When you have a blade that is razor sharp, is the edge rather fargile ...vs a blade that is sharp but not razor blade sharp. What im trying to ask is when the blade uses a very acute angle to achieve sharpness, does it not hold up to hardcore use and chopping as in what you would use a survival knife for?
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Does super sharp mean less durable???
- Thread starter RubyFan
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A finer(sharper) edge will cut longer than a less sharp edge, because it will take more cuts to wear the edge vs an edge that is already duller or worn. However the risk of chipping, rolling or cracking is greater with a finer edge. While some steels such as CPM 3V can hold a very fine edge while still remaining relatively "tough" it is still more fragile than a "thicker" edge. I use different edges for different tasks. For wood, or harder materials where carving, shaving, or whittling is needed I use a very fine(thin) edge. For soft materials such as cloth, rope, canvas, cardboard or straps(nylon) etc., I use a "coarser" edge. For chopping I go with a thicker, high beveled edge.
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Good answer; match the tool to the job.
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IMO, that is true. Very thin edges are generally more fragile, but of course, cut better. Tougher knives designed for heavy-duty chopping, etc. have generally a thicker blade, a more obtuse blade edge, and a lower heat treat...perhaps in the 57-59 region to make the blade "tougher" and less subject to chipping or rolling.
Certainly, the particular steel employed is just as important. There are many folks here who will soon answer this in much greater detail, although I believe that the generalities are correct.
Sonny
Certainly, the particular steel employed is just as important. There are many folks here who will soon answer this in much greater detail, although I believe that the generalities are correct.
Sonny
I hope not, because the generalities you stated more than adequately explain it!
:thumbup:
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Important note: bevel angle ≠ edge sharpness. 
Bevel angle will effect edge durability more than the degree of edge sharpness, but a sharper edge WILL be thinner than a dull edge of identical bevel angle. Think of it as a pyramid vs. a pyramid with the top lopped off. Which one would have a more fragile point?:thumbup:
Bevel angle will effect edge durability more than the degree of edge sharpness, but a sharper edge WILL be thinner than a dull edge of identical bevel angle. Think of it as a pyramid vs. a pyramid with the top lopped off. Which one would have a more fragile point?
:thumbup:
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You asked, "... when the blade uses a very acute angle to achieve sharpness... " Remember to separate in your mind sharpness and angle: they are two different things.
Keep in mind that the angle of the edge actually has nothing (or rather, very little) to do with the sharpness. A 20 degree inclusive angle (10 degrees on each side) can be a poor cutter if it isn't finished properly. And a 50 degree inclusive angle (25 degrees on each side) can be made shaving sharp. But for any angle, the more refined and polished the edge, the more durable the edge. So in that sense, it always makes sense to bring your edge to the maximum finish [for example, on ultra-ultra fine stones (2500+ grit) and/or a strop].
Otherwise, I'm not sure what you mean. If using your knife to chop, you will get cleaner and faster chops with a more polished edge. That edge will eventually get dull, yes, but an already dull knife will.... already be dull, so... it'll just get even duller.
As for how "fragile" an otherwise well-done edge is depends on the steel/HT. You can get much better edge performance and durability from a superbly heat-treated chef's knife in, for example, Hitachi Super Blue at 20 degrees than a cheap 420 Ikea chef knife at the same angle and refinement.
So remember to separate in your mind sharpness and angle: they are two different things. Remember that a more-refined edge is always better (although some people disagree with this statement). And remember that steel matters! Better steel will hold a more acute angle better.
Now then, what angle is too acute (or too obtuse) depends on your blade and what it is being used for. If you have a big, thick chopping knife (like the "camp knife" style that is popular among BF members), you obviously don't want to put too acute an angle on. A typical "user" angle is 40 degree inclusive (20 degrees on each side). And the more time you spend finishing and refining that edge (finishing on a strop, for example), the better durability and performance you will get from that knife.
Hope this helps
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You asked, "... when the blade uses a very acute angle to achieve sharpness... " Remember to separate in your mind sharpness and angle: they are two different things.
Keep in mind that the angle of the edge actually has nothing (or rather, very little) to do with the sharpness. A 20 degree inclusive angle (10 degrees on each side) can be a poor cutter if it isn't finished properly. And a 50 degree inclusive angle (25 degrees on each side) can be made shaving sharp. But for any angle, the more refined and polished the edge, the more durable the edge. So in that sense, it always makes sense to bring your edge to the maximum finish [for example, on ultra-ultra fine stones (2500+ grit) and/or a strop].
