How do you decide that you've reached the ultimate sharpness a particular blade can attain?

[EdipisReks]

the same edge that allows me to easily cut translucent slices of carrots needs a quarter inch of forward movement to cut through the ripest and juiciest heirloom tomatoes grown 15 miles away from where i live. *shrug*

 

[EdipisReks]

What kind of cutlery are you using? Variety is the key here. Comparing a Shigefusa to a Tojiro is really not that great of a leap. Comparing a Takeda to a Chicago Cutlery, however, you will find that different knife designs and steels will require different edges to perform similar tasks.

my current gyutos are Mizuno Blue, Hattori FH, Konosuke White, and Shigefusa. i've owned Akifusa, Shun, Tohiro, and Yoshihiro gyutos and chefs knives. i've had the same experience with all of them. my Usuba cuts everything the same way with the same polished edge i put on my gyutos. i haven't used a cheap knife in a long time.

 

[Eamon Burke]

That is the reason why you do so well with polished edges! I don't deal with as much high-quality steel personally as this forum discusses it, and the edge in question was on a 20 year old Chicago Cutlery Walnut Tradition Chef's knife. I've heard that cheap knives do best with cheap sharpening, but I never understood it until then.

 

[EdipisReks]

hmm. i could see that. i can also see why a blade that can shave a hair can't cut a tomato. the blade in your Schick isn't all that sharp, after all.

 

[Lefty]

I'd bet my life savings on my knives not being even close to their "full potential" in the sharpness department. They are however, VERY sharp (I've burst my knuckles and tips like overripe cherry tomatoes by accidentally tapping the edge).
The funny thing is, I don't want them as sharp as humanly possible. I like my edges to be able to shave with 1k, then I refine it on a couple finer grits. My bevel angle is about 12-15, per side, depending on the knife.
Even though I'm an admitted sharp addict, I like a bit more stability in my edges than a lot of guys here. To me, I like an edge that I can use - beat up on - and the next time I need the same knife, a quick stropping is more than enough. To be honest, I feel my edges aren't a true success if they don't last for AT LEAST a week.
Let's not forget, these are tools that we hope to have around for a long time. If we thin a knife and keep it going at sub 10* angles and sharpen every two or three days, how long will we be able to use the knives we love so much?
There's a balance and I hope to achieve it every time I sharpen.

 

[EdipisReks]

you can always buy a new one if you wear it out.

 

[Lefty]

Have you no heart? Haha

 

[EdipisReks]

nope, i cut it out by accidentally tapping my knife edge against my chest.

 

[Lefty]

That sounds about right!

 

[Tristan]

Easiest way to rapidly improve your edge is to finish with a handful of VERY light strokes on both sides of your edge and get a cheap leather strop, load it with chromium oxide or diamond and abrade that wire edge off. Finish with light strokes and listen to the sound. It shouldn't sound like it's slipping across the leather. You should hear a very faint scraping. If you pick up your knife and there's a bunch of leather "dust" on your blade, the scraping isn't faint enough. If you don't want to get a leather strop, almost anything will work but it will take longer. If it still doesn't work, you can raise your angle some to work off the burr. You'll get a microbevel but at least it'll be a stronger edge...
It seems like yesterday that I was in your exact shoes except I learned to sharpen on a crystolon oil stone (yuck) and then went to a 3kSS single water stone solution. That was tough. Lots of gouging for a while.

I purcased a leather pad, and what looks like a crayon of chromium oxide. It comes in a hard cardboard tube, and the chromium itself it not a paste - it is like a very very hard crayon. Do i just rub it on the pad? Or does the chromium need to be prepped in some way?

 

[tk59]

There's no prep necessary. You can just rub the crayon on the leather until it's all green (hopefully, it isn't as hard as you're making it sound) then go to town. Go slow and make sure you check out what's going on and check out your edge after a few strokes. Get to know your equipment.

 

[Tristan]

Ok, I typically use full strokes the way curtis does it in his videos... I realise it isn't like the de facto way here on the forum...

I've alternated learning full strokes and also doing sectioning... I scuffed a blade pretty badly through sectioning and realised I wasn't keeping the angle consistent, somehow a full stroke seems easier to me.

 

[rockbox]

Tinh,

Here is a million dollar question. Can you pass your tomato test with a forschner? I understand that the edge may not last at all but can it pass it one time?

