Wire Edge Prevention

[KnifeGrinders]

Inspired by the thread by Mike and Grepper http://www.bessex.com/forum/showthread.php?tid=371

What wire edge is

Well-known 2 steps in sharpening a knife are apexing and deburring, and deburring is more challenging since it determines how sharp and stable your edge will be.

There is one very special zone at the base of the burr, right between the burr and the apex, designated as LOW on the below optical microscope image showing layers of the burr (the image is from the above thread).


After you deburr the edge, the base of the burr turns into the wire edge.
The wire edge is often regarded as a structural continuation of the apex – it is its sharpest but also the weakest structure. From a logical standpoint this poses straightforward reasoning – the burr formation is the result of plastic deformation, why would one expect the steel at the base of the burr stay the same as the apex?

In the ultra-sharp sharpening we distinguish more steps in deburring, namely: exposing the base of the burr also known as wire edge, and cleaning the apex of it.

The following optical microscope images show a burr off a coarse abrasive that is easily felt by brushing a finger across the edge, and next to it a blade with the wire edge that you cannot see and cannot feel. (By courtesy of Tony Spielberg, USA)




The wire edge on SEM edge-on view (all SEM images are by courtesy of Todd Simpson scienceofsharp.wordpress.com)


“Feather burr” and “Foil edge” are two more edge geometries that can be created in the finishing stage of removing the burr – these two are near synonymic and are a product of edge-trailing honing at the edge angle; shown on the following optical and SEM microscope images.




We can recognise presence of the wire or foil edge by the edge behaviour in cutting stuff.
An obviously ultra-sharp edge that whittles hair will start a smooth cut but end with tearing, or show clean cuts alternating with ragged - indicating a weak edge folding in the process. If the edge is not cutting well, it can only mean two things: either it has not been fully apexed, or there's a burr or crushed wire/foil edge getting in the way.
The wire edge crushes under a minimal load by mushrooming seen on SEM microscopy.



What we see on the BESS sharpness tester?

Because the wire edge is too weak to cut the test line, it crushes on it and, as we increase the downward pressure, mushrooms against the line allowing to apply more pressure onto the widening point till the line gets finally severed – in the point of testing we see a micro-dent in the edge with the mushroomed apex displaced to the dent bottom, and the sharpness reading is times worse than we would expect by seeing the same edge whittle hair and push-cut rolling paper.



A knife that fails early is the result of a wire edge that hasn't been properly removed.
A good sharpener knows how to apex and deburr the edge; an expert sharpener knows how to clean the apex of the weak wire edge not rounding it.
The wire edge is very common in edge-trailing deburring as too often the base of the burr is not removed completely. It is just so fine that it is not detected by the 'finger method' most people use. The end result is the wire edge that dulls extremely quickly once the wire gets mushroomed with the first cuts.

How do we clean the apex of the wire edge?

It's a bad idea to simply draw the edge through a wood block, rubber or cork to “rip off” the wire edge. If you do, the metal crud will build up on the front of the slice, and you'll be dragging the rest of the edge through the crud and this, together with breaking off of ledges of material along the edge, will roughen the edge and worsen sharpness.

An edge-leading pass on an ultra-fine bench stone can accomplish the wire edge removal, but at the risk of micro-chipping and abrading off the apex when done by inexperienced hands. A shortfall of this method is that you are introducing a new microscopic burr.

We remove the wire edge by honing with fine diamonds or CBN and raising the honing angle very slightly, from 0.4 to 2 degrees – the softer the steel, the higher the angle. The edge only needs to “sink” the apex into the compressible material, and you can do this on leather, balsa, hard felt or a paper wheel just as easily as on a hanging denim strop loaded with a fine honing compound – the microscopic diamonds will cut at the base of the burr.

Only once you eliminate the base of the burr, there is no more wire edge. A correctly deburred edge shows nothing except the clean scratch pattern going to the end of the apex.
Optical and SEM microscope images of a cleaned edge follow.




Uncertainty

Methods to assure completeness of deburring and removal of the wire edge we have at our disposal, on the one hand, and the miniscule nature of that edge on the other, bring us to the point of uncertainty, IMHO.

