Can a knife blade be too sharp?

[rodrigaj]

Just got my first good knife, a Benchmade mini Barrage. Out of the box the blade edge was about 80 grit. I got it to a nice 1500 grit finish. Scary sharp.

But I got to thinking. As a woodworker I use hand planes. I seem to remember that many woodworkers at woodworking shows, years ago, felt plane blades should not be made really, really sharp (say 8000 to 10000 grit). The argument as I recall, was that they only got duller faster.

Wondering if the same is true of knives. 1500 grit seems plenty sharp, yet I see these mirror finishes, and I wonder.

What are your preferences are for your EDC knives?

 

[Hair Scraper]

I've used the Spyderco Tri-Angle Sharpmaker for years. It comes with two different "grit" triangular rods, medium (brown) and fine (white). You can buy others for it, including an Ultra Fine Tri-Angle. The Tri-Angles are made of high alumina ceramic, so "grit" is kind of a misnomer. Spyderco has said, "An approximate "grit" for the Spyderco High Alumina Ultra Fine Ceramic is 2,000 , Fine is 1,800 and Medium is 600."

I'll usually start with the optional diamond and CBN Tri-Angles to set the bevel at 15° per side, and eventually finish with the brown Tri-Angles. The medium Tri-Angles give a slightly "toothy" edge that acts like micro-serrations that'll grab your fingerprints. On some blades, (Super Blue,) I'll dust off the edge with the fine Tri-Angles.

In all cases I put a 20° micro bevel on the edge.

 

[DesertIguana]

First Emerson I bought had a warning card, that the Knife was sharp.

Think the card was for people who were not SHARP between ears.

 

[EclipseRedRing]

I am not a kife guy - any knife I use is merely a tool; if I can cut what I need to cut, then the knife is sharp enough. If not then it gets a few strokes on an oilstone, only about 300 grit, followed by a sharpening steel; that is plenty sharp enough for me. Not sure that a knife can be too sharp, but I have no interest in maintaining extreme sharpness.

 

[Possum092]

Depends on what the edge is intended to do. A combat knife and a fillet knife are sharpened to perform totally different roles. Use the right edge and knife for the job.

 

[brucered]

Depends on what the edge is intended to do. A combat knife and a fillet knife are sharpened to perform totally different roles. Use the right edge and knife for the job.

This.

A hair cutting razor sharp thin edge, will roll if I am cutting through a chicken bone (kitchen knife) or caring something some camping (pocket knife)

Sharpness depends on what knife I am using and what edge gets put on it.

 

[Whiterook]

I think the edge gets fagile when you sharpen at higher grits. For EDC the edge could roll, so not too sharp is best given typical usage.

 

[rodrigaj]

Depends on what the edge is intended to do. A combat knife and a fillet knife are sharpened to perform totally different roles. Use the right edge and knife for the job.

Of course your right, but an EDC function is sort of all over the place.

Sometimes a letter opener, sometimes tearing up cardboard, sometimes slicing tomatoes, sometimes cutting a water hose, stripping insulation from wire... (Those are all of the things I used my knife for today).

The convenience of not having to get that special knife or tool... just using the handy knife that's always in you pocket.

 

[wlshephard]

Absolutely

 

[rodrigaj]

I've used the Spyderco Tri-Angle Sharpmaker for years. It comes with two different "grit" triangular rods, medium (brown) and fine (white). You can buy others for it, including an Ultra Fine Tri-Angle. The Tri-Angles are made of high alumina ceramic, so "grit" is kind of a misnomer. Spyderco has said, "An approximate "grit" for the Spyderco High Alumina Ultra Fine Ceramic is 2,000 , Fine is 1,800 and Medium is 600."

I'll usually start with the optional diamond and CBN Tri-Angles to set the bevel at 15° per side, and eventually finish with the brown Tri-Angles. The medium Tri-Angles give a slightly "toothy" edge that acts like micro-serrations that'll grab your fingerprints. On some blades, (Super Blue,) I'll dust off the edge with the fine Tri-Angles.

In all cases I put a 20° micro bevel on the edge.

Thanks for the detail. I always put micro bevels on my plane blades. Never thought of putting them on my knife.

Like you my bevel on the mini Barage is at 15deg, which was the factory setting.

(I have a KME sharpening system.)

 

[Keyvan]

I am sure many other members are more knowledgeable than I am. My understanding is that the maximum sharpness of a knife is related to the hardness of the steel. Japanese knives, for example, can take on sharper (thinner) edges and retain them. Because European knives are made with softer steel, they cannot retain similar edges. The softer steel has the advantage of being able to survive more abuse without chipping.

Fisherman use knives made with softer steel for filleting fish, but they constantly hone the knives to maintain the edge. It depends on how often you are willing to hone the knife.

 

[AimlessWanderer]

I don't think a knife can be too sharp, but it can have the wrong edge.

If it's going to be used for slicing, a larger grit size will leave microserrations on the edge, which will help performance, and could well lead to it "feeling" sharper for longer. A finer grit edge would work better for push cutting tasks, but it might not slice as well, leading to a feeling that the knife is duller than it actually is.

As to the apex angle, this can easily be too acute, irrespective of steel hardness. A softer steels edge might roll, and a harder edged steel might chip. A rolled edge may be straightened (steeled), whereas a chipped edge will always need time on the stones. Modest blade harnesses work just fine for me, so I don't tend to have chipping issues. If an edge seems to dull too quickly, whetting the edge with a teeny extra bevel might help longevity.

