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 Post subject: Re: Starting a new edge?
PostPosted: Mon Feb 17, 2014 5:59 pm 

Joined: Fri Aug 03, 2012 10:01 pm
Posts: 202
This forum devalues quickly when it becomes a personal insult session. It stays unique when everyone feels comfortable in sharing their own experience on the stones, then it retains value. I've been sharpening for well over a decade, but I enjoy taking bits and pieces from other's observations and feedback and comparing/contrasting it to what I experience in my own sessions. Sometimes we dismiss people's opinion as error, other times it challenges us to refine our own thinking and skill set. Whether it's truth or error, let's refrain from making members feel slighted for sharing. Thanks to all the moderators for keeping things in check.

More on topic, I would agree that with enough patience one can indeed learn to FEEL when the apex has been met, generating no noticeable burr, and becoming very comfortable with the "three finger test" is certainly helpful. I would also agree that when employed correctly, the effect is sudden and significant, like the edge awakens. For me, it usually occurs on my 1K stone when I finesse the blades that I use regularly which rarely see lower grit stones because I keep them performance ready. I wake up the bevel on the 1K with alternating strokes and no noticeable burr, then close the deal on my finish stone/s. -Josh


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 Post subject: Re: Starting a new edge?
PostPosted: Mon Feb 17, 2014 9:14 pm 

Joined: Fri Feb 14, 2014 4:23 pm
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It would be useful to define what is meant by burr, it is usually used to mean an edge bias that you can see and feel and which reduces edge durability and edge retention.

In an ultimate sense even the best edges which are formed have some manner of edge bias, usually between 0.3 and 0.5 microns, but again this usually isn't what people mean when they say "form a burr" they mean the bias is so heavy you can feel it.

Cutting the edge off and leaving a line of light reflecting from the edge eliminates the need for a microscope and the sharpie trick and many other things that are often advocated because you can simply look at the edge and tell if you are hitting the apex or not.

In general, to minimize burr formation then don't take the edge to the apex on your coarse stone, don't take the edge to an apex with very high force, and don't form the edge with a coarse slurry.

For illustration, all edges have the same angle, use the same stone (Bester 700X) :

Image

This is an edge which was not fully destressed and was sharpened to the apex with shaping force, coarse slurry. It is the perform storm of worse case of everything. It formed a burr you can feel and it is obvious under magnification (50X true linear).

Image

This was destressed, but the edge was formed with heavy shaping, coarse slurry. Improved but you can see the edge is not forming ideally and is irregular (the burr is still large).

Image

This was destressed, and as the light started to be removed it was sharpened by honing-to-dry which means the force is vastly reduced and the stone is not fully watered (to prevent coarse new slurry).

Again this is a semi-coarse 700X stone and it still produces a very even edge which is decently sharp (will shave, etc. ).

If you sharpen as many people do :

-coarse sharing
-micro-bevel

This is fairly critical as just imagine what happens when you try to apply a micro-bevel to the above edges. Even if you try to work up in polish the first edge does not respond well and will crack off and leave irregular finishes and the finer stone will not produce the expected results.


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 Post subject: Re: Starting a new edge?
PostPosted: Tue Feb 18, 2014 3:06 am 
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Cliff Stamp wrote:This is fairly critical as just imagine what happens when you try to apply a micro-bevel to the above edges. Even if you try to work up in polish the first edge does not respond well and will crack off and leave irregular finishes and the finer stone will not produce the expected results.



This can also be seen when going to finer stones without microbeveling. Most people point to the steel or stone and scream "MICROCHIPPING!" at the top of their lungs , when in reality there are just leftover coarse scratch marks that were not fully removed earlier in the process.

Out of curiousity what did you use leading into the bester stone?



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 Post subject: Re: Starting a new edge?
PostPosted: Tue Feb 18, 2014 11:13 am 
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To define a burr entirely in terms of edge bias is ignoring a key point and really redefining the term inaccurately. The key problem with a burr is that it is fatigued metal - even if no bias is present. Realigning this fatigued metal simply produces a symmetric burr. It is still a burr.

