Do I need to worry about heat with a Ken Onion work Sharp?

[IXLR8]

I am not a fan of powered sharpening at all. There have been a few studies done, Roman Landes coming to mind, that showed that any and all powered sharpening will over temper those last few edge microns, if not deeper than a few microns. Lubricated power sharpening helped tremendously, and if you do any powered sharpening I would say use some sort of lubricant. If the system doesn't allow lubricant, I won't use it.

IIRC, this study went so far as to show that HAND sharpening on a stone without lubricant can/will over temper those last few microns. I was surprised to hear that, but figured it was so with powered sharpening. When I first saw that device introduced at market, I cringed.

With that said, I know of many pro knifemakers who sharpen their knives on their 2x72 grinder! Many use a mist system because of Roman's study. Many do not. It's up to you, but my opinion is stay away from it. But I'm more of a "purest" or OCD anyway.

What the study is saying is that keeping water handy in a bucket to dunk it in isn't going to help when sharpening. The heat being generated when contact is made with the belt, and immediately dissipated when lifted off. (at the edge micron level....not the whole blade). If the whole blade is warmed up by powered sharpening, my guess the very edge is already over tempered.

My two cents. I guarantee there are other opinions of powered sharpening.

My opinion of powered sharpening with this Ken Onion gimmick is the same as yours.
It is not needed. It does not provide a well finished symmetrical edge, introduces an abundance of human error, rounds off tips........takes off more blade steel than necessary..........and a host of other problems.

 

[HeavyHanded]

Does anyone have the link to Roman Landes study where he discovered these extremely high localized temps? Every time I do a search all I get are more references back to it, but never the study itself. I've always been curious how one could distinguish between the temp of the edge at the micron level and the temp of any adjacent ground off swarf or even bits of abrasive for that matter. The tale of the burned eye - does not seem possible that a piece of metal that small produced by hand sharpening could retain that much heat traveling the 18 odd inches from the workpiece to the eye, and have enough heat energy left to overcome surface moisture and still burn the eye.

For myself I have never noticed any difference in edge retention based on dry, wet, or powered sharpening, at least none that was apparent relative to other considerations. A difference of 4-5 points Rockwell C generally makes a notable difference in edge holding, I'd think a loss of same for any reason would be fairly obvious.

Not that heat buildup isn't a concern, where there's smoke there's fire and powered sharpening needs to be approached with care in any event. But as pointed out in earlier responses - I've noticed a fair amount of heat generation while using various cutting tools, in some cases far more than I've ever detected while sharpening, even on powered equipment.

 

[samuraistuart]

My opinion is based on personal experience with sharpening on paper wheels vs hand sharpening & Roman's work. There is a difference with fine edges with powered sharpening dry vs hand sharpening. If you don't notice it.....GREAT!!!! Roman's work was done in Germany, and I don't know if there is a link. I don't think there is. AFAIK, it is published, in German, on paper, in Germany. Roman did this all in lab settings, which I can promise is more than any of us have attempted to do here.

This is why I know of MANY great contributors to this forum who have simply left. Someone chimes in with an opinion based on fact, and look out....here they come. Messengers are shot on site on this site.

I've given my opinion, based in on personal experience, and a study done by a scientist in lab conditions.

If you don't agree, fine. I said it at the beginning, there will be differing opinions. When it comes to sharpening knives.....everyone's an expert in their own eyes.

As far as the physics behind what is going on....if dealing with carbon steel. Let's say a 52100 blade that is at 64 HRC after a 365F temper. 400F can be generated VERY VERY VERY quickly AT THE APEX of a micron thin edge when using dry powered sharpening. And now you have a keenly sharpened edge that went from 64 to 61 at the apex instantly. If you don't notice it........GREAT!!!!!!! If you are using powered sharpening, and are able to use your brain enough to know NOT to keep the blade against the belt for the length of time it will take to generate that heat.....GREAT!!!! How long is too long??? I DON"T KNOW. But it will depend on grit, speed, pressure, edge geometry, and the rotation of the Earth probably. OK....that was joke.....in case you think I'm being serious there.

If you think powered sharpening is the way to go, and by using such there is NO way to over temper an edge.....then use it. I will NOT.

Some men you just can't reach. Everything is contrary to them.

