Why sharpen to such high grits?

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tuffluv

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Feb 24, 2015
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Been reading and learning here, then practicing hand sharpening with silica carbide sandpaper on a flat surface.

tried: 800, 1000, 1500, 2000 grits. Wasn't impressed with the edge.

then tried: 320, 600 800 grits. Edge felt toothier and sharper.


Yesterday I had the opportunity to talk with some employees who sharpen knives at a reputable, quality knife company. They sharpen at 180 grit, buff with around 2500, then strop on wooden dowels. The low grit number surprised me.


So, why sharpen to such high grits?
 
Short answer:

Edge refinement.

Longer, somewhat rambling answer:

You don't want a "toothy" edge for a scalpel or razor just like you don't really want a razor's edge on something where you draw cut soft abrasive (cardboard for instance) or slick materials (like wet rubber).

A lot of it comes down to the steel, too. For a razor's edge you probably want the blade to be made of a low carbide steel taken as thin as reasonable, unless you're push cutting a lot of, say, plastic or wood where you'd probably want to thicken the blade a little but still want to push cut.

For a high carbide steel with high wear resistance where you want an aggressive draw cut, then you probably don't want to refine it that much because it's basically a waste of time because when you draw cut you take advantage of those hard carbides vs push cutting where you'd just basically break the carbides off the apex.

Most people don't want nor need their knives as sharp as a straight razor honed by a professional honemeister so I'd think most professional knife sharpener just make it sharp enough to take some arm hair off and call it good without regard to just how smoothly and unnoticeable it is to remove that hair. That's really in a nutshell how to explain edge refinement, just how cleanly it will push cut something. That's why you hear guys saying they can push cut receipt paper 4 inches from their fingers or whatever. That's at least fairly refined. That refined edge won't last that long though.

With most knives taken to a decent (arm hair shaving but not face shaving) sharpness like that I can (very) lightly run my finger along the length of the apex and not get cut but the edge will last awhile if the steel is formulated to do so. When you take a different steel formulated to have a lower or smaller carbide volume or have diamond stones/paste to go as high as 50,000 grit or 100, 000 grit and it's as refined as one can get it you'll easily slice your finger doing the same and you probably won't even feel the cut for awhile. But most people don't want that in a knife and those that do go out of their way to make it happen themselves because so few professionals can get it like that for a decent price.

The sharpest razor will not draw cut through, say, rubbery fish scales where a toothy edge can. Reverse that and the toothy edge cannot push cut through dense plastic. So it depends on what you want.
 
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Thanks for the info.

I'm coming to the conclusion that for my purposes sharpening at lower grits will suffice. I need to cut random stuff at random times and don't shave my face (or arms for that matter) nor perform surgery.

I'll likely stay in the 180-400 grit range followed by an oak dowel as a strop.

Lot's to learn.
 
I've wondered this same thing for years. Some, just love sharpening, not that they need it that high level to cut something. They just love it. Others are OCD. I take mine to 320 grit and rarely any higher. Because I Rarely have the need. Still, there is room for all kinds here. Let them enjoy sharpening. We all don't see it the same way. DM
 
Fantastic explanation. Somebody give that guy a cookie.

I usually sharpen to 3 microns then strop on black and green (sometimes white too) simply because I like my knives being showoff sharp. That is the best part of owning decent sharpening tools. I will never use my knives in a manner that anything past a 600 grit edge will be needed, and in most cases the highly refined edge may work against me, but I love my knives being absurdly sharp. Note that my absurdly sharp is not whittling valence elections off of atoms, I consider clean cutting tissue paper to be absurdly sharp.
 
Even though lower grits can draw cut easily, I find very refined edges are often sharp enough that it doesn't matter. Why slice rope when a knife just goes right through it with a push cut? The other reason is that in my experience, a highly refined edge tends to last almost twice as long as a roughly sharpened toothy edge and resists breaking down.
 
To reiterate--it depends on what you are cutting.

In the kitchen I want my paring knife in the 6 - 15 micron range, gyuto in the 3 - 8 micron range, and my usuba in the sub-micron range. Each knife sees different cutting actions and different materials, and so I try to optimize the refinement of the edge to best match what I need them to do. Cutting strawberry tops with a paring knife? The 12 - 15 micron range makes it easier not to slip around. Cutting soft vegetables/fruits with a tough skin? A 3 - 6 micron edge slides through the flesh effortlessly, while retaining enough "bite" not to slip on the skin. Cutting down cooked protein? A 6 - 8 micron edge helps the make the cuts smooth rather than ragged like you used a saw. Doing katsuramuki? Getting below 2 microns helps enormously in getting paper thin sheets.

I keep my S30V Spyderco Military around 15 microns and my ZDP-189 Caly 3.5 around 6 microns. For EDC I've come to find that anything coarser is too toothy for my liking, and anything finer doesn't "bite" as much.
 
