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 AFDavis11

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 could easily be wrong, but if I understand it correctly, the grit system was originated by the abrasives industry long time ago. They use mesh screens to classify particle sizes. The biggest particles that pass the holes of the screen define the particular grit class. I was told this is reasonably accurate within the lower grits sandpapers, the mesh being defined in holes per square inch. Of course the mesh wires are also made out of something, so the holes must be smaller than the math in my initial post.

In the higher grit ranges, different manufacturers seem to use different size/grit ratios.
Some even may refer to the average particle size, while others use the largest particle size present.
All very confusing.

from ]http://www.supergrit.com

ABRASIVE GRIT SIZE COMPARISONS
There are three measurement systems for the size of abrasive grit: US CAMI (Coated Abrasives Manufacturers
Institute) or ANSI, European (FEPA Federation of European Producers Association), and Micron grading. CAMI
tolerates the most deviation of grit size for a specified grit. FEPAhas tighter tolerances. Micron is even tighter. Up
to 240 Grit, CAMI & FEPA grading is similar. As grits go finer, FEPA grit numbers go up faster than CAMI.
Example: FEPA 600P = CAMI 360, FEPA 1200P = CAMI 600. 20 MICRON corresponds to about 400 grit CAMI or
800P FEPA. The trend is to adopt the European FEPAgrading system even in the USA.


Going by the above, grit and mesh can be, and ARE, significantly different, depending which scale you use. The following excerpt from the next page.

http://www.supergrit.com/downloads/S...og05_page4.pdf


based on that, I think Bart is headed in the right direction. Possibly.

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.

Grit is the number of 'particles' in one square inch surface. So in case of our Coticule and BBW stones this is the number of garnets in one square inch surface.

The sharpening particles in Coticule and BBW stones are garnets.
Arkansas stones contain Quartz particles in stead of garnets.
Carborundum stones are made of carborundum particles.
Diamond plates are made of diamond particles.
And so on ... .

Grit is only an indication of the number of particles, it doesn't say anything about the shape of the particles and the way the particles are hold together.
These last two subjects are also very important for the behavior of the whetstone.