Testing for Overheated Edges

[Bud]

It might seem like six of one and a half dozen of the other to me Mr. KnifeGrinders. Apply more pressure and pull the knife through fast or less pressure and pull the knife through more slowly. In either case the same amount of metal would be removed and that is what the charts in the EOU post are talking about, the amount of metal removed.

[grepper]

This evidence indicates that with even a modicum of care heat is just just not an issue at all.

[EOU]

Not to turn this thread into a review of SET testing and edge rolling but it seems to us that one person's interpretation of SET testing data is just as valuable as the next persons. To us, subwoofer's review was amongst the most telling in that it showed us that, seemingly regardless of manufacturer, sharpness level or steel composition, that all edges roll and do so significantly under the same test conditions. SET testing is not definitive but evidentiary in nature and only gives us good reason to continue to question what we think we knew once.

[grepper]

Of course I could be laboring under a delusion Mr. KG, but I don’t think that I’m misinterpreting SET or other data presented here, but rather looking at it from a different perspective.
 
Indeed, I don’t disagree when you stated, “In applications where the sharp blade is a requirement, it all matters and matters a lot.”  No doubt those types of applications exist, as well as other applications where even a small improvement in sharpness and edge longevity is significant.  I believe I have often mentioned special use environments as an exception in my posts.
 
What is important to me, and how I interpret the data is from a “for all intents and practical purposes” point of view.  In other words, general use knives and cutlery that I would use in my kitchen or around the house.  These blades get to 250 quickly and probably won’t be resharpened until they are somewhere around 300 – 350.  Sure, it would be great if all my blades were always 150 or sharper, but even though I hate to admit it, that’s just not what happens. 
 
So, when I consider this stuff, it’s from a practical, general real-world use perspective.  From that point of view I’m not very concerned about creating the most perfect edge in every detail, or the minutia of metallurgical and molecular details about sharpening.  It’s interesting, but of little consequence when I’m in the basement touching up (umm..  slopping out?) my kitchen knives on my Kally. 
 
It may be sort of a cave man perspective, but for the most part what I find myself doing in reality is to create a good useful edge in the most expeditious way I can. Make ‘em sharp (150 or less), make ‘em toothy, use them, and repeat as necessary.
 
I applaud your attention to detail and perfecting the ideal edge.  It’s very impressive and your results speak to that.  I’m sure your expertise is appreciated and respected by your customers. 
 
I can understand that when you consider the test data your perspective is toward perfection and detail.  When I view the same data I do so with less lofty, more Neanderthal oriented goals.  Both are equally valid, just different.

[Mark Reich]

Both studies indicate sub 200C (392F) temperatures when something on the order of only 5-8 microns of material is removed in a single pass.  We'd think that 5-8 microns per pass would be regarded as a considerable amount of material removed when grinding (sharpening) a knife edge. These studies are detailed and we admit to only studying what seemed to be the pertinent parts. If anyone gleans something from them that we haven't, we would be pleased to learn what that might be.

 
5-8µ is approximately .0002- .0003". A tenth of thousandth  of an inch is hard for me to describe. The only relatively common power tool I can think of that works with that kind of tolerance would be an extraordinarily expensive surface grinder.  

It might be possible to remove that little material from a blade in one pass on a Kally with a 4K grit belt, but not even remotely possible with a 400 grit belt.  

That seems to be the difference between what is possible under laboratory conditions compared to what is not even remotely applicable to sharpening knives. 

Good try, Mike. I know you're trying to come up with scientific data that might be translatable to sharpening, but the more I see the less I believe such studies have been accomplished. 

I still think Tempilaq can be used to gain some practical understanding of how much grinding it takes to produce a significant amount of heat. I'll give it a shot.

[EOU]

We couldn't advance a meaningful argument one way or the other Mark. In terms of the sorts of distances most are accustomed to working with daily, 5 - 8 microns doesn't sound like much. Relative to the thickness of an edge apex it sounds like a bunch.

[Jan]

Both studies indicate sub 200C (392F) temperatures when something on the order of only 5-8 microns of material is removed in a single pass.  We'd think that 5-8 microns per pass would be regarded as a considerable amount of material removed when grinding (sharpening) a knife edge. These studies are detailed and we admit to only studying what seemed to be the pertinent parts. If anyone gleans something from them that we haven't, we would be pleased to learn what that might be.

 
5-8µ is approximately .0002- .0003". A tenth of thousandth  of an inch is hard for me to describe. The only relatively common power tool I can think of that works with that kind of tolerance would be an extraordinarily expensive surface grinder.  

It might be possible to remove that little material from a blade in one pass on a Kally with a 4K grit belt, but not even remotely possible with a 400 grit belt.  

That seems to be the difference between what is possible under laboratory conditions compared to what is not even remotely applicable to sharpening knives. 

Good try, Mike. I know you're trying to come up with scientific data that might be translatable to sharpening, but the more I see the less I believe such studies have been accomplished. 

I still think Tempilaq can be used to gain some practical understanding of how much grinding it takes to produce a significant amount of heat. I'll give it a shot.

Mr. Mark, you are correct! Size of grits determines the size of chips.

 
Jan

[Jan]

Allow me a general reminder for our discussion concerning overheated edges.
 
Heat is form of energy, which is spontaneously transferred from the hotter body to the colder body. There exist several transfer mechanisms.
 
Heat is measured by its effect on temperature of the interacting bodies.
 
The relationship between heat and temperature change is given by specific heat.

   
 
The specific heat per gram of water is some ten times higher than that for steel.
 
Jan

[KnifeGrinders]

Not to turn this thread into a review of SET testing and edge rolling but it seems to us that one person's interpretation of SET testing data is just as valuable as the next persons. To us, subwoofer's review was amongst the most telling in that it showed us that, seemingly regardless of manufacturer, sharpness level or steel composition, that all edges roll and do so significantly under the same test conditions. SET testing is not definitive but evidentiary in nature and only gives us good reason to continue to question what we think we knew once.

Mike, you told me once "For me, I never fear the light, only the dark."
For those who can read numbers given in the SET tests on this forum, it is obvious that the SET testing is good for "working edge", but not for testing edges sharper than 250 BESS.
I'd suggest revisiting the raw data we've made available, including those for 12 dps ceramic knife http://www.bessex.com/forum/showthread.php?tid=322
Ceramic edges don't roll, but respond the same way as steel knives - a single SET roll drops sharpness to 300 BESS, telling us that the impact is too much for the thin edge.

Reality is that quality knives roll less than mainstream, and hold the edge better along the whole range of sharpness, from razor sharp to working edge.
High-end knives and mainstream knives lose the initial keenness under 80 BESS similarly easy, but past this point the similarity ends.
Typically sharpness of a quality knife drops from the initial 40-60 BESS to 90 BESS, stays there for a few dozens of cuts, then moves into the 150-220 BESS range, and lasts there.
While a budget knife sharpness drops into the 300+ "working edge" range in the first dozen of cuts.
One does not need the SET-tester to know that, anyone with a BESS sharpness tester can see it.
You don't have to take my word for it, watch the tests done on high-end knives by the Sydney Sharpness Contest winner on YouTube
https://www.youtube.com/channel/UCcfBINH...QOA/videos
Summary of his tests: http://knifegrinders.com.au/Manuals/High...ention.pdf

This does not lessen role of the standard SET tester, only defines the area of its applicability to "working edges" of 250-500 BESS.

[EOU]

Thank you for your interpretations and opinions concerning SET testing KG. Perhaps now we can turn this thread back to overheated edges.