can a "rounded" edge show later on in use?

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whitefox

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Mar 3, 2011
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From what haveI read and experienced, most rounded edges happen through stropping. Either from too much pressure or not maintaing the proper angle for every pass. However can some rounded edge show later on in use? Or is it mostly noticeable with the first few cuts after a sharpening, then a strop?

For example; one of my knives had a rounded edge that I didn't know about. Heres how I didn't know or perceive the edge was rounded. It could shave arm hair very easily. It had no trouble cutting small slivers of nail fragments off the back of my thumb nail. But it could not cut my skin. At all. The knife literally just ran across my skin on the back of my hand. I didn't do this testing till after a few days of use. The steel was aus8. RC was 57-59. It could cut printer paper, but it looked the paper was folded back along the edges and I could see little fibers.

Pretty sure a bur wasnt left on the edge. Even a slight one. I check through a led light.

So can rounded edges show later on in use or right way? Ive read some rounded edges will still shave arm hair to an extent.
 
Are you sure you're pressing hard enough? A knife that will shave, but won't cut skin at all doesn't sound right. A knife with a highly polished finish will slide some, but it should still cut your skin with enough pressure.

For example, a knife with a sticky edge will bite into the skin on your fingers (three finger test), but will not shave hair as easily as one finished at a higher grit, that doesn't have as much bite (but will still cut the skin as you slice, just won't do it as easily as the stickier edge).

I wouldn't suggest trying to cut the back of your hand (you might get what you're asking for), but you might just be using the wrong technique or pressure.
 
Well, I'm glad I'm not the only one who has noticed this happening. I've also found it quite strange that edges will shave and whittle hair, but not really cut anything. I have no idea why it happens either, once I get to this point I just conclude that it needs to meet an actual hone again instead of the strop. But I have observed what you're talking about so I don't think it's a problem with your technique.

I think I know what you're describing with the paper too. It's not so much like it's torn the paper, but it leaves the edges very soft and "worn" looking. Not a crisp, clean edge like when a knife actually cuts. It's almost more like the knife edge is pushing/pulling the paper apart.

When this happens to me, as I said I just conclude that I've "overstropped" and go back to a hone.
 
KennyB said:
Well, I'm glad I'm not the only one who has noticed this happening. I've also found it quite strange that edges will shave and whittle hair, but not really cut anything. I have no idea why it happens either, once I get to this point I just conclude that it needs to meet an actual hone again instead of the strop. But I have observed what you're talking about so I don't think it's a problem with your technique.

I think I know what you're describing with the paper too. It's not so much like it's torn the paper, but it leaves the edges very soft and "worn" looking. Not a crisp, clean edge like when a knife actually cuts. It's almost more like the knife edge is pushing/pulling the paper apart.

When this happens to me, as I said I just conclude that I've "overstropped" and go back to a hone.
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How do you sharpen your knives? I sharpen mine with the wicked edge. I also use polishing paste on my strops.
 
An otherwise good edge, that has been rounded off by stropping will still shave and cut newspaper, but it won't cut a tomato without a good deal of pressure and it'll feel slick in the three finger test. I tend to strop less with compounds these days and use finer stones instead.
 
mrdeus said:
An otherwise good edge, that has been rounded off by stropping will still shave and cut newspaper, but it won't cut a tomato without a good deal of pressure and it'll feel slick in the three finger test. I tend to strop less with compounds these days and use finer stones instead.
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^ This. I still usually finish with compound on paper, but is entirely possible to have an edge shave hair yet perform very poorly on many other tests. It sharp but overly wide and toothless. Imagine a reasonably flat-sided cutting bevel when rotating it under a light source, the light will play across it very quickly and reveal very little curvature. If the edge shows a lot of curvature from shoulder to apex, chances are its rounded and is considerably more broad at the cutting edge than you imagine. It could also have an overly broad edge angle to begin with and will perform poorly in a similar fashion.
 
KennyB said:
When this happens to me, as I said I just conclude that I've "overstropped" and go back to a hone.
Click to expand...

I would say it's more improperly stropped as opposed to over stropped. I did an experiment where I stropped a knife with 1000 passes on each side, and had absolutely no problems with edge performance. Proper angle and light pressure go a long way! When an edge is properly stropped, it will have no problem slicing printer paper.
 
whitefox said:
From what haveI read and experienced, most rounded edges happen through stropping. Either from too much pressure or not maintaing the proper angle for every pass. However can some rounded edge show later on in use? Or is it mostly noticeable with the first few cuts after a sharpening, then a strop?

For example; one of my knives had a rounded edge that I didn't know about. Heres how I didn't know or perceive the edge was rounded. It could shave arm hair very easily. It had no trouble cutting small slivers of nail fragments off the back of my thumb nail. But it could not cut my skin. At all. The knife literally just ran across my skin on the back of my hand. I didn't do this testing till after a few days of use. The steel was aus8. RC was 57-59. It could cut printer paper, but it looked the paper was folded back along the edges and I could see little fibers.

Pretty sure a bur wasnt left on the edge. Even a slight one. I check through a led light.

So can rounded edges show later on in use or right way? Ive read some rounded edges will still shave arm hair to an extent.
Click to expand...

The bolded point above SCREAMS "BURR!!" to me. Burrs will usually grab/fold/snag/tear the paper in the manner described. And in tandem with the other behavior (shaving, scraping fingernail), but sliding across skin, a burr that's folded over to one side can do that. Do the shaving and fingernail scraping tests from both sides of the edge; if there's a 'leaning burr', it'll shave & scrape the nails from one side, but slip/slide from the other. Edges like these often won't cut/slice well when drawn in conventional fashion across other media (like skin), with the spine of the blade perpendicular to the media being cut.

To me, if an edge is truly rounded, cutting performance will fall off across the board; especially shaving and nail-scraping, which are usually the first to go. In paper cutting, a rounded edge will mostly slide/slip over without cutting (try this with fine paper, such as from a phone book). Edge geometry (angle) plays a huge part in that as well; a moderately rounded apex on a very thin edge grind (30° inclusive or less) can still do many tasks reasonably well, sometimes including cutting tomatos (up to a point). But, on relatively wide edge geometry (~35° inclusive or more), cutting performance will drop off a cliff pretty fast, if the apex starts rounding off.


David
 
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