Otherwise, I'm not sure what you mean. If using your knife to chop, you will get cleaner and faster chops with a more polished edge. That edge will eventually get dull, yes, but an already dull knife will.... already be dull, so... it'll just get even duller.
As for how "fragile" an otherwise well-done edge is depends on the steel/HT. You can get much better edge performance and durability from a superbly heat-treated chef's knife in, for example, Hitachi Super Blue at 20 degrees than a cheap 420 Ikea chef knife at the same angle and refinement.
So remember to separate in your mind sharpness and angle: they are two different things. Remember that a more-refined edge is always better (although some people disagree with this statement). And remember that steel matters! Better steel will hold a more acute angle better.
Now then, what angle is too acute (or too obtuse) depends on your blade and what it is being used for. If you have a big, thick chopping knife (like the "camp knife" style that is popular among BF members), you obviously don't want to put too acute an angle on. A typical "user" angle is 40 degree inclusive (20 degrees on each side). And the more time you spend finishing and refining that edge (finishing on a strop, for example), the better durability and performance you will get from that knife.
Hope this helps
Remember, however, like in my example above that a dulled 30-degree inclusive will be less prone to further damage than a finely sharpened 30-degree inclusive. This is because the actual width of material contacting the cutting medium is thinner on one than the other in spite of having identical bevel angles. So technically a sharper edge IS more prone towards damage than a duller one...except that the dull one is already "damaged." You wont as easily nick a dull edge if striking a pebble as compared to a finely sharpened edge. But you also will be more likely to damage a dull 10 degree inclusive compared to a fully sharpened 40 degree inclusive due to the lack of supporting material. So it's a factor of both edge sharpness and bevel angle.
When dealing with how much wear the edge is able to take before cutting becomes ineffective it is best to keep the blade very finely sharpened. When dealing with how much hard impact an edge may take without nicking, denting, or rolling, it becomes a slightly more grey area. On my machetes I still opt for the finer edge due to increased chopping performance and take the additional risk for what it is. On my new rice shovel I ground a thin bevel on it but left the edge about .5mm thick, so that it wouldn't ding when hitting all the rocks in the soil around where I live.
Thanks guys, I was all wrong, in my mind i thought a very accute angle ment it would be sharper because the cutting edge was thinner. I didnt know you could have a razor sharp 40 degree angle knife that was sharp. I think of sharp like william henry knives because the blade is thin, i didnt know i could make my ontario 499 survival knife super sharp, i thought it was to thick to ever do that. Thanks again
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Your confusing actual sharpness with perceived sharpness. Perceived sharpness is just another term of ease of cut. The blade geometry combined with the edge angle and actual sharpness combine to create this. A thinner blade/edge will pass through material easier than a thick one, and so will be perceived as being sharper when in fact it cuts easier.
Just because you'll be able to get your Ontario hair-shaving sharp doesn't mean it'll slice a melon as well as a dull but very thin full flat-ground Victorinox/Forschner chef's knife.
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For more learning & enjoyment, visit the Mantenance subforum. There all the sharpening masters and metalurgy analyst argue on these.
I've personally learnt a lot (and a long way to go still) reading it.
I've personally learnt a lot (and a long way to go still) reading it.
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An edge at 45 degrees can be polished razor sharp, but it won't cut as well as a more acute edge with a coarser grind (though it will shave arm hair better, it probably won't slice paper or rope anywhere near as well). In general you should use the most acute inclusive bevel that can hold up to the job you need doing. This, more than type of grind is going to determine longevity for most applications. After that its all a question of preference. Personally I believe a coarser edge holds up longer when used for a draw cut, and a polished edge holds up better to pressure cutting or chopping. Using a coarse edge to chop or a fine edge to draw will give poor results from the get-go and the edge won't hold up for long. If your knife is too thick to cut well for what you're doing, you can always thin the back bevel, tho this winds up being a lot of work on a thicker knife you'll notice a huge difference. My Fiskars hatchet (polished on a hard Arkansas stone) can shave armhair all day long and I once dry-shaved facial stubble with it, but it still won't cut a sheet of paper or a piece of leather as well as a thin blade with a medium-grit edge. Geometry is extremely important.
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Chris "Anagarika";10686044 said:For more learning & enjoyment, visit the Mantenance subforum. There all the sharpening masters and metalurgy analyst argue on these.
I've personally learnt a lot (and a long way to go still) reading it.
