the exact numbers he used to represent importance of various factors, but the general claim is solid.

https://youtu.be/Z8nkmoivptQ" onclick="window.open(this.href);return false;

If you look at that video and the previous ones, it shows how edge angle can easily swamp out steel even on applications which are really steel sensitive.

[HarleyXJGuy]

All that cardboard cut but utility steel and for it to still be shaving sharp. Guess I can sell my 204P and Cruwear knives.

Ha, I have as many, or likely more duper steels than most people. However angle/finish play a larger role in performance. Roman Landes was the first knife maker I saw really make this argument. He broke performance down in to various factors and he ended up making the argument that the steel used was ~1% of the performance when you consider all aspects. Now you can always debate/argue over the exact numbers he used to represent importance of various factors, but the general claim is solid.

https://youtu.be/Z8nkmoivptQ" onclick="window.open(this.href);return false;

If you look at that video and the previous ones, it shows how edge angle can easily swamp out steel even on applications which are really steel sensitive.

I have noticed the same thing without all the testing since I changed the angle on my S30V Millie. Cuts a ton better and longer now that is is thinner.

[Bodog]

But if the cbn is less coarse, this means it also is slower in reprofiling?

The Diamond and CBN rods I have are near identical in grit.

Would it make sense to start the reprofiling with a metal file?

If it can be cut with a file then a file is faster than even very coarse stones.

I am reading elsewhere that Diamond is better for carbides, and actually cbn is not good at all for carbides.

There is a bit of confusion here because this is true in industry but they don't mean the same thing by the terms. In industry Diamond would be used over CBN for grinding carbide, but by that they mean actual solid carbide/ceramics. In that case the g-ratio or efficiency of Diamond is 100:1 meaning Diamond removes 100X the amount of material as CBN for a given rate of wear. However you won't see Diamond being used to grind steel generally and it will be behind CBN because it has rapid diffusion based wear from the carbon/carbon interaction (there is carbon in steel and Diamond is essentially carbon).

Now for hand grinding, diffusion based wear can't be just assumed because the temperature/pressure is much less. I have not seen a lot of data on wear rates in hand sharpening, but from what I have seen the rates of wear are so slow that damage is likely to set in before the tools wear out. Just think that the Spyderco stones are alumina which is much softer than CBN and Diamond and how long does it take to wear out a Spyderco medium stone? Used properly with lubricant and low force they last a long time, used dry with heavy force you could damage either the CBN or diamond in literally seconds.

Holy cow, why couldn't you say that in the diamond vs cbn rod thread? Seems like everything you just posted correlates with what I was saying in that thread where you so vociferously argued against what I was saying because the initial hypothesis was formed based on a statement made by someone who studies this stuff and then sells it. *breath*

[Cliff Stamp]

I have noticed the same thing without all the testing since I changed the angle on my S30V Millie. Cuts a ton better and longer now that is is thinner.

Mike Swaim was the first person I saw write about that extensively. This was in the late nineties and the internet was a pretty crazy place for claims about performance. Mike, and then later Joe and Steve, took a bunch of knives, reground them and repeated cutting performance and edge retention (mainly Mike) and provided some hard numbers on relative performance. It was the first time that the argument was made that geometry and sharpening was far more critical than steel. Ironically, Mike determined almost immediately that the reason a Mora cut well was because the angle of the edge (10-11 dps) was much lower than most production knives (20-25 dps) . It wasn't the case that it was a single bevel, it was the angle of the bevel.

[Sir Joe]

The Diamond and CBN rods I have are near identical in grit.

Maybe I did not understand something. You had said something about steeling, and I understood that a less coarse stone could do this steeling more (moving metal instead of biting). So when you said that CBN had a steeling effect and that although it was sharpening it was also moving metal, I thought it was less coarse than Diamond, and so also slower.
What did I miss? :confused:

If it can be cut with a file then a file is faster than even very coarse stones.