In all honesty, where a freshly sharpened edge scores over 100 BESS we can not tell for sure whether this results from some residual wire edge or not – because at this BESS score only SEM imaging is able to exclude the weak apex mushrooming against the test line.
Only when the BESS score taken on the standard test media line is near 50 BESS, i.e. that of uncompromised DE razor, we can be absolutely sure that the edge apex is clean of the wire edge, and this is the only instrumental indicator we have readily available at present.

Experiments on wire edge removal

I experimented on a budget stainless steel kitchen knife - WiltShire brand.
We know these knives as producing that nasty malleable mutant burr that is very difficult to clean off, and I used to be happy if I could get them score 170 BESS.

Sharpened on Tormek, the edge was set at 13 dps on #1000 CBN wheel.

Then honed on a paper wheel with 5-micron diamonds at the edge angle - honing mainstream stainless steels this way invariably produces a microscopic feather burr, similar to pictured.
At this step we thin away the original burr and gain access to the base of the burr.


The top layers of the burr are removed but leave the base of the burr intact and still stuck to the edge in the form of the wire edge. The wire edge, by its genesis, is the very first layer of the burr laid down and is really well stuck to the edge apex. We think this layer at the base don’t flip with the rest of the burr in the process of deburring.

I then cleaned the hardly visible fine feather burr on a rock-hard felt wheel with 1-micron diamonds on Tormek, using our Frontal Vertical Base for honing away from the wheel, similar to shown on the next picture, only in place of the legendary AL MAR imagine the cheap WiltShire kitchen knife.

The experiment plan was in repeating the sharpening-honing-cleaning sequence, gradually raising the felt honing angle, and recording the resulting BESS scores.
Grinding and honing angle was controlled with our computer software for Tormek and paper wheels.



Off the #1000 CBN the edge burr scores 250 BESS.
After the 5-micron diamonds paper wheel the edge feather burr scores near 500 BESS; micro-denting is easily detectable in the point of testing. The high BESS score is result of the feather burr crushing and mushrooming against the test line.

Now 1-2 passes on the felt wheel with 1-micron diamonds on Tormek, alternating blade sides.
At this step we hone away the flimsy feather burr and clean the apex of the wire edge.

Felt wheel at the exact edge angle = 100 BESS
Felt wheel at +0.4 degree higher angle = 80 BESS
Felt wheel at +1 degree higher angle = 175 BESS
Felt wheel at +1.5 degree higher angle = 140 BESS
Felt wheel at +2 degree higher angle = 80 BESS
Felt wheel at +2.5 degree higher angle = 120 BESS

I then repeated the two best results, i.e. re-sharpened the edge on #1000 CBN, honed on the 5-micron diamonds paper wheel at the edge angle, and then on the felt at +0.4 vs +2 degrees higher angle, after the felt wheel finishing the edge on a paper wheel with CHROMOX for final cleanup.
Felt wheel 1-mcrn diamonds @ +0.4 degree = 90 BESS >> CHROMOX = 100 BESS
Felt wheel 1-mcrn diamonds @ +2 degrees = 80 BESS >> CHROMOX = 55-60 BESS, hair-splitting.

We see that for the lower-end mainstream stainless steel the best cleaning of the apex is achieved by high-angle honing at 2 degrees higher than the edge angle.
In this case, the edge set at 13 dps, we cleaned at 15 dps, and by the BESS score near 50 BESS we seem to have cleaned off the wire edge.
For that lower end s/s steel, 55 BESS is a record sharpness score on an obviously stable edge.

How I interpret the other failed sequence of "Felt wheel 1-mcrn diamonds @ +0.4 degree = 90 BESS >> CHROMOX = 100 BESS" - I think it tells us that the base of the burr had not been honed away completely on the felt, and the paper wheel with CHROMOX, rather than cleaning the apex, added volume to the remnants of the wire edge, turning it into the foil edge; when it pressed against the test line and mushroomed we saw that increase in the BESS score.

