Is hone flatness all that important?

Jeff Clark

Jeff Clark

Joined
Apr 27, 1999
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My question is who actually has experience honing on a heavily worn hone? When I was a kid I used an inherited aluminum oxide oil stone that was dished about 1/16-inch when I got it and was dished about 3/16-inch by the time I moved on. As a teenager I started sharpening semi-professionally and wore through a two-sided oil stone. By this time I had learned the advantages of starting with a rough hone and finishing with a fine hone and strop. That hone was heavily dished before I moved on. From there I moved on to a tri-hone with a medium-coarse silicon carbide stone, a soft Arkansas and a hard Arkansas. I did most of the work on the SiC hone and it ended up heavily dished.

Nowadays I have diamond hones and waterstones for most of my freehand work. Of course the diamond hones wear without dishing, but the waterstones wear comparatively quickly. I may have flattened a waterstone once or twice, but it wasn't because I noticed any performance issues.

I have sharpened thousands of knives and I have never noticed performance issues on dished hones. Has somebody out there actually detected a difference in performance?

From my calculations the curvature of a dished hone is much lower than the curvature of convex edges. If you are not working a broad flat bevel like a chisel or scandi grind where does a curved hone get in your way? Someone mentioned that it is more important with a blade with a straight edge (like a sheepsfoot or Warncliff), but I have sharpened many long straight kitchen knives on worn hones without noticing any changes as my hone wore down. I can see that there might be a problem with an edge gouging into a soft waterstone more easily if the hone is dished, but that's kind of a secondary effect.

So, opinions and preferences aside, who has actually used worn hones extensively and can tell me what they observed in the way of reduced honing effectiveness?
 
Jeff,

I can't vouch with lots of experience, but I will offer a few thoughts from working with my Norton 220/1000/4000/8000 waterstones that have seen some dishing when I got lazy with the flattening:
1) Your intuition on dishing curvature versus convex edge curvature is pretty good. It takes a lot of dish to make a difference.
2) The effect of the dish is to vary the bevel depending on where the blade is on the dish and what part of the blade length was in contact. Long blades are naturally more sensitive to this.
3) Normal dishing seems to vary the bevel angle less than what a less-than-robotic freehander (like your's truly) can produce.
4) Worst case: you get a non-uniform burr along the length of the edge, easily adjusted for in freehand if you pay attention.

Just my $0.02,
Ray
 
Well, for most knives, there is not much of a difference, even though I find that you tend to catch on the edge on dished hones (I keep mine flat, but some of the really coarse waterstones wear so quickly that rebeveling a single blade will dish them). For straight edge, though, I think it is absolutely paramount. Sharpening a straight razor or a true Wharny or a chisel or planer blade is near impossible on a worn hone, you just don't get a nice straight edge. And when I prepare a convex edge (now I mean lateral extension not point to heel) I even prefer instead of a flat hone an "anti-dished" hone :), I mean one that is a tad higher in the middle than on the edges. I read that the professional japanese Katana sharpeners use a convexed honeing surface and thought I would try it out, and found I like it. It is easier to roll the blade on it.

I think the importance of the flat hone has really been adopted from the wood workers, for whom it might be important. For our typical knives, I think it is not much of an issue.

Oh, I forgot, what I observed: On a dished hone it is very easy to hone a curve into a straight edge. This tends to happen even on a flat hone but I found it is much worse on a dished hone. Now, normally the curves is very slight and of no consequence. I doubt you would notice much even on a long straight kitchen knife, but the microtome blades that I used to sharpen for work don't cut properly anymore if the blade is curved. They are very sensitive to it. Same I found to be true for a straight razor and a lot of woodworkers say that a curved edge on a chisel will leave an undesirable finish, especially when the edge has a negative belly. On a planer blade (which is essentially like a reversed microtome) it certainly holds true. As always just my $0.02.
 
Even on a flat hone it can be easy to catch your blade on the edge of the hone (if you hone edge-leading). Rather than flattening the hone my old approach was to knock of the edge of the hone. I would intentionally do some light sharpening with a blade tilted to ride along the hone edge. That would round the hone edge and kill that catching problem. On new hones I sometimes rub the hone edges on cement of sand paper to break the edge.

I guess that I am more finicky if I plan to hone a straight razor. I don't do many microtomes, but I haven't noticed a big issue sharpening Xacto blades.

