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Jan inquired, " the toothy burr is an iconic photo for me. (reply #3)  What is the scale?"

Jan, you are a pest!    You always ask me that!    I didn't calibrate and throw a scale under it so I can't say exactly.  Probably ~200X. 

That was a unique burr.  It was extremely thin.  Just lightly breathing on it caused it to wave in the breeze and sparkle under the light. I wish I remember the conditions that created the thing, but that was some time ago and memory fails me at this point.  Kind of cool looking though!

Ken, "procedures beyond initial grinding can increase the longevity of the sharp edge."  That's a loaded question!  Obviously after sharpening the burr must be removed.  It's easy to imagine by looking at the pictures of burrs what would happen if you didn't remove them.  All of that crud (technical term) would get smashed down over and around the edge.  Some of it gets torn off, but some does not.  Not a good thing. 

Strain hardening does work for carbon steel.  To the extent that happens as a result of stropping off a burr, or how much that changes edge retention, I have to admit ignorance.  I mean, burr removal by stropping does not flex the burr very quickly, or generate much, if any heat. 

This subject has made me understand that I don't know what metal fatigue really is either.  You know, flex metal enough and it gets brittle and breaks or cracks.  I've seen that.  I can demonstrate it and create it.  Can metal fatigue happen without strain hardening, or is the fatigue the result of it?  Or, is fatigue unrelated?

I really think that the more you know the stupider you get!  At this rate, in a few years I will be reduced to a babbling imbecile.

This is a true story:  On another forum, one member is a old sage that lives in the deep forest.  He has moose and bear in his back yard.  He has been sharpening for about as long as as I am old. And, I'm pretty old.  In a post he spoke an utterance of great wisdom.  I don't remember the exact phrase, but, basically he said, "often people's blades are sharper than their minds".  Now..., how cool is that! 

It would be great if we had a metallurgist on the forum!

You can think of the sharpened edge and the burr as two, totally separate things.  Almost like a bunch of glue stuck to the edge.  Removing the burr does not make the edge sharper, it just exposes the edge.

Once the burr is removed, what you are left with is the actual, sharpened edge of the blade.  Obviously, a sharp edge is very thin and prone to damage as it is used.  As it is damaged and deformed the knife dulls.  Generally the damage is that the edge bends and folds to one side or the other, or just gets kind of smushed (technical term) or bashed (another technical term) or smashed or crushed or stove in one way or another.

So when you then strop or steel the blade, the deformed edge is straightened.

You are correct, Ken.  When the edge is straightened by stropping or steeling, the bending back of the metal fatigues it.  Do that enough times and it's going to fracture and break off, just like bending any piece of metal back and forth until it breaks in half.

That said, with most blades, you can do this a number of times before the metal fails and keep a blade sharp and performing well for a long time before it starts to crap out on you and actually needs sharpening again.

Now consider this:  If you take a paper clip and bend it back and forth only one degree side to side, it will take many more bends before it breaks than if it's bent 90 degrees each time.  It seems to me that a blade that is stropped before every use could be maintained much longer than if it is allowed to get really deformed because the edge does not have to be bent as far to get it straight again.

So, stropping or steeling an edge will induce fatigue and cause the edge to fail.  But... it will keep an edge sharper and useful much longer than if it is not maintained. 

This is actually a good thing because it means that all blades will need sharpening eventually.  If all blades remained sharp forever, life would be dull because we would have nothing to sharpen! 

Does that make sense?

Here is a great explanation of work hardening:
https://en.wikipedia.org/wiki/Work_hardening

Here's my take on the sharpening / stropping / steeling thing:

I agree Herman.  A burr can be very sharp, but is very wimpy.  A good indication of incomplete burr removal after sharpening is if the blade almost instantly becomes dull from normal use.  A burr is not the sharpened edge of a blade, but rather small metal shards and thin, possibly even rolled metal waste remaining from the sharpening process.

If the burr is not removed, two things happen; some of it breaks off into what you are cutting (broccoli and steel shards anyone?) and the rest folds down over the edge or off to one side.  This remaining burr makes the blade appear to be dull, when in fact it is not.  Once the burr is removed the true edge will be exposed and the blade will be as sharp as it can be.  You can actually see this with a microscope and verify the observation sharpness tester.

A burr is different than the true edge of a blade bending or deforming from use.  This is what happens when a blade becomes dull.  When that blade is stropped or "steeled", the deformed edge is straightened and almost magically becomes sharp again.  Contrary to popular belief, unless a blade is cutting an abrasive that is harder than the steel of the blade and therefore capable of removing steel, dullness is not caused by the edge wearing away, but simply that the thin edge of a very sharp blade folds over, gets deformed or just bashed in one way or another.  You cannot, for example, actually sharpen a blade using broccoli or a wood cutting board because sharpening requires steel to be removed to form the edge.  This is why judicious use of a knife "steel" keeps a blade sharp.  The deformed edge is straightened, and the blade sharpness is maintained.