 

[HeavyHanded]

My opinion is based on personal experience with sharpening on paper wheels vs hand sharpening & Roman's work. There is a difference with fine edges with powered sharpening dry vs hand sharpening. If you don't notice it.....GREAT!!!! Roman's work was done in Germany, and I don't know if there is a link. I don't think there is. AFAIK, it is published, in German, on paper, in Germany. Roman did this all in lab settings, which I can promise is more than any of us have attempted to do here.

This is why I know of MANY great contributors to this forum who have simply left. Someone chimes in with an opinion based on fact, and look out....here they come. Messengers are shot on site on this site.

I've given my opinion, based in on personal experience, and a study done by a scientist in lab conditions.

If you don't agree, fine. I said it at the beginning, there will be differing opinions. When it comes to sharpening knives.....everyone's an expert in their own eyes.

As far as the physics behind what is going on....if dealing with carbon steel. Let's say a 52100 blade that is at 64 HRC after a 365F temper. 400F can be generated VERY VERY VERY quickly AT THE APEX of a micron thin edge when using dry powered sharpening. And now you have a keenly sharpened edge that went from 64 to 61 at the apex instantly. If you don't notice it........GREAT!!!!!!! If you are using powered sharpening, and are able to use your brain enough to know NOT to keep the blade against the belt for the length of time it will take to generate that heat.....GREAT!!!! How long is too long??? I DON"T KNOW. But it will depend on grit, speed, pressure, edge geometry, and the rotation of the Earth probably. OK....that was joke.....in case you think I'm being serious there.

If you think powered sharpening is the way to go, and by using such there is NO way to over temper an edge.....then use it. I will NOT.

Some men you just can't reach. Everything is contrary to them.

Is this directed at me?

I'm not discounting anyone's observations, studies conducted elsewhere, rigorous or not, others personal findings or practices. I simply asked a question, shared my observations, and asked if this material could be examined a bit closer as I don't understand how the readings were differentiated from other possible sources - a reasonable question. If that creates a reflexive outburst, you need to relax. If this isn't directed at me, please disregard the entire content.

We're all here to learn and share observations. You'll find I assign very few definitive conclusions to the observations I recount, mostly just more speculation. There's a reason for this - while not entirely unfamiliar to me, I don't much care for the taste of my foot in my mouth.

Personally I go out of my way to avoid powered sharpening, and when I do, I use a stop to prevent the edge from generating anything more than minimal contact pressure. But I'm also not going to pretend a layer of oil or water will absolutely prevent my edges from heating up when ground on coarse stones, or that my axe, hatchet, or machete edges do not grow warm when used heavily, or that a utility knife doesn't get warm to the touch when drawn through cardboard for a long pull etc etc, and all of these tools function very well for long periods of use. I have no idea what temp the final micron or so of edge reaches in use.

I'm also not going to claim any observable difference when I haven't experienced such, though, again, I'm not calling BS on anybody else nor am I unwilling to listen to what others have observed and add that to my own calculations when approaching a problem to be solved.

Edit to add: Discourse on this site is about as respectful as it gets and far more accessible than many other forums I've been on.

 

[BluntCut MetalWorks]

iirc - Lande's 2000+F temp it got mentioned & corrected http://www.bladeforums.com/forums/s...d-water-stone-review)?p=11184875#post11184875

As for projectile burnt eye - a shrapnel flies at mach1 will well-done your eye

Powered grind, I've burned my finger tips many time - pain for days. Just momentary lapse of focus + slightly dull belt will burn (blue-up & sometime melt sub-micron edge). At 400+grit belts burn rate is excessively fast on a thin edge - even in a single pass 1 second on a 4" blade.

Belts for powered sharpening probably not over-taxed like grinding, so less dull = less heat. i.e. clean fracture = low kinetic -> to thermal. because of edge-trailing nature, heat can accumulate toward the apex. If you can feel the blade too warm to touch, well a good chance the apex maybe over-tempered. Ppl, throw away dull belts <= easy to say but I enjoyed those burning sensation hence an exception - ahahahah

Manual sharpening - I only managed to burn my fingers twice or thrice trying to flatten a thing zero-grind blade on dull AlO sandpaper. However in normal sharpening sessions heat shouldn't be an issue at all dry or wet abrasive.

