Hello good grinders and smoothers of FPN

We have discussed several times the difference between regular grid size and the MicroMesh scale. I took a look at the existing standards... and it's not pretty

In the US, the Department of Commerce officially defines grits no higher that 280. Besides that, there are three standards, which are comparable only for macrogrits of 220 and coarser. When it comes to microgrits, the three become fairly different. In a nutshell, around 240 and slightly under, they fairly agree and diverge from there to finer abrasives.

The three standards are defined by the Coated Abrasives Manufacturers Institute (CAMI) in the US, the Japanese Industrial Standards Committee (JIS) and the Federation of European Producers of Abrasives (FEPA). On top of that, the FEPA defines two scales, one for coated abrasives (noted Pxxxx) and one for bonded abrasives (Fxxxx).

In brief, a 1000 grit for CAMI is approximately a 1200 for JIS, a P2000 for FEPA. That's more or less a MicroMesh MM3200. Also, CAMI 2000 = JIS 8000 = FEPA F2000.

Of course, manufacturers are also free to define their own grit, just as MM does. The pure number of the grit can also be misleading, as it is based on the average size of the particles. A 200 grit for example can have particles that range from the size 190 to 210 or from 150 to 250.

My personal conclusion is that grit is a very inaccurate indicator of an abrasive if compared for different manufacturers of even just lines of product. If you are shopping for abrasives, look for the micron size or, if you can, get a sample to compare it to another one you know, or ask around to people who have tried it.

That's it

I think you said it all, right there, Denis. I applaud your delving into this arcane area and coming up with what you did even if it appears to add to the confusion.

I'm comfortable with micron measurements and will stick with them as long as they are accessible to me from reputable manufacturers. I'll grant that MM users who have a stable source of supply and are comfortable with those grits, fine for them, too!

In my view, however, one person's micron is another person's micron...and that's a fact!

Hi Roger,



... and I am adding to the confusion ?!

I think you are right that not all microns were created equal. Besides "marketing optimism", I'm sure abrasive experts could tell us a lot about the media on which the abrasives are coated or bonded and the effect on final use for example.

Hi Denis,

Thanks for delving this all up. I would like to add something here. I knew about the different standards, but the one used most often is the CAMI one. This is also what I refer to in my nib smoothing article (which you can find here: Nib Smoothing), in the tables where I add grit sizes to micron based particle sizes.

I have deliberately kept it simple there, as the original definition of grit size is the number of particles per linear inch. IOW, establish the particles on any abrasives coated material, by drawing an imaginary line of an inch, and counting the number of particles found along that line.

This indicates one of the problems with grit size: it is not indicative of actual abrasive grain size in absolute terms at all.

Now, the differences in abrasiveness and actual smoothing capabilities are linked to particle size, obviously, and the coating material. If there is an even distribution of approximately the same size particles, embedded in their entirety in a coating (like in 3M ILF), the result is obviously going to be be a much smoother surface than in case of a bunch of particles sticking out from a coating (like in 3M MFF), or where the particles vary a lot more in grain size.

The material also matters: silicium carbide is much harder than aluminium oxide, as the hardness scale is logarithmic, not linear. Therefore, silicium carbide is much more abrasive than aluminium oxide. IOW, the former will give you results faster, but not necessarily smoother if the material is ordered in a different way. Silicium carbide often comes in a coating form where the grains extend from the coated surface (eg. MFF), while aluminium oxide often is embedded in the coating entirely (eg. ILF). I get better results with 0.3 micron ILF aluminimum oxide coatings for example, than with 0.1 micron MFF silicium carbide type coatings.

The backing is also important, both from the point of view of materials that can be smoothed easily, and from the point of view of the effectiveness of the coating. This is why MicroMesh has a slight advantage for polishing in comparison with other abrasives, which have much harder backing materials. OTOH, it certainly isn't as extreme an advantage as MicroMesh is trying to make us believe . My experience is that 12000 MicroMesh gives about the same results as 1.0 micron ILF aluminium oxide, which is approximately 8000 grit.

Another interesting thing is that with the higher grit sizes, a decrease of grain size by a factor 3, increase the grit size by approximately 4000. A grit size not in my list, for example, is 0.1 micron. That is approximately 16000 grit, which is 4000 up from the 0.3 micron version.

Finally, lately I have been mentioning 9 micron MFF here as being 4000 grit. Obviously (now anyway ), that should have been 2000 grit. I guess I should check my own tables more often .

Warm regards, Wim

try looking at sites by telescope mirror makers, we use grit and we have very tight requirments on grit size and quality.

Google ATM for mirror grinders theres a tonn of info on grits and polish. Bellow a certain point it is not regarded as grit.

kevin