Removing the burr by abrading it off perpendicular to the edge is something I reserve only for the most draconian circumstances. When doing this you sometimes have the unique circumstance of producing burr on BOTH sides of the edge simultaneously. This is sometimes done intentionally when using the instrument as a scraper, but it produces two burrs to remove - hardly ideal. In addition this also results in even more metal being removed than is necessary compared to continuing to abrade until the two sides are approaching a point of union. This technique is referred to as 'breadboarding' by razor honers and used when the edge is uneven - again as a last resort. I use this when removing a great deal of metal - belly reductions, uneven grinds leaving holes in the edge, etc. Not as a routine technique.

So in the first micrograph, continued abrasion is required. It is simply stopping too soon to remove the [severely] damaged edge.

I also don't think reducing the water availability is an ideal approach to prevent new slurry formation. It will simply increase slurry density and cause the metal swarf to accumulate. If one wishes less slurry formation or less total presence of slurry, more water would produce a more dilute slurry if that is your goal.

I do agree that the minimization of burr formation is ideal and that reduced force allows you to reach minimal burr formation more precisely. Coarser grits, especially with diamonds, makes for more edge damage when ground all the way to the point where the sides meet so it is advisable to not make the edges meet when using a DMT XXC or Atoma 140 on single bevel knives for instance. Here the issue is the scratches crossing over to the other side and producing chipping that can be avoided by switching to finer grits. This is even more obvious when doing ceramic blades where burr formation is irrelevant (doesn't occur).

---
Ken



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 Post subject: Re: Starting a new edge?
PostPosted: Wed Feb 19, 2014 12:40 pm 
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I enjoyed reading this thread, and while I have nothing really to add, I found it interesting. Good discussion so far.



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 Post subject: Re: Starting a new edge?
PostPosted: Wed Feb 19, 2014 2:59 pm 

Joined: Tue Aug 27, 2013 2:10 pm
Posts: 174
+1 to Dan_Crubenew's comments. I also found this thread educational. A good read.


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 Post subject: Re: Starting a new edge?
PostPosted: Thu Feb 20, 2014 3:56 pm 

Joined: Fri Feb 14, 2014 4:23 pm
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Sadden wrote:This can also be seen when going to finer stones without microbeveling. Most people point to the steel or stone and scream "MICROCHIPPING!" at the top of their lungs , when in reality there are just leftover coarse scratch marks that were not fully removed earlier in the process.


Yes, nice point and interestingly enough often compounded by some of the newer polishing stones that cut very fast. If I take a Sigma Power Select 3K I can actually use it right after a 240X and the bevel will quickly look like a 3K bevel but the edge will not because of what you noted, especially if the 240X was taken to a full apex, and especially if it was heavily burred.

Sadden wrote:Out of curiousity what did you use leading into the bester stone?


If you mean what stone before that, neither one. A lot of the sharpening I do is experimental. I used that same stone to zero the primary on a 121REX knife for example, really not the stone to do that at all but I wanted to explore the ease of grinding and the limits of steel that stone can work.

I often take one stone and use if for all work for a period of time, shaping to finish and seeing how to best adapt it. This is mainly academic of course, but it keeps the process interesting and on a practical side some people can not afford a multitude of stones.

If you are looking for efficiency then a wider collection of stones will assist in that (I have them of course).

ken123 wrote:To define a burr entirely in terms of edge bias is ignoring a key point and really redefining the term inaccurately. The key problem with a burr is that it is fatigued metal - even if no bias is present. Realigning this fatigued metal simply produces a symmetric burr. It is still a burr.


Ken, I am not using bias strictly as in the apex is not laterally symmetric, I mean bias in the sense that it is used academically where you say a result it biased as it isn't the true/ideal result if all non-wanted influences were removed.

ken123 wrote:So in the first micrograph, continued abrasion is required. It is simply stopping too soon to remove the [severely] damaged edge.