Does anyone have the link to Roman Landes study where he discovered these extremely high localized temps? Every time I do a search all I get are more references back to it, but never the study itself. I've always been curious how one could distinguish between the temp of the edge at the micron level and the temp of any adjacent ground off swarf or even bits of abrasive for that matter. The tale of the burned eye - does not seem possible that a piece of metal that small produced by hand sharpening could retain that much heat traveling the 18 odd inches from the workpiece to the eye, and have enough heat energy left to overcome surface moisture and still burn the eye.

For myself I have never noticed any difference in edge retention based on dry, wet, or powered sharpening, at least none that was apparent relative to other considerations. A difference of 4-5 points Rockwell C generally makes a notable difference in edge holding, I'd think a loss of same for any reason would be fairly obvious.

Not that heat buildup isn't a concern, where there's smoke there's fire and powered sharpening needs to be approached with care in any event. But as pointed out in earlier responses - I've noticed a fair amount of heat generation while using various cutting tools, in some cases far more than I've ever detected while sharpening, even on powered equipment.

 

[samuraistuart]

Heavy handed....no sir. Not directed at you. More to where this is going. This was a SCIENTIFIC STUDY DONE BY A SCIENTIST. Many of you browsing this thread know exactly what I am talking about. The reason I brought it up was because not everyone is aware of this fact of life. Bluntcut is painfully aware of these facts of sharpening. No PUN intended there Bluntcut!!

I was stating a fact, verified by LOADS and LOADS of scientific data (pages and pages of Romans study may or may not qualify as loads and loads to some). It seems that if a person cannot provide a picture, or link, or "prove it to me now this instant", then they must not be right. This is something that has been gone over and over. It is a simple fact of sharpening on powered equipment. I didn't make up the laws of physics....I'm just relaying them...and I get "I dont think so".

The person disagreeing with me here also wants to disagree that the Eastern bladesmiths call their primary bevels the "secondary bevel". "I remain skeptical" is the reply. I'm sorry if you don't like it!!!! I'm just stating what it is.

Like I said, some men you just can't reach. They are like others that I know. If you say "X is this", then they just HAVE to say "no it isn't".

To the OP of this thread, in direct answer to your title question.....YOU MOST CERTAINLY NEED TO WORRY ABOUT HEAT WITH A KEN ONION WORKSHOP OR ANY OTHER POWERED SHARPENING SYSTEM.

I am hearing from people here, "You do NOT have to worry about heat with a Ken Onion Workshop". And that is just as wrong as it gets. THAT gets me upset.

I have nothing more to input here. My goal was to help the OP, and he has been given contradicting opinions on how to approach powered sharpening. It is up to him/her to make the call and sharpen how they see fit.

 

[chiral.grolim]

Lost half of my post....

As far as the physics behind what is going on....if dealing with carbon steel. Let's say a 52100 blade that is at 64 HRC after a 365F temper. 400F can be generated VERY VERY VERY quickly AT THE APEX of a micron thin edge when using dry powered sharpening. And now you have a keenly sharpened edge that went from 64 to 61 at the apex instantly. If you don't notice it........GREAT!!!!!!! If you are using powered sharpening, and are able to use your brain enough to know NOT to keep the blade against the belt for the length of time it will take to generate that heat.....GREAT!!!! How long is too long??? I DON"T KNOW. But it will depend on grit, speed, pressure, edge geometry...

Nothing in this I disagree with.

But regarding chainsaws, most of us sharpen our chainsaws with files and Dremels, the stones on my dremel are finer grit than my coarse 325 DMT which is 45-micron particles with a lower effective grit and capable of producing a hair-shaving edge on the order of 1 micron or less. My dremel runs 5,000 - 32,000 rpm but I keep it on the low side when sharpening my chain. So YES a chainsaw CAN and I dare say SHOULD be sharpened to the micron level. It should be able to push-cut paper and skin if not shave hair.


Regarding strops, how much heat can you generate stropping rapidly on a loaded strop at very fine grit with a very thin and wide piece of metal? Enough to burnish the edge. Again, what is burnishing?

Paper-wheels heat an apex extremely quickly... and are also very common for final polishing of a bevel. If you think they are weak, perhaps it is because the metal is so thin at the apex, esp. if hollow-ground by the wheel? Just a thought, geometry always wins.

