Understanding a burr

[grepper]

Hey Kids!  Wanna see a burr on a knife at 200X magnification?  Well, now you can, with the new Burr-Omatic microscope!

You are looking down from spine towards the edge at about a 50% angle.

I ground the knife on one side at 80 grit, which forms a burr on the other side.

The side I ground, opposite the burr:



One view of the other side with the burr.  You can see the burr protruding from the edge:



If you look carefully, below you can see that a burr is not just bent shards of metal, but rather it actually rolls over the edge and forms little tunnels of steel.  As you  sharpen with finer and finer grits going from side to side of the knife, some of the burr gets torn off, and the thicker parts get bent back and forth until they break off due to metal fatigue.



I could document this process of going from 80 grit to 9 micron abrasives, but it's sort of a pain to take these pictures.

It also shows that if you are looking for a slightly more aggressive "toothy" edge, that one should not mistake burr junk hanging off the blade for "tooth" left by finishing with a coarse abrasive.  It's always a good idea to give it a light strop to remove the junk, or the junk may end up as a microscopic tasty condiment in your sirloin.

Anyway, I think it is pretty interesting to see what is actually happening when you sharpen a blade. 

[Herman Trivilino]

It's always a good idea to give it a light strop to remove the junk, or the junk may end up as a microscopic tasty condiment in your sirloin.

Who among us couldn't use a bit more iron in our diet?

[mike40]

I'm glad I don't have one of those microscopes Grepper. I would never be totally satisfied with any edge I looked at through it. Self deception works much better and it's faster too, lol.

[Elden]

That kind of iron might give you some micro perforations in the stomach.

[Ken S]

At my age, my fingers feel better than my eyes see.  I'll stick to the tried and true method of feeling for a burr. 

Fascinating post, and funny responses.

Ken

[grepper]

I'm glad I don't have one of those microscopes Grepper. I would never be totally satisfied with any edge I looked at through it. Self deception works much better and it's faster too, lol.

Actually Mike, you would be surprised.  Once a knife starts getting sharp, 200X is not nearly enough magnification to show anything very interesting.  The edge appears to be just a boring, straight line.

This handy little tabletop SEM might be just right.    I just need to find a way to come up with an "extra" $15-$30K.

http://www.hiscope.com/tm3000.html

[Rob]

now guys...there's an edge and an edge.....reminds me of that thread with the Japanese hand planning competition!!

[mike40]

GrepperI  probably need that $15K scope just to read the news! I'm trying to keep calm and trying not worry too much about that ultimate edge. That is my way of keeping my sanity.

Ken  Hmm....Sort of like honing braille. I like the concept.

[Herman Trivilino]

The ultimate edge is an illusion.  A fact exploited by clever marketers.

[Rob]

I entirely agree.  The fact that there is no universally accepted means of objectively measuring the fine-ness of an edge (at least not without scanning electron microscopy) leaves it open to tinkers and pedlars of all shapes and sizes.  Manufacturers and dealers make outrageous claims based on "personal experience" none of which can be verified.

That's one of the reasons I like exchanges with real customers like this....it means you can develop a discussion to get behind the marketing and honestly discuss the cracks and issues "warts n all" which is complete anathema to anyone in sales.  It becomes like a political debate right versus left....you can predict that the one will disagree with the other before they speak...thus you know the syntax of the argument is politics and not truth.  The language is rhetorical.
Personally I find that rather offensive since it presumes the public are too un-intelligent to discern one point of view from another.

Forums like this allow the protagonists to develop a common language that promotes shared understanding.  For example I like our standards for sharpness testing (which I accept aren't unique to here but have become well accepted) which are the paper, nail and even hair shaving tests. I variously use all three and they can be relied upon.  I particularly like the nail test for its convenience.

Wow....that turned in to quite the sermon...sorry bout that :-)

[Ken S]

Mike, I like your term, "honing braille".

I can appreciate the scientific curiosity involved in making photographs of an edge with high powered microscopes.  What would interest me is how an edge judged to be superior under high magnification performs with our everyday sharpness tests.

Does that edge slice paper more easily than an edge deemed to be merely quite sharp? 

Does that edge catch using a fingernail or a plastic pen differently or at a lower angle?

With turning tools, does such an edge require less sanding than a quickly acquired edge?  This could be examined from the concept of total time involved in sharpening and turning.  Does a superior edge warrant the extra time involved in polishing in the total turning time?

It could also be examined from the perspective of pleasure.  Does the extra time involved in superpolishing make a more pleasant turning experience?  (This assumes one actually wants to diminish such a fine "show" edge by degrading it with real woodworking.)  I realize this is more subjective.

While I tend to lean toward a tool being sharp enough for the task at hand, exploring the sharpness frontier can advance the middle as well.  Interesting posts.

Ken

[Rob]

Good points Ken.  Whats even more fascinating to me is what on earth is it that drives (particularly men) to spend huge amounts of time and effort discussing and indeed chasing after that holy grail edge.  Is it nature or nurture do you think?  Are we wired this way genetically, if so probably to do with our role as hunters in early ancestral times or has our culture "grown" us this way?

As sure as eggs, we don't half spend a lot of time and money trying to achieve the perfect edge whether more than or just fit for purpose or otherwise.  And that's not just the case on this forum....oh no.  On other wood working forums there are endless debates about sharpening, on some its a banned topic now due to the heat generated :-)

[grepper]

Aside from the satisfaction of restoring a tool from useless to useful, I just like sharpening.  I find it engrossing, relaxing, enjoyable and fun.

Why do I like the aroma of a rose?  I can smell a rose, and then I can think about it.  I could call it a woodsy sweet smell.  But those thoughts, those labels, are distinctly not the aroma itself.  I cannot smell the thoughts.  They are kind of like background noise, or clutter.  They are superfluous. 

It has been said, when standing, just stand.  So, I suppose you could say, when sharpening, just sharpen.

There is however one thought that I notice frequently comes to mind when I'm sharpening.  That thought is:  It could always be sharper.   

I probably think this because I'm a man..

[CleanCut]

I am of the view that members of the forum are perfectionists and find a satisfying outlet in pursuing a perfect edge (fit for purpose of course). Over the years I have used bench stones, with or without jigs, followed by tools that attach to a power drill. None assisted me, an amateur weekender, to approach perfection. At wood shows I watched Tormek demonstrations and lusted for such a tool. I am currently renovating the shed to accommodate a T7 that should arrive in two days (that's another non-perfectionist story). Yes Rob, I believe we are wired this way and some may may find an outlet in chasing the perfect edge.

[Rob]

Good thoughts chaps :-)
Keep em coming :-)