Eventually this bending/straightening of the edge causes the very thin, sharp part of the edge to break off due to metal fatigue.  Once this happens the blade is actually dull, and no amount of stropping or steeling will help because the thin, sharp edge no longer exists.  At this point, it's Tormek time!

So, a really good question Herman brings up the relationship between steel hardness and edge retention.  Hard steel will resist deforming, but is more brittle and will chip off more readily from stropping or steeling or normal use.   Like everything there is always some trade off.  Where is the sweet spot between hardness and the ability to maintain an edge between sharpening?  I wish I knew.  I'm still trying to get a handle on that.

I understand basic work hardening, but I don't understand what it means to previously hardened steel.  I'm still trying to figure that out.

My $0.02

Some burrs:

Thanks for the reply, Marie!   Bumps in the road are totally understandable especially with a big project like getting up a new website.  Your feedback is really appreciated!

I just tried to log into the new site and my email was not recognized.  It's now been 11 days since Marie posted that they are importing registration information into the new site.

Maybe they have something going on that is causing problems.

Did you watch the video on the Amazon page?  A cool little video on how they are manufactured.  I want one of those robots.

"Years ago, I softened (rounded) the back of my Henckel knives."

By that do you mean that you rounded the handles?

I have a 12 cm Wusthof knife. It's a wonderful knife!

https://www.amazon.com/Wusthof-Gourmet-2-Inch-Steak-Knife/dp/B002CZOSMC
 
It's very light weight, the spine is only slightly over 1 mm and tapers down to the edge.  Basically a very thin blade.  It takes an extremely sharp edge and edge retention is good too.

The thing does great for small tasks like slicing apples.  It can slice so thin that one apple can server about 100 people!  Think of the savings!  Well worth $20.

Curt-

Another thank you for your review!

I'm not quite as concerned about cutting speed as the finish of the edge.  I'm looking for a slightly toothy edge that will cut things like broccoli and tomato skin well without just riding on the surface.  Grapefruit rind is another good test material.  A super sharp polished edge works fine for a short time, but soon starts riding on the surface.

I've been trying to decide between a 400, 500 or 600 grit wheel, but they are too expensive to buy all three just for experimentation.

It would be interesting if you could test your 600 grit edges on some of the tough, smooth skin vegetables and fruits and see how they perform after a moderate amount of use.  I've found that is a actually a pretty good test for how well a particular grit finish is going to perform in general and kitchen use.

You might want to pick up a USB microscope.  They are inexpensive, ranging from $25.00 - $100.00 and are produce images that are very informative.  I would suggest a 5mp with 200X or more optical magnification.  Ignore the digital zoom numbers.  Digital zoom is meaningless as it is just the same as zooming in on an image in an image viewer.

My microscope and PT50B sharpness tester have become just part of how I sharpen.  A microscope and sharpness tester combined provides an amazing gestalt of empirical analysis of the edge.  Once you get use to that data, it's hard to believe sharpening is even possible without it.  Instead of just guessing what is going on, you can actually understand by measurement and observation.

The attached image, as well as the following links are some of my USB microscopy images:

https://forum.tormek.com/index.php?PHPSESSID=bsum39h9llrfedila1dig6tiq3&topic=3165.msg18073#msg18073
https://forum.tormek.com/index.php?PHPSESSID=g2oeq2479qc0cp6ab8qkrrd4i5&topic=3191.msg18467#msg18467
https://forum.tormek.com/index.php?PHPSESSID=nap2bgf53nbmoh4n6i0i9vupe0&topic=3190.msg18443#msg18443

Again, thanks for the review!  Please keep us informed of your further testing and experience.

And, of course, it depends on how the blade is going to be used.  Some balance between steel hardness, sharpenability, and edge angel for the best performance in the environment that the blade is used in.

What I liked about this and the reason for the post is that for most everyday uses a toothy edge is more useful than a polished edge.  I was happy to see evidence that it may actually have superior edge retention.

I'm sure my tomatoes would feel quite differently, but I'm happy. 

The VLC media player, available for both PC and Mac, plays just about any video format you can throw at it, including MP4 and DVD's.  It even plays audio files like Wav and CD's.  You have to be trying to play something pretty obscure if VLC won't play it.

I've used it for many years.  It's a great media player and it's free.

http://www.videolan.org/vlc/index.html

I purchased the PT50B, which is the next iteration of the PT50.  It's not widely available yet, but just shoot Edge On Up an email and order directly from them.  Here's a hint- You might as well get an extra spool of test media while you're at it.  EOU is in the process of redoing their web site to reflect new stock, and it should be live very soon.