This isn't optimal because each pass on the side deforms the metal which keeps straining the steel under it. The optimal solution is to not form it in the first place by removing the steel before sharpening. When it forms cutting it off with minimal abrasion produces the least metal removal to stability. How high an angle you have to go depends on the extent of the weakening. Jeff Clark used to promote at least 2x the apex angle, I have found in general even higher is better, but I also back sharpen as well.

ken123 wrote:I also don't think reducing the water availability is an ideal approach to prevent new slurry formation. It will simply increase slurry density and cause the metal swarf to accumulate. If one wishes less slurry formation or less total presence of slurry, more water would produce a more dilute slurry if that is your goal.


The goal is to refine the scratch pattern, more water does the opposite. The slurry has to stabilize and the abrasive of the stone has to be masked for that to happen.

As noted, this isn't the optimal method in general, you would of course just move to a finer stone, it was an experiment to make the most out of a particular stone by adjusting how it was used to maximize its cutting speed or maximize its edge finish depending on what was needed.


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 Post subject: Re: Starting a new edge?
PostPosted: Thu Feb 20, 2014 4:05 pm 

Joined: Mon Jun 03, 2013 2:37 pm
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Very interesting and thanks to all who are participating in this discussion. If nothing else, it's given me some ideas and things to try in my own sharpening routines. Again, thanks everyone.


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 Post subject: Re: Starting a new edge?
PostPosted: Fri Feb 21, 2014 9:03 am 
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Cliff, Thanks for an interesting discussion. A few points regarding your responses.

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. This is obvious under magnification. You are abrading the peaks of the 240 grit scratch pattern and leaving the depth of the scratches not being removed. The overall look of the edge bevel will look 3k 'ish' but this is not an ideal 3k edge at all. While this is an interesting 'experiment', the conclusion is 'don't do this'. Further compounding this experiment with a leftover heavy burr reduces this 'experiment' to a poorly designed experiment with too many variables to draw useful conclusions. The cutting rate of the stone is also not the critical parameter - it is the duration of abrasion at that grit times the abrasion rate, ie the total amount of metal removed to reduce or eliminate the coarser scratch pattern. The scratch pattern of the bevel is an indication of the actual edge characteristics, compounded by how closely the two sides meet, any damage from burr removal producing fractured and weakened metal, etc. This problem of properly removing the scratch patterns from previous stones is abundantly clear when reviewing kasumi finishes produced by natural stones.

If you are sharpening a Rex121 blade, I don't know that using a stone like a 700 Bester is a useful experiment for bevel setting. Most people on this forum KNOW that this is so suboptimal that they wouldn't do that. For a task like this, diamonds or CBN are a far better solution, especially for determining the primary bevel. 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. IMHO, this is a pointless exercise. Not really what I would call academic. So for instance, you could hammer in a nail with the handle of a screwdriver, but as you state, "not the stone to do that at all ". In fact, even a collection of stones is not an ideal solution for this type of steel. For most, an ideal approach is of far more interest than demonstrating the results of perseverance with the wrong tool for the job.

Cliff, you are using two definitions of the word 'bias' simultaneously. Biased as in 'I am biased' and when referring to 'edge bias', where you imply that this is a lack of symmetry. Neither use is very useful in redefining the meaning of a burr. And of course these distorted definitions have absolutely nothing to do with any 'academic definition'.

"you say a result it biased as it isn't the true/ideal result if all non-wanted influences were removed. " This is a confused statement.

If you say a true/ideal result [IS, not it] biased because it isn't the true result if non wanted influences are removed' there are some double negatives in this statement. I believe you meant that the true/ideal result is biased because the non-wanted [unwanted] influences are not removed.

What you are describing 'academically' is referred to in statistics as 'covariance'. Again you are distorting the term 'bias' in yet an additional way to confuse the discussion of what a burr is. Uncontrolled covariance due to multiple variables in an experiment is academically referred to as poor experimental design :) It makes it MUCH harder to attribute the variable of interest as having a causative relationship.

