Sharpening S110V, Are Diamonds A Must?

[David Martin]

Agreed. The Mohs scale was never meant to be a precision scientific chart used to list mineral hardness. It is a general guide and likely the most
precise it could deliver is a number with a .5 after it. Any more and it is a educated guess (with experience in your area) or sort of a 'feel' test. DM

 

[Obsessed with Edges]

The Mohs scale is meaningless, in terms of accurately describing a hardness of any one material, in relation to another. It's an 'ordinal' scale, meaning it shows a simple ranking of materials listed in the chart, indicating if one material in the list is harder or softer than another in that list, but providing ZERO indication of HOW MUCH harder or softer it may be. And the 'test' for hardness, to be ranked in the Mohs chart, is simply whether one material is, or isn't, able to scratch another compared material in that list. No actual measurement at all, of anything. That 'scratch test' is valuable, in knowing in the simplest terms if one material can effectively abrade (cut) another. If it can't scratch it, it can't effectively cut it. Simple. So, it's useful there, but still doesn't tell the whole story.

A scale based on actual measurement by calibrated tools is more meaningful, like the Knoop scale, or Vicker's, etc. On the Mohs chart, diamond is called a '10' based only on that value being arbitrarily assigned as 'the hardest of all'. A material like aluminum oxide may be called a '9', which seems to imply it's almost as hard as diamond. So is it 9/10ths as hard as diamond? Nope - not even close. In reality, by measurement, aluminum oxide is less than 1/3rd as hard as diamond. And something like silicon carbide may be called a '9.5', but is actually a little over 1/3rd as hard as diamond. The only reason for the fractional (decimal) values like '9.5' is, they have to 'fit' somewhere in a scale that was only designed for 10 materials, in relation to one another. So if it's able to scratch the #9 material, but not able to scratch the #10 material, it gets arbitrarily assigned somewhere in between those two. Something like CBN might be assigned '9.7' or '9.8'; but it's still only about ~2/3rds as hard as the diamond.

Diamond = 7000 (Knoop scale's 'hardest' reference point)
Cubic boron nitride (CBN) = ~4500 Knoop
Vanadium carbide = ~2800 Knoop
Silicon carbide (SiC) = ~2600 Knoop
Aluminum oxide (AlOx)= ~2100 Knoop
Tungsten carbide (WC) = ~1800 Knoop (varies; up to/nearly as hard as AlOx, at times)
Chromium carbide = ~1700 Knoop

 

[Mo2]

So, synthetic Sapphire which is mentioned is confusing me... Regardless of Sapphire its still aluminum oxide and still not as abrasive as sic or Vanadium etc?

Thanks guys for the replies on this

 

[Obsessed with Edges]

So, synthetic Sapphire which is mentioned is confusing me... Regardless of Sapphire its still aluminum oxide and still not as abrasive as sic or Vanadium etc?

Thanks guys for the replies on this

That's right. It's still aluminum oxide. Same for synthetic 'ruby'; it's also a form of AlOx. There's always some variation in hardness and how it'll cut, within a relatively narrow range. But the hardness isn't going to be significantly different, as compared to SiC, VC, CBN, etc.

Depending on how it's made (if synthetic) or where it comes from (if natural), aluminum oxide varies more in properties such as crystal shape, toughness (resistance to fracturing) and friability. All of those things will affect how durable it is (toughness), or how it breaks down in use (lesser toughness and/or more friability), OR if it's a better cutter (sharper crystal shape) or polisher (not as 'sharp'). But hardness isn't going to vary enough beyond it's rated maximum (usually around ~2100 Knoop) to make much of a difference, as compared to other abrasive types like SiC, CBN, etc.

 

[RadialBladeworks]

So I recently was gifted a Spyderco Native 5 in S110V by my father, which is pretty dope, but anyway, I remembered this thread and I wanted to add my own sharpening experience to the mix.

I used Shapton Pro stones which are comprised of aluminum oxide, and for the strop, I used chromium oxide compound as well as bare leather.

The JNS 300 is an excellent stone. Very hard, much like the King 300, but the abrasive density is considerably higher, making it a far faster stone.

I then hit the Shapton Pro 1k. You can definitely feel how much harder this steel is from your average Aus8 blade or something. But converting my scratch pattern was no real issue.

Next was the 5k...

Then the 12k. I really love this stone as a finisher. It's just so damn hard. I often use extreme-grit stones like this or the SG16k to strop off my burrs. It works flawlessly, and they are high enough that 1 or 2 stropping strokes won't effect your specific edge performance. That is, you can sharpen on a 220, strop the burr off easily on the SG16k, yet still reap the performance of a 220 grit edge. It's fantastic. I just recently ordered the Gokumyo 20k (.5 micron) for that same purpose. Very excited. Anyway, I digress. As I said, the 12k:

I was very gentle on this stone, and switched sides a few times. I like to do this just to really make sure I am minimizing that burr as much as possible.

Next up was stropping on chromium oxide on one of the Stroppening strops:

And then some bare leather, extremely gently at a slightly higher angle to really make sure I cleaned that apex up:

And the results were quite standard:

I do have to say, I think a lot of the talk about the impossibility/gross difficulty/poor results of sharpening extreme steels on aluminum oxide are regurgitated information. The steel was obviously more difficult to sharpen than, say, Aus8, or S30V because the carbide volume is considerably higher and the matrix steel is harder at around ~62, but I think people tend to forget that the carbide volume in a steel is only a fraction of the entire composition. CPM states in their own literature that carbide volume is anywhere from 5% to over 20% volume, with the implication being that 20% volume is extreme. Well the other 80% of what you are abrading is merely the steel matrix at about 62 rockwell, which even chromium oxide can easily abrade. So as far as the ability to sharpen such a steel on aluminum oxide, I was completely unsurprised by the results.

Anyway, I just wanted to post my own experience because it does seem to differ rather largely from the generally accepted notion, therefore I think it may add something valuable to the conversation