The grit paradox (Callin' Cliff)

[daberti]

Cliff, if you are here hit a shot.
Everybody else's tought are welcome of course

I've recently purchased a Fallkniven P/3G folder and re-sharpened it with Edge-Pro 320 grit whetstone, 21° per side (factory setting) no microbevel.
My tests are currently limited to push cut shaving and I scored far better results reverting back to a 220grit EdgePro whetstone.
I'm somehow confused
It should have been right the opposite!

Any explaination?

 

[bbcmat]

1) Your 320 stone was not cutting - either too little pressure used or its working surface is glazed (req lapping).

IMO

MAT

 

[Cliff Stamp]

Any explaination?

Several years back I stopped recommending in general fine stones and now almost exclusively suggest x-coarse/fine DMT or similar to sharpen and to always start with the x-coarse when sharpening.

This is very much a novice approach to sharpening and one you hope to move beyond but it is based on general principles which hold no matter the skill/experience and thus are always of consideration.

For many reasons sharpening with fine grits tends to produce greater burrs, mainly the very low cutting speed and aggression/pressure ratio. So first check the edge carefully for a burr, under light at least, and ideally under at least 10X magnification.

bbcmat also makes an excellent point, make sure both stones have clean and aggressive surfaces.

-Cliff

 

[daberti]

@bbcmat
320 stone is ok. It carries steel's residuals over it, after working.

@Cliff
I guess the trouble has something to do with carbides and high alloy st/steels.
I experienced same troubles with S90V and S30V. Now with SGPS.
I used Red DMT against S90V and found that Edge Pro 220grit whetstone is its equivalent on EdgePro universe.
Another tought could be that less than optimal heat treatment left carbides sunk from cutting edge surface. This happened lotta time with commercial S30V blades, and even with a hyped 5.5" fixed blade (Cliff you do know which brand I'm talkin' about).

 

[cbwx34]

daberti,

It's actually kinda tough to diagnose why you got the results you did, based on your post. Here's a few more things to consider...

Are you sure you were hitting the edge with the 320 stone? You might have been right to the edge, but not quite, and then reached the edge when you went back to the 220, since the 220 is more aggressive.

Don't use too much pressure... let the stone do the work. When I get to the finer grit stones, I apply almost no pressure to the handle.

Finish up with a few very light alternating strokes (less than the weight of the arm, and cover several inches, at least the table width, on each pass).

My experience has been that I see smaller burrs with the finer stones. I use an Edge Pro quite a bit.

Not sure if any of the above applies in your case, just thought I'd throw them out there.

cbw

 

[HoB]

Well, it also depends on the stones you are using and what you are doing with them. In general, I see smaller burrs with finer stones as well, but that refers more to the fact that the burr formation is slower and more controlled because you are removing in general less material per stroke. However, if you were using a hard and fine abrasive to bring an excessively blunt edge back instead of using multiple grits, you could see very large burrs.

I would suspect a burr problem for this "contradiction" aswell. Even though I wouldn't expect large improvements on pushcutting going from 220 to 320 anyways.

 

[Cliff Stamp]

I guess the trouble has something to do with carbides and high alloy st/steels.
I experienced same troubles with S90V and S30V.

These steels are often problematic with fine finishes because of the low grindability. As a rough estimate, consider the cutting speed to be proportional to the grit size of the abrasive so if you go ten times as fine you will cut ten times as slow.

This is combined with the fact that as the abrasives gets very small it will move below the size of the carbides and thus try to sharpen them directly where the larger abrasive grits will just tear out the carbides. This means that you expect an even slower cutting speed, several times easily, on the higher carbide steels.

As a first suggestion I would suggest using microbevels at the finer finish. So sharpen at 19 degrees with 220 and then finish at 21 degrees with 320. This will pretty much make grindability a nonfactor as you will be honing a very small bevel which will respond very fast.

Now it is very true that finer polishes are ineffective on high carbide steels but it typically takes much more acute angles before you see carbide tearouts being a factor. Angles of more than 20 degrees are typically only required on the really large carbide steels like 440C/D2.