 

[Cadillac J]

My passion for rubbing steel to rocks will never go away, but I no longer feel I'm trying to chase some mythical 'perfect' edge---I know what I like, and I know how to sharpen to meet these requirements. I would estimate all my versatile double-beveled knives are between 8-12 degrees per side, extremely sharp, and they hold up really well with my cutting style in my environment...they might not be for everyone, but seem perfect for me.

Sharpness is all relative as we all know---a Wusthof might of been the sharpest knife you used years ago, but now it might not meet your current standards at all---edges you were happy with on your Tojiro in the first few months of sharpening, might embarrass you today if your results were the same. The whole reason I got into Japanese knives and whetstones in the first place is because I wasn't happy with the performance of European and other knives, so I was searching for something on a whole new level. It seems to be either discontent with the present, or curiosity of what could be, that push us to get to that next level.

 

[mikemac]

...Sharpness is all relative ...

So these discussions always seem to make my head spin (and I'm sure Dave will see my post and be somewhere between :bashhead: and :crying: ...sorry Dave)

Throw edge retention out the window for now....

Sharpness - for the sake of the discussion add an EP for consistency. Set the angle to "X" - could be 10, or 12 or... doesn't matter. And limit this to a 1k stone....no more, no less. Raise a burr on one side, flip the blade, push the burr to the other side, de burr with hard felt or cork, back to the EP, repeat to refine the edge, but still with only the 1k, and finally use the EP w/ 1k to strop.

Is a Forschner equally as sharp as a Shige, or Watanabe, Carter, Konosuke at this point? Each knife - exact same angle, stone, etc.
Are they or are they not all equally sharp? Why?

Now do the same with Blue #2, White, AS, CrMo, or PS quenched in virgin dew....aren't they still equally sharp?

OK - now change the scenario...this time what about Polish? If you start with two identical knives, and angles remain constant, but one is sharpened with the 1k, and the other is taken up thru the progression to a 5k or 10k....do you think one is 'sharper' than the other ? Why?

 

[Cadillac J]

Mike, not sure if your questions were directed at me or not, but here is my quick overall opinion, although I don't think it really help answer your questions (sorry!)

I'll be honest and say that I'm not even sure what a good definition of sharpness is...we might judge it by how easily the edge cuts things, but other factors such as geometry and whatnot also come into play that might alter our perceptions of one knife being 'sharper' than another. Even if an objective test was created...would it matter? If your favorite knife felt like the sharpest in your arsenal, yet when tested, it was found to be lower on the 'sharpness meter', would it change how you viewed this knife?

All I care about is if my knives cut how I like/expect them to for their intended purpose---if not, they need some work...if so, smiles all around.

Sometimes I think we tend to complicate things in search of 'truths', or based on other peoples' personal experiences reflected upon our own. Nothing wrong with that at all, but I like to keep things simple and do what works for me.

 

[StephanFowler]

So these discussions always seem to make my head spin (and I'm sure Dave will see my post and be somewhere between :bashhead: and :crying: ...sorry Dave)

Throw edge retention out the window for now....

Sharpness - for the sake of the discussion add an EP for consistency. Set the angle to "X" - could be 10, or 12 or... doesn't matter. And limit this to a 1k stone....no more, no less. Raise a burr on one side, flip the blade, push the burr to the other side, de burr with hard felt or cork, back to the EP, repeat to refine the edge, but still with only the 1k, and finally use the EP w/ 1k to strop.

Is a Forschner equally as sharp as a Shige, or Watanabe, Carter, Konosuke at this point? Each knife - exact same angle, stone, etc.
Are they or are they not all equally sharp? Why?

Now do the same with Blue #2, White, AS, CrMo, or PS quenched in virgin dew....aren't they still equally sharp?

OK - now change the scenario...this time what about Polish? If you start with two identical knives, and angles remain constant, but one is sharpened with the 1k, and the other is taken up thru the progression to a 5k or 10k....do you think one is 'sharper' than the other ? Why?

actually, potentially no, they would not get as sharp

when you abrade the surface of the edge you are removing steel right?
removing that steel makes the edge thinner, hopefully on a consistent plane equal and opposite to the other side (50/50 edge)
as the edge gets thinner those two planes will eventually meet, creating a "sharp" edge.

now, depending on the steel in question, the overall carbide size will determine how "sharp" that edge can become.
a steel with very large carbides CANNOT be sharpened as much as a steel with small carbides.

as the edge thins towards sharpness you will always eventually reach a point where the carbides are ripped out of the iron matrix, leaving ragged holes in the edge (on a microscopic level) with large carbides this is even worse.

if the carbides are sufficiently small and sharpening angle is not to aggressive you will be able to achieve an exact meeting of the two planes without losing the carbides, thus achieving a "sharp" edge.