How I interpret changes in the BESS score with the raise of the honing angle on the felt:
Felt wheel at the exact edge angle = 100 BESS      <- feather burr removed, we are nearing the base of the burr
Felt wheel at +0.4 degree higher angle = 80 BESS  <- the base of the burr exposed
Felt wheel at +1 degree higher angle = 175 BESS   <- adding volume to the base of the burr through burnishing
Felt wheel at +1.5 degree higher angle = 140 BESS <- adding volume to the base of the burr
Felt wheel at +2 degree higher angle = 80 BESS     <- the base of the burr cut off, the apex exposed
Felt wheel at +2.5 degree higher angle = 120 BESS <- rounding the edge apex

[EOU]

As usual, great stuff KG and much of it really matches up with our own findings and observations and we would only like to add this:

Oftentimes and after much burr removal effort, that LOW is still apparent under close observation. Even so, the edge often measures better than one would think it should and this perplexes us. It is our feeling that a lot of 200-225 edges could be 125-150 if the LOW had been properly removed. Your correlation KG of the LOW to mushy metal is right on as far as we are concerned. We've seen instances where this crap can be formed and shaped into sharper edges using only a plain leather hone many times. These have to be edges that wouldn't last through one cucumber though. 

How tough can the LOW be to remove? We've seen some that can't be picked up even with a wire wheel on a bench grinder. We know that sounds incredible but that fact has been confirmed more than once and by more people than just us. The LOW can be just so tiny and low profile that even the steel bristles of a wire wheel can't grab it and stand it up. We're not certain how or if this applies to the polished edge world but if you're producing toothy edges with a belt grinder, its an issue.

We've been preaching proper burr removal as the key to sharp edges for some time now and if you happen to be sharpener who is having trouble achieving really sharp edges a thorough study of KG's burr removal suggestions might just be the answer. It's not just about producing sharp edges though, its about producing long lasting edges, be they 100 or 200, that are free of this crap metal hanging off the apex.

[KnifeGrinders]

Mike's comment inspired additional experiments.

We know that the base burr adjacent to the apex is more difficult to remove than the outer layers of the burr.
Leather, balsa, felt, paper wheel and linen or cotton strops used in deburring are not equal - not every blade can be “de-wired” on all of the abovementioned substrates.

By aggressiveness we group them in 3 groups:
linen/cotton, paper wheels and balsa;
next comes leather;
and the most aggressive is felt which works well for both super-steels and those deburring headache stainless steels at the low end (jewelers use felt as the base for polishing their gems for a reason).

But this grouping is experience-based and rather intuitive, so we decided to check it experimentally.

The same WiltShire stainless steel kitchen knife had edge set at 13 dps on #1000 CBN, then honed at the edge angle on a Paper Wheel with 5-micron diamonds to thin away the burr - the result is a flimsy feather burr that you cannot feel and can hardly see under the right light.

From here we did it differently.
In the 1st round we honed it on Tormek on a paper wheel with 1-micron diamonds (using a bushing to fit the shaft).
In the 2nd round we honed it on Tormek leather wheel with 1-micron diamonds.
In the 3rd round we honed it on Tormek on the felt wheel with 1-micron diamonds.

In all cases we honed the knife at 15 dps, i.e. at 2 degree higher than the edge angle - that in the previous experiments has shown the best "de-wiring" effect. The honing angle was controlled using our Frontal Vertical Base for honing away from the wheel and computer software.

Tormek - Paper Wheel

After the 5-micron paper wheel the feather burr scored 215 BESS;
After Tormek with 1-micron paper wheel 120 BESS.

Tormek - Leather Wheel

After the 5-micron paper wheel the feather burr scored 285 BESS;
After Tormek with 1-micron leather wheel 100 BESS.

Tormek - Felt Wheel

After the 5-micron paper wheel the feather burr scored 255 BESS;
After Tormek with 1-micron felt wheel 80 BESS.

As you can see, the resulting BESS scores confirm our a priori grouping of the honing base substrates.
In the context of these tests, the lower BESS score indicates the better deburring, and the felt shows the best "de-wiring" of all, i.e. the best removal of the base burr; leather follows, and paper as the finest substrate shows the worse score.

