My sharpening technique: A polished edge that is coarse, best of both worlds

[cotdt]

A polished edge is better at push-cutting and shaving. It also lasts a long time.

A coarse edge is better for rope slicing, and slicing in general.

Which to choose? Both!

What I do is I first get my mirror polished edge with an ultra fine grit stone. Aim for a few degrees bevel broader than what you intend. This can shave in both directions and whittle hair. But right now, its slicing ability still isn't great. And if you're slicing cheese, it could stick onto the blade while slicing.

Next, I take out my coarse stone, around 200 grit. I set the angle to 2° degrees more acute per side, and sharpen until the coarse bevel just about touches the polished edge, but not quite. If it goes past the edge, then the smooth mirror polished edge is completely ruined. If it's not close enough, then the blade would not get the benefit that a coarse edge gives in slicing.

I check carefully and usually get it just right at the edge. Now, it should push-cut like a polished edge and slice like a coarse edge!

In short, polished cutting edge with coarse sides. The difference in performance is absolutely staggering!

 

[Javelin]

you sure it doesn't just feel like a coarse edge?

I agree with you, best of both worlds but I go a different way about it:
Step 1: sharpen on 36 grit belt
Step 2: Buffer + compound


This is the kind of edge you'll find on some production knives (Case, Rough Rider, Japanese Brass Cased friction folder) and it works well in my opinion.

 

[cotdt]

you sure it doesn't just feel like a coarse edge?

I agree with you, best of both worlds but I go a different way about it:
Step 1: sharpen on 36 grit belt
Step 2: Buffer + compound


This is the kind of edge you'll find on some production knives (Case, Rough Rider, Japanese Brass Cased friction folder) and it works well in my opinion.

That's basically the reverse of my method, going coarse->fine instead of fine->coarse. But does this method give a smooth edge? The reason why I go for the mirror polish first is because it gives a smooth edge when you run the edge across your nail or look at it through the microscope.

 

[Jason B.]

I'll stick to my polished edges, they work just fine for me.

Why have the polished sides and a coarse edge?

 

[Javelin]

I haven't check under a microscope, but it'll readily shave hair. I like to think of it as a very finely serrated blade with a fine finish. Again, I'm not sure if it's actually that good of an edge but it works for me.

 

[cotdt]

I'll stick to my polished edges, they work just fine for me.

Why have the polished sides and a coarse edge?

It's a polished edge and coarse sides, under the microscope. Visually it just looks like a coarse edge, until you slice cheese with it. The difference in performance is staggering.

 

[Jason B.]

It's a polished edge and coarse sides, under the microscope. Visually it just looks like a coarse edge, until you slice cheese with it. The difference in performance is staggering.

That basically goes aginst everything I have discovered through years of sharpening. If the surface behind the edge is rough the material has more of a chance to stick to it and when the bevel is completely polished materials slide over it much easier. A lot of it also depends on the width of the bevel but I just don't understand how having a coarse surface helps with cutting.

 

[C.S. Graves]

Used to do a toothy "shaving sharp" edge myself, though these days I focus more on maintaining the shaving sharpness, and the coarser grits are primarily for a little profile touch-up here and there. Still, it's a nice "jack of all trades" edge.

 

[cotdt]

That basically goes aginst everything I have discovered through years of sharpening. If the surface behind the edge is rough the material has more of a chance to stick to it and when the bevel is completely polished materials slide over it much easier. A lot of it also depends on the width of the bevel but I just don't understand how having a coarse surface helps with cutting.

Cutting vinyl tubes and cheese, I find the opposite. The polished bevel tends to get get stuck from being sticky, and it takes more force just to use a slicing motion. When I used coarse sides, the blade no longer sticks to the vinyl tubes or cheese.

Still, it's a nice "jack of all trades" edge.

It is indeed!

 

[just10minreader]

That basically goes aginst everything I have discovered through years of sharpening. If the surface behind the edge is rough the material has more of a chance to stick to it and when the bevel is completely polished materials slide over it much easier. A lot of it also depends on the width of the bevel but I just don't understand how having a coarse surface helps with cutting.

I think suction is key. Cutting cheese (monterey jac, or mozarella) is like getting stuck in the mud, a smoother surface means a better vacuum is formed (its more sticky). Its like the Battle of Agincourt, mud sticks to polished armour better than to cloth, so knights had a harder time walking, and when fell, harder time getting up

Walk Hard
[YOUTUBE]2lOW2IjpM-4[/YOUTUBE]

 

[bgentry]

It seems like *maybe* you're getting an edge a lot like mine. Maybe not.

I do a back bevel at 15 degrees on a medium SiC stone. Then I raise up to 20 degrees for the primary edge face, still on that stone. Next I move to a medium spyderco ceramic, staying at 20 degrees to polish that primary edge. Sometimes I graduate to the spyderco fine, and/or strop it on cardboard with compound.

That leaves the back bevel "rough" and the primary edge face fairly polished. Seems to be about what you're describing, except maybe your bevels are closer together in angle, like 15/17 or 15/18 instead of my 15/20.