 

[tk59]

Tinh,

Here is a million dollar question. Can you pass your tomato test with a forschner? I understand that the edge may not last at all but can it pass it one time?

Well, I don't have a Forschner on hand BUT, I just sharpened a 4" Henckels Pro S on 1k Gesshin, 5k Gesshin, 8k SS and 0.5 mcn chromium oxide and it passed the tomato test with slightly more than the weight of the knife but it's a pretty small knife. I'm seeing a friend of mine in a couple days that currently has one of my Forschners. I'll see if I can get that back for a test, too.

Tristan, I find that sectional sharpening really helped me work on my consistency but I do a variety of strokes depending on what seems to be working. I think the direction I stroke affects the way the knife cuts significantly.

 

[tk59]

actually, potentially no, they would not get as sharp

when you abrade the surface of the edge you are removing steel right?
removing that steel makes the edge thinner, hopefully on a consistent plane equal and opposite to the other side (50/50 edge)
as the edge gets thinner those two planes will eventually meet, creating a "sharp" edge.

now, depending on the steel in question, the overall carbide size will determine how "sharp" that edge can become.
a steel with very large carbides CANNOT be sharpened as much as a steel with small carbides.

as the edge thins towards sharpness you will always eventually reach a point where the carbides are ripped out of the iron matrix, leaving ragged holes in the edge (on a microscopic level) with large carbides this is even worse.

if the carbides are sufficiently small and sharpening angle is not to aggressive you will be able to achieve an exact meeting of the two planes without losing the carbides, thus achieving a "sharp" edge.

This is interesting, actually. I've been thinking about this a lot and trying to test it out and I've noticed a couple of observations I think might be worthy of adding:
1. Carbide size doesn't seem to affect the ability to pass the tomato test but it does seem to make it a bit more difficult AND it seems to make it through fewer times.
2. I really notice the difference when shaving and under the microscope. I have yet to have a comfortable shave with a knife made from stainless. Semi-stainless is a lot better, esp. the Heiji... :biggrin2: Shigefusa and Fujiwara Terayasu give the best shaves, so far, beating out the Heiji by a hair, maybe. It could just be my bias/preconcieved notion that carbon is going to be better, it was pretty close.

 

[Lefty]

Hmmm. Are the stainless you're testing powdered?
Do you come up a bit at the end of your stropping like a straight razor user?

 

[EdipisReks]

i've never gotten as good an edge with stainless, whether it be powered or non, japanese or swedish, as i do with carbon steel of any variety i've tried. same polish, same angles, just not as keen.

 

[mikemac]

actually, potentially no, they would not get as sharp

when you abrade the surface of the edge you are removing steel right?
removing that steel makes the edge thinner, hopefully on a consistent plane equal and opposite to the other side (50/50 edge)
as the edge gets thinner those two planes will eventually meet, creating a "sharp" edge.

now, depending on the steel in question, the overall carbide size will determine how "sharp" that edge can become....

So, this is the intersection of geek knife user with geek knife maker? :biggrin2:

Lets limit this to a 1k stone and a 'reasonable' (?) 12* per side....are there any knives that we typically use where the steel carbides are large enough that they are getting pulled out?

 

[StephanFowler]

So, this is the intersection of geek knife user with geek knife maker? :biggrin2:

Lets limit this to a 1k stone and a 'reasonable' (?) 12* per side....are there any knives that we typically use where the steel carbides are large enough that they are getting pulled out?

properly HT'd I don't know of any steels that would have carbide issues like that.
but again, that assumes properly Ht'd

very small variations in HT can have HUGE impacts on final carbide/grain size

one thing that I've been working on with 52100 is trying to find a balance between small grain/carbide size and hardenability.
It is not difficult to decrease the grain size to the point that the steel will not harden.
Annoyingly, the larger the grain size the easier it is to achieve high hardness (and typically blade failure as a result)

The holy grail for me ideally is to decrease the grain size to the point that I can just barely harden to 62HRC and then temper back very very slightly. If my understanding of 52100 is correct that will give me the toughest possible blade at the hardness that I want.