Anyway, thanks for the input so far. Keep em coming gang.
 
Jeff,
I learned sharpening as a kid (about 30-35 years ago) using the stones you mentioned. At first I couldn't understand why the knives were so "unstraight", or the stones so "unflat". (It hadn't occurred to me immediately that someone would sell a non-flat surface to sharpen a straight edge; or a non-straight straight edge. or were they both off?) I was trying to sharpen straight edges and chisel ground knives.......well, try restoring a zero edge on an "unflat" surface.

THE best thing that ever happened to my sharpening was to sharpen on a large, stable, flat surface. IMO with a straight edge it is imperative to have a frame of reference which is both straight and flat otherwise you are moving your knife further and further away from "true" and will be chasing it forever. Also, imagine progressing from one grit to the next and each stone is "dished" slightly differently. Where's the fun in that?

And yes, the difference can be perceived in the performance of the knife depending on what the knife is used for. Slight deviations are usually cause to reject the blade.

In my experience kitchen knives are more forgiving than a razor-style or a straight edge. I enjoy letting my hair down on a kitchen knife from time to time.:)
 
Hi annr, The hones that I am talking about were not unflat when they left the factory, they all became unflat (worn down in the middle like a sagging bridge) from years of use. In my experience the fastest way to wear down an oil stone was to get it all nicely filled up with oil and then use it dry (without oil on the surface). The oil that was soaked into the stone would make it soft and the lack of oil on the surface increased the blade drag during honing. The combination made an oil stone wear like a waterstone.

My experience was that it more often unstraight blades that most frequently caused uneven sharpening. I often found that blades were bent or warped and looked crummy when sharpened on any reasonable flat and wide hone. It often looked better if I sharpened these using the side or edge of the hones rather than using the wide flat topside of the stone. For these knives the narrow rods of a Sharpmaker or an Idahone ceramic V system gives a prettier result.
 
Jeff,
I don't doubt what you are saying. If I'm getting you correctly, it sounds like you need to compensate for blades that are out of true and you may have found a technique extends the life of the knife without a regrind or repair, or discarding the knife. Also if you are using the knife to cut or slice this may not ostensibly affect the knife's performance.

We are probably talking about very different kinds of knives, but just to answer you question is it possible that a flat hone matters, my answer remains unequivocally yes. I'm thinking of a purely razor-style, double hollow ground straight edge or chisel, or a wedge. The problem I would experience without the flat surface is that my blade would "dish". I use the knife to remove a very thin curl of uniform depth over a certain straight width of the blade.

That being said, I did use those less than optimal stones for years and I can see that they just made my life more difficult and caused me to run through knives more quickly. The longer the knife is true, the less steel I need to remove to sharpen or hone. I use the Scary Sharp method which is not expensive. For my line of work it is the fastest, cleanest, most functional day-to-day way to sharpen and manicure my edges.I still have a boatload of other stones but every time I go back to them I am amazed that I used them at all. Just my experience.:)

Re the stones: I'm talking about all kinds of deviations from flat, including a surface that may have higher and lower areas or striations. These stones are out there, new and used.

Re: unfit knives. With enough time and patience and a flat surface I find I can put the knife right, even a new knife, but if not, I will pay the piper sooner or later.
 
Hey Jeff,
This is a good discussion thread, and you make some good points on why stones needn't be perfectly flat.

I'm no expert, but my experience tells me that flat is good, especially when trying to maintain a perfectly flat bevel and carry that from one stone to the next. I sharpen straight razors (for my own use only) and I find that it is very troublesome to use non-flattened stones. You gently guide the blade across the stone and the angle is totally controlled by the razor's spine. If the stone is not flat, you lose all sense of fine control. If you move from a 2,000 or 4,000 grit to an 8,000 or 10,000 you want to be very confident that the angle of attack is precisely the same. If the finer stone is flatter, you won't make contact with the edge for a long time. The very fine grits can't take up the slop.

When freehanding knives without a guide, the flatness may be less important. However, I think it would still work against you and make the job less efficient to some degree
 
I started on lopsided combo stones, and would get my first sak shaving with a little time. I can get a blade sharp on a dished stone, but then moving to a higher grit with no dish can screw it up again.
 
I used a dished silica hone to regrind alot of knife edges and didn't think it mattered at all that it was dished. I now use water stones for most of my sharpening and do flatten them but I'm not real concerned about them being perfectly flat. I just keep them from becoming heavily dished. I should ad I convex almost all my knife edges on the stones now.
 
