Burnishing ??

J

JD Spydo

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Nov 20, 2004
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Burnishing is a term I have seen used in several different applications and used to describe several job operations in several contexts. Also I have seen so many things associated to burnishing but yet I have not heard a concise definition that really clearifys what is meant by the term.

I just read a testimony from a guy who said that a sharpening stone burnishes as well as abrades and sharpens :confused: . I always thought that true burnishing was metal against metal. At least that is what I derived collectively from my experience in machine tool shops.

I have also heard that some strops are "burnished leather". I have a set of carbide sharpeners. One side of one of the tools is called a Burnisher. I am not yet clear as to what it's intended purpose is. I have recently asked 2 machinists what their definition for burnishing is. They both stumbled all over their words like a politician trying to give you an answer to a straight question but never making their postition totally clear.

I guess I could narrow it down by asking what does the term burnishing mean in relation to metal work and knife sharpening in particular? Even my huge Webster's Third New International UNABRIDGED dictionary doesn't even have a clear and concise definition of BURNISHING in relation to metal work :confused: I really want to know your all your thoughts and your definition of this term. I really want to narrow it down.

I always thought that a Sharpening Steel was a type of Burnisher?
 
Burnishers, in regards to steel, are deformation based, whereas a stone is abrasion based. A cabinet scraper for example is generally burnished (with a smooth very hard steel rod) after is is sharpened with a stone, to give the edge a hook and that is what does the scraping. Traditional smooth knife steels are also burnishers as you noted. Stones which are heavily loaded will also turn into burnishers because they can't abrade any longer.

-Cliff
 
Hi, Cliff's defenition is essentially how I understand burnishing. It is the polishing of metal through the platic flow of the surface of the metal. The backs of Japanese swords are polished this way... they take a powdered wax made from some sort of insect and apply it to the back of the blade to reduce sticking and then take these really hard and smooth steel needles called "migaki" and rub them on a section of the blade until the surface gleams, and proceed up the blade burnishing one tiny section at a time. http://www.shadowofleaves.com/polishing_tools.htm

Judging from the microscope pics of the ultra-fine Spyderco hone, it consists of a smooth rounded abrasive of about a 2,000 grit (JIS/waterstone) abrasive that is tightly bonded in a dense matrix. Watersones and India stones have sharp little grains that slice out neat little shavings like a plane shaving a board (Here is some swarf I washed and put under the scope):


The larger smooth grit of the Spyderco hones won't dig into the metal as deeply as a sharp abrasive and, since it lacks the sharp corners and angles, it doesn't neatly slice out little shavings. Instead it plays bulldozer. On the microscopic scale, the pressures at the contact points between the grit and the steel can be great enough to cause the steel to flow like putty, so it both flows around the sides of the grit and gets bunched up in front of it. When these little bits of bunched up steel get big enough they can break off the surface and roll along between the grains or get caught under them, get flattened and drug along the surface (metal on metal) and smeared into any low spots, like spreading putty on a crack. The result is that the spyderco stone can leave a much smoother surface than a 2000 grit waterstone, but can leave streaks where large balls of metal were gouged into and smeared along the surface. Here is a shot of a block of stainless steel polished on a Spyderco ultra-fine:


You can see the smooth areas that look almost as polished as an 8k or 10k waterstone and places where balls of swarf gouged the surface and were smeared along, and little raised streaks and domes where it looks like bits of metal were smashed into, and possibly pressure welded to, the surface. To the naked eye it looks a bit like the surface gets as bright and shiny as an 8k-10k waterstone but the reflection off it isnot as clear... more like off a 5k or 6k waterstone (and looks streaky if you hold it at the right angle). I guess you could say the Spyderco both cuts (shallow, wide cuts, probably by breaking off little balls of metal. Sharp abrasives of the same grit size would cut much deeper furrows and take off large clean shavings, which can curl up like plane shavings) and burnishes by smashing and dragging the bits of metal that break loose over the surface (especially when it starts to load up).

Anyway, that is what it looks like to me.
 
Wow yazuha. Cool micro photos.:cool:

My Sharpmaker skills recently increased to the point that I'm adding the ultra-fines to my toolbox. They're in the mail.
 
Thanks. The quality isn't too great considering that the originals were over 3 megabytes and I compressed them down to about 150k to keep from killing the folks still using dial-up, but still good enough to show what I was talking about. (the depth of field was too low to get all of the swarf into sharp focus at the same time too, so part of that is a bit fuzzy, but you can still tell where the shavings curled up like little coil springs)
 
It was black but not as loaded as it could be since I used water to lubricate it a little and that probably cut down on some of the loading.
 
You might want to see what surface it produces when it isn't loaded. When I use that stone to sharpen it is only as a final finish and thus the number of passes is very small. Any stone which is loaded will start to act as a burnisher and not as an abrasive.

-Cliff
 
I agree, it does burnish when it gets loaded. It loads and gets black quickly and needs cleaned with soft scrub to keep cutting well.
 
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