Thread: A theoretical discussion about honing particles

"Honing a razor is often said to be no rocket science." A much quoted statement on Basic Honing Topics section of SRP. It's as true as false, I guess.
Grab a Norton, read the recipe, practice a little and a shaveready razor dawns at the horizon.
But beware, because the lure of ever increasing sharpness lies literally "just around the corner" and soon the aspiring honing finds himself on a quest for more than shavereadiness. In this new realm, whiskers should be swept off the face, leaving the skin as smooth as that of a newborn baby. At this point, many questions arise. Does the grain of the steel matter? Which forces are at work during the sculpting of the cutting bevel? How do they relate to the hardness of the steel? How to they relate to the plasticity of the steel? etc, etc... This has been the subject of serious scientific study. The work of professor Verhoeven at the Iowa State University is often cited in that regard.
Verhoeven reports that edges are not only formed by abrasive action, as we run a razor over the hones' surface, but also undergo plastical deformation. This principle makes it nearly impossible to fully understand how a particular hone will affect an edge. But since most of the action seems to come from abrassion, and it is the easiest to figure out, I'd like to elaborate on that a bit, just for the sake of having an informative discussion.

About particle size and grit counts.
I'm no big fan of grit counts. They raise confusion. For starters, few realize that doubling the grit count doensn't half size of the scratch marks. Let's supose a grit count of 4000. That's 4000 particles per square inch. If the particles were touching eachother, we can easily calculate their size. The square root of 4000 is approximately 63. This means one inch contains 63 X 63 particles. One inch is 25400 micron. 25400 divided by 63 is 403 micron. It is clear that most 4000 grit hones have particles much smaller than 400 micron. That's because they are surrounded by the substance that binds them together. A 4000 grit hone could contain particles of any size from 0.5 to 400 micron. (I hope someone reviews my math)
Now, let's suppose that a manufacturer has the decency to keep his hones' particle sizes relative to his grit counts. Would this mean the particle size halves everytime the grit count doubles? Not necessarily. The square root of 8000 is approximately 89, leaving us with a mesh of 25400 divided by 89 equals 285. Hence, when the grit count doubles, the particle size decreases with a factor 1.4. Otherwise put, when the particle size halves, the grit count quadruples.
Unless, they're all just doing whatever they think is the best for marketing their hones.
Which is more likely than my math excercise...
Between different brands, I wouldn't bet my money that 6000 is finer than 4000.

Even so, there's more to define the properties of a hone than its grit count. Particle shape and aggressiveness are not to be underestimated. I'd like to illustrate this with a drawing that compares small, but deep scratches of a fast hone with a wider but more shallow and rounded scratch pattern. I was after a better understanding why Coticules create such fine edges with relatively big particles when I started making this drawing.

I'm confused. I thought a 4K hone contained a substrate that held, generally, all 3 micron sized grit particles, and an 8K hone contained, generally, substrate that held 1 micron sized particles.

4,000 particles per square inch? Really?

I don't think this is correct. I believe that the grit number is the designation for the size of abrasive that can pass through a mesh screen with various sizes of openings. At least that's the case for grit definitions for sandpaper. A 200 grit sandpaper has particles that would pass through a mesh screen that has 200 openings in either one linear or one square (I don't recall which) inch.

I always assumed this was the same for hones but I'm not certain. I don't think you can go strictly by particles per square inch because the hone surface is three dimensional.

Bart, you are a little confused.

What you are calling grit count is actually known as mesh size.

The mesh is a sifter used to size the cutting particles found in hones and on sandpaper. The number references the number of holes per square inch in the mesh. In the industry I'm sure there is a standard size wire used to weave the mesh out of as well. once you have your sifted medium you then incorporate it with a matrix material giving you the components of a man made hone. While particle shape does effect the aggressiveness of a hone, its speed is also very much a factor of the proportion of cutting medium to matrix in the particular hone you are using. Thats why a Norton is faster than a Sun Tiger hone, they probably use exactly the same medium just in far different proportions.

Originally Posted by Wildtim

Bart, you are a little confused.

That's true for sure. Hence my desire to get into this swamp of particles.

Originally Posted by Wildtim

Thats why a Norton is faster than a Sun Tiger hone, they probably use exactly the same medium just in far different proportions.

A valid point for sure, but wouldn't the Norton actually cut more aggressively as well, in that case.
If it contains more particles, it probably releases fresh particles at a higher ratio too. And we all know that fresh sandpaper leaves deeper scratches than used sandpaper.

In addition to the grit designation discussion, sifting particles may be the starting point in the production of synthetic hones, but of course that's not the fact with natural hones. Only a few days ago, Rob Celis of Ardennes Coticule wrote in a thread that the Belgian Blue approximately contains 4000 garnets per inch² and the Coticule 8000 garnets per inch². Although he suggested as well that the grit rating of Belgian Naturals is also inspired by product orientation on a market that's dominated by grit/mesh numbers. (I can hardly blame them for that).

My point is merely that I feel people are far to often focussed on the grit numbers, a bit like everyone seems focussed on "Watt" when buying new speakers and on Megapixels when buying a new camera. Nothing wrong with that for the avarage honer/listener/photographer, but we're in the advanced honing section, so why not get carried away a bit?

