Why are large jumps (16k) after a (Shapton Glass) 2K recommended?

[davidpb]

I wonder if you could help me understand what finishing stones do when incorporating major skips in grit.

Where this comes from: I've seen it recommended on this forum by people who are well respected (e.g. JasonB) to progress Shapton Glass 500, 2k...then 16K. This seems like a massive jump.

My understanding (could be incorrect) is that with gradual refinement e.g. 500/2k/6k/16k, or 320/1k/3k/8k/16k or something similar, you are slowly refining the edge/removing lower grit scratches to get the smoothest surface possible in the shortest time.

But the 2k-16k jump: isn't that just too large to get such a smooth surface (without tons of work)? My best guess is that the 2k-16k jump isn't trying to get the smoothest edge, but keep some 'toothy' edge and slightly smooth out its outer edges (as opposed to creating a completely smooth surface) to improve its performance. How is this similar/different to a stop?

Also, can anyone comment on how much the 2k-16k actually significantly improves the edge and how long it lasts?

Or let's put the question another way: suppose I go:

500/2k/4k
Or 500/2k/6k
Or 500/2k/8k
Or 500/2k/16k
Or 500/2k/strop

How would the results differ? I'm very curious. (The first two make the most sense to me, but are not recommended)

Finally, how would your answer differ with respect to chisels and kitchen knives.

 

[UncleBoots]

For kitchen knives, you've got it exactly right. The big jump keeps some tooth, so you can still cut tomatoes, while refining the edge. This is a process I'm just starting to play with, so I don't have a systematic view of the results yet.

I have not done any woodworking in a long time, but I remember chisels as being pure push-cutters for severing tough wood fibers, so you want that ultimate polished sharpness, not teeth. In that case, all that a big jump would do for you is waste your time getting to the proper result.

 

[ToddS]

The short answer is that there is very little difference in the surface produced by the 2k and the 16k, so it take very little effort to "remove the 2k scratches" with the 16k. And that is not even considering that you could just microbevel with the 16k.

I'd suggest reading these two articles:

It’s too big of a jump!

When sharpening, the choice to apply a multi-step progression from coarse to fine abrasive is predicated on the belief that there is a limitation in keenness or sharpness or uniformity for a partic…

scienceofsharp.com

Abrasion Rate vs “Grit”

It is a common assumption that coarse hones (lower grit rating, larger grit dimension) remove metal faster than fine hones. However…. In the Swarf! article, it was observed that coarser hone…

scienceofsharp.com

 

[catspa]

Because the returns diminish. Your scratch pattern is already smaller/finer than the human eye can see, your knife is already sharp enough to slice toilet paper and shave hair off your arm (or leg, if you’ve been doing this awhile), and the bundle of stones you’d need in 200 grit intervals would require more money out of your wallet, another filing cabinet to store them, and more hours out of your life to use. You’re well past “make my knife cut stuff” and far into “sharpening for sharpening’s sake.”

That said, if you have the resources to do 200gr (or 500gr, or 1000gr) steps, and you wanna do them, full speed ahead. More sharpening practice can’t be bad for you, and you might learn something you can share with us guys who don’t have time to do that.

Recommendations on BF (and other places) are more “here’s what I do” than “you gotta do it too.”

Parker

 

[Mr.Wizard]

Shapton Glass Stone 8K has huge inclusions way outside of JIS specification. I would not take their grit specifications literally.

 

[eKretz]

ToddS Hey Todd, any chance you might put up a blog write-up on slurry honing you mentioned having some thoughts on (in passing) to me a ways back? Itching to read that.

--Eric

 

[davidpb]

Hi all,

Just wanted to say thanks for these answers, particularly ToddS pointing to those articles. Found them very interesting and read a heap of them. (Are you their author? Great work!)

So now I understand why one can jump in grit size. What's missing in my understanding is whether one should go to a high grit. I know why sometimes there are recommendations to stop at a given grit for a 'toothy' edge, which from these articles doesn't seem to exist.

I could easily have misunderstood, but on the 'too big of a jump' article, sharpening to higher grit sizes appears to improve the keenness towards the apex, as well as remove scratches (the latter mainly improving the look as the scratches have less to do with sharpness/keenness?)

If that is the case, I could understand that after use, particularly with a soft steel, this added improvement at the apex could be lost, hence why some recommend stopping at a lower grit size as the benefits from additional effort quickly disappear (is there any studies to this/how long these last?)

But what is all this talk of 'toothy'? Can a lower grit (perhaps with some quick pass on a high grit) actually ever be better?

 

[UncleBoots]

But what is all this talk of 'toothy'? Can a lower grit (perhaps with some quick pass on a high grit) actually ever be better?

Sure. Cutting a tomato is the archetypal case.

Scenario 1: sharpen on low grit, maybe quick pass on high grit
Scenario 2: Make a beautiful high-grit edge that reflects the letters in a magazine

Now use both knives for a while. Then try slicing a tomato. People have done this, and found that the Scenario 2 edge loses that crazy keenness that lets it cut the tomato skin at first, relatively rapidly, while the more ragged (microscopically) edge of the Scenario 1 knife will still slice through tomatoes just fine, even after some use.

 

[Jason B.]

I wonder if you could help me understand what finishing stones do when incorporating major skips in grit.

Where this comes from: I've seen it recommended on this forum by people who are well respected (e.g. JasonB) to progress Shapton Glass 500, 2k...then 16K. This seems like a massive jump.

My understanding (could be incorrect) is that with gradual refinement e.g. 500/2k/6k/16k, or 320/1k/3k/8k/16k or something similar, you are slowly refining the edge/removing lower grit scratches to get the smoothest surface possible in the shortest time.

But the 2k-16k jump: isn't that just too large to get such a smooth surface (without tons of work)? My best guess is that the 2k-16k jump isn't trying to get the smoothest edge, but keep some 'toothy' edge and slightly smooth out its outer edges (as opposed to creating a completely smooth surface) to improve its performance. How is this similar/different to a stop?

Also, can anyone comment on how much the 2k-16k actually significantly improves the edge and how long it lasts?

Or let's put the question another way: suppose I go:

500/2k/4k
Or 500/2k/6k
Or 500/2k/8k
Or 500/2k/16k
Or 500/2k/strop

How would the results differ? I'm very curious. (The first two make the most sense to me, but are not recommended)

Finally, how would your answer differ with respect to chisels and kitchen knives.

I don't really like the 16k too much anymore. It does work well with the 2k and for some knives, like those used for sushi or fine wood working it has some uses, but for the most part the 500/2000/4000 makes a more capable set.

The only knives I go beyond 2k with is fine Japanese kitchen knives and that is only because they are hard enough to handle it.

For wood working tools I've found that most people will be shocked with anything beyond 2k so do whatever make you happy making wood chips.

The 16k leaves an odd almost scratchy scratch pattern but every bit of 16k refinement. It's densely packed with abrasive so the jump from 2k is really nothing and the edge (depending on steel hardness) is quickly converted by this stone. A bit too much though because the refinement becomes too great and the edge too smooth for edc tasks, imo. Tbh, I use it to micro bevel Yanagi blades and that's about it. Cool stone but limited practical uses.