M390 (and cognates) rolling?

dkb45

dkb45

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I love razor edges. I always sharpen as best I can to a near mirror finish. I've finally found a technique that lets me get a hazy mirror with diamond stones, and wicked sharp edges.

The problem lies in M390 (and 20CV and 204P) rolling like crazy. It's happened on a multitude of knives, so it wouldn't possibly be an issue with a specific knife or sharpening job, could it? Does M390 just not have terribly high edge stability with a highly refined edge? Using my older methods that didn't give as keen of an edge or as high of a polish I didn't have any rolling. Other steels, like K390, Cru-Wear, and Elmax don't give me these same rolling issues, using the same method of sharpening.
 
dkb45 said:
I love razor edges. I always sharpen as best I can to a near mirror finish. I've finally found a technique that lets me get a hazy mirror with diamond stones, and wicked sharp edges.

The problem lies in M390 (and 20CV and 204P) rolling like crazy. It's happened on a multitude of knives, so it wouldn't possibly be an issue with a specific knife or sharpening job, could it? Does M390 just not have terribly high edge stability with a highly refined edge? Using my older methods that didn't give as keen of an edge or as high of a polish I didn't have any rolling. Other steels, like K390, Cru-Wear, and Elmax don't give me these same rolling issues, using the same method of sharpening.
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Yes, you haven't given us much to go on and this would be better in maintenance/tinkering.
 
Because it sounds like you are trying to generalize ("M390 (and cognates) rolling"), to respond, it would help to know....
  • What's your sample size? How many knives have you observed this behavior on?
  • What type of knife tasks are you doing when the edge rolling occurs?
  • What is your basic sharpening process (freehand, guided system, etc., and what abrasives and progression do you use)
  • Edge details: as somebody else said, what's the edge angle, and if you have a caliper, what's the thickness of the blade just above the shoulder
 
Alright so my sharpening methods are DMT Magna-Guide, XC-XXF and stropping with emery compound. The knives with approximate edge angles and thickness behind edge are ZT 0562CF ( 0.38 15 dps), ZT 0456 (0.32 18-20 dps) Kershaw Link M390 (0.24 15 dps) Real Steel Griffin M390 (0.26 18-20 dps) and a Benchmade 556-1 reground (0.10 15 dps). Of all, only the Griffin hasn't had significant rolling, but any rolling is quickly corrected with a swipe or two edge trailing on cardboard.

I cut a fair bit of single wall corrugated cardboard at work. I've also gotten some rolling from M4 on my Gayle Bradley and Stretch HAP-40, but those are likely from a botched sharpening (also those steels don't like keen edges as much as toothy).
 
Hmmm, you have a pretty good variety of different makers using M390, and you have a range of edge geometries that experience the rolling, so it's pretty diverse sample. Does the rolling happen 100% when cutting the corrugated cardboard, or in other tasks too? I think M390 probably is somewhat less tough than those steels you listed, but I wouldn't have expected such consistent rolling from M390 at those edge angles versus other steels based on my usage. I have even lower angles with M390 and no rolling problems, but then I've only done light work on cardboard boxes, usually just 3 to 5 boxes at a time.

The one thing all your rolling edges have in common is your 'hazy mirror' finishing process. Have you thought of trying an experiment, resharpen one knife with a more coarse edge, say a DMT C, then strop it just lightly and a few times, don't take the toothiness out of the edge, and see if that makes any difference. To me, if what you're doing isn't working and you have a good diverse sample of knives in the same steel showing the behavior, you try something different with one knife. I would also ping the mods and see if you can get this thread moved into the sharpening forum, ping some of the sharpening pros there for additional ideas. It's possible that M390 is just less tough than these other steels and is going to roll in certain types of tasks, but I sure haven't seen that yet myself, it holds up amazingly well in folders and fixed blades.
 
The edge on my s90v will roll but not on cardboard. It requires several cuts on hard wood limbs. Like oak or apple trees. Then I notice it.
I suspect along the path to obtaining a polished edge and it requires much stone work. The apex gets thinned. So, when some firm material
is encountered during cutting this edge lacks the strength to support it and folds. No fault of the steel, it's just been worked thin. Redo the
edge bevel to a 16* and stop at the coarse or fine. No excessive refining. Just work the burr off on the stone and stop. Then start cutting
the same cardboard and see how the edge responds. DM
 
dkb45 said:
Alright so my sharpening methods are DMT Magna-Guide, XC-XXF and stropping with emery compound. The knives with approximate edge angles and thickness behind edge are ZT 0562CF ( 0.38 15 dps), ZT 0456 (0.32 18-20 dps) Kershaw Link M390 (0.24 15 dps) Real Steel Griffin M390 (0.26 18-20 dps) and a Benchmade 556-1 reground (0.10 15 dps). Of all, only the Griffin hasn't had significant rolling, but any rolling is quickly corrected with a swipe or two edge trailing on cardboard.