Another tought could be that less than optimal heat treatment left carbides sunk from cutting edge surface. This happened lotta time with commercial S30V blades, and even with a hyped 5.5" fixed blade (Cliff you do know which brand I'm talkin' about).

Yes, he who will not be named. In general you want a high hardness when you have a lot of carbide. This is both to make the edge less "gummy" when sharpening as well as to prevent edge roll in use. It doesn't do you a lot of good to have lots of carbides in a highly deformed edge.

-Cliff

 

[daberti]

daberti,

It's actually kinda tough to diagnose why you got the results you did, based on your post. Here's a few more things to consider...zip

I did it per your guidelines, that are mine too. I've done 25 knives with EdgePro up to now. From fillet knives to hunters from AUS6 to S90V and ZDP189. The stone is nearly brand new, with 320 numbers well visible. And it's still perfectly flat.

@HoB
I've triple checked with either stones against burrs under 20x magnifying and light. I've checked against wire edges. None detected. These were tipically S30V issues (bad heat treated ones, to tell the truth, see ^).

@Cliff
At present time I'm investigating how the edge can withstand to a wide spectrum application environment. Cutting rope is a joke with it, but having it cutting rope (slicing) AND hairs (push cutting) at the same time without any microbevel tells me where the limits of the blade geometry/steel/heat tr. are.
When I got my most recent my new car, I drove it for some time without ABS, EBD, ASC or other electronic devices enabled, doing some careful lap at a track near home

Back to the knife: Angles of more than 20 degrees are typically only required on the really large carbide steels like 440C/D2.
I do agree and I must underline one important thing: while sharpening blade rested with its whole relief on EdgePro base, instead of taking the very flat side of the blade, near the heel, resting on the base. Thus some degrees must be subtracted from the 21 setting, which will turn much more into a REAL 18.

With 320 I achieved really good results with the FK P/VG10@59 .
But there the real angle was 15/18 and only 18 had been done with 320.

 

[Cliff Stamp]

... some degrees must be subtracted from the 21 setting

Yeah, I should have been more clear, I was talking about the actual edge angle, not a jig setting. It is kind of interesting though that you are still having to use a somewhat high edge angle. It is still reasonable for that class of steel but I just would just have expected it to be a few degrees lower.

S30V should also be able to take a significantly more acute/polished edge than S90V. How much performance do you lose with the finer grit? You might want to try a finer abrasive which is significantly harder, boron carbide or diamond.

In nay case it is very much appreciate to see real quantitative comparisons being presented, I would hope you are keeping some kind of notes/record. I am interested in any data of this nature (grits/angles) and will even provide web hosting space for any results you want to write up.

I want to see how well the user reports compare to the materials data and the edge stability testing done by Landes, Verhoeven and others.

-Cliff

 

[daberti]

Yeah, I should have been more clear, I was talking about the actual edge angle, not a jig setting. It is kind of interesting though that you are still having to use a somewhat high edge angle. It is still reasonable for that class of steel but I just would just have expected it to be a few degrees lower.

I just tried to keep the original angle setting from factory.
I could go some more degrees lower, but no more than 2-3 degrees per side. Otherwise I'd sharpen the whole SGPS clad part, which would not properly happen to be the best choice

S30V should also be able to take a significantly more acute/polished edge than S90V. How much performance do you lose with the finer grit? You might want to try a finer abrasive which is significantly harder, boron carbide or diamond.

Here steel is SGPS. Yet it is true that S30V could take a significantly more acute/polished edge than S90V. If you mean a custom made and properly heat treated S30V. Otherwise you'd go with S30V edge rolling lottery....
On the other hand my Kevin Wilkins F4 with S90V@59.5HRC and a 26ish deg. per side setting (microbevel, with a 23-24 primary) done with Red DMT outperforms many S30V blades resharpened at 18/21 with Green DMT on microbevel also as far as push cutting (hair) is concerned.
Back to FK P/3G with finer grit i simply lose any ability to push cut hair.

In any case it is very much appreciate to see real quantitative comparisons being presented, I would hope you are keeping some kind of notes/record. I am interested in any data of this nature (grits/angles) and will even provide web hosting space for any results you want to write up.