It's very easy to blow the grain up a little, HT to 64 or even 65 HRC and then temper back to 61, but the final blade would suffer due to increased carbide and grain size. It would show up as a blade that takes a good toothy edge at a very high grit but loses it very quickly.

a perfect HT (IMHO) takes a very high level of finish easily (this requires the smallest grain size possible) keeps it for a good while (which requires a fairly high finished hardness) and will not fail due to moderate edge abuse (tempered martensite is significantly stronger than non tempered martensite, thus the reason I don't reduce grain until I can barely harden the blade and leave it untempered)

 

[tk59]

It is common for stainless steels to have enormous grain sizes in the tens and even over 100 microns due to the aggregation of chromium carbides. That's why properly HT'd AEB-L is a nice stainless. It has carbides on the order of 1 micron in diameter. That's also why powdered steels are generally stainless since it reduces the probability of the aggregation.

 

[Tristan]

Well, I don't have a Forschner on hand BUT, I just sharpened a 4" Henckels Pro S on 1k Gesshin, 5k Gesshin, 8k SS and 0.5 mcn chromium oxide and it passed the tomato test with slightly more than the weight of the knife but it's a pretty small knife. I'm seeing a friend of mine in a couple days that currently has one of my Forschners. I'll see if I can get that back for a test, too.

Tristan, I find that sectional sharpening really helped me work on my consistency but I do a variety of strokes depending on what seems to be working. I think the direction I stroke affects the way the knife cuts significantly.

Today I took a long look at Jon's videos from the media section (all sectional sharpening), and then followed your advise on stropping. Loaded up the chromium crayon as much as the leather would let me smear on.

I must say that it is quite a nice edge! But of course, I made a wavy sharpening trail up 1/4 of the blade height... I still lack control.

I forgot to buy tomatoes. Tomorrow morning...

 

[StephanFowler]

It is common for stainless steels to have enormous grain sizes in the tens and even over 100 microns due to the aggregation of chromium carbides. That's why properly HT'd AEB-L is a nice stainless. It has carbides on the order of 1 micron in diameter. That's also why powdered steels are generally stainless since it reduces the probability of the aggregation.

but not necessarily assumed,

to get even close to apples to apples comparison you need to take a stainless as HT'd by someone who has spent a lot of time and effort working on getting an exact process defined for their stainless.
take Butch for instance, I would bet hand's down that Butch's HT of cpm154 would blow away any production cpm154 blade. because production by it's very nature will optimize HT towards the least failure, whereas Butch has spent a LONG time optimizing HT towards performance.

I would bet good money that Butch's cpm154 does NOT have an enormous grain/carbide size. (can't speak from experience as I've never used one of his knives)

 

[JBroida]

but not necessarily assumed,

to get even close to apples to apples comparison you need to take a stainless as HT'd by someone who has spent a lot of time and effort working on getting an exact process defined for their stainless.
take Butch for instance, I would bet hand's down that Butch's HT of cpm154 would blow away any production cpm154 blade. because production by it's very nature will optimize HT towards the least failure, whereas Butch has spent a LONG time optimizing HT towards performance.

I would bet good money that Butch's cpm154 does NOT have an enormous grain/carbide size. (can't speak from experience as I've never used one of his knives)

based on my experience with it, i would say it feels like a very fine grained stainless

 

[Eamon Burke]

I have yet to have a comfortable shave with a knife made from stainless. .

Totally my experience here, but I had to say it.

I've had no trouble getting a comfortable shave, and I think it has a lot more to do with the prep you do on your face than the actual characteristics of the steel.

This is somewhat relevant, because the same goes with food prep knives--there is a point to which your knife's performance will require you enhance it's environment. Put a great knife on a cheap bamboo cutting board and sure, it'll have edge retention problems.

 

[heirkb]

...I think the direction I stroke affects the way the knife cuts significantly.

I'm curious to hear a little more about your experiences with this. Do you find that doing certain types of strokes inherently lead to different cutting qualities (in your experience) or is it an issue of which stroke you're "better" at and therefore get a better result from?

 

[tk59]

Tristan: Sounds good. Looking forward to seeing how it performs for you.
Stephan: I didn't say stainless can't be fine grained. I cited AEB-L and powdered steels as examples of stainless with small or fairly small grain size, in general. I think it is safe to say that most stainless knives out there are med to large grained steel.
Eamon: I'm not a razor/shaving guy (yet). Prepping the skin differently for one edge vs another would defeat the purpose. The objective is to evaluate the edge, not achieve a comfortable shave.
heirkb: I'm not ready to say anything really definitive but there does seem to be an effect. I'm planning on testing this on a pro chef. The problem is I need to acquire a stainless knife to test him with because I don't want to jack up the finish on my semi stainless stuff.