David Martin said:
I've wondered this same thing for years. Some, just love sharpening, not that they need it that high level to cut something. They just love it. Others are OCD. I take mine to 320 grit and rarely any higher. Because I Rarely have the need. Still, there is room for all kinds here. Let them enjoy sharpening. We all don't see it the same way. DM
Click to expand...


:thumbup::thumbup::thumbup::thumbup:
 
Today sharpening has gone two different ways in my opinion. We still have the traditional way of using knifes and sharpen knifes - but we also have the urban way of using knifes and sharpen them.

Today lives 90% of the population in Urban areas, 10% lives not in Urban areas. This 10% use, and shapen, knifes in the traditional way.

People in urban areas lives a another type of life, use other materials, they dot hunt, fish or whittle and so on. They by expensive knifes, show the knifes and talk about how sharp it is- and show how the edge kan whittle in hair. They like shiny edges that give pretty reflexes in eliectric light...and they do not use knifes a lot.

The 10% traditionals live not in citys, they use knifes daily, they hunt, fish, make up fires, whittle things, cut leather - and for hem are knifes a daily tool - along other daily tools.

So, today we ave two different ways of knife using, knife design and knife development. There is nothing wrong with that - and knifes has sins the stone age been developt from needs and from use. Today we have urban use - and traditional use.

Traditional knife user end the sharpening in around 25 micron and then they use a ceramic sharpener for some seconds to take away burr.

Urban knife user like to have murcury edges and can shapen for houers to get them shiny - and very very sharp.

When a edge is veey very sharp, there is very little material in, and behind, the cutting edge. If a traditionalist use that edge it will be dull in seconds becouse he shapen edges with a balance between sharpness and retantion - for him it is important that the edge is sharp enough for the job he shall do - and that the edge hold just that sharpness as long time as possible.

Today urban people dominate all knife forums - and they, sorry to say, dont know so much about traditional use of knifes. They use "urban edges" outdoors - and they do not work so good there...

Today exists also "office desk knifes" and "fantasy knifes". For traditionals they are the same thing...

I often meet urban people (I am traditionalist) that show me there knifes. Very often they tell me that they have change the blade to "make it better". They have bougt a traditional blade - and change it for urban type of use - or ro what they think is a better type of blade design for outdoor use - and in my mind, they have totally destoyed a perfect working outdoor blade that people have use for more then 1000 years.... :) but, perhaps, the change make the blade work better in urban type of life...but I do not think so...

What I have write above can be seen as provocative - but that is not my intention. I just try to explain two different worlds that use knifes in two very different ways.

The problem sometimes are that urban sharpening advice dont work in traditional use of knifes - but traditional type of edges work also in urban areas - this becouse that in the traditional use of knifes is a "mantra" that "edges only shall be as sharp as they need to be for its type of use". That means that a knife can be to dull, and ro sharp, for its use - for traditionals - but for urban knife use shall a knife be as sharp as possible- allways..

Thomas
 
It seems common when first learning to sharpen ones goal is to achieve the sharpest edge possible and then slice various materials as proof of sharpening success. Later on settling on a sharpness that just works for there EDC uses. I like my EDC knife finished on med to fine stones and my collection in
'sticky edge condition one'.:D
 
Cynic2701 said:
To reiterate--it depends on what you are cutting.

In the kitchen I want my paring knife in the 6 - 15 micron range, gyuto in the 3 - 8 micron range, and my usuba in the sub-micron range. Each knife sees different cutting actions and different materials, and so I try to optimize the refinement of the edge to best match what I need them to do. Cutting strawberry tops with a paring knife? The 12 - 15 micron range makes it easier not to slip around. Cutting soft vegetables/fruits with a tough skin? A 3 - 6 micron edge slides through the flesh effortlessly, while retaining enough "bite" not to slip on the skin. Cutting down cooked protein? A 6 - 8 micron edge helps the make the cuts smooth rather than ragged like you used a saw. Doing katsuramuki? Getting below 2 microns helps enormously in getting paper thin sheets.

I keep my S30V Spyderco Military around 15 microns and my ZDP-189 Caly 3.5 around 6 microns. For EDC I've come to find that anything coarser is too toothy for my liking, and anything finer doesn't "bite" as much.
Click to expand...

This really sums it up well for me and nowhere better than the kitchen to illustrate different edge finishes for different tasks. The finish progression is the same strategy I use.

I also apply it to other tasks, understanding this principle is one of the nicer paybacks for learning how to sharpen to a variety of finishes and experimenting with same. Sometimes that highly polished edge is the better tool, sometimes it isn't. If you cannot reliably whip it up, as well as clean coarse edges and finishes in between, you cannot reliably test them.
 
It's probably my poor technique, but I'm unable to completely eliminate a burr with hard stainless -- let's say VG-10 -- without using a JIS8k.
 
Nice discussion bodog. Thanks for the information. I find sharpening my knives to a 600 grit works well for me.
 
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