Why are burrs so malleable?

[Mark Reich]

I've been studying the burr at the speed of smell, by sharpening on stones. There are two reasons it's difficult, if not impossible, to see at the speed of a belt. Belts just remove too much steel too quickly, and it's MUCH more distinct with edge leading strokes, especially on stones. 

I've been sharpening with Kallys for about a decade, without noticing this phenomena, all the while cussing the floppy burr. Now I know why the burr seems so floppy, and much has to do with getting to the base of the burr.  

I've learned at least two surprising, significant things about the burr, with the help of THESE little things I've mentioned before. If you don't have at least a handful, I pity you. It would cost twice the price for me to send you one, so just order some. If nothing else, kids of all ages go ape over them (I just ordered 30 more for stocking stuffers). But seriously, Nothing comes close for examining the edge. 

This is going to tie in with 2 things I've heard Mr Mike say. One was, "That line of crud on the edge" the other was, "This always happens on the burr side". Also, Mr KnifeGrinders statement about the "base of the burr". I actually coined that exact phrase before I ever heard it, so it is a real thing, and that's the best way to describe it. I was absolutely stunned to hear someone else say it.

I've already written a few drafts on this subject, but it's very difficult to describe what I've learned. I think I need to draw a picture, then scan and post it along with the drafts.

In the meantime, Mr KnifeGrinders, could you please describe "the base of the burr" as you understand it? I just know we must be talking about the same thing, because recognizing what you're seeing is absolutely critical. 

I'll give y'all something to ponder- Just because you can feel that the burr has flipped does not mean you've flipped the whole burr. When you've reached the base of the burr, there is no more flopping. The burr is gone.

I think this thread is going to solve a thing or two, but I'm edge leading on diamond plates, and y'all are edge trailing on belts. I have been able to duplicate removing the burr from a belt on a stone. The little microscopes have opened at least one of my eyes. 

[me2]

So I checked the knife block at home and found I have 4 knives in the condition described. There are 2 stainless, relatively inexpensive kitchen knives, a Santoku and a chef's pattern, and 2 relatively inexpensive Japanese kitchen knives. One is a small petty, the other a stainless laminated Bunka. I'll sharpen these later and see if there is a lot of difference with how they sharpen up. I also use 2 different methods. For the Petty and Bunka, I use 220, 1000, and 4000 grit water stones. For the 2 stainless knives, I typically use a Norton Economy Coarse/Fine combo stone with a DMT Aligner clamp. Edge angles are 12 to 13 degrees with a 3 to 4 degree increase for microbevels.

[KnifeGrinders]

Mark, spare my blushes please.

A priory I thought coarser grits give a thicker edge, and the purpose of working the edge through progressively finer grits is to thin the edge to make it sharper.

That turned out to be an errancy.

Since I turned my sharpening hobby into a business and number of knives I sharpen a month jumped from tens to hundreds, I desperately needed a sharpening protocol for effective volume sharpening.

Having studied through the Todd S SEM images at https://scienceofsharp.wordpress.com and his comments for the 3rd time, it dawned upon me that the edge often well below 0.1 micron is already there even after a 300 grit stone, for sure after grit #1000 - 0.1 micron is a DE safety razor edge as we know.
For the 300 grit it depends on other variables, but for the CBN/Diamond #1000 edge-leading invariably.
On #1000 stones the apex edge-leading is 0.5 micron, and edge-trailing 0.1 micron or less.

In knife sharpening we raise an even burr all along the edge to make sure that the sides of the edge have met at the apex, and now I know that the edge apex is sharp right at the burr base.

Our desired sharpness is already there, we only have to deburr completely without rounding the very apex, and expose that 0.1 micron edge that already is there.
Sharpening knives is all about deburring.
If having deburred we get an edge duller than 50 BESS, it means we've rounded the edge and worsened the initial sharpness hidden behind the burr.

As this became clear, the very first trial of honing off the burr at -0.1 degree less than the edge angle to spare the very apex, gave 50 BESS i.e 0.1 micron DE razor edge, and proved the concept.
The rest is history.

Explanation to why the burrs may be so malleable is in that thickness of the burr is reduced to a few tenth of μm at the edge apex, and this band of foil between the edge and the burr is strong to flopping with some steel. SEM images show that while edge-leading grinding produces 0.1 micron apex, the edge-trailing - well below that; therefore burrs produced edge-trailing are more malleable and difficult to get rid of.

[Jan]

I've already written a few drafts on this subject, but it's very difficult to describe what I've learned. I think I need to draw a picture, then scan and post it along with the drafts.

Mr. Mark, please be so kind and prepare for us a simple drawing explaining your burr thoughts.

You know, as an alien I am sometimes misunderstanding an iota or a dot in your post and it may prevent me from clearly understanding the whole thing. Thank you.