I can lean into a blade on my grinder and generate enough heat to change the color. But I can also sharpen on a grinder such that the edge seems to get no hotter than an edge used for cutting up cardboard boxes. If the temper is affected by power-sharpening in this way, then it is also if not moreso affected by actual cutting. I certainly advocate use of a coolant or lubricant, but the real test is performance, and if the edge cannot hold-up to cutting as intended due to heat-generation, then the sharpening method is irrelevant. If on the otherhand the edge CAN hold up to heat generated during cutting, then the generation of LESS heat during sharpening should not be a problem. As posted, surgical scalpels are power-sharpened evidently dry.

 

[BluntCut MetalWorks]

Just to clear & add. KOWS is a variable speed grinder also very low fpm due to small form factor (tiny belt on tiny motor). Heat issue can be easily mitigate to non-existence by using sharp belt + low rpm + light pressure + water dip every pass or 2.

When final grind my test blade for perf tests, I use extremely rapid grind pass - with water dip per pass - to apexed (either zero grind or tiny convex cutting bevel) it with 120grit ceramic. Then switch to 120 & 220 & 600 AlO stones, 1K & 4K (sometime 8K) waterstones.

btw - 400F been throwing around as magic temper temperature point. Well, many of my knives are tempered below 280F, some as low as 225F, therefore excess heat can be a problem quickly.

 

[chiral.grolim]

Here is the image Landes presented: https://docs.google.com/file/d/0B3dKJopPCAfCRWFkS1RuclhZQk5KN0VQSjVvb0lmYXFvR3lB/edit?pli=1

I can find no reference to a "study", only the above "test" performed in Fall 2013 that shows garden-shears hardened to 55 Hrc dropping to ~50 Hrc at 50 microns back from the apex. I cannot find any controls: wet-ground shears, hand-ground shears wet and dry, etc. I can find no indication of how much force was used, the abrasive grit, the time-frame, etc. Without that information, this is not a "study", it is just a demonstration.

For the record, I am a scientist, i work in biomedical research. The word "science" does not impress me. DATA is what i rely upon, and data must be put into a context of relevance. THAT is what i am working toward here, helping all to recognize the context of relevance. Do you have any idea how many "studies" are published, how many discoveries are achieved where the context of relevance turns out to be too limited for real-world application?? Keep it real.

Regarding the "Eastern" thing, it is not the term "secondary bevel" samuraistuart, it is the term "secondary edge" to refer to a primary bevel. Read. I love you too.

 

[HeavyHanded]

To the OP of this thread, in direct answer to your title question.....YOU MOST CERTAINLY NEED TO WORRY ABOUT HEAT WITH A KEN ONION WORKSHOP OR ANY OTHER POWERED SHARPENING SYSTEM.

I am hearing from people here, "You do NOT have to worry about heat with a Ken Onion Workshop". And that is just as wrong as it gets...

I would be concerned, as in worried - we are in 100% agreement there. Especially as pointed out, when doing the finishing work where a worn belt will cause much more friction due to increased contact area compared to a rougher surface (all other things being equal - applied force, feed-rate). Belts in good repair and very light contact pressure at the slowest possible speed setting should mitigate most of the risk or at least reduce any damage to imperceptible levels.

I still have many questions re the study Landes references, and not because I doubt friction generates heat, or that I am discounting the possibility of the findings. There are real technical challenges to mounting thermocouples to a block and registering temperature as its manually dragged across an abrasive surface per the description, especially if these temps are exceedingly brief and vary wildly (literally by thousands of degrees across periods as short as fractions of a second).
2000 C is hot enough to melt steel along the very apex. Again, it might be happening at the submicron level and I'm not saying anything else about it, but I'm agnostic on this one without knowing a lot more than I do.

EDit to add: the study Roman refers to involved a 2"x2"x4" steel block manually dragged across 1000 grit wet/dry. Sensitive thermocouples detected very high spike temps. This is all I have on it...

Edit #2: burnishing does not need to generate high heat loads - plastic deformation is not dependent on temp or high friction coefficients.

 

[samuraistuart]

I can't help myself!!! Just gotta chime in here!

Chiral, regarding the chain saw......just how long do you really expect the tooth of a chain saw to remain sharp compared to a knife edge? Like comparing apples to tennis shoes. Just no comparison there, bud.

