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 Post subject: Re: Starting a new edge?
PostPosted: Fri Feb 21, 2014 8:20 pm 

Joined: Fri Feb 14, 2014 4:23 pm
Posts: 7
ken123 wrote:
So jumping from a 240 grit edge to a 3k stone will give you a finish looking like a 3k edge, but a poor one indeed.



Ken, in context I was replying to a comment where Sadden noted that failure to eliminate apex scratches would cause issues with polishing, and I agreeed and noted an example of how that could be compounded by current stones. I was not describing a sharpening method which was claimed to be ideal, or even advocated for general use.

However if I was for some reason limited to a 240X and 3000K SPS-II stone it is easily possible to form the edge without this issue and I have described it in detail on the T0.1M forum with the 50X shots. The process is :

-hone to dry on the 240X and stop at the point of light reflection being eliminated
-the edge thickness is just under 20 microns at this point
-hone with the 3000X SPS starting with a saturated stone and honing to dry

There is no need for magnification at any stage in the sharpening, for reasons noted. I did this experiment for many reasons, one of them was to see if I could 2-stone like Carter but over a wider range of applications and the 240X is much more capable of removal of damage than the 1000 King he uses, but it then requires more work to clean up. Thus the technique to hone-to-dry which allows greater speed of material removal and a finer edge finish than the 1000/6000 combination he uses.

As a side note, if the steel is very prone to burr formation and especially if it is very easy to grind it may be necessary to put a burr minimization step in between and this can be done with either stone depending on how severe the problem is produced. Of course the SPS stones are not special in this regard, any two stones can be used in the same combination and it works on any steel, not just the easy to grind ones, I have done it all the way up to 121REX at 70 HRC and I have done it with non-specialized stones. Though of course nicer stones make it easier and if you can afford them there is no reason not to use them aside from some self imposed challenge.


ken123 wrote:This is a particularly abrasion resistant steel (high vanadium carbide content) and cutting this steel with a stone with softer abrasives does little more than wear a stone down, producing an inconsistent bevel angle in the process of dishing the stone.


In regards to the Bester 700X, I took the 121 REX down from ~0.010" to full zero with no visible hollow in the Bester. The wear in the stone induced an edge curvature of ~1 dps in the primary bevel. Of course the stone was used in a staggered pattern. As for its use, I had not used the Bester on a high carbide steel and wanted to explore at that carbide level it was outperformed by the more costly SPS-II series stones and as well to compare the grinding times as a function of abrasive and the longer the pass count the more accurate the comparison.

Had I just wanted to do it in the shortest time I would have power sharpened it with coolant, but again, this wasn't about the fastest sharpening time.

ken123 wrote:What you are describing 'academically' is referred to in statistics as 'covariance'.


I am not talking about covariance which is the correlation between variables.

I am talking about bias as in measurement bias, any influence which shifts the sample statistics away from the population. A burr is just the extent to which the edge is formed less than ideal and is therefore biased because of various influenced from the true value (perfect apex). I have also been using the exact same definition for 20 years.

Again if you don't like it no issues, use whatever term you want.

ken123 wrote:So in the first micrograph, there is more than a simple burr present. There is significant edge damage too.


The damaged steel has long been removed, what you are seeing is the fatigued steel which was under the original damaged edge not being able to form properly as it is over strained. To be clear that always happens on some level, the exact same thing will happen on any edge, you just have to go to higher magnification shots to see it. Now to be really clear we are talking about traditional sharpening, it is possible to sharpen and form edges on a atomic level which are perfect of course.

ken123 wrote:Here removal of the damaged edge is best achieved with ...


As before, I have stated my position and the physics behind it, it is also very easy to see if you file sharpen as the same thing will happen but you can then see the burr visually and what happens if you just alternate sides compared to cutting it off. As noted, I rarely do 90 cuts after the initial destressing, in fact since I don't burr sharpen I rarely have to remove a burr at all.