I cut a fair bit of single wall corrugated cardboard at work. I've also gotten some rolling from M4 on my Gayle Bradley and Stretch HAP-40, but those are likely from a botched sharpening (also those steels don't like keen edges as much as toothy).
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Depending on what's meant by stropping with 'emery compound', you might also omit that part of the process. If it's actually 'emery', a.k.a., 'corundum' or aluminum oxide, it may not be handling the vanadium carbides in this high-wear steel very well. It'll erode the matrix steel from around the carbides (vanadium) at the edge, while failiing to cut or shape those carbides effectively, which leaves them standing proud with little support and weakens the edge. You'll effectively end up with an edge that behaves just like a folding burr.

If going for a high-polish finish with these high-VC steels, a diamond or cbn compound for stropping will do a much better job with the carbides, leaving the edge crisper and more durable for the polish attained.

Corrugated cardboard shouldn't ordinarily cause many edge rolling issues, even in relatively low-wear steels (abrasive wear is the bigger issue for those). So something else in the process is disproportionately weakening the edge, part of which may be the emery compound stropping.

A polished edge by itself isn't necessarily a problem for cardboard cutting, and can even enhance it. My own favorite for similar modern/tactical knives used for cardboard, is a polished, thin convex ( < 30° inclusive ). I like the same edge treatment in other knives in simple steels like 1095, used for the same task and with no edge-rolling issues.
 
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Not that m390 is very prone to creating a foil edge but I'm wondering if that is what is happening? High carbide steels at relatively high (~30deg inclusive+) are not really prone to rolling but rather wear blunt from abrasive cutting (and a lot of it!). If you are actually seeing rolling than you must have a thinner wire edge remaining from your sharpening technique.
Given that it is happening with multiple knives and multiple steels (M4 too) than it is not an isolated bad steel formulation/heat treat.
I'm inclined to think there is something going on wth your sharpening technique or that what you're seeing is not infact "rolling of the edge". Macro pics would help.
 
If the edge already had damage to begin with, if it wasn't De stressed before sharpening it, you could just be sharpening a weak edge. I've been watching too much cliff stamp over the weekend so don't mind me. But trying to help if the above tips dont solve the problem.
 
I dislike M390 and variants for the same reasons and have always received huge backlash anytime I have mentioned it. Like calling someone's baby ugly...

Good luck in getting it resolved as no one will believe it's the poor heat treatments used by production companies. Everyone wants the newest steel and forgets it takes time to perfect just one steel... Buck 420hc anyone?
 
So I sharpened my new Modus CF last night to 600 grit, and I'm also getting rolling of the apex. It has to be something to do with my strop, I'd say. I get a really crisp, stupud sharp apex, but this much rolling on high carbide steels means that I have to be weakening the matrix around the carbides, but I get no rolling on D2 and steels with softer carbides, so I'm afraid it is the stropping compound.

If it is the stropping compound (which seems likely), what us a good micron to strop with after 3 micron? Also is it preferred to use CBN or diamond? Spray or powder? I know pretty much nothing about stropping compounds outside of standard wax sticks (none of which I've found have an abrasive that will work on vanadium carbides).
 
dkb45 said:
So I sharpened my new Modus CF last night to 600 grit, and I'm also getting rolling of the apex. It has to be something to do with my strop, I'd say. I get a really crisp, stupud sharp apex, but this much rolling on high carbide steels means that I have to be weakening the matrix around the carbides, but I get no rolling on D2 and steels with softer carbides, so I'm afraid it is the stropping compound.

If it is the stropping compound (which seems likely), what us a good micron to strop with after 3 micron? Also is it preferred to use CBN or diamond? Spray or powder? I know pretty much nothing about stropping compounds outside of standard wax sticks (none of which I've found have an abrasive that will work on vanadium carbides).
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I'd suggest in the short-term, just omit the stropping step completely after your last diamond hone (DMT EEF). See how your edges hold up, if they're still rolling or not in the cardboard. Obviously, since you'd not be stropping it, it'll place more emphasis on making sure your edge is as clean as it can be, coming straight off the hones. If the work there is good, then the cardboard itself should strip away most remaining remnants of light burrs left on the edge, after which the working edge should be pretty strong and durable. If it is noticeably more durable, then you'll know for sure that's something's going astray in the stropping, as you've used it. If the edges still roll in cardboard, across multiple steels and blade manufacturers, then something else in the process is likely going really wrong. At that point, I'd approach it as others mentioned earlier, in finishing the edge at a somewhat coarser grit (maybe the EF), still leaving out the stropping, and try again with the cardboard. Taking single steps back in the progression should eventually show where the threshold is, where the edge has been degraded and weakened.