Concerning stropping.....there should be very little heat. All you are doing is "pushing" mis-aligned steel into position, in line with the edge apex. And the more you strop, the weaker that steel that is out of alignment becomes. Like a paper clip that is bent over and over. Stropping SHOULD be done with very light pressure, with very few strokes. My experience is that if you see big gains in sharpness when stropping, you need to go back to the stones.

Your comment on the paper wheel hits on exactly my point. Thin edges.....powered sharpening....not good!!!!!!

It doesn't matter if it is the sharpening system, or the amount of cutting, if the temperature rises above the last tempering temperature the knife saw, the hardness will go down. How much loss is, again, dependent on a few variables, but it is LOSS. I don't sit here and type this stuff to "hear myself". I stand by what I say and my personal experience with paper wheels. I readily admit that using paper wheels was some time ago, before I even knew about heat treating/tempering all that stuff. There were times, obviously, that I let the heat get too high when using that system, and the edge retention suffered. I wish I knew then what I know now! I went thru a few of those swiss army box cutters because I was ignorant in my powered sharpening. WHICH IS WHAT I AM TRYING TO HELP OTHERS WITH HERE.

And I see we are waiting for someone to comment on the surgical scalpels. First of all, most of them now are disposable, but that doesn't matter. Let's take one that isn't. Scalpels cut material that is such NON abrasive it doesn't warrant the hardest edges, and if a point or two is lost in powered sharpening, the surgeon is going to be able to tell cutting thru someone's stomach. Again, they are sharpening scalpel after scalpel after scalpel. As long as it's sharp.....that's what matters to the surgeon. Not if the guy sharpening his scalpel reduced the hardness by a point or two.

I could make a knife like a razor blade in a minute with the paper wheels. Customers would "ooh" and "aah" over the edge I could put on their knife, and how quickly it was done. But it wouldn't last compared to hand honing.

 

[chiral.grolim]

HH, see my post above, hardness-testing, not temp-testing.

Also, the shears were sharpened with 220 grit Trizact. Landes has commented that running a blade across dry sand-paper by hand results in substantial heat-generation, some think this temperature reaches into the thousands at the very apex... that is by hand. Regarding his story about the burned eye, his colleague was sharpening a kitchen knife on a ceramic V-stick set-up like the sharpmaker... again, this is a story from the scientist himself.

 

[chiral.grolim]

I could make a knife like a razor blade in a minute with the paper wheels. Customers would "ooh" and "aah" over the edge I could put on their knife, and how quickly it was done. But it wouldn't last compared to hand honing.

THAT is the test.

Regarding chainsaws, with the speed and applied force and number of cuts achieved prior to losing that edge, I'd rate those teeth well above most knives :thumbup: My wood-chipper is pretty impressive too. You claimed that they don't get micron edges, that is flat false, they do and they should, just like knives, and they need to endure substantially more abuse than knives in terms of cutting-force and speed and repetition. What they do NOT need is 60+ HRC at the cost of durability! Like a machete, they are at much greater risk of impacting something they are not intended to cut.

Regarding scalpels, which i use on a regular basis, I need them to form a very fine and very crisp edge, no burrs and no corrosion. The ones we use are usually Aus-6 steel, not sure what hardness... Why are you bringing up edge retention and abrasive cutting? I'm not sure of the relevance ...

 

[HeavyHanded]

A last thought, shaving razors are sharpened on wheels with water, some of them used to use use a thin slurry on an iron wheel for the final pass, not sure what a modern shop uses.

Amazing that those scalpels are done in open air in the video link from pg1. I wonder if there's another unshown step that uses coolant in the process or the edge would be pretty poor if that one step was all there was to it. The scalpels I've seen, while still somewhat toothy, looked to have a secondary finish treatment along the cutting edge.

 

[chiral.grolim]

Edit #2: burnishing does not need to generate high heat loads - plastic deformation is not dependent on temp or high friction coefficients.

Burnishing: http://en.wikipedia.org/wiki/Burnishing_(metal)

When you drag one material across another as occurs in burnishing, you generate frictional heat. Plastic deformation is not dependent on frictional heat, the latter is unavoidable and may aid in lowering the yield-strength of the material to ease deformation. Or am I mistaken?

 

[chiral.grolim]

...The scalpels I've seen, while still somewhat toothy, looked to have a secondary finish treatment along the cutting edge.