As for the micro-bevel, when Clark first proposed his method a number of people made the same objection, however the bevel which is formed at the 1-2 passes which are needed to remove that burr is so small it isn't even seen under 50X magnification, it can not even be detected under very fine measurements of sharpness.

ken123 wrote:You are simply causing a clogged stone and reducing the stone's efficiency.


Yes, because at that stage the maximum rate of cutting ability is no longer what is desired.

Ken, just to state the obvious, not everyone has a wide range of stones, this data might not be of interest to you, fine, it is of interest to me and because of this and other experiments I can do things like this easily :

http://www.youtube.com/watch?v=5At3NtNKHFA

That is the edge right off of a 24 grit stone, which readily cuts fine papers, shaves, and does other high sharpness work and it is achieved with techniques such as described in the above and on a knife which has far less than ideal steel and thermal processing.

Again, this might not be of interest to you, fine, please realize that lots of people can not afford high end stones, or a wide collection and some people are even interested on how to field sharpen on very non-ideal abrasives.

The ability to take a knife from completely dull with the edge cut off to formed to shaving sharp in ~two minutes with no sharpie, no magnification, with a very coarse stone (and as well I did the same thing with an ordinary red brick) is again of interest to a lot of people.

And yes, I also sharpen with regular hones in more traditional methods and I have natural and synthetic stones of all makes and models and power equipment and have used high end jigged systems as well.


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 Post subject: Re: Starting a new edge?
PostPosted: Sat Feb 22, 2014 12:34 am 
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"I was not describing a sharpening method which was claimed to be ideal". I think we have a point of agreement :)

"However if I was for some reason limited to a 240X and 3000K SPS-II stone ..."
Now if I was on a desert island, or in some bizarre sharpening contest, I might resort to doing this sort of thing, but might either look for something intermediate between the two as a more logical choice. I might even resort to using the 3k stone as a slurry stone on the 240 grit stone [probably not]. Somehow I can't imagine even the poorest of sharpeners somehow only having these two stones to choose from. Even a King Combo stone would be more appropriate. You are using a ~ 10x difference in grit here and would be better served with a 1k stone. I guess I just have a more practical approach than solving non-real scenarios. Of course then I would have to lap the stone or otherwise refresh the clogged stone using this approach. This is confusing at best to fellow sharpeners.

You're mentioning edge thicknesses of 20 micron (without supporting data) and go on to say magnification isn't needed. I really don't see where the 20 micron 'data' is relevant. Please expand on this.

While I prefer an intermediate stone between a 1k and 6k, extending this gap even further seems quite impractical and unwise as an approach. The approach is not one of practicality, but rather one of 'Can I do this with that?' I think we are simply appealing to two different approaches to problem solving to be kind.

'some of the newer polishing stones that cut very fast' vs 'Of course the SPS stones are not special in this regard, any two stones can be used in the same combination' Thank you for clarifying the point that fast cutting stones is not the relevant criteria here. This is a point of agreement.

'aside from some self imposed challenge.' This is becoming a common thread in your approach. Again I seek utilizing an optimal approach. For something like Rex121, quickly putting an edge on it using the right abrasive for the job seems a better approach than selecting a less appropriate approach and spending an inordinate amount of time doing it. Again this is pounding in nails with a screwdriver handle. You could do it, but why? I don't feel you get extra points in life for suffering unnecessarily.

You are yet redefining again your use of 'bias' to mean measurement bias. This is clearly not the case. If there is a burr present, that is the data. Observer bias implies that the observer is somehow biased into seeing or not seeing the data correctly. You are describing deviation from a theoretical norm, not measurement bias. 20 years? I'm glad I caught this one in time :)

'The damaged steel has long been removed, what you are seeing is the fatigued steel which was under the original damaged edge not being able to form properly as it is over strained. ' No this is clearly not the case. This edge is still showing significant damage and burr. If the damaged steel had been removed, the burr would be far more uniform. Saying it was 'under' is confusing at best. Just not buying this explanation. Sorry.