We should go back to a more basic understanding of what a burr is and avoid introducing 'bias' into the discussion especially with multiple definitions of the word 'bias'. This is simply obfuscating an otherwise straightforward discussion.

So in the first micrograph, there is more than a simple burr present. There is significant edge damage too. Of course not having the burr or edge damage to remove is ideal but this is not the case. Here removal of the damaged edge is best achieved with continued abrasion at the angle you wish to use as your final angle (primary bevel). I am not stating that heavy force need be applied, but rather that the burr and damage be removed in place ('in situ' for the 'academics' LOL) to not exacerbate the edge condition. Approaching this by grinding at a 90 degree angle to the edge does cause unnecessary metal removal. Grinding the edge at a more obtuse angle introduces a microbevel and a microbevel at 2x the angle is overkill. Further, to go back to the original edge angle will now require even more metal removal. A better approach is to GRADUALLY increase the angle until the edge angle is optimized for the required task. Going in the other direction causes unnecessary metal removal. This sort of fine tuning is what makes a knife truly your own.

Finally, to use less water as a technique to refine the scratch pattern is basically clogging up the stone to make it less effective. This is a recipe for glazing the stone and removing the available abrasive for cutting. On a synthetic stone, the abrasive breakdown is minimal, just reducing the total amount of fresh available abrasive resulting in slowed cutting and not an improved finish. While an interesting experiment - with the obvious conclusion of 'don't do this', as you suggest simply using a finer abrasive is the preferred approach. This tactic neither stabilizes the slurry and the term masking is not at all accurate. You are simply causing a clogged stone and reducing the stone's efficiency. You are coating the stone and causing the sharpener to prematurely restore the stone's surface to an optimal working surface using a lapping plate or (less desirable) a 'cleaning stone'. While the topic of optimizing water and slurry densities are worth a thread in itself, running a stone dry to achieve a finer finish is not an approach I recommend.

Cliff, again I thank you for an interesting discussion.

---
Ken



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 Post subject: Re: Starting a new edge?
PostPosted: Fri Feb 21, 2014 11:09 am 
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This is one of the most in depth and polite discussion of sharpening I have seen. I think Ken and Cliff are agreeing on some points, but are coming at it from opposite perspectives. Cliff is doing this academically, and trying things to see what it does, even though it is not the most efficient, easiest, best way to do things. Ken is coming from the standpoint of a sharpener, who is trying to get the sharpest edge possible and from his experiences, what works/has worked best for him.

240 grit edge, taken to a 3K grit, is a bad thing, leaves the deeper 240 grit scratches in the edge itself, but areas around it are polished to the 3K level. Yup, bad thing!

Yes, both agree that a 700 grit stone on REX121 sucks. Cliff did this to test and see how the stone performs at that task and what the limitations and work arounds are for that one stone (like Cliff said, more academic) to maximize the effect from that stone. Ken agrees that stone is very slow and not the optimal stone to use, and recommends a different stone/type of abrasive.

Same with the slurry. Cliff is using the slurry to purposefully clog the stone to try to use the slurry on top of the stone as a more refined abrasive instead of the stone itself (masking the abrasive) and Cliff also says this is not the optimum way to do this. Ken says adding water helps build the slurry to keep it wet and let the slurry break down to a more refined state. Dry slurry would clog the stone so it would slow down, but not refine as much. Again, this depends on the stone. Some slurry/mud breaks down well and needs to be wet to do this, other slurry doesn't break down much at all, but the clogging will make the stone polish a bit more than cut with the fresh sharp abrasive of the stone itself. Adding too much water and thinning the slurry will remove the mud and clean out the stone a bit and expose the original abrasive at that level, which does not help to refine the edge. Both agree that clogging the stone is not the best approach and both recommend using a finer grit (new stone or more broken down slurry).

Cliff is saying to remove the damaged edge at the beginning and deal with fresh/clean metal all the way through, Ken is saying to remove it as you refine the edge. Both agree on removing the metal, but differ on the how and when.

Keep it up guys, learning some good info here!


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