Losing temper when sharpening? Has anyone tested this?

[Horsewright]

I have a buddy that writes articles for outdoor sporting magazines. Couple of three years back I assisted him in testing two identical hunters for an article. One was 440C the other D2, otherwise identical. I did not make these knives nor do I know who did as they were not marked. The test was to cut through 1/2" sisal rope until the knife would no longer cut, resharpen and repeat and repeat. Everything was done 3 times, all results were written down and then averaged. I did all the cutting and the sharpening as my friend was recovering from shoulder surgery and simply couldn't. We literally filled a 55 gal oil drum with 1/2" pieces of cut off 1/2" rope over three days. To get to the point of this thread was that we also tested between hand sharpening and power sharpening (vfd grinder on pretty darn slow, 220 belt and then hit the very edge of the secondary bevel with a buffer, sewn muslin wheel and green scratch remover). Now I KNOW that power sharpening over heats the edge and the thinner the edge the more so. I know this. I'm a huge fan of hand sharpening and was a waterstone fanatic before it was cool. But in this test and maybe this cutting medium (quien sabe?) it made no difference whatsoever. Hand sharpening was done first and resulted in no more cuts than the power sharpening done later. There was no difference.

 

[Stacy E. Apelt - Bladesmith]

Roman Landes has done extensive research in the temper change in sharpening and stropping. In his opinion, both procedures should be done lubricated and by hand. Any power machine will have some loss.
IIRC, there was a discussion with him on this subject on hypefreeblades.com after last years Ashokan seminar.

 

[P. McKinley]

As a retired chef I've hand sharpened thousands of blades over my life. A pair of whetstones has always been my set up.
Making knives these days, I usually set the edge on a belt then clean it up on the stones.

But, when it comes to re-curves, how do you sharpen this on a whetstone:

 

[james terrio]

Slightly out-of-context, but still worth repeating:

I sharpen under power. I do this at low speeds and sopping wet. I don't dip, I'm running a dripping wet belt on an ice cold platen chiller. And even then, if it really matters I still finish on oil stones.

I sincerely apologize to Nathan if I'm quoting him out of turn... But I didn't edit a word he said. He's put a great deal of time and study into grinding cool... and still finishes his edges manually when they really matter.

That said I sharpen my lawnmower blades and my mother's shitty kitchen knives hot and dry. Some applications it just doesn't matter.

I agree with that, too, like I said before about my lawn/garden tools. Knock an edge on 'em, knock the burr off, beat 'em like a rented mule and start over next week.

But when it comes to a knife that means the difference between gawd-awful frozen burritos, or steak and fresh salad on my table this week... my clients sincerely care about this kinda thing, and they pay me to take my time and do it right. The extra effort is worthwhile.

But, when it comes to re-curves, how do you sharpen this on a whetstone:

Speaking of off-topic... I would (and have) sharpen an edge like that with stones that are narrow enough to "ride" through the inside curves. That concept is far from unheard-of.

 

[Hengelo_77]

But, when it comes to re-curves, how do you sharpen this on a whetstone:

That is why I don't understand the hype around recurved blades.
But look up "scary sharp sharpening" and use a round glass bottle or so with the sandpaper. That is how I would do it.

The way I understand it only the first "steel atom" does the cutting, everything behind that only holds that first "atom"
It makes sence to me that sharpening dry heats that tiny small bit of steel up quickly. Far less then we can see or feel.
I just sharpen wet on DMT

 

[Nathan the Machinist]

Slightly out-of-context, but still worth repeating:



I sincerely apologize to Nathan if I'm quoting him out of turn... But I didn't edit a word he said. He's put a great deal of time and study into grinding cool... and still finishes his edges manually when they really matter.



I agree with that, too, like I said before about my lawn/garden tools. Knock an edge on 'em, knock the burr off, beat 'em like a rented mule and start over next week.

But when it comes to a knife that means the difference between gawd-awful frozen burritos, or steak and fresh salad on my table this week... my clients sincerely care about this kinda thing, and they pay me to take my time and do it right. The extra effort is worthwhile.