Could you define 'destressing'? Is this the same as grinding the edge off @ 90 degrees to the blade's central axis? This too is an unfortunate term implying that this is an optimal approach to removing 'stress' as opposed to simply saying removing damaged or fatigued metal.

Regarding the microbevel, it is surprising to a lot of people how much metal is removed even with a few passes on a strop, let alone a fine stone. Having repaired microsurgical instruments for 12 years under magnification, I can certainly attest to this. EVERY stroke counts. Again a more moderate microbevel is IMO a more useful approach optimized for the task. It is far easier to go more obtuse than to regain the acuteness at the edge of the edge.

I must compliment you on your excellent choice of stones in the video! While the session does get an excellent edge from a 24 grit Nubatama, it is not a demonstration of clogging the stone to do so. It is running the stone somewhat dry, but it is not clogging the stone which is quite porous. You would achieve a similar result using more water. It would take significantly more work to clog the surface. I do agree that the light strokes after the initial sharpening are to advantage in refining the edge maximally for the coarse grit of the stone. As an aside, you seem to have focused only on the heel portion of the blade during the initial sharpening of the blade. Overall though it is a good demonstration of technique.

In the end, although I do have an interest in finding all sorts of things to sharpen steel, I do have a practical approach to it all. I rarely find myself in an environment where I can't find a piece of paper to strop on or some means of abrading steel. If you want to have some fun, try finding a piece of slate or a rock you can develop into a flat surface and apply some CBN on it for some surprising results. While I've used 'bricks for kicks' it really is less than ideal - the surface glazes over far too quickly for my tastes. I think we tend to appeal to two different audiences. I'm more of a Snap-on tool guy, rather that a 'what can I do with a monkey wrench' guy. Both skills have use under some circumstances.

---
Ken



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 Post subject: Re: Starting a new edge?
PostPosted: Sat Feb 22, 2014 12:52 am 
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ken123 wrote:
Regarding the microbevel, it is surprising to a lot of people how much metal is removed even with a few passes on a strop, let alone a fine stone. Having repaired microsurgical instruments for 12 years under magnification, I can certainly attest to this. EVERY stroke counts.

Ken


Couldn't have said it better myself... :ugeek:



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 Post subject: Re: Starting a new edge?
PostPosted: Sun Feb 23, 2014 4:28 pm 

Joined: Sun Aug 11, 2013 11:00 pm
Posts: 37
Cliff wrote:Resetting the edge however removes the need for burr sharpening as you can tell by eye visually when the apex is < 20 microns thick (most people stop being able to see the light reflecting at this point). With no requirement to form a burr this removes all burr removal techniques, many of which are actually stressful on the edge, such as smashing it back into the edge to attempt to break it off.


This is interesting to me, as I've been "burr sharpening" now for several years and have wondered how the advanced guys sharpen with minimal to no burr formation as I've seen claimed. So I decided to try this out on my Spyderco Yojimbo 2 in CPM-S30V.

I started by cutting into a SiC stone edge first using a small amount of force, then checked the edge for a reflection. I wanted a very clear reflection on the whole edge and I probably cut into the stone 4 or 5 times until I saw it on the entire edge length. I'm certain I removed more metal than was necessary, but I wanted to be sure. I was doing this in bright sunlight, outdoors; I'm not sure if that helped me see the reflection or not, but it was very clear and easy to see.

I sharpened on my DMT C 8x3 plate and switched sides after a couple of minutes, checking periodically for reflection or lack thereof. After maybe 5 minutes or so, the reflection was mostly gone from the heel and middle of the blade. I kept going, but concentrated my efforts on the rest of the blade where the reflections were still obvious. Periodically I did "blending strokes" to hit the entire edge; the same as I always do when I sharpen. It took a good bit more time to get the last quarter of the blade (near the tip) to stop reflecting light, but I eventually got there. I wondered before I started, "once the reflection is gone, how sharp will it be? How will I know how much further to go?".

