Thread: How is grit determined?

This is actually my first post on SRP - so happy I'm finally getting involved. I'm much more active and knowledgeable in the knife community at kitchenknifeforums.com, and have a respectable collection of Jnats, with a dozen or so other hones from around the world, as well as a dozen or so synthetics. Anyways, oddly enough, I've found it nearly impossible to find an answer to how grit is determined in synthetics (this question can't really be applied to naturals as we use synthetics to reference estimated grit in naturals, and the abrasive density is much less uniform in naturals than synthetics, obviously).
Does anyone know, especially in JIS and AISI? I think I once read long ago that it's the average density of abrasive particles in 2.5cm^2, but that seems like an odd and arbitrary number. Any insight would be appreciated.

Thanks!

It has to do with sedimentation rate, or at least that's how the finer grit particles are separated. Here's a table with the particle diameters of common synthetics, along with some natural stones, which I'd take with a grain of salt.

grit particle size

Originally Posted by KenWeir

It has to do with sedimentation rate, or at least that's how the finer grit particles are separated. Here's a table with the particle diameters of common synthetics, along with some natural stones, which I'd take with a grain of salt.

grit particle size

Thanks. I'm also aware of this chart, which is a bit more comprehensive.

I guess a better way to state this is 'how is grit measured'? It certainly is a function of particle size, but what about the area? Is it squared, ie sandpaper, or cubed, ie stones? Or something else entirely?

No, it might as well be thought of as arbitrary.
1k grit shapton isn't the same as a 1k norton

1k grit sandpaper in the us isn't the same as 1k sandpaper in uk

Edit: there's no hard and fast rule, this grit has this size particles, because every manufacturer is different.

Edit2: other considerations might be how well the particles are bonded, that will control how much slurry you generate, and how jagged or smooth the particles are. One manufacturer may use smaller particles than another, but if those particles have more sharp corners/edges it may still cut faster than the stone with larger but smoother particles. Other manufacturers might be using different materials all together, which may cut differently

Edit3: each manufacturer may have its own formulae for max, min and avg particle size for each grit, but there isn't really anything industry-wide because every manufacturer is different.

Welcome to SRP, just to add to the confusion .......... from '09, by smokin'tbird ;

http://straightrazorpalace.com/advan...tml#post446896

I love it!

As far as how a manufacturer determines what grit to call a product, its approximation. They'll either make their own abrasive particles or buy in bulk, adjust binder strength, binder to grit ratio and overall density to get the final product some where close enough to what people expect out of a certain grit, let's say 4K, that they can get away with calling it 4K, instead of 3379 or 4400.

Originally Posted by KenWeir

No, it might as well be thought of as arbitrary.
1k grit shapton isn't the same as a 1k norton

1k grit sandpaper in the us isn't the same as 1k sandpaper in uk

Edit: there's no hard and fast rule, this grit has this size particles, because every manufacturer is different.

Edit2: other considerations might be how well the particles are bonded, that will control how much slurry you generate, and how jagged or smooth the particles are. One manufacturer may use smaller particles than another, but if those particles have more sharp corners/edges it may still cut faster than the stone with larger but smoother particles. Other manufacturers might be using different materials all together, which may cut differently

Very much this.

Binder will have a large effect on a hone's performance. Barber hones are the perfect example of this.

Barber hone cutting material is actually in the range of 300-600 grit, yet a good barber hone will leave an edge equivalent to or better than an 8K hone. This is because those large particles are both very tightly bound - they do not break free or slurry - and they are very well worn. Almost dead flat with the surface of the hone and just barely poking up enough to remove a very small amount of metal. Those same particles in a loose binder that allows for slurry would wreak havoc on an edge.

It's quite an intriguing dynamic.

I'm at the point now where I am less concerned with any stone's 'grit rating' and more concerned with it's performance relative to a known quantity. For me, that's the Norton 1/4/8K because I own them and I'm quite familiar with those hones. YMMV.

Far t many variables to consider for there to be any simple formula.

Here is the Glen system use it if you want

Grit

A Norton 1k is more abrasive then a Norton 4k which is more abrasive then a Norton 8k

A Naniwa SS 3k is more abrasive then a Naniwa SS 5k or 8k or 12K

A Naniwa Pro 1k is more abrasive then a Pro 3k or 5k or 10k

A Shapton GS 4k is more abrasive then an Shapton GS 8k

A Shapton Pro 8k is more abrasive then a Shapton Pro 15k

These are things I know

As soon as you move away from a Brand of hone or even a series within a brand of hone then you do not know any longer you are simply Hypothesizing

Any grit rating on a Natural hone is a WAG, (or marketing) and that is the Glen theory of Hones and Stones it has served me well for honing a couple of SR's

These are all great answers - thank you. Yes, less of a concern, and more of just wanting to see if anyone knew. An intriguing subject, especially since it varies from brand to brand. Sometimes I wish there was more oversight, but the variation is also part of the magic. Thanks!