***

From the above findings one could make a logical conclusion that the final cleanup of the edge on the fine paper wheel might give somewhat better sharpness than finishing on the leather wheel.
We tested this as well.
The knife deburred on the felt wheel as described above, we finished differently:
- on a paper wheel with CHROMOX at 1400 RPM; versus
- on a Tormek leather wheel with CHROMOX at 90 RPM.

Final cleanup on a paper wheel with CHROMOX

55-65 BESS

Final cleanup on the Tormek leather wheel with CHROMOX

85 BESS (i.e no sharpness improvement over the preceding felt honing)

***
Well, we've got an experimental proof of what already know - that the edge you get depends on both the honing compound and the substrate this compound is on.
Felt is not a panacea though, neither is a paper wheel - for a given class of steels there is its own best combination of the honing compound, substrate, honing angle and amount of honing.
The practical takeaway of this series of experiments is that now we know how to get a sharp and strong edge on those lower-end stainless steel knives.

[grepper]

Once again, excellent research Mr. KG.  Thanks for sharing!

I’m sure that my burr removal experience and research is not as extensive as Mr. KG’s, but I have never been able to definitively verify complete burr removal with only BESS data as evidence.  I know, but am too lazy to find it, that Mr. KG has mentioned before that the wire edge, or line of crud, or burr base or whatever you wish to call it can actually be sharpened or burnished into a sharp edge.  It’s junk metal and will crush and dull quickly but can nonetheless be formed into an edge.

I have sharpened numerous blades to the 50 to 80 sharpness range where still existing burr clearly presents under microscopic observation.  That difficult to remove crud metal was obvious along the edge, but had been ground or burnished into a sharp apex.

FWIW, microscopic observation is the only way I’ve found to really determine if burr exists or not, and that observation requires very careful attention to lighting.  If the angle of the light is not absolutely perfect, a burr covered edge can appear completely clean.

[KnifeGrinders]

Once again, excellent research Mr. KG.  Thanks for sharing!

I’m sure that my burr removal experience and research is not as extensive as Mr. KG’s, but I have never been able to definitively verify complete burr removal with only BESS data as evidence.  I know, but am too lazy to find it, that Mr. KG has mentioned before that the wire edge, or line of crud, or burr base or whatever you wish to call it can actually be sharpened or burnished into a sharp edge.  It’s junk metal and will crush and dull quickly but can nonetheless be formed into an edge.

I have sharpened numerous blades to the 50 to 80 sharpness range where still existing burr clearly presents under microscopic observation.  That difficult to remove crud metal was obvious along the edge, but had been ground or burnished into a sharp apex.

FWIW, microscopic observation is the only way I’ve found to really determine if burr exists or not, and that observation requires very careful attention to lighting.  If the angle of the light is not absolutely perfect, a burr covered edge can appear completely clean.

In my experience, it is true for hard quality steels that their wire edge may score 50-80 BESS, but for budget knives such a good score is an indicator of the strong edge and burr-free apex.
The sharpness test itself is a challenge for these lower-end steels, as any remnants of the burr will crush against the test line. Yes, it is possible to hone their base burr sharp enough to cut hair, but it will mushroom against the test line and score over 100 BESS. Only when their apex is burr free, it will score near 50 BESS.

[EOU]

In our experience, the clear champion of wire edge producing sharpening techniques is the pull thru ceramic sharpener. The sort with small, overlapping ceramic wheels. If done just right, not too many pulls and not to few, edges that measure 110-130 can be produced. A couple of whacks on a wooden dowel later, the same edge measures 700-800. 

It is interesting that some wire edges can be measured accurately and some not. KG attributes this to good versus poor steel. There could be other factors as well such as the height of the wire edge and other form factors. We just don't know. We do know this; widely varying edge readings along the blade are almost always a clear indication that burr still remains on the edge, at least in some areas. As Grepper points out this stuff is often difficult to detect. If you learn how to detect it and how to remove it properly you will be well on the way to producing the near perfect cutting edge.