Jan

[Bud]

I've been reading your posts Jan for several months now and I think that there is not very much that you don't understand. I don't know where you are from, I doubt that it is Mars, but I would like to understand what Mark is saying better too. I'm a long way from where you guys are skills wise so i guess that I feel like an alien most of the time too. Burrs are a problem for me and any help, especially from someone like Mark would be very much appreciated.

[Jan]

Bud, thanks for your kind words.

I am from the Czech Republic, a small country in Central Europe. https://en.wikipedia.org/wiki/Czech_Republic

Our western and southern neighbours are Germany and Austria and so the first foreign language here was German followed by English. This is true for elderly people, for young people the order is opposite.

During the era of Soviet influence after the WWII, Russian language was compulsory. Thanks God it is over.
With hindside, what languages concerns, I can say it was a good training for our little grey cells.

Jan

[Bud]

Well that explains your remark Jan. I would never have guessed from your writing that weren't born right here in the the USA. Your teachers must have done a way better job of teaching you English than mine did teaching me Spanish. I can order a beer in Spanish and that's about it. It might not all be teachers, could have something to do with the student too. Thanks for letting me know more about you. That's really neat!

[me2]

Finally got the chance to do some sharpening.  I sharpened up both Japanese kitchen knives and had no trouble getting to the usual level of sharpness for those.  I used a 220 Norton waterstone, then a King 1000, each at 12 degrees per side (dps), followed by the Sharpmaker brown rod flats at 15 dps.  The resulting edge would tree top my arm hair with the grain and against, and sever a hair held between my fingers, similar to a hanging hair test, but instead of about an inch from my fingers it's more like 1/8".  I used the larger knife, a 175 mm Misuzu Bunka, to cut some apples and onions, and the edge dulled from corrosion.  I resharpened it tonight starting with the 1k King waterstone, followed by a 4000 grit King water stone.  Sharpness was about the same at severing a hair about 1/8" from point of hold.  I'm still getting the hang of the 4k stone.  

Before resharpening the Bunka, I cut into the 1k stone to remove any corroded material.  The double burr is not unique to the ceramic rod, as cutting into the 1k stone produces the same effect.  

I have the 2 stainless knives left to sharpen, but one requires rebeveling to my standard 12/15 dps/microbevel for kitchen knives.  It will be a couple more days before it's done.  

Also, I had a chance to check out the size effect article.  I have heard of this before, but it was related to silicon carbide whisker reinforced composites.  As size gets smaller, in these at least, fewer flaws are present in the structure, and they approach the theoretical strength, which is over 1,000,000 psi.  I will have to read the other link later.  I do not work with such large structures or thick steel sections and had not heard of the size effect in the negative direction.  Well, I had, but I thought it was something specific to rolling heavy sections of plate and related to differences in cooling rates and alloy distribution and such.  I hadn't heard of it being applied to structures as a whole, nor to reinforced concrete.

[EOU]

Interesting comments all round Me2. We took note of your comment " I used the larger knife, a 175 mm Misuzu Bunka, to cut some apples and onions, and the edge dulled from corrosion." We assume that you are referring to the acidic effect on the edge? Interesting because we've noted and measured the effects of oxidation on edges before but hadn't really considered possible corrosive effects. That would be a whole new area of interest, particularly for kitchen users.

[me2]

I resharpened a couple of stainless knives, one of which was dulled on the ceramic rod. I used a different procedure by using my Norton Economy stone coarse & fine stone, then the ceramic rod. This was done free hand, so the angle is somewhere between 10 and 15 degrees per side. This procedure resulted in an edge that would tree top head hair. I have not found dulling with the ceramic rod specifically to be detrimental. Dulling by lightly cutting into the abrasive appears to produce a two sided burr, even on abrasives other than the ceramic rod. As far as the sharpness tests I use are able to tell, there isn't a detrimental effect on sharpness if the edge is dulled by lightly cutting into the abrasive prior to sharpening. Further testing will need to be done to confirm this, and this is limited to low alloy carbon steels and simple 420HC and similar stainless steels.

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Interesting comments all round Me2. We took note of your comment " I used the larger knife, a 175 mm Misuzu Bunka, to cut some apples and onions, and the edge dulled from corrosion." We assume that you are referring to the acidic effect on the edge? Interesting because we've noted and measured the effects of oxidation on edges before but hadn't really considered possible corrosive effects. That would be a whole new area of interest, particularly for kitchen users.

For this effect alone, I am somewhat curious about the preference for non-stainless steels in Japanese kitchen cutlery.  I'm also curious if the edge finished on the ceramics of the Sharpmaker is less susceptible to corrosion than the edge finished on my 4k water stone.  I may have to sacrifice some onions and find out.