Here's one example of how it's useful.  I wanted to regrind the bevel on a knife to a more acute angle, and it needed sharpening anyhow.  I knew it was sitting at about 225g BESS.  So I ground away with a coarse grind, gave it a light hone and tested it.  It had the same reading. 

How could that be?  Under a light, it looked like I had completely set the new angle.  I knew that I must not have ground completely to the edge, but just for grins and to test my gut feeling I threw it under the microscope.  Sure enough, there was still a micro bevel from the old edge angle. 

So after a little more grinding and a light hone I tested again; 140 this time, which was about where I wanted to be for that knife.  Yes, it could be sharper, but 140 really is pretty sharp, and I generally don't want to turn my kitchen knives into a DE razor blade.

It does not take long to get a good feeling for about how sharp your general method of sharpening gets a blade.  If a test shows it's out of spec, then you know something's up. Maybe there is some micro burr left, or the blade still needs more grinding, etc.

As well as learning by experimenting with different methods, and how consistent you are in getting the entire edge sharp, etc., it also helps with QC/consistency of the final edge.  Once a blade is pretty sharp, it's, well, pretty sharp.  Without test equipment, that's about all you can say about it... It seems pretty sharp and call it good.  But with the tester you can quantify it with an actual number.

One thing about the Tormek is repeatability and consistency.  A sharpness tester provides the same to the level of sharpness you are producing.  A cool tool to add to your arsenal I think, and it's fun.

I suspect that was simply showing that there was a big old, nasty, gnarly burr and your most excellent honing procedure removed it.

Edge inspection without even looking at it.

I was a bit reticent to post this as it has been discussed here before, and at this point I'm more than fashionably late in joining the party, but the Cliff Stamp stuff got me interested enough in edge retention that I needed some way to measure edge sharpness.  So, finally, I ponied up and bought an Edge On Up sharpness tester.  I had delayed because at my age I'm trying to shed rather than collect stuff, and I thought I'd test a few edges, get a feeling for what it meant, and it would become yet another closet dust collector.

I had suffered the same misgivings about getting a microscope, but now I use it all the time.  I am finding the same to be true of the sharpness tester.  In just a few short days, it has joined the microscope as simply part of my regular sharpening routine.

One aspect I hadn't really appreciated was how informative the thing is in experimenting with what does and does not work in various sharpening procedures.  Things like how more or less pressure when honing affects the sharpness.  Did additional honing increase or decrease sharpness?  And this can vary from blade to blade, with different edge angles, steel types and amount of burr present.

I'm finding its accuracy and repeatability good enough to provide real, useful information, especially in conjunction with a microscope.  A sharpness tester does not provide visual edge assessment, and a microscope does not test sharpness, but together they provide a pretty broad picture of what is happening down there at the cutting edge that isn't readily apparent without instrumentation.   Cool tools.

Anyway, I thought it was interesting enough that, even though I'm late to the party, I'd chime in too.   

After reading Cliff Stamps's studies on edge finish vs edge retention, I've started to question some assumptions I have about sharpening. 

That being said, I thought I would pose this question:

With a kitchen knife for example, does a too sharp edge reduce edge retention?

Sharp, by definition, means thin.  It would make sense that a thinner edge would be more prone to wear, rolling and damage.

Onion other hand, a sharper edge requires less force to cut, therefore reducing force concentrated at the edge.  It would make sense this would increase edge retention.

For example, would a knife sharpened to BESS 50 (DE razor blade) have more or less edge retention than if it were sharpened to 150 (a sharper than average utility razor blade)?  According to the BESS folks, new high end cutlery is somewhere between about 250-350.

So, with a kitchen knife for example, does a too sharp reduce edge retention? 

Is there a happy medium?

Does anyone have an opinion on that?  Can you relate it to BESS numbers?

I've decided to change the way I sharpen.  I'm going to completely bail on the Tormek and simply sharpen using the rough side of the stone grader @ 6 dps.  That should do it!  Gotta love this stuff.

"In regards to the lower angle having increased edge retention the reasons are :

•   the 15 dps edge is already strong enough to resist rolling
•   there is no issue with carbide tear out or fracture in such low carbide steels
•   the higher angle concentrates forces around the edge
•   as the edge angle increases it takes less metal removed to increase the width of the apex

Thus increasing the edge angle does not offer a practical increase in strength and durability as it already is strong and durable enough to resist damage at 15 dps. The increased edge angle just makes the edge into a heavier wedge which actually thickens faster under a given amount of wear and the wear will be accelerated due to concentration of forces around the edge due to the higher angle."

http://www.cliffstamp.com/knives/reviews/angle_experiments.html

Well, this is amusing.  These guys actually sit around and do thousands of rope cuts.  Scroll down a little:
https://www.spyderco.com/forumII/viewtopic.php?t=65685&start=20

Some of the comments are funny! "can we smoke the hemp first.lol", "I use mine for ground cover, still have boxes full of it to dump out yet"