Best way to sharpen a knife

[HowardLi]

If you know what you're doing, a belt sander is great for major repairs and for sharpening stouter, softer European knives. I wouldn't recommend them for the thinner or harder Japanese knives. You're not going to get the kind of edge that's possible on waterstones. Any properly formed edge will shave your forearm. The difference between an edge made at 600 grit vs. 8000 grit will mostly show itself in the quality of cuts in the most delicate foods (fish, herbs, fruits that brown, etc...).

I have a leather belt that I prep with 0.5 micron chromium oxide. I think that should get me to beyond the limits of most waterstones.

[paulraphael]

I have a leather belt that I prep with 0.5 micron chromium oxide. I think that should get me to beyond the limits of most waterstones.

An issue with leather is that it's compressible, so it becomes challenging to produce a flat bevel without any rounding of the edge. I suspect that someone with middling sharpening skills (like me) can do about as well with leather as with a finishing stone, but that a skilled sharpener will do better on stones. The sharpest knives I've ever used were produced without any stropping, by friends who are very skilled.

The bigger issue: what succession of belts do you use to lead up to the leather strop belt? Do sander belts come in fine grits (like above 4000)? A 0.5 micron abrassive is useful as a polish after an 8000 to 10000 grit stone or paper. It can't remove the deeper scratches of anything coarser.

I'd ask Dave Martell at Japanese Knive Sharpening. He's got reasons for using the belt sander for softer knives and for reparis, and stones for the higher end knives. If he could get the best results on a belt sander, he'd have no reason not to.

[HowardLi]

I have a leather belt that I prep with 0.5 micron chromium oxide. I think that should get me to beyond the limits of most waterstones.

An issue with leather is that it's compressible, so it becomes challenging to produce a flat bevel without any rounding of the edge. I suspect that someone with middling sharpening skills (like me) can do about as well with leather as with a finishing stone, but that a skilled sharpener will do better on stones. The sharpest knives I've ever used were produced without any stropping, by friends who are very skilled.

The bigger issue: what succession of belts do you use to lead up to the leather strop belt? Do sander belts come in fine grits (like above 4000)? A 0.5 micron abrassive is useful as a polish after an 8000 to 10000 grit stone or paper. It can't remove the deeper scratches of anything coarser.

I'd ask Dave Martell at Japanese Knive Sharpening. He's got reasons for using the belt sander for softer knives and for reparis, and stones for the higher end knives. If he could get the best results on a belt sander, he'd have no reason not to.

I don't think the goal is necessary a flat cutting bevel, but just the refinement of what's already there. The convex bevel obtained from a belt obviously doesn't need to get flattened out in order to become sharp.

I have 100, 150, 320, 30 micron (~800), 16 micron (~1400), 6 micron (~2000), then leather. Note that waterstone grit is not the same as regular sandpaper grit.

Oh, in case it wasn't clear, the leather belt goes on the sander too - it's not a bench-style belt.

Edited September 4, 2011 by HowardLi (log)

[infernooo]

I know many will snuff at this, but about 10 years ago I purchased a Furi Tech Edge System and it has worked BRILLIANTLY ever since... I have never had to learn how to properly sharpen/hone a knife either!

[Broken English]

I know many will snuff at this, but about 10 years ago I purchased a Furi Tech Edge System and it has worked BRILLIANTLY ever since... I have never had to learn how to properly sharpen/hone a knife either!

I bought Mum one of those about 5 years back, it seems to work pretty well, at least with her Furi set anyway. They're actually pretty decent knives for home.

[paulraphael]

6 Micron is slightly finer than a 2000 grit waterstone. It's a medium grit, suitable as a final grit for a European knife. To get the best performance from a harder knife, you need to go at least to 4000 grit; preferably 8000 or higher.

The jump from 6 microns to 0.5 microns is much too large. You're not accomplishing anything with that, except maybe reducing any lingering burr or wire edge.

The risk with leather isn't rounded bevels but a rounded edge.

[HowardLi]

6 Micron is slightly finer than a 2000 grit waterstone. It's a medium grit, suitable as a final grit for a European knife. To get the best performance from a harder knife, you need to go at least to 4000 grit; preferably 8000 or higher.