Sometimes they are buffed on paper or cloth wheels with polishing compound.

 

[samuraistuart]

What, exactly, do you mean "That is the test"????? What I get from that statement is "All that matters is how sharp it is."

 

[chiral.grolim]

What, exactly, do you mean "That is the test"????? What I get from that statement is "All that matters is how sharp it is."

This:

I could make a knife like a razor blade in a minute with the paper wheels... But it wouldn't last compared to hand honing.

Comparing how long the edges last on edges with identical geometry but different sharpening methods - that is the "real world" test. I trust that you are very good at sharpening. What i would wonder is, what sort of task would be put to each test knife and would the stress of that task overshadow any difference in how the knife was sharpened? For example, you've seen the SEM of the hand-honed razor-blade that sliced through a few centimeters of paper, right? Ruined. Would a machine-honed edge perform any worse in such a test, or is the test too harsh to generate a comparison? I believe that power-honing has more potential to damage the apex, especially when dry, what I doubt is that most users would notice the difference in the stresses they apply to each blade. Just like I believe that CPM-10V has more abrasion resistance than 420HC, I just think most users would damage their edges in some other way that obfuscates the advantages that 10V blade may have lent. The context must be relevant. If you hand-hone a blade for me which i then "ruin the temper" of while cutting cardboard, would I be able to tell the difference from a blade with "ruined temper" from power-sharpening? That is the study I want to see.

Regarding the WSKO, if users report "lasting edges" of "excellent sharpness", then either they don't have a proper comparator or any detriment of the power-grinding is overshadowed in use. *shrug* If you'll never notice, why worry?

 

[HeavyHanded]

Burnishing: http://en.wikipedia.org/wiki/Burnishing_(metal)

When you drag one material across another as occurs in burnishing, you generate frictional heat. Plastic deformation is not dependent on frictional heat, the latter is unavoidable and may aid in lowering the yield-strength of the material to ease deformation. Or am I mistaken?

There will be some friction, but needn't have a high coefficient, needn't be high enough to cause any real generation of heat, at least not compared to the action involved in a grinding operation. The burnishing action is deforming the surface of the steel, not scratching it away. Pressure is the more important component, frictional sliding isn't even necessary to create the effect.

Burnishing also occurs when the ball can rotate, as would happen in the above scenario if another flat plate was brought down from above to induce downwards loading, and at the same time to cause rotation and translation of the ball...

True enough, in some stropping actions there is certainly more friction than described above, but at hand speeds it would be presumptuous to assume any substantial heat generation without proof of some sort. Consider the act of using a smooth steel on lower RC cutlery - in my experience it actually increases edge retention by work hardening a relatively soft piece of steel. Has the opposite effect if overdone or used on higher RC steel - brittle failure and chipping. I cannot imagine heat plays any roll at all worth mentioning.

 

[chiral.grolim]

Yes, the ball is not rolling, the bevel is being dragged against the surface of the hone, and the contact is high = high coefficient of friction.

If the normal force is low, the ball will rub against the plate but not permanently alter its surface. The rubbing action will create friction and heat, but it will not leave a mark on the plate. However, as the normal force increases, eventually the stresses in the plate's surface will exceed its yield strength. When this happens the ball will plow through the surface and create a trough behind it. The plowing action of the ball is burnishing.

http://en.wikipedia.org/wiki/Friction#Coefficient_of_friction
COF wood:wood, which can be used to start a friction-fire by hand on relatively large/thick pieces of wood = 0.4
COF Metal:metal, which on a knife is at much smaller geometries than sticks being used to start a fire = 0.8
I admit I am not a physicist, but that suggests to me that sharpening and burnishing involve a lot of heat in the affected areas. If frictional heat were not in effect, you should be able to accomplish "burnishing" by simply pressing the hone on the bevel and lifting off again, no stroking or stropping required, correct? That is the "rolling ball" scenario.... but it doesn't work that way. Keep in mind that the surface of the bevel, even with the scratch-pattern, is quite robust with a thick geometry in those scratches, lots of supporting material that needs to be squashed and "smeared". What hardness is that martrix such that deformation is plastic rather than elastic, that the yield point can be exceeded on such thick geometry at high hardness? Why does it work?

The story Landes relates is a colleague sharpening on a ceramic V-stik set-up ... by hand ... being burnt. *shrug*