Why use honing compoound?

[grepper]

Simple question:

After sharpening, why do people use honing compound for honing/stropping?  Simply to polish the bevel?

[Mark Reich]

Simple answer;

Compound adds abrasion or polishing quality to the hone.

[grepper]

First of all, I know that "Why use compound" sounds like a very obvious and stupid question! But there are so many compounds and folks invest so much time in it that I was wondering why. What's all the fuss about?

Is it just to polish the side of the bevel and give it a more mirror finish? Is it expected to have any additional benefits?

[Mark Reich]

Pardon me, grepper, but I don't think that you're question is obvious, and it's certainly not stupid or even sophmorish.

I wasn't poking you with a simple answer at all. I just boiled it down to answer your "simple question". Now you're gonna get it. 

The reason you hear so much about compounds is simply because they really do work better than anything else for finishing and maintaining whatever type of edge you like, especially with the newer abrasion resistant steels.

Don't let the plethora of compounds stymie you. There are only a handful of different types, but the range of particle size is pretty enormous.

A decade ago there weren't many choices of abrasive compounds, and most guys were actually using buffing compounds. The most common types were black emery and green chromium oxide. Neither of these were meant for leather, but leather has been a most effective substrate for hundreds of years. Only very recently have synthetic hones come into play at all, and their existence precipitated from the quality of extremely fine abrasive found in high end compounds.

We can skip buffing compounds completely. Even the type of grit in buffing compounds has been totally eclipsed. Emery and CrO have been replaced with diamonds and CBN, in compounds that carry the "supergrit" at near saturated levels. Buffing compound hardly has any grit in comparison. 

There is exactly one exception. Ken Schwartz has formulated diamond buffing compound with a high enough concentration of diamond grit you can almost give it away as jewelry.

I categorize grit particles into two basic types, polishing and cutting. Boron Carbide (BC) is the least abrasive supergrit. That means the particles are relatively smooth, so they don't cut very aggressively. This makes BC best suited to polishing and deburring.

Cubic boron nitride (CBN) has harder, sharper particles, so it cuts more aggressively, especially with modern, abrasion resistant steel, but still polishes and deburrs well as it breaks down into smaller particles.

Mono diamond abrasive is probably the oldest supergrit. The particles are about as sharp and aggressive as CBN, but it doesn't break down as quickly, so it cuts more than it polishes. This means it leaves it leaves an edge with tooth, so I put it into the "cutting" category rather than polishing.

Poly diamond is the most aggressive supergrit. The particles are jagged, and they cut more efficiently. Poly diamond compounds work quickly and leave the most tooth of all.

All of these abrasives are available with different size grit particles, and this is where we get so many compounds. I have 80 micron CBN (200 grit), down to 0.1 micron (160,000 grit). I have poly diamond compounds from 16u (1000 grit), down to .025u (640,000 grit).

Since I've been using compounds for so many years, I have quite a collection. As newer compounds became available, I wanted to try them. As the envelope widened, I wanted to see how far we could go.

Thanks to my great friend Ken Schwartz, the Kompound King, we went there and back. It's been a great ride.

[Ken S]

Grepper, thanks for starting an outstanding topic.

Mark, thanks for posting such an informative and thorough reply. It makes me realize how twentieth century my honing technique is. Do the new compounds perform better with O1 steel?

Ken

[Jan]

Mark, thanks for your comprehensive compound overview. Much appreciated.  

I would like to use this opportunity to share my opinion what happens on the edge during honing on leather wheel without any compound. Please take it with reserve it was not yet verified by any authority in metallurgy or engineering. 

My idea is that during dry honing we are shifting dozens of surface atomic planes towards the cutting edge. Because BESS sharpness of 150 gf corresponds only to several hundreds of iron atoms near the apex than several dozens of shifted atomic planes may improve the apex sharpness significantly.

This process is not uniform along the whole edge because steel is composed of grains with random mutual orientation. So within one grain we can shift dozens of atomic planes while in the neighboring grain, with different orientation, this number can be significantly different.

So called slip planes group together within a grain, form slip bands, and are visible under optical microscope.


Jan

[Mark Reich]

Thank you, Ken. 

Yes, the modern grit in the new compounds work far better on every type of steel, beyond doubt. 

It's a simple fact that the new compounds are superior in every way. The abrasives are much better, and the compounds are designed specifically for use on knives.

[Ken S]

Thanks for the info, Mark. One of my life philosophies is that we shouldn't all have to drive over every pot hole in life. Your posts have helped me miss a couple pot holes.

Ken

[Mark Reich]

Mark, thanks for your comprehensive compound overview. Much appreciated.  

I would like to use this opportunity to share my opinion what happens on the edge during honing on leather wheel without any compound. Please take it with reserve it was not yet verified by any authority in metallurgy or engineering. 

My idea is that during dry honing we are shifting dozens of surface atomic planes towards the cutting edge. Because BESS sharpness of 150 gf corresponds only to several hundreds of iron atoms near the apex than several dozens of shifted atomic planes may improve the apex sharpness significantly.

This process is not uniform along the whole edge because steel is composed of grains with random mutual orientation. So within one grain we can shift dozens of atomic planes while in the neighboring grain, with different orientation, this number can be significantly different.

So called slip planes group together within a grain, form slip bands, and are visible under optical microscope.


Jan

Thank you for the kind words, Jan, and thank you for your input on the subject. It sounds like you have some metallurgic background, which is awesome! I have no formal metallurgy training, but I've studied a lot, and have hands on experience.

I do understand that the grains of steel have random orientation, which become visible after the surface is polished and etched. To my understanding, it would be analogous to the grains being like a pile of firewood, crushed to the point of being without voids. If you could cut the pile in half and stain it, you could see the pieces oriented with porous end grain on the surface would be darker than pieces showing more side grain. 

That would be similar to how they go about measuring the size of the grains in a piece of steel, except with steel they use an acidic etchant, which acts visibly similar.  

I don't understand your statements about, Quote;  
"shifting dozens of surface atomic planes towards the cutting edge", or "within one grain we can shift dozens of atomic planes while in the neighboring grain, with different orientation, this number can be significantly different".
-Unquote

It's actually the "shifting" part that eludes me. 

Probably in addition to other things...

---

Thanks for the info, Mark. One of my life philosophies is that we shouldn't all have to drive over every pot hole in life. Your posts have helped me miss a couple pot holes.

Ken

Thank you, Sir! 
That's all I could hope for!

[Jan]

Mark, you are correct, several decades ago, as a student, I was working in RTG lab of a large metallurgical institute. I was measuring lattice constants of different steels. But later I have dealt only with Earth Sciences. Hence my posts about iron and nickel in the Earth core.

Sorry for my uneasily understandable statement, English is my secondary language.

Steel is composed of densely packed atoms arranged in a regular manner. For some atomic planes it is energetically easier to slip with respect to the neighbouring plane than for some planes with different orientations. The picture may help to understand what I mean.

   

My idea is that during dry honing some suitably oriented surface atomic planes may slip (be shifted) towards the edge where they disintegrate. Atomic planes in grains with non-suitable orientation do not slip, or slip only in a limited extent.

When I am sure that the burr is removed, I strongly reduce the pressure on the honed edge and flip the blade after each pass. I do it because I will not force too many atomic planes to slip towards the edge in this final stage of honing.

But again, it is only my working hypothesis!

Jan