I generally don't get myself too hung up on steel so long as the heat treatment is good and the steel used in a piece is from an appropriate "class" of steels. I find that the deal breaker for me tends to be the actual blade geometry and dimensions. Steels have advanced so far that even the lowest end of the commonly used cutlery steels is more than enough for the average individual's purposes. Heck--look at what Kershaw was able to do with lowly 440A! As a result I find that geometry is a much greater priority when it comes to design consideration, though steel choice is still an important factor!
Bolded for emphasis!
Your confusing actual sharpness with perceived sharpness. Perceived sharpness is just another term of ease of cut. The blade geometry combined with the edge angle and actual sharpness combine to create this. A thinner blade/edge will pass through material easier than a thick one, and so will be perceived as being sharper when in fact it cuts easier.
Just because you'll be able to get your Ontario hair-shaving sharp doesn't mean it'll slice a melon as well as a dull but very thin full flat-ground Victorinox/Forschner chef's knife.
Beautifully put.
If one's 1/4 inch thick bombproof smasher/basher/chopper and ones Opinel have the exact same edges (same level of refinement, same angle measure), the Opinel will out slice the basher/smasher/chopper.
Because the Opinel is sharper? No. Both knives are equally "sharp".
It's because the Opinel has the thinner geometry.
It's one of those things that sounds complicated but really isn't if you spend a little time thinking about it and maybe draw yourself a picture. The most complicated part is everybody using the same terms.
I agree. Though I feel that steel isn't really a factor as far as sharpness is concerned. (Granted, I'm not a steel junkie.) It's a huge factor, however, in how long that sharpness lasts. And how easy/difficult it is to get that sharpness back after the edge has dulled.
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^Precisely. What I was referencing was appropriate class of steel for a particular overall design is more important than the specific steel as a whole, and neither have anything to do with sharpness. Rather what makes steel selection important are the other factors like impact and corrosion resistance, as well as edge-related issues like edge stability, wear resistance, and whatnot.
Remember--folks used to shave with bronze razors in ancient times! Doesn't mean that edge lasted as long as steel though!
Thanks. You do express things much more clearly that I can!
I wonder if a lot of this confusion about geometry/sharpness (and it does seem to come up a lot) is a result of thin blades going out of favor. I think people don't see that something thin like an Opinel or Peanut (even with a crappy/dull edge) will slice the pants off a thick blade with a mirror polished edge.
I mean the big ol' ZTs and Striders and CSs are cool and fun, but anyone who took the time to register for this place really owes it to themselves to spend the 10 buck on an Opinel (or something thin and flat ground like it) and go cut something with it. Even if you never use it again, it shows you that, as HeavyHanded put it so well, "geometry is extremely important."
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I think you're onto something, and furthermore I postulate that the reason why thick blades are so popular is because people are mortified of the idea of damaging their knives. Thus they continuously choose very thick blades to reassure themselves that their knife will hold up under hard use, yet they never get up the guts to try using a thin blade for the same tasks and so underestimate just how much a thin blade can actually withstand!
One need look no farther than machetes for evidence of the incredible toughness that thin knives are capable of if heat treated for such.
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The confusion over geometry and sharpness seems to be thinking that they are separate. Sharpness measurements are done of cutting force required, which is affected by geometry, and the tests reflect this.
The closest I can think that this discussion has been revolving around is the level of refinement at the meeting of the two edge bevels. This is also a question of geometry, as what is measured is the radius of the curve joining the two sides. As this is less than a micron for highly refined edges, this has little to do with cutting. That is why geometry is such a critical component of sharpness, the blade needs to penetrate the media to some depth, and I think that we have always needed that depth to be greater than a millionth of a meter. The real challenges in measuring sharpness are the differences in elastic ranges and fracture mechanics of the various materials we cut.
Check up on ISO 8442.5 and related discussions for measuring sharpness in knives, scalpels, needles, etc. There are several papers on sharpness tests outside of CATRA REST/REDS, such as non-destructive tests in gel and fiberglass test media.
The closest I can think that this discussion has been revolving around is the level of refinement at the meeting of the two edge bevels. This is also a question of geometry, as what is measured is the radius of the curve joining the two sides. As this is less than a micron for highly refined edges, this has little to do with cutting. That is why geometry is such a critical component of sharpness, the blade needs to penetrate the media to some depth, and I think that we have always needed that depth to be greater than a millionth of a meter. The real challenges in measuring sharpness are the differences in elastic ranges and fracture mechanics of the various materials we cut.
Check up on ISO 8442.5 and related discussions for measuring sharpness in knives, scalpels, needles, etc. There are several papers on sharpness tests outside of CATRA REST/REDS, such as non-destructive tests in gel and fiberglass test media.