It is worth noting that KG and Grepper grind edges in very different ways. Their burr removal techniques are different in the tools and materials used but their underlying concepts are the same. They both produce sub 100 edges at will. Grepper's well known 150 edges are a page from the past and the only change in process are newly revised burr removal techniques and materials. One thing that is shared by both is their commitment to not only producing sharp edges but their commitment to understanding those things that make edges... not sharp. Simply repeating a process that seems to work is not enough, understanding "why" it works is. This understanding is accomplished through study, experimentation and measurement. These two guys are well worth giving a listen.

[KnifeGrinders]

I've got more test data confirming the rule "the softer the steel, the higher the angle" for cleaning the burr base.
Victorinox and SWIBO knives sharpened and deburred by similar routine gave the best sharpness scores at 1.2 degree higher than the edge angle when honing on the felt with 1 micron, as compared to the WiltShire 2 degrees.

As it was shown above, the WiltShire kitchen knife sharpened at 13 dps and deburred on Tormek with the 1-micron felt wheel at 15 dps scores 80 BESS, and after final cleanup on the paper wheel with CHROMOX 65 BESS.

Victorinox boning knife sharpened at 13 dps and deburred on Tormek with the 1-micron felt wheel at 14.2 dps scores 60 BESS, and after final cleanup on the paper wheel with CHROMOX 60 BESS.

SWIBO boning knife sharpened at 13 dps and deburred on Tormek with the 1-micron felt wheel at 14.2 dps scores 70 BESS, and after final cleanup on the paper wheel with CHROMOX 50 BESS.

Victorinox and SWIBO knives, honed on felt at 2 degrees higher, score slightly worse.

Next level up, Global knives get a strong and sharp edge when deburred at an angle within 0.4 degree higher than the edge angle.

As a sidenote, these differences may seem negligent, but they matter when we are putting together a new sharpening protocol.
Because when it comes to a hurried production sharpening, with no control till the final sharpness is checked, especially when we check sharpness by sampling a batch of knives rather than every knife, variations and approximations come into play, and to get all knives sharp within the target range, the protocol must be the best possible.
E.g. when the deburring is set at 15 dps, we expect the actual honing angle in real life sharpening (not the experimental setup) be within 14.5 - 15.5 degrees.

If you are deburring by Tormek means only, you get better sharpness on lower-end knives by 2-step honing, i.e. when you hone on the Tormek leather wheel with the Tormek honing paste or Autosol first at the exact edge angle, and then 1 pass each side at a higher angle - one full revolution of the Universal Support micro-adjust wheel gives approximately 1 degree change in the honing angle.

[KnifeGrinders]

Real Life Check


I've sharpened a couple of boning knives (on the photo) using the deburring method detailed above, and have given them to a beef boning room. They have 7 bull "bodies" to bone and butcher on Monday, and tomorrow I will get the butchers' feedback - will then update here on how well the edge lasts.

Our production sharpening of boners is 4-step, 3 of which are deburring.
We aim at under 2 min per knife, and I have taken a few more photos to show how the all-controlled experimental setup translates into production sharpening.
For speeding up the process we do not clamp knives in a knife jig.

The edge is set on Tormek (90 RPM) on the side of a #400 CBN wheel, using our volume sharpening attachment.



Because the side of the wheel is flat, the edge geometry is pretty much the same as that off a benchstone. We set the edge at 12 dps, and this step is quite accurate - the CATRA laser protractor shows the edge angle of 12 dps.
Off the CBN #400, the edge has a burr that can be seen and felt by brushing your finger across it, and scores near 500 BESS.

Next step is deburring on a slotted rock-hard felt wheel with Autosol run on a half-speed grinder (~1400 RPM) - we do it at the edge angle, but because we use a horizontal platform to cotrol the angle, practically, of course, it is somewhere near. As we know, Autosol metal polish abrasive particles average 3-6 microns in size.
I had cut slots in the felt to cool the edge, and you can feel it actually blows air as a a fan.



At this step we thin away the burr and you cannot feel the burr anymore, and can hardly see some micro-fringe on the edge under certain light, but we know by microscopy that the edge does have a feather burr.
Interestingly, the BESS score is still near 500 BESS because of the feather burr mushrooming - looking just at the sharpness tester scores you'd say that we have done nothing to the edge.

