Double bevel or single bevel on chefs knifes

It really depends on the individual knife, and your sharpening style and abilities.  There are a lot of really good ways to skin the "best geometry for a gyuto" cat.   

What are you using, and how are you sharpening it now?

BDL

A comment and a clarification. I'll start with the latter:

Double/Single/etc. Bevels

Since you're obviously a bit of a knife crazy, like myself, you may find it helpful to distinguish your terminology. I don't mean this as a snipe: there's so much to learn! But you'll get more out of the various debates and stuff.

What you're calling "single bevel" is usually called "asymmetrical." What people usually call "single bevel" is a peculiar way of grinding certain Japanese knives that is utterly unlike anything I've seen elsewhere. You'll sometimes see the term "chisel-ground," which is often misused but does have a legitimate meaning.

Imagine looking point-on at a knife, and draw a line through the core of the blade. Two bevels flare outwards from the edge itself, and can be defined by their angles from that center line.

1. Double-beveled: the two angles are >0 degrees.

1a. Symmetrical: the two non-0 angles are equal. So it looks like an isosceles triangle.

1b. Asymmetrical: the two angles are unequal.

2. Chisel-ground: one of the two angles is 0. So it looks like a right triangle. This is rare, but does occur in some old-fashioned or "country-style" nakiri, and probably some other knives. (I actually think of a chisel-ground knife as a double-beveled knife, where it just so happens that one bevel is at angle 0.)

3. Single-beveled: like chisel-ground, except that about 1mm along the 0-degree bevel the surface curves inward and then back out toward the spine, creating a concavity that spans almost the entire inner surface of the knife.

Hope you find this useful!

Asymmetrical Grinding

There is a good deal of disagreement about this. I speak here largely from my personal experience -- in no sense as extensive as BDL's or that of many others here -- and from having read a great deal.

Asymmetrical grinding is a way of getting a thinner edge in order to make the knife act sharper. It has the disadvantage of making a knife steer in the cut. It is also mildly destabilizing, in that it weakens the edge somewhat.

If your knife is thin-bladed, the steering will be trivial. Basically you get more steering the farther the "shoulder" is out from the more strongly angled side. Imagine you ground a knife at 45/1, that is, with a 45-degree angle on one bevel and 1-degree on the other. You can see that it's the 45 side which is going to have a noticeable shoulder pushing against the food, right? And if you had 45 on both sides, the shoulders would balance and cancel out? Okay, so if the blade is really thin, that shoulder, even with the 45/1 grind, is just not going to be very far away from core of the knife, so although it will steer, the effect will be inconsequential. In my experience, decent Japanese double-beveled knives don't steer significantly even if you grind them pretty asymmetrically. I wouldn't count on that with a Wusthof or similar thick-bladed knife.

If your knife is made of high-quality steel and tempered quite hard, the weakening effect is not going to make much difference. Basically the point is that the steering effect already noted also means that the food will push crosswise on the edge as you cut. You can see that if you just imagine the same thing with the steering but from the point of view of a big carrot or something, right? In my experience, a decent Japanese knife is made of high-quality steel and tempered very hard, but not so hard that it's like glass or something. I have never heard of anyone having much of a problem with this weakening except when dealing with freakish extremes. So I would not worry about it.

One great advantage of asymmetrical grinding arises if you're using bench stones and are not a huge fan of the supposed fun of sharpening all the time. You only have to grind one side, you see, because then you just sort of strop a few times on the back face to get the burr to flip and return to the front face for all your real grinding. It's not the most precise thing in the world, but you do get an asymmetrical grind, a wickedly sharp edge, and approximately half the work (and time) of grinding in the first place.

Some people find the whole thing really weird and complicated, and they get very wound up about the details. If that's how it seems to you, just don't do it. The advantages are pretty slight, to be honest. To me, it all seems quite obvious and highly suitable to my basic laziness, and what's more I get to pat myself on the back for it!

Hope that helps. BDL will be along to explain more coherently, I imagine, and also to correct my usual bizarre mistakes.

Quote:

Originally Posted by martinc 

I have version 1.0 built of my sharpening jig.  It's made of found objects, a stone holder,  and a few new pieces of steel rod.  It's essentially a big Edge Pro that uses standard size stones.  There are a few changes needed, but it provides a very accurate angle.  I actually looked at my stones- they are 250/1000, 4000, 1200/8000

 

On the double bevel- is there any point in going over 1000 grit on the back bevel?

As I mentioned, I use henkle and Shun knives now.  Is there a best set of angles for those two lines?

You might get in touch with Ken Schwartz, of Ken's Sharpening Services. He built a thing a lot like what you've built, which he calls the "Gizmo," and you guys could definitely share information.

I generally think that you should always take both bevels to the same grit level. I can't be sure I'm right, but I have a feeling that it's not a good idea to have a significantly different number of scratches on one side than the other -- I'd think you'd get some problems that way.

I'm not entirely sure you gain much by going above 1000k with a Henckels in any case, though perhaps you're using Miyabi or something? Maybe then. Shun -- probably depends on the Shun line, but I wouldn't think you'd really gain much over maybe 2k-3k. Basically above 1-2k you're polishing. I generally think it's not worth polishing a steel that won't retain the polish effectively. So for example, with a Masamoto KS, that'll take and keep all the polish I can throw at it -- which is up to something on the order of 12k. But with the yellow steel knife I was given as a wedding present, I don't bother taking it over 2k because it just doesn't gain me anything and is basically a waste of effort. I should say that I have rarely heard it said that over-polishing is actually a bad thing, i.e. that you shouldn't keep polishing if you want to, but as I say I'm pretty lazy and just can't see putting in the effort when I don't gain anything. On the other hand, the more stones you use, the greater the odds of messing up your work, so perhaps it's best to stop when you've reached the knife's limits.