I can't comment on precise edge angles, as I hand sharpen, and just give blades the edge they need to perform how I want them to. It doesn't take long to figure out if I need to lift the edge a little more when sharpening, or leave it a little more toothy than last time. I don't try and put a polished edge on anything, as a bit of tooth works better for me on pretty much everything, but different steels can leave the same stones with different scratch depths.

 

[Hair Scraper]

Earlier this morning when I originally responded to your post, rodrigaj, I had an article from knifesteelnerds.com in mind. I didn't want to mention it until I had a chance to look it up again. It's here: Maximizing Edge Retention - What CATRA Reveals about the Optimum Edge - Knife Steel Nerds - https://knifesteelnerds.com/2018/06/18/maximizing-edge-retention/

In the article Dr. Larrin Thomas uses a CATRA test to test edge retention while varying the edge angle and finish of a couple of types of steel. The CATRA test only tests push or pull cuts, it doesn't test whether an edge will roll from having a side load or twist put on the blade. It doesn't test hardness of the steel either.

The chart below is from Dr. Thomas' article, and his conclusion is that edge angle makes much more of a difference than the grit used to finish the edge when it comes to edge retention.

Conclusions and Further Testing

Like the forum members mentioned above, it depends how you're using the knife, though. As always, YMMV.

 

[Possum092]

I prefer a single edge for my EDC for a lot of different reasons. Emerson knives has mastered this type of edge. I can attest to it standing up to the most extreme use and being easy to maintain in the field with a simple wet stone, sandpaper, or even a flattish rough surface. Mine has been serviced twice by Emerson (wore out the scales and chipped off the blade tip batoning the blade through an ammo can). The edge never rolled, chipped, or failed to remain serviceable.

 

[Bhugo]

I don’t usually go past 1000 grit on an edc or kitchen knife, sometimes less, regardless of the angle of the bevel. The toothy edge works much better for most of my cutting tasks. I never go for a mirror polish just because most of my ed cutting is slicing. A strop or steel to refresh the edge between sharpening.

The bevel angle is what I change based on the knife and it’s use. With almost all my Spyderco knives I use a 30 total angle bevel. It seems to work well with all their steels. On my cheaper stainless knives, I go a little higher.

with my woodworking chisels, plane cutters and so on, I mirror polish. Again, the bevel changes based on use, but I really want the mirror finish with no toothiness as they are all push cuts vs. slicing.

 

[NorthernSoul]

Yes, it depends on the purpose of the knife. This also depends on the edge profile. If it is too sharp, the edge can degrade quickly in use.

 

[rodrigaj]

@Hair Scraper
Thank you for the link to that paper. I did read it thoroughly and found it very informative. Clearly it shows that the angle is far more important than the final grit. I especially enjoyed the scanning electron microscope images.

 

[duke762]

I like this question, Yes, I've created edges for hunters but were incorrect for the job They wanted a toothier edge. I've done wood working tools with the same edge, and they were a big hit with the users.

This also brings to mind free hand knives sharpening vs. machines and contraptions to sharpen your knives. Repeatable only if you can position the blade exactly as sharpened previously. Good luck. I trust my feel to achieve repeatability, not tools, even if they are set up on a dang surface/inspection plate.

Two things influence how I feel about my free hand sharpening. One thing is the Katana sharpening methods for hard targets and soft targets. By freehand sharpening, I unwittingly create a radius instead of a bevel during refinement and finish.

The second thing that influences me is s YouTube video highlighting a professional Katana polisher. The guy that sharpens and finishes the blade. He's using stones the size of rice grains to finish his edge at one point.

They inquire if he ever cuts himself while handling one of the sharpest things known to man. He replies,"Yes when I was starting out. Not so much anymore". Totally legit Katana edges, not the cheap Katanas, with the western style, bevels.

I believe any slightly radius-ed edge , would be inherently stronger than a truly, accurately, beveled, edge. This may allow a more durable edge. Sharpness, would be limited to the skill of the honer, not the gizmo..... Consider if this minor reconfiguration of the edge, could possibly support a keener edge with out instant degradation due to sheer geometry.

Keen/sharp, achieved at shallow angles can be down right delicate. One of the sharpest things found in sharpening is the darn burr produced while sharpening. If not removed and it goes on to the finisher......a properly aligned burr is fearsome sharp for a little while......

 

[rodrigaj]

@duke762
Free hand sharpening is definitely the way to go, but after decades of sharpening freehand, I bought myself a KME sharpening system and have never looked back. I am currently experimenting with micro bevels to strengthen the edge, but touchups are such a breeze with the KME, that the micro bevel experimentation is just for fun.

I went through the same process with plane blades, bought a Veritas sharpening system and never looked back.

Also, I pooh-poohed the diamond stones for years and now they are the only kinds of stones I use.

Looking back, I don't think I ever really got the hang of free hand sharpening, even though I did that since my cub scout days. If you don't apply any pressure and just use the weight of the stone, the KME system gives great results. I leave it always set up in my work room, for touch ups.

 

[Rapt_up]

I use a working relatively low angle edge from a 600 grit diamond stone/hone. Depending on the blade steel and the use of the knife the edge retention varies. But most last weeks to months for regular EDC and kitchen use. I don't tend to go to steeper angles with knives intended for harder use. My Spyderco K2 in 10V at Rc65.5 has been custom ground to .007" behind the bevel, and I use a low angle for this knife and use this hard, as a knife. If you're batoning through ammo cans then I suggest you use something other than a knife, like a breaching tool, tomahawk or cold chisel.