I must admit that my edges still don't "bite" into slick surfaced work very well, like the classic test: Ripe tomatoes. I have to slide my blade a bit before it will get through the skin, but once it does, it cuts very easily and very fine. This is a shaving sharp edge, so I shouldn't be surprised.

I keep meaning to experiment with a more coarse edge to see how it works on tomatoes and things.... Hmmm...

Brian.

 

[me2]

Have you tried a shaving sharp edge from the ~200 grit stone? A hair whittling edge is possible off my 220 grit water stone with no other stones needed. Thats not what I use, but its an option if you need high sharpness with slicing aggression.

 

[bgentry]

^ Hair whittling sharp with a 220 grit water stone? I've never used water stones, so maybe that's the difference. Or maybe I'm just not all that skilled. I've never had luck in producing a hair shaving edge (much less whittling) from anything less than around 500 to 600 grit (same as 800 to 900 grit water stone).

I've read some material saying you could get a hair shaving edge with a 100 grit belt sander, but I don't have access to that equipment. I suspect that's more about a consistent and *thin* angle than a fine edge.

I'm here to learn and this all falls into the category of things I do not yet understand.

Brian.

 

[Dog of War]

I never polish relief or primary bevels, but always apply a microbevel at high polish for the final edge.

I've come to the opinion that the whole issue of slicing performance is extremely complex. Weighing against the benefit of slicing aggression you get with a coarser edge are the drawbacks of reduced cutting performance overall -- a slice is, after all, actually part slice and part push cut -- and reduced edge life/retention. So deciding on the optimal edge finish is going to depend on a whole bunch of factors, ranging from materials to be cut and just how they're going to be cut, to properties of the steel itself, and even unknowables like how long it will be until you'll be resharpening the blade.

So bottom line ... if it works for you, and gets the job done, that probably counts for 90% of the results you can expect. Until somebody really sorts it all out, that is.

 

[cotdt]

Have you tried a shaving sharp edge from the ~200 grit stone? A hair whittling edge is possible off my 220 grit water stone with no other stones needed. Thats not what I use, but its an option if you need high sharpness with slicing aggression.

They shave, but not cleanly. There is some sort or zigzag edge under the microscope. Push-cutting is clearly easier with a mirror polished edge.

 

[cotdt]

I never polish relief or primary bevels, but always apply a microbevel at high polish for the final edge.

That's basically the same idea, except in a typical microbevel you are putting on the polished edge after the coarse one, not before. This technique here puts on the polished edge first so that you can get the coarse sides really really close to the smooth edge.

In a microbevel, you need to remove a good amount of metal to remove the scratch pattern of the coarse grind (otherwise you won't acheive a smooth edge). So you end up not being able to get the coarse sides as close as possible to the smooth edge.

 

[65535]

Seems like a lot of hard work for advantages that I doubt truly exist.

 

[cotdt]

Seems like a lot of hard work for advantages that I doubt truly exist.

Try cutting cheese with such an edge. The difference in performance is absolutely staggering! Both a true coarse edge and a true polished edge require significantly more pressure to cut through the cheese. Here, you can literally drop the cheese onto the blade and it will cut all the way through.

It also catches onto tomato skin without any slicing motion, which a coarse edge has trouble with. W/o using any pressure whatsoever, the edge eats into the tomato. You can literally drop a tomato from 1" inch above the edge and the knife would cut it through. The difference in performance is absolutely staggering!

 

[yablanowitz]

That's basically the same idea, except in a typical microbevel you are putting on the polished edge after the coarse one, not before. This technique here puts on the polished edge first so that you can get the coarse sides really really close to the smooth edge.

In a microbevel, you need to remove a good amount of metal to remove the scratch pattern of the coarse grind (otherwise you won't acheive a smooth edge). So you end up not being able to get the coarse sides as close as possible to the smooth edge.

Actually, you're wrong. The end result is the same, whether you set a coarse backbevel and polish a microbevel at the very edge, or polish the edge bevel and then grind a relief bevel. If you are any good at sharpening, the end product will be identical. Of course, most "microbevels" are not exactly "micro", usually because the sharpener gets carried away while forming it and removes far more steel than necessary.

 

[cotdt]

Actually, you're wrong. The end result is the same, whether you set a coarse backbevel and polish a microbevel at the very edge, or polish the edge bevel and then grind a relief bevel. If you are any good at sharpening, the end product will be identical. Of course, most "microbevels" are not exactly "micro", usually because the sharpener gets carried away while forming it and removes far more steel than necessary.

End result is not the same. Try a very coarse side bevel and tell me how thick the microbevel needs to be to remove all the scratch patterns from the initial coarse grind. My guess is that it will have to be more than 0.2mm, probably more. This is what I see under my 200x microscope.

My technique (same thing but reverse order, mirror polish -> coarse) allows you to take the smooth edge down to arbitrarily small. Yes it's technically also a microbevel, but by reversing the order you get a different end result.