The jump from 6 microns to 0.5 microns is much too large. You're not accomplishing anything with that, except maybe reducing any lingering burr or wire edge.

The risk with leather isn't rounded bevels but a rounded edge.

Meh. I'm getting edges that are good enough. If I ever wanted to step it up, I could go with micromesh belts (up to 12000) but I really don't see the need right now.

[threestars]

Well I guess I'm weird. I don't like my knives to be so sharp that I can get cut in just a very small mistake when cutting. So I just keep my knives' sharpness in a normal level.

[paulraphael]

Meh. I'm getting edges that are good enough. If I ever wanted to step it up, I could go with micromesh belts (up to 12000) but I really don't see the need right now.

I'm not saying that 0.5 microns isn't fine enough—it's plenty. The issue that you don't get any benefit at all when you jump straight to that from a 2000 grit belt. You're getting a 2000 grit finish.

And sure, this is "good enough," for most purposes, and as good as makes sense on softer knives. My whole point is that if you're dealing with higher end knives, this approach isn't going to get you near their potential. I don't think it makes sense to spend a lot of money on high end knife if you're not going to sharpen it beyond what you can do with a more pedestrian knife.

[weinoo]

I like my Edge Pro. Works great and I don't have to be an expert. At anything.

[HowardLi]

Meh. I'm getting edges that are good enough. If I ever wanted to step it up, I could go with micromesh belts (up to 12000) but I really don't see the need right now.

I'm not saying that 0.5 microns isn't fine enough—it's plenty. The issue that you don't get any benefit at all when you jump straight to that from a 2000 grit belt. You're getting a 2000 grit finish.

And sure, this is "good enough," for most purposes, and as good as makes sense on softer knives. My whole point is that if you're dealing with higher end knives, this approach isn't going to get you near their potential. I don't think it makes sense to spend a lot of money on high end knife if you're not going to sharpen it beyond what you can do with a more pedestrian knife.

Why would it matter that a soft edge has the same geometry as a hard edge? Of course one will probably need to be touched up more frequently than the other, but I'm not sure what point you are trying to make - that one should have to live with inferior performance simply because they haven't the right knife?

Edited September 5, 2011 by HowardLi (log)

[paulraphael]

Why would it matter that a soft edge has the same geometry as a hard edge? Of course one will probably need to be touched up more frequently than the other, but I'm not sure what point you are trying to make - that one should have to live with inferior performance simply because they haven't the right knife?

I don't think I made my point clearly. Knives with softer steels can be sharpened to whatever level of polish you like, but there's no advantage in going past a medium coarseness (2K or so) because the fnish won't last more than a few minutes of cutting. The toothier kind of edge you get at 1K or 2K has proven serviceable and durable on softer knives, and is easy to maintain with a steel. Even when such an edge dulls, it's capable or cutting because the toothiness of the edge stays agressive and works like serrations. When a polished edge dulls it just loses its ability to cut. So polished edges work best on higher end knife stieels that have greater edge stability.

I hadn't said anything about geometry, but of course that's an issue also. Softer steels need to be sharpened with fatter bevel angles or they'll crumple. Standard for German knives is around 22° on a side, although if you're willing to be careful you can go a couple of degrees lower than this. On Japanese stlye knives, depending on the steel and the skills of the person using the knife, you can go from 15° all the way down to 7° or so, and also sharpen with radical assymetry. A knife sharpened like this will cut like a straight razor, but will require the cook to adopt Japanese cutting techniques.

It's all a question of which tradeoffs you're willing to make.

[DanM]

I chatted with some local chefs and got a reference for a guy who sharpens knives for many local restaurants and businesses. At $5-10 per knife, it was worth knowing that it was done correctly.

Dan

[dcarch]

There are those who really go for a polished edge that can literally split a hair (really, check youtube).

Do you need that for the kitchen?

Here are a few magnified views of a brand new blade for a surgeon’s scalpel.

dcarch

[paulraphael]

I chatted with some local chefs and got a reference for a guy who sharpens knives for many local restaurants and businesses. At $5-10 per knife, it was worth knowing that it was done correctly.

At those prices you can bet it's a grinding service. Those are great for house knives and beaters but you really don't want to send a high end knife to a service like that. It will be ruined.