I tested it on phonebook paper and it cut it very cleanly with the grain. I was quite surprised. Checking for a burr, I couldn't feel one on either side. Tried shaving hair, and it cut a few, but not at all "clean" or easy. I tried stropping on a loaded strop, literally two passes, and got nothing extra. I just wondered if there was a minor burr I had missed.

So I moved on to the DMT EF plate and did something like 1 minute of work on each side, checking the scratch pattern with a loupe in between. I honestly wasn't sure exactly how much of the scratch pattern was from the C and if the EF was making it's own, but I thought it was changing. I don't use a loupe a lot for this purpose, so this was very inexact. At some point shortly after, I checked for a burr and had formed a very small one on about 3/4 the length of the blade on one side. Tried forward strokes to remove it and it formed on the other side. Finally did one or two parallel to the edge strokes and eliminated it as far as I could tell. Ran it through cork a few times just to be sure.

I tested this one phonebook paper again and it was much quieter and very, very clean. Tried shaving and it fairly popped hair off my leg. Then I tried a cross grain phonebook cut: I couldn't believe it; it worked. Not a pure push cut, but very close.

I'm very, very surprised and impressed with the results of this experiment. While I did accidentally form a burr, it wasn't much of one and I eliminated it very quickly. I'm going to try this on some more blades to see how I like it. I have to confess that the Yojimbo 2 is a pure wharncliffe design and as such is very "easy" to sharpen IMHO. So my results may be skewed by a very easy subject. Most kitchen blades seem very easy this way also since they have long straight sections that encourage consistent angle holding. At least in my experience, they are much easier than your typical folding knife.

My question remains: Once I've eliminated the reflection and want to polish the edge bevels, how do I know when to stop? Normally I'd say until I form a small burr, but in this method I'm supposed to avoid the burr. I've read Ken saying "detect an increase in sharpness", but I'm unsure how to do that unless I'm using fingers or paper after every few passes on the stone or something.

This has been a really good thread and I think I've learned something valuable here.

Thanks,

Brian.


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 Post subject: Re: Starting a new edge?
PostPosted: Sun Feb 23, 2014 4:55 pm 

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What is the significance of a "reflection"?


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 Post subject: Re: Starting a new edge?
PostPosted: Sun Feb 23, 2014 5:45 pm 
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I believe the "reflection" mentioned would be burr.



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 Post subject: Re: Starting a new edge?
PostPosted: Sun Feb 23, 2014 5:48 pm 

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If you look straight down at the edge of a sharp knife, you should see no reflected light. But if it has dull areas, chips, or other damage, you should see areas that reflect light back to you. This shows you where the knife needs to be sharpened. When I cut the blade edge straight down into the stone, I essentially ground the entire edge flat. Flat enough that light would strongly reflect back when I looked straight down at the edge.

I then used that to measure my progress; as I ground the edge to an apex again, the reflection disappeared in the places where the apex had formed again. When there was no reflection on the entire blade, I knew the edge was at least narrow enough to no longer reflect light and was somewhat sharp. Cliff says 20 microns wide; I dunno; I just know it got sharp, and then QUITE sharp after the DMT EF.

I hope that helps.

Brian.


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 Post subject: Re: Starting a new edge?
PostPosted: Sun Feb 23, 2014 6:00 pm 

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Sorry but I want to make sure I understand this correctly. When you say to "look straight down the edge," do you mean to hold it by the handle with the tip pointing away from you, edge side up, and look down the entire cutting edge, like in those photos known as a "choil shot"?


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 Post subject: Re: Starting a new edge?
PostPosted: Sun Feb 23, 2014 6:02 pm 

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Sharp edge pointed at your melon, spine of the knife facing away. Don't sneeze.


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 Post subject: Re: Starting a new edge?
PostPosted: Sun Feb 23, 2014 9:24 pm 

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TD&S: Sharp edge pointed at your melon, spine of the knife facing away. Don't sneeze.

I got a good chuckle with the "Don't sneeze."


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