Next step is removing the base burr using the method from the above experiments, on Tormek (90 RPM) on a rock-hard felt wheel with 1-micron diamonds at approximately 1 degree higher than the edge angle, i.e. in this case at approx. 13 dps.
Again, to avoid clamping the knife in the jig we use a horizontal platform to control the honing angle - and that's why I say "approximately".



The sharpness score is now 85-90 BESS, telling us we've removed the flimsy feather burr.

Final cleanup is done by 4-5 swipes on a hanging clean leather strop, alternaging sides - this improves sharpness score by about 15 BESS, and the final sharpness comes to 70 BESS.
Such a good score on mainstream s/s steel tells me that we've hopefully removed the base burr, but only a real cutting can tell if the wire edge is still there.
(Although the experimets have shown that a good final cleanup is achieved on a paper wheel with CHROMOX, the horizontal platform does not have the required accuracy of angle control, and we changed to the hanging leather strop.)

A short video on our volume sharpening: https://youtu.be/LP1_kjUC89U

In real volume sharpening we deburr on a single wheel with a 3-6 micron honing compound, by deburring at the edge angle and finishing at a higher angle by simply sinking the edge into the felt.
The above sequence of the 2 felt wheels was to "dissect" the process of deburring and better understand peculiarities of its different phases.

Residual stress check shows the BESS score worsening by 15-20 BESS in 17 hours, telling us of a low level of stress as compared to the typical 50 BESS we see after paper wheels.

We've agreed with the butchers that they will start the beef boning with our knives and continue with them as long as they last, steeling them the normal way they always steel.
The butcher I spoke to says he uses primarily the polished steel through the day, every 5-10 cuts, and the ratio of polished to fine-cut steel is between 10:1 and 20:1.
I will honestly update this post tomorrow night with what butchers say about our knives performance.

[EOU]

Thanks once again KG. It would seem that a clean, properly deburred edge would greatly aid edge longevity. I guess we'll see if that thought turns out to be just supposition or fact. Looking forward to learning your customer's experiences.

[KnifeGrinders]

The two knives in live boning:



Feedback:
"The knives were very sharp to begin with, and kept the edge well, but only for a couple of bodies. I would say the test knives lasted about half the time my own knives usually last."

The butcher's own knives are the same kind of SWIBO and VICTORINOX boners, the only difference is that he sharpens them on benchstones, deburring with a fine-cut steel.
While his own knives last through 4-5 steer carcasses (with steeling), our test knives lasted for 2 carcasses and performed well, though for a shorter period.

This tells us, firstly, that the knife is free of wire edge and, secondly, that the edge strength had been compromised in the process of sharpening, and therefore dulled sooner.
If the knife had had a wire edge it would have been discarded after first cuts; a crushed wire edge cannot be steeled back to sharp.
Professional use of knives includes both cutting and frequent steeling.
Cutting dulls the edge through rolling and abrasive wear, while steeling recovers the edge back to sharp.
Steeling keeps the edge sharp mainly by microbevelling and removing metal, and the softer is the steel the sooner the edge gets steeled off to unusable.

I blame this edge softening on the felt with Autosol causing overheating as it is run on a half-speed grinder at about 1400 RPM and is the only sharpening step I can think of blaming. I know of myself that when deburring knives on that felt wheel I neglected the common rule for high RPM that "Better do 2 quick passes than 1 slow" - being too focused on the edge angle control, I was slow in sliding the knife across, gave the knives 2 slow passes each side and could feel the blade warmed up. I hoped that slots in the wheel would mitigate the overheating, and they do but obviously not well enough.
To improve the edge longevity I should reduce the knife contact time with the felt run at high RPM.

As to the wire edge removal this trial concludes our experiments nicely, and confirms that deburring at a 1-2 degree higher angle cleans the apex of the base burr not rounding it.
The proper deburring requires minimum 2 steps: first honing at the edge angle to thin away the burr, and then at a 1-2 degree higher angle to clean the apex.