Speaking of off-topic... I would (and have) sharpen an edge like that with stones that are narrow enough to "ride" through the inside curves. That concept is far from unheard-of.

I think that what really matters is what type of knife it is.

It doesn't matter if you sharpened it wet under power or wet on a stone, after a few feet through something like cardboard those first few microns are going to be wore away regardless.

But! Some knives you wouldn't dream of using to cut cardboard. A nice thin Santoku, Usuba or a Yanagiba sashimi knife is expected to be hair popping sharp and the edge should tolerate incidental contact with the cutting board. These edges are extremely thin, they can easily be flexed over your thumbnail, and can be ten degrees included angle. The combination of a thin edge like this (where heat can easily build up) and an application where the edge must remain very sharp during use dictates wet hand sharpening.

 

[BluntCut MetalWorks]

Heat is one of many factors contributes to poor edge performance when power sharpening. Is it the most important factor? Not necessary.

Beside heat & steel type+ht ...

1. Insufficient velocity - yes too slow, where abrasive rough-up the edge by bounce & skid against the matrix (and carbides).
2. Burnishing - matrix plastic flow toward the apex, thus a blanket of weaken matrix and sans carbides.
3. Fractured/cracked apex - not enough force to carbides & grains pull/pop out but edge is weaken.
4. Abrading direction (edge away vs edge into) - affect 2 + 3 + heat flow.
5. Abrasive type+size+bind+state - affect 1+2+3 + heat generation.
6. Pressure & Incident angle - e.g. platen vs wheel.
7. Edge geometry - flex/rigid amount.

I am sure there are more than what listed but we shouldn't simple put all the bad perf blames in the heat-catch-all bucket.

 

[james terrio]

I am sure there are more than what listed but we shouldn't simple put all the bad perf blames in the heat-catch-all bucket.

Certainly! But since the OP's question is specifically about heat, we can fairly assume that all other factors are equal.

I think that what really matters is what type of knife it is.

Again, I agree completely. I wouldn't filet a trout with a splitting maul, and I wouldn't split firewood with a nice thin boning knife Nor would I sharpen them the same way.

 

[Bo T]

Heat is one of many factors contributes to poor edge performance when power sharpening. Is it the most important factor? Not necessary.

Beside heat & steel type+ht ...

1. Insufficient velocity - yes too slow, where abrasive rough-up the edge by bounce & skid against the matrix (and carbides).
2. Burnishing - matrix plastic flow toward the apex, thus a blanket of weaken matrix and sans carbides.
3. Fractured/cracked apex - not enough force to carbides & grains pull/pop out but edge is weaken.
4. Abrading direction (edge away vs edge into) - affect 2 + 3 + heat flow.
5. Abrasive type+size+bind+state - affect 1+2+3 + heat generation.
6. Pressure & Incident angle - e.g. platen vs wheel.
7. Edge geometry - flex/rigid amount.

I am sure there are more than what listed but we shouldn't simple put all the bad perf blames in the heat-catch-all bucket.

A well thought out set of parameters. And some reasons why there are professional sharpeners out there.

 

[Rhinoknives1]

As a retired chef I've hand sharpened thousands of blades over my life. A pair of whetstones has always been my set up.
Making knives these days, I usually set the edge on a belt then clean it up on the stones.

But, when it comes to re-curves, how do you sharpen this on a whetstone:

Recurves can also be done using a hand held spyderco sharpmaker rod or any of the other round and epitical stones out there. On something as thick as your Kukuri I do them on my 2 x 72 belt grinder at slow speed and with a sharp belt.

 

[tryppyr]

I set my edge using the Edge Pro Apex, then do all the real sharpening on Norton Waterstones, followed by about three passes on a pigskin strop (by hand). I guess one of the advantages of being a hobbyist is that I don't care how long it takes to achieve the desired results... I don't have to care because I'm not trying to recover the cost of my time.