Best regards,
Bart.

Originally Posted by Bart

That's true for sure. Hence my desire to get into this swamp of particles.



A valid point for sure, but wouldn't the Norton actually cut more aggressively as well, in that case.
If it contains more particles, it probably releases fresh particles at a higher ratio too. And we all know that fresh sandpaper leaves deeper scratches than used sandpaper.

In addition to the grit designation discussion, sifting particles may be the starting point in the production of synthetic hones, but of course that's not the fact with natural hones. Only a few days ago, Rob Celis of Ardennes Coticule wrote in a thread that the Belgian Blue approximately contains 4000 garnets per inch² and the Coticule 8000 garnets per inch². Although he suggested as well that the grit rating of Belgian Naturals is also inspired by product orientation on a market that's dominated by grit/mesh numbers. (I can hardly blame them for that).

My point is merely that I feel people are far to often focussed on the grit numbers, a bit like everyone seems focussed on "Watt" when buying new speakers and on Megapixels when buying a new camera. Nothing wrong with that for the avarage honer/listener/photographer, but we're in the advanced honing section, so why not get carried away a bit?

Best regards,
Bart.

Exactly... I love this stuff. Just wish I was smart enough to actually contribute! Ah, well... consider me your captive audience!

Originally Posted by FloorPizza

Exactly... I love this stuff. Just wish I was smart enough to actually contribute! Ah, well... consider me your captive audience!

Yeah I'm with you It is way over my head but I love it too. I may even learn something before it is over. It is sort of like the light in the kitchen, I don't need to understand nuclear physics to be able to flip the switch and turn it on. So I don't need to know this to hone my razors. OTOH, I do enjoy reading it and as I said before I might come away knowing more then when I arrived so keep it going gentlemen.

Originally Posted by Wildtim

Bart, you are a little confused.

What you are calling grit count is actually known as mesh size.

The mesh is a sifter used to size the cutting particles found in hones and on sandpaper. The number references the number of holes per square inch in the mesh. In the industry I'm sure there is a standard size wire used to weave the mesh out of as well. once you have your sifted medium you then incorporate it with a matrix material giving you the components of a man made hone. While particle shape does effect the aggressiveness of a hone, its speed is also very much a factor of the proportion of cutting medium to matrix in the particular hone you are using. Thats why a Norton is faster than a Sun Tiger hone, they probably use exactly the same medium just in far different proportions.

I am confused about the mesh that the particles are sifted through. If you, for example, were to us a mesh that has 300 holes squared per inch then when you sifted the particles you would get everything smaller than the 300 holes per inch mesh. It would seem to me that one would have to resift using say 305 holes per inch to sift out the smaller particles. From a quality control standpoint one could then say that I have a bag of particles that had a size that was between 300 and 305. No?


Thanks,
Richard

I posted a conversion table of American grit, Mesh and Particle size earlier in this thread. The mesh numbers are the range of particle sizes in microns since meshes at these small sizes don't exist. Mesh is a theoretical calculated number not a screen since as I said, meshes of this size don't exist. So, an 8000 grit has a mesh or range of particle sizes form 2 to 4 microns and an average particle size of 3 microns. Above 400 grit, particles are not seperated by actual meshes but by other processes which are mostly of interest to mechanical engineers involved in grinding technology.

Thanks for starting this thread, Bart.

There are a lot of good points brought up already, I'm just going to add some more variables and stir the pot and see what floats up!

Particle density... take abrasive papers, there's open coats and closed coats. Each could be sold as 400 grit but is it possible to have the same grit size on both papers? The same can be done in hones, more binder=less grit, less binder=more grit. Low volume of dense binder ~ closed coat. High volume of porous binder ~ open coat.

Cutting pressure, often forgotten in our discussions. Take two hones, one with spaced out open coat grit, the other dense closed coat but both have the same grit. One will cut faster than the other, one might create deeper scratches than the other. Why? Cutting pressure. The bevel rides on the tops of the grit particles on the surface of the hone. More particles means less pressure between each particle and the bevel but more scratches in the bevel for a given distance of movement. Coarse open coat means more pressure between each grit point and the bevel means fewer, but deeper scratches for a given distance of movement. This will change during honing... swarf will build up in the areas between the grit... big space, lots of room, little space, little room. If open coat, grit will dull faster as there are fewer in contact with the blade but won't clog up... closed coat won't dull as fast but might clog up with swarf reducing contact with the blade... Lubricant has a large effect as well, water, lather, saliva or what have you.

The grit itself, let's say aluminum oxide... it could be mined or it could be man made. If mined, how pure is it? If man made, was anything else added to the recipe to modify it's performance. How was it crushed to make the grit? There are various types of mills... one might produce duller grit than the other. How carefully was the screening done, how much time does a manufacturer spend on this kind of work? All these things add up and there is no way for the end user to predict the outcome except by trail and error for his/her particular situation. There is an almost unlimited number of variables that can affect the outcome.... I just don't see how we could distill this down to something basic. We can however come to realize that the more we know, the more we know we don't know!

So in the end, we'll be back to doing what we've always done.... Hey, anyone ever use this type of hone? You did? And it works OK for you? Great... I guess I get one and give it whirl then, maybe it'll work for me.....

Regards

Christian