From screaming sharp to butter knife dull I'm one cut?

No1up said:
But do guys think the edge would be lost after only one cut? The Wicked Edge would allow for strokes on both sides reducing a formation of a burr.
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Honestly, one cut should have not left it 'dull'. Even if the wrong edge finish for the job, it should have been able to pressure cut a number of times before it failed outright. I have to believe it had a wire edge or burr of some sort.

Edge finish will determine best use, but a well finished edge will endure far longer than one pass thru some rope. The edge couldn't have been finished cleanly - no burr, no wire.
 
With a loupe I'm able to recognize a wire edge... I think. When I re-did the knife on the worksharp KO, I could not make the light shine at the apex. I remember after the chosera stones there was a very very slight shine if you directed the light juuust right.
 
It's almost certainly a sharpening issue. I don't know of any steel that will dull that fast that much in one cut on rope. Will it not cut at all in the area where the cut was made on the edge? Is it really that dull, or just duller than when finished sharpening?
 
Put it this way... I shaved my beard the night I sharpened it... after the rope I could put this full force on my neck and pull it with no worried... (I haven't done this, just saying.)
 
No1up said:
Put it this way... I shaved my beard the night I sharpened it... after the rope I could put this full force on my neck and pull it with no worried... (I haven't done this, just saying.)
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A high-finished shaving-fine edge can disappear in a flash (i.e., one cut) on abrasive rope. If the blade had gone from a more 'utility sharp' and coarser-finished edge to dull in one cut, there may be more going on, like a burr folding over. I'd expect the same if something as simple as paper-cutting had produced a change like that. But the abrasion from a rope of natural fibers can erase a polished shaving edge immediately. I've seen it many times after such cutting, drawing the edge across a fingertip with no cuts, and verified under magnification that the edge had been rounded off. I'd actually expect a true shaving edge to diminish that quickly, when tested that way with most knives. Some exceptional blades can occasionally get past it, but it's not unusual for many to show a noticeable loss when cutting very abrasive materials like rope or heavy cardboard with a highly-polished edge. As I mentioned before, if the edge geometry is also relatively wide, the drop-off in cutting performance will be even more extreme, as the crisp apex itself is really the only thing pulling off shaving sharpness, and it'll erode quickly on abrasive cuts, leaving only a thick and rounded apex behind. Burrs are always a possibility with any steel; but what I'm saying is, it's not at all uncommon for a fine shaving edge to disappear that quickly after some brief abrasive cutting. Shaving sharpness is always the first to go away, and it usually goes away quickly if an edge is used for anything other than shaving.

BTW, if your PM2 is S30V:
S30V is known for losing a shaving edge quickly; the Maint forum and others are awash in other threads & posts noting the same tendency about the steel. Depending on how highly finished it may be before that happens, it'll fall back to a 'utility sharp' edge at a coarser/medium finish, OR it can go extremely 'dull' (losing all aggression) if the edge was highly polished before the shaving sharpness went away. I've noticed the same tendency in attempting to polish S30V blades from CRK (Sebenza) and Kershaw/ZT (Leek, ZT-0350). They've all done much better when taken back to a finish around ~325 - 600 (such as DMT Coarse/Fine), instead of polishing up to/beyond about ~2K or so.


David
 
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HeavyHanded said:
Honestly, one cut should have not left it 'dull'. Even if the wrong edge finish for the job, it should have been able to pressure cut a number of times before it failed outright. I have to believe it had a wire edge or burr of some sort.

Edge finish will determine best use, but a well finished edge will endure far longer than one pass thru some rope. The edge couldn't have been finished cleanly - no burr, no wire.
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I agree with this. I also think a 10K edge can cut rope...

P1020392a.jpg


...as long as the edge doesn't have a burr/wire edge, and isn't 'rounded' (i.e., doesn't feel smooth to the touch). IME, a more refined edge (not necessarily a 10K) will outlast a coarse one... under a variety of uses. Like OwE said, a lot depends on the geometry, and how carefully an edge is finished. I don't typically finish a blade to a 10K level... but I don't leave them coarse either, for example I might finish at: 2K waterstone, or XF diamond, with some light stropping. (I posted the picture mainly to show a 10K edge doesn't necessarily, and shouldn't 'fail' after one cut.)
 
My experience with my homemade rope-cutting test unit shed some light on this for me. Also somewhat verified what I already had come to understand from experience.

Two edge finishes on the same knife, same angle, the finer edge could pressure cut with less force than the more coarse one to start, but failed draw cutting earlier in the test.

The less refined edge draw cut over 30% longer than the more refined one, but its start value for a pressure cut was higher than the finish value for the refined edge.

If the edge is highly refined it will perform better longer if used with a press, drawing with it will dull it more rapidly than a more coarse edge.

If the edge is coarse, pressure cutting with it will be less efficient than a fine edge to start and only get worse.

All else being equal, there will theoretically be a sweet spot that about evens this factor out for a given material, but a lot will come down to how its used. It still shouldn't fail in one whack without some other factor being involved.
 
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Jason B. said:
10k is for Straight Razors not knives. Knives need that toothy edge because most things you cut are very abrasive, meaning it will wear down a finely polished edge in as little as one cut. The coarser the better.
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Are you saying that a polished edge will have a narrower apex than a toothy edge, even if they have the same bevel angle, and thus it will wear faster?
 
SteevB said:
Are you saying that a polished edge will have a narrower apex than a toothy edge, even if they have the same bevel angle, and thus it will wear faster?
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He means that a polished edge does not possess those many tiny "teeth" or micro serrations that a coarse edge inherently has. Those are what stand up to abrasives in the material being cut. In essence, there are more opportunities for a toothier or coarser edge to grab on to the medium being cut. While a very polished edge, rather toothless may excel at shaving (push cutting), it will have a much harder time at all other task (draw cut). When drawing a polished edge over an abrasive thing you are cutting, you will destroy the crispness of the apex. Instead of a clean meeting of two sides (edge bevels) that meet to form a sharply defined point of intersection (apex), you will have two defined sides that become rounded at the point of meeting. This edge will seem to dull much faster.
 
I like the edge the sharpmaker fine rods give, followed by a few passes on the UF rods and very light runs through the strop.

This has given a burr and wire edge free, long lasting edge.
 
Polished edges cut better on a push but will blunt faster. Low grit edges, properly apexed, will hold an edge much longer in slicing cuts.
 
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