Hi Jeff!

I've used dished hones and hated the results!. The coarse stones dish faster than their finer counterparts and that leads to more work to fix everything up. Not so hard freehand, but a nuisance with EdgePro waterstones. My edges are rounded enough from free-hand slop - I don't need the hones to do me any "favors."
 
My coarser stones get very dished out, which is a real problem for me. I use convex edges mostly, meaning I always try knocking down the shoulder where the edge bevel meets the primary grind to smooth the transition. So the blade is riding over the stone at just a few degrees. I can keep the edge at the same angle in relation to the stone as it curves with no problems; however, by the time the edge gets to the center of the depression, the spine is now too close to that higher portion. This means I either can't sharpen at as fine an angle as I'd like to (especially with saber grinds or narrow hollow grinds), or I risk scratching up the blade with one ever so slightly off pass. I get people asking me to sharpen their knives on a regular basis. Considering how utterly dull most of their knives are, they're in awe of someone who can produce a shaving edge. I really hate handing back their Chinese POS saying, "It's pretty sharp now, but I really screwed up the finish for ya." The rare occasions that's happened, they don't care anyway, but it really bothers me. And I don't want to scratch up my good knives unneccesarily.
 
the possum said:
I really hate handing back their Chinese POS saying, "It's pretty sharp now, but I really screwed up the finish for ya." The rare occasions that's happened, they don't care anyway, but it really bothers me.
Click to expand...

Good point. I didn't mentioned the cosmetic aspect. My knives looked bad too. Even to this day I favor performance over appearance, but I find that the two often go hand in hand. I know that I draw a straighter line with a ruler.:D
 
I too have sharpened professionally and all of it was freehand. I exclusively used Arkansas Stones (novaculite) for about 25 years. Many, many knives I worked on were D-2 steel at Rc60 or so. My favorite stone had a worn spot on it that I actually looked for when I started because it was an indicator of my "edge first" sharpening style. Unless I sharpened a Wharncliffe style I always grabbed the old Arkansas. Thieves stole my chest and alas the stone with it. (Always wondered what they thought about the ashes of my daughtyer-in-law which were respectfully stored in the chest along with other memorabilia and the last Lile knife I owned.) When my old stone was gone forever, I bought another, and it never seemed right. Nowdays I start with a diamond hone and finish with a black hard Akransas I retrieved from the scrap pile in Hot Springs, Ark. Alot to be said for a "personal" stone being dished a bit....I like it!
 
I won't say you can't get a knife sharp on dished stones, but to me a flat stone is more multi-dimensional and precise, while a dished stone may have more soul. To each his own!
 
What I want to weed out are the kind of recommendations to novices that start with "OMG make sure that your hone is flat!" when someone is having trouble sharpening his first knife. For general knife sharpening I wouldn't even mention hone flatness as a potential source of problems. I would go down the regular list of making sure that honing is at a reasonably low angle, it is getting all the way to the edge (the felt pen trick), and burrs are removed. I would ask about the type of hone and whether the novice is using a reasonable tool for the edge that is desired. For basic sharpness I don't think that either hone flatness or precise angle control are critical and yet they pop up in basic advice. When someone starts sharpening a scandi edge, wood chisel, straight razor or toilet paper slicing edge I might mention hone flatness, but otherwise I consider it a low priority topic.

I appreciate your input as to how I should adjust my thinking.
 
As I said, I would agree with you. Especially, the really nitpicky flatness is nonsense IMHO. I have been one of those, who bought a straight-edge to check for hone flatness, because I read recommendations to do so. That is not necessary IMHO. If you can't see it by sighting down the surface, I think it should be considered flat.
 
I completely agree and think angle control is sometimes given way too much importance. Heck it is my opinion sloppy angle control is prefered. :)
 
I've hand-honed for years, and I think any hand-honer automatically articulates honing strokes to suit stone curvature - just as we do to suit blade-shapes.

I know this. I believe this. But, still I use a flat-surface hone for my favorite EDC blades. I guess it's a 'logical' bias.

I have an 'old pal', a Washita stone that's so dished it fits my belly profile. Can't bear to discard it, so I use it to hone our kitchen knives. Definitely an emotional bias.

We all have our quirks.
 
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