[paulraphael]

There are those who really go for a polished edge that can literally split a hair (really, check youtube).

Do you need that for the kitchen?

Here are a few magnified views of a brand new blade for a surgeon’s scalpel.

dcarch

It's not a question of need, but of efficiency, quality of cuts, and edge longevity. If you have a chance to use a good knife that's sharpened at 2K vs 10k you can feel the difference and decide for yourself it's worth it.

One reason for polishing is that with very low bevel angles, coarsely sharpened edges will have exremely long, thin "teeth," which are unsupported and which crumple easily. This isn't a big issue with a 15° or higher bevel angle, but when the edge starts getting thin it makes a difference.

Scalpels aren't good analogues for kitchen knives. For one thing, surgeons replace their blades after just a few inches of cutting. For another, they get a lot of their performance just from their sub-milimeter thickness. A well sharpened knife will actually have a sharper edge than a scalpel (at least than those generic blades) but it will never cut as well because it has to be several milimeters thick behind the edge.

[HowardLi]

I just put in an order for a couple of 4000 and 8000 grit belts to pick up the slack (heh) after the 6 micron Trizact belt. Let's see how well they prep the edge for the leather...

Edited November 3, 2011 by HowardLi (log)

[ScoopKW]

Scalpels aren't good analogues for kitchen knives. For one thing, surgeons replace their blades after just a few inches of cutting. For another, they get a lot of their performance just from their sub-milimeter thickness. A well sharpened knife will actually have a sharper edge than a scalpel (at least than those generic blades) but it will never cut as well because it has to be several milimeters thick behind the edge.

Having been cut with a scalpel, and having been cut with my kitchen knives, I can say with certainty that my knives don't hurt as much, and the cuts heal quicker. A LOT quicker. That being said, I've never cut myself so badly with a gyuto that I've needed stitches. (Knocks on wood at this point.)

[threestars]

Good thing you didn't get cut by your knives. I got cut just 3 weeks ago. That's why I don't like my knives to be super sharp as much as possible.

[paulraphael]

I find dull knives to be much more dangerous. If your knives are very sharp, you will undoubtedly get more dumb little cuts, like from bumping into the edge when the blade is sitting on the cutting board. But dull knives force you to use force, which means the knife can slip and go out of control. Most of the nasty cuts I've seen are from dull blades and bad technique. With a sharp blade and good technique, you will never use much more force than the weight of the knife itself, so deep cuts become very unlikely.

The only time I cut myself badly enough to consider stitches, it involved a serrated bread knife, bad lighting, and a lot of alcohol.

[phatj]

Is there a simple, easy, inexpensive method that's adequate for upkeep of a non-premium knife? If somebody *gave* me the Edge Pro Apex, I doubt I'd use it. Same for traditional stones. I'm talking about one of those electric grinder type gadgets or something similarly easy to use.

And back to this question: the answer is "get a cheap benchstone and learn to sharpen freehand." It's not rocket science and it's pretty hard to screw your knife up permanently as long as you stay away from power tools.

*UPDATE - on a whim, I bought a combination stone at an Asian grocery. The thing was labeled entirely in what I'm guessing was Korean, without even any discernible numbers that might indicate grits. The grits seem to be "pretty coarse" and "less coarse". The results aren't pretty (the blade has some significant scratches) but the edge is MUCH better than it was. I'm sold on freehand sharpening - I figure if I do this once in a while when I would otherwise steel and I'll keep the knife plenty sharp enough for my needs indefinitely, no?

My only problem now is that the edge is very "grippy" to the point that it bites into my cutting board unexpectedly at times. I'm assuming getting a fine grit stone will help take care of both that and the scratches?

Edited December 15, 2011 by phatj (log)

[paulraphael]

My only problem now is that the edge is very "grippy" to the point that it bites into my cutting board unexpectedly at times. I'm assuming getting a fine grit stone will help take care of both that and the scratches?

Yup. The coarse stone made deep scratches, which gave you an edge with big teeth. It will work really well on things like rope, or fibrous cuts of meat. Or your wood cutting board. The trick is to follow that stone with one that's fine enough to leave much smaller teeth, but not so fine that it takes you hours polish out the scratches from the previous stone. Moving to a stone that's half as coarse (a grit number that's twice as high) is usually a safe bet.