I understand what you mean by "double bevel," and will use it as you do.  I'm also going to use the terms "secondary" and "primary bevels" to refer to the two parts of a double bevel edge.  The terms are often mixed up, there's no one way of using them that's significantly more popular than the other, so just to make sure we're on the same page, I'll clarify.  "Primary bevel," means the cutting bevel with the edge.  "Secondary bevel" refers to the more acute bevel further up the knife's face without the edge.  

After all the introduction it would be nice to get a straight answer, wouldn't it?  No such luck.  The answer is contingent.  Whether you can or should polish and sharpen the secondary and primary to different grit levels depends on your stone kit and the final polish level you want for the primary.  There's no reason to fully polish out a secondary bevel; but on the other hand you don't want a lot of scuff either.

Putting that in terms of grit, if you're polishing the edge to 8K, you'd want the secondary to be around 3K or finer.  Rather than thinking in terms of specific grits, If I were polishing out the primary bevel to a fine/'ultra-fine polish, I'd want the secondary bevel to be at least a solid medium. Or, for those of us who use a four stone kit, if we took our primary to the fourth stone, we'd stop at the third for the secondary.  Even more generally, for most well chosen kits you'd stop your progression for the secondary bevel one level coarser than for the cutting bevel.

This saves time, more than anything else.  Otherwise, the only other good reason not to take the secondary to the same level as the primary is that it doesn't need it.

A double bevel isn't always the best choice.  Again, it depends.  This time the right choice is mostly contingent on which knives you're sharpening; and partly on what experience you've had with durability for that knife sharpened to a normal, "V" edge.  One thing about a rod guide tool and jig gag like yours is that it makes the angles sufficiently repeatable for tight double bevels.  I find that a 5* difference is often a good choice.  For instance, 15*/10* works particularly well for MAC Pro; and a 20*/15* is worth sharpening on to a Wusthof.  But a 15* "V" works best for a carbon Sab; and you certainly don't want to double bevel a super-thin knife like a "laser." 

As to deburring on sandpaper stuck to a mouse pad, it's not a great idea unless you're specifically pursing convex instead of double bevel edges.  It's one or the other, as the two are mutually exclusive.  Even if you choose to convex, you'll find that you need some other deburring material like a cork or felt cube.  I don't think convex edges bring enough extra in durability or saved maintenance to make the difficulty in sharpening consistent edges worth it.  However if you're as curious and mechanically minded as you seem, you'll try convex edges no matter what I say and end up with your own opinions -- a good thing.

BDL

Quote:

Originally Posted by martinc 

Pardon my terminology.  When I say double bevel I'm referring to a blade with the same angle on both sides, but with a second grind on both sides near the edge.  I'm enjoying playing around with the stones and blades.  I've been able to get one of my Shun knives sharper than the guy that we were paying to do it..I still think I can go further.  I'm still a bit confused on what is the best angle for the knives that I currently have.  I do have a digital angle gizmo that seems pretty darn tight.  So getting the angle down is pretty solid.  I'm going to throw together a mousepad/1500 sand paper pad to try to strop off the wire bead.

There's nothing to pardon. But we all see now why these stupid terms are so irritating! And as BDL says, there is nothing consistent to refer to what you're talking about. I think Chad Ward has a term for this, but I forget what it is. Personally, I am far too lazy to do this kind of primary/secondary beveling stuff, but I salute your willingness and skill!

I do have a few remarks, even following after BDL's wonderful account.

1. The best angle is probably the one where it doesn't collapse when you use it. Isn't that helpful? [Not] The kind of split-level stuff you're doing is a complicated and effective way of getting more thinness out of things. So I'd say that you should probably figure that the primary bevel (the one at the edge) shouldn't be much lower than 15/side, for safety, and then you can go pretty darn thin above that -- Shuns are not trash, despite the unnecessary dissing they take on knife sites. In essence, you'll know when you've gone too far, because you'll get chipping or whatever all over the place.

2. I would tend to agree with BDL on mousepad stropping and so on. It works -- beautifully! -- but in your current situation I don't think you want that result. That kind of thing is fabulous when you actually want a very smooth convex edge, for example when you are trying to smooth out a hamaguri grind on a big deba. But you don't actually care, so far as I can tell: you're interested, at this point, in angles and precision. Stropping on a mousepad will blur your precision and make it very hard to measure things. It won't hurt the edge or anything, but I think it's going to get in the way of what you're currently searching for. 6 months from now, when you're into something completely different, I could be saying the exact opposite. Does that make sense? Hope so.

I have been sharpening knives all my life.  I could shave my arm hair with my pocket knife well before I had facial hair to shave.  I was a professional Cabinetmaker and home cook for 25 years.  I am now a professional chef and hobby woodworker.  Point being that I have sharpened many tools.   Every cutting tool be it a knife or chisel is ground to what the maker considers the optimal angle for the compromise of sharpness and durability. The angle for most knives is 15 degrees, that is the angle that ceramic stick sharpeners, Smith tools and electric sharpeners are set to. In my experience all these tools will give you a good functional edge.  When hand sharpening you have the ability to fine tune the edge by adding a second bevel,  in wood working this is referred to as a micro bevel.  The micro bevel both increases the sharpness but also make the edge hold up longer.  In the cooking knife world this is being called a compound bevel.  The technique for the micro bevel (compound angle) is to sharpen at the primary angle through your finest stone then give it a few strokes on that stone at a slightly steeper angle.  If you have a knife that is ground to a chisel edge, ie angled on one side and flat on the other do a micro bevel on both sides.