I thought at a file because when I said in BF that I wanted to sharpen a Axe with a stone I was said a file was faster.
But I could eventually use a Dia 120 like the DMT extra extra course.

There is a bit of confusion here because this is true in industry but they don't mean the same thing by the terms.

Yes you are right, that is what I had read, it was exactly in websites about grinding wheels and was talking of high temperatures.
I had understood this of carbon/carbon and I supposed it had no relevance in hand sharpening, but I still wondered if the fact that steel has got carbides means that Diamond would be better than CBN also in hand sharpening.
So, you mean that those carbides of industrial sharpening has nothing to do with the carbides in steel?
I have no idea :D

Used properly with lubricant and low force they last a long time, used dry with heavy force you could damage either the CBN or diamond in literally seconds.

Is lubricant a must or as long as I do not go heavy I can avoid lubricant?
And, is lubricant also for Allumina? On their shop Spyderco says no lubricant is needed with the SM :confused:


About the geometry vs steel: would steel have an important role in long term performances and edge retention, if geometry is the same?
Besides, does not steel play an important role in allowing a knife to have a very thin edge? I could be totally wrong, but I have read this. That not all steel can support a thin edge...

[Cliff Stamp]

What did I miss? :confused:

This part :

I checked this as I was curious and the CBN has the same steeling effect. If I just do 2 passes on the CBN rods the edge is very sharp, but at that point while it did remove metal it also pushed a lot of it back into place. I was doing the same amount of passes with all, but of course the more coarse ones remove far more material.

Maybe I wasn't clear, I meant to say that the CBN also has a steeling effect but because its rate of metal removal is high enough, it quickly cuts off the deformed metal it pushed back into place in the first 1-2 passes. The Diamond rods have the same behavior. If you just do 1-2 passes the edge will be pushed back into place, but in just 5-10 passes all of that fatigued metal is removed. The Medium and Fine rods don't remove as much metal through abrasion and thus they will leave fatigued metal on the edge. I don't think it would be possible with the Fine rods to ever remove it as at some point they would just be fatiguing metal as fast as they remove it.

I thought at a file because when I said in BF that I wanted to sharpen a Axe with a stone I was said a file was faster.
But I could eventually use a Dia 120 like the DMT extra extra course.

If a file can cut it, it will even be faster than an XX-coarse DMT. The problem is that most modern knives won't be readily cut with a file at all, and even if you can cut them it will take a lot of force and it will rapidly degrade the file. Depending on the quality of the file, you will start to struggle to file any steel past the mid-50's with a significant alloy carbide content.

So, you mean that those carbides of industrial sharpening has nothing to do with the carbides in steel?

The carbide they grind in industry is solid carbide, meaning it is all carbide. In steels, even a high carbide steel will only be 5-15% carbide, the rest is martensite (which is simply hardened iron) which is much softer and easier to cut. In fact when you grind steels, what you cut is mainly the iron part, the carbides are tiny and just pushed out of the way. Only when the abrasives get very fine do they start to cut the carbide directly. This is why it is very hard to polish high carbide steels compared to grinding them to shape.

And, is lubricant also for Allumina? On their shop Spyderco says no lubricant is needed with the SM :confused:

Yes, in general all abrasives benefit from lubricant as it reduces friction, slows loading, and keeps dust out of the air (and your lungs). It isn't needed in the strictest sense, but it is almost always beneficial.

Besides, does not steel play an important role in allowing a knife to have a very thin edge? I could be totally wrong, but I have read this. That not all steel can support a thin edge...

Yes, but almost no one goes to this extent so for practical purposes it has little influence. The failure point for ropes, woods, and cardboard for example is in the range of 4-6 degrees per side. Most people sharpen in the range of 15 to 25 degrees per side which can be held with any steel in almost any application. This is the range of angles used for splitting and felling axes, so for small knives any steel is functional in that range basically.

[Sir Joe]

I kind of understood all. Thanks.