To Nathan's point, we all know (or at least those who've read the study know) that sharpening under power is not ideal, and that we make a trade off between quality and expedience when doing it. If I recall the data correctly, even vigorous hand sanding creates more heat than we imagine on the finest part of the edge. But since most of us aren't making straight razors, the difference would be all but impossible to discern.

So the question that seems to be underneath this discussion is when does absolute perfection matter enough to invest the time to achieve it? In industry the question is reworded to "What is required to make the product good enough?"

- Greg

 

[elementfe]

Anecdotal evidence:
In the local restaurant sharpening business, my predecessor used a water cooled Tormek, I use a HF 1" belt grinder.
His edges were a constant frustration, he took off too much material, and the edges never seemed to last.
Mine make the eyebrows go up (you've seen the look) when they feel them, and I don't get to sharpen as often because of the edges hold up for weeks. My final step is a 5 micron polish, on the belt grinder.
By all current thinking, it should be a terrible edge, but the restaurant folks think it lasts and lasts. (I use sharp belts, and stay the heck off the platen)
Now, I'm as big a fan of water stones as anyone else, I'd use them for the pure pleasure of finishing an edge by hand- apart from the advantages you all have mentioned.
I'm not trying to "prove" anything, just passing on my experience sharpening thousands of knives by different methods.
If it was up to me, I'd charge several times as much and do em all by hand...
Landes is doing some great work, it's changing my approach, for sure.

In the Ashokan excerpt he attributes sparking to energy put into (induced) the edge by force and friction- I suspect this is at least partly a mistake: The pyrophoric reaction that produces sparks may or may not affect the edge, since it occurs mainly away from the fine edge....but coolant almost certainly takes that out of the equation.
The right kind of steel will spontaneously (I'm not sure that's an appropriate term) combust if small enough particles are suddenly exposed to oxygen-thus grinder sparks. A flint and steel does the same thing. My question is, does this occur close enough to the fine cutting edge, during sharpening, to compromise the temper of the edge? My guess is not- but that has nothing to do with heating by friction, which we all know can and does.

 

[james terrio]

So the question that seems to be underneath this discussion is when does absolute perfection matter enough to invest the time to achieve it? In industry the question is reworded to "What is required to make the product good enough?"

That's a fair question, to which I have three responses. Of course, I'm speaking as a guy who makes handmade knives in a one-man shop for a living, not as a hobbyist or someone running a factory. There's a huge difference...

First, I'm not terribly interested in "absolute perfection" on an edge, since I make EDC's, hunters, survival/tactical knives, and knives for daily kitchen use. I typically only go up to 1000-grit stones. Not one of my clients has ever asked me for a novelty edge that will cleave a silk scarf as it falls across the blade. They just want an edge that will cut paper cleanly and shave hair off their arm... and stay that sharp for a reasonable amount of time. That sort of edge will perform well in deer camp, in the kitchen, on the jobsite, etc. with minimal maintenance.

Second, it doesn't take that much longer to set bevels on a fine belt and then finish sharpening a raw blade by hand if the geometry is good to begin with... and my clients don't seem to mind paying for the time it does take. If the edge is crazy thick, yeah that's gonna take a while. Now, if I was working in a factory and had per-hour quotas to meet, I'd leave the stones to the side and just hammer out a basic edge as quick as I could... like I do on my own yard tools.

Third, I put a lot of time and money into design, materials, grinding, assembly, HT, etc... I'm not going to piss that away by blowing out the temper on my edges just to save a few minutes at the very end of the process. Which just happens to be the part that really matters most... whether or not I deliver a sharp knife that keeps its edge through a lot of work.

Again, our clients willingly pay a premium for our craftsmanship. If "good enough" was good enough for them, they'd buy factory knives. They certainly do not want to resharpen a knife they spent many hours of wages on several times, just to get back to the un-burnt steel.

By all current thinking, it should be a terrible edge, but the restaurant folks think it lasts and lasts. (I use sharp belts, and stay the heck off the platen)

Your approach makes sense to me, because it seems you're addressing the problems of avoiding heat build-up as well as being productive and efficient. That may well turn out to be the best compromise between two extremes. :thumbup:

 

[Stacy E. Apelt - Bladesmith]

Many folks who cut a lot of meat and fish have discovered that a 220 grit edge on a slack belt will make a very aggressive cutting edge. 400 is finer than many like.