I want to see how well the user reports compare to the materials data and the edge stability testing done by Landes, Verhoeven and others.
-Cliff

I'm not skilled enough to show any quantitative based comparison, though I keep records on Steel/angles/grits and their performance.
But just as perceived in some testing applications.

 

[Cliff Stamp]

Otherwise you'd go with S30V edge rolling lottery....

There is that yes, I was speaking of ideals. As a customer you don't have to put up with anything else. SPGS is a lower carbide steel further than S30V at a higher hardness so should be able to take an even more acute edge.

Back to FK P/3G with finer grit i simply lose any ability to push cut hair.

That is interesting, I would be curious as to the response of a finer abrasive of a different type.

I'm not skilled enough to show any quantitative based comparison, though I keep records on Steel/angles/grits and their performance.
But just as perceived in some testing applications.

Quantification doesn't actually demand any specific precision requirements.

-Cliff

 

[daberti]

There is that yes, I was speaking of ideals. As a customer you don't have to put up with anything else. SPGS is a lower carbide steel further than S30V at a higher hardness so should be able to take an even more acute edge.

Potentially I could, actually I cannot: there is the clad profile issue.

That is interesting, I would be curious as to the response of a finer abrasive of a different type.

Such as Green DMT? Just done. Hair cutting is a marvel. Rope is a worse.
Tried also Red DMT: rope just a teensie weensie better than 220 EdgePro, Hair a teensie weensie worse.

Quantification doesn't actually demand any specific precision requirements.

See just above if my experience may be helpful.

 

[Cliff Stamp]

Potentially I could, actually I cannot: there is the clad profile issue.

Are you speaking here of a cosmetic concern?

Such as Green DMT? Just done. Hair cutting is a marvel. Rope is a worse.
Tried also Red DMT: rope just a teensie weensie better than 220 EdgePro, Hair a teensie weensie worse.

Thanks, these make sense from change in grit and how it influences slicing and push cutting performance. If you really reduce edge angle/thickness a lot then you can get improvement in both slicing and push cutting at a higher polish because the cutting ability becomes so great that the blade almost sink right through the media on a draw with little actual forward motion.

-Cliff

 

[daberti]

Are you speaking here of a cosmetic concern?

Judge it yourself
http://www.egoproject.info/download/left.jpg
http://www.egoproject.info/download/right.jpg
With particular reference to the right side

Thanks, these make sense from change in grit and how it influences slicing and push cutting performance. If you really reduce edge angle/thickness a lot then you can get improvement in both slicing and push cutting at a higher polish because the cutting ability becomes so great that the blade almost sink right through the media on a draw with little actual forward motion.

That was actually what I experienced with one of the ZDP Caly I had.
But here I cannot go lower for above mentioned reasons :grumpy:
It looks like they had serious quality control issues on 3G blades, for I've noticed similar clad discrepancies on their Kronor blades as well as in U2.

 

[Cliff Stamp]

Judge it yourself ...

I see the lamination line being higher on one side which is common due to an asymmetric primary grind. I am not sure about your concern about the angle, do you think you will then cause the edge to move off of the center core?

-Cliff

 

[daberti]

I see the lamination line being higher on one side which is common due to an asymmetric primary grind. I am not sure about your concern about the angle, do you think you will then cause the edge to move off of the center core?

-Cliff

Yes, lamination is asymmetrical and yes the concern you mentioned is what I'm afraid of.
But there is one issue left to mention: should I go for 15 degrees, only one side would take it. On the other I would end sharpening above the lamination line.

 

[Cliff Stamp]

This is mainly a cosmetic issue as long as the edge itself forms on the core. It isn't though a laminate problem as much as a primary grind issue, these are in general not overly even, not a problem which is restricted to Fallkniven.

-Cliff

 

[daberti]

This is mainly a cosmetic issue as long as the edge itself forms on the core. It isn't though a laminate problem as much as a primary grind issue, these are in general not overly even, not a problem which is restricted to Fallkniven.

-Cliff

I'll give it a try at 15/18deg. Not less than this for this knife is meant to be used also on my trekking sessions