My buddy who runs a BBQ place (and makes knives) has a little Hobart belt sharpener that takes 16" belts. He has 320 and 600 grit belts for it. He never changes to the fine belt, and sharpens on the medium only. He cuts a LOT of meat with that edge.

 

[elementfe]

Bladsmith, it would be fun to take a place like that and try him out with some various techniques, from fine waterstone to 220, and see what he thinks.
In fact, I think I'll try that with some of our local chefs.

 

[marthinus]

Example from Roman Landes of a power sharpened edge, 220 grit Trizact :

https://docs.google.com/file/d/0B3dKJopPCAfCRWFkS1RuclhZQk5KN0VQSjVvb0lmYXFvR3lB/edit

Josh,
What you see is a professional gardening scissor examined. It show an angle on the edge of 45° and an hardness loss on the edge of minimum 5HRC through grinding. While the scissors work with more force its not so significant when they loose some edge quickly.
Lets say they degrade form 5µm sharpness to 15µm sharpness within a few cuts.
You wont notice much difference in force through this effect.
But you start to loose cutting quality by squeezing more than clear cutting.

Now lets go to the other end of cutting a razor blade.
Your razor blade is around 0,2-0,3 microns sharp the angle is around 18°-20° total.
The volume fraction that has to absorb (cool away your heat) is far less than with a scissor.
Is will be much more effect you can see.
This is why the razor blade industry and high quality knife making companies (Japanese) cool their edges whilst sharpening.

 

[Rhinoknives1]

Anecdotal evidence:
In the local restaurant sharpening business, my predecessor used a water cooled Tormek, I use a HF 1" belt grinder.
His edges were a constant frustration, he took off too much material, and the edges never seemed to last.
Mine make the eyebrows go up (you've seen the look) when they feel them, and I don't get to sharpen as often because of the edges hold up for weeks. My final step is a 5 micron polish, on the belt grinder.
By all current thinking, it should be a terrible edge, but the restaurant folks think it lasts and lasts. (I use sharp belts, and stay the heck off the platen)
Now, I'm as big a fan of water stones as anyone else, I'd use them for the pure pleasure of finishing an edge by hand- apart from the advantages you all have mentioned.
I'm not trying to "prove" anything, just passing on my experience sharpening thousands of knives by different methods.
If it was up to me, I'd charge several times as much and do em all by hand...
Landes is doing some great work, it's changing my approach, for sure.

In the Ashokan excerpt he attributes sparking to energy put into (induced) the edge by force and friction- I suspect this is at least partly a mistake: The pyrophoric reaction that produces sparks may or may not affect the edge, since it occurs mainly away from the fine edge....but coolant almost certainly takes that out of the equation.
The right kind of steel will spontaneously (I'm not sure that's an appropriate term) combust if small enough particles are suddenly exposed to oxygen-thus grinder sparks. A flint and steel does the same thing. My question is, does this occur close enough to the fine cutting edge, during sharpening, to compromise the temper of the edge? My guess is not- but that has nothing to do with heating by friction, which we all know can and does.

One of the most blatant reasons the Tormek edges don't last is that they are a hollow ground edge and your edges on the belt sander are convexed, there could be other reasons but just to let you know I had a Tormek and after awhile saw that my edges on my 2 x 72 belt grinder were far superior, so I sold that Tormek. I have a Twice As Sharp machine for sharpening scissors & con vexing beauty shears.

 

[elementfe]

The more I think about this the more questions come up.
What about doing final sharpening into rather than away from the edge? With power tools, we do it away for safety, and a non chrome -heavy steel will throw sparks away from the knife...what if you could go into the edge, would heating effects be moderated because the abrasive wouldn't be pulling a wire edge out of the body of the knife? Distorting the steel like that would just about have to produce significant heat, perhaps if it wasn't pulling wires out, the heat might be reduced considerably.
And on my mind goes....