Regarding stropping with diamond:
After DMT's EEF (3 micron), or even after the EF (9 micron), I've liked going to 3 micron diamond. I've used DMT's Dia-Paste on wood (basswood), which will bring up the polish very fast following either of those two hones, while leaving the edge crisp and durable. Go as far beyond that as you wish, in grit. But for me, I often just finish at the 3 micron, and maybe occasionally touching up the edge at 1 micron, after the fact.

I've not used diamond sprays; but many here seem to prefer them over the pastes. The sprays are likely easier to apply evenly, if for no other reason. DMT's Dia-Paste gets the job done, and works very well. But it can be a little tedious in first applying it to the strop. Part of the key in using it, is not to overapply it. It's too easy to lay it on too heavily, and the excess just gets scrubbed off the surface of the wood in use and will be wasted. So, a couple or three BB-sized drops of it on an 8" x 2" surface is a decent starting point for application. A little goes a very long way.
 
I'll try just leaving a knife without stropping and see if the edge responds better. As a sharpening junkie, it will kill me, but I must for science.

For the stropping, would you suggest hard leather, pine wood, or MDF for the base? I have all 3 available.
 
dkb45 said:
I'll try just leaving a knife without stropping and see if the edge responds better. As a sharpening junkie, it will kill me, but I must for science.

For the stropping, would you suggest hard leather, pine wood, or MDF for the base? I have all 3 available.
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If the pine is smooth, flat and clean, I'd probably choose that first among those three options. DMT suggests MDF, I think; my only reservation with it is, the process for making it can be kind of dirty. At high-mirror finishes, it's capable of leaving some scratches on the finish from dirty grit embedded in the material. It's known for inducing extra wear in woodworking tools & bits used to cut & shape it. But at slightly coarser finishes (hazy mirror and coarser), I'd likely choose it first, because it's so uniform in smoothness and flatness, and it won't compress either, as it's very dense & hard. The slightly 'dirty' nature of MDF is even capable of some abrasive stropping when used bare. I sometimes use the mdf surface on a garage worktable of mine to fix & straighten rolled edges on my utility-sharp edges, and strip burrs away after touching them up.

I generally avoid using leather, except when used bare and as a hanging strop only. Used as such, it's not as much a risk for edge-rounding or over-burnishing edges. Specifically, I use a leather belt as such, and only for cleaning up loose remnants of burrs on edges. I don't rely on it for polishing or (significantly) thinning an edge.
 
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Obsessed with Edges said:
If the pine is smooth, flat and clean, I'd probably choose that first among those three options. DMT suggests MDF, I think; my only reservation with it is, the process for making it can be kind of dirty. At high-mirror finishes, it's capable of leaving some scratches on the finish from dirty grit embedded in the material. It's known for inducing extra wear in woodworking tools & bits used to cut & shape it. But at slightly coarser finishes (hazy mirror and coarser), I'd likely choose it first, because it's so uniform in smoothness and flatness, and it won't compress either, as it's very dense & hard. The slightly 'dirty' nature of MDF is even capable of some abrasive stropping when used bare. I sometimes use the mdf surface on a garage worktable of mine to fix & straighten rolled edges on my utility-sharp edges, and strip burrs away after touching them up.

I generally avoid using leather, except when used bare and as a hanging strop only. Used as such, it's not as much a risk for edge-rounding or over-burnishing edges. Specifically, I use a leather belt as such, and only for cleaning up loose remnants of burrs on edges. I don't rely on it for polishing or (significantly) thinning an edge.
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So leather isn't the best choice even when it is 12oz+ saddle skirting? I used it to make armor for my larp, and it barely even needed hardening, cutting the blanks out for my demi-greaves completely dulled two box cutter blades. Honestly the firmest leather I've ever comes across.

That said, I ordered an assortment of diamond pastes, so I will be able to load up a few different MDF sticks with different compounds. I'd assume since it's coarse on its own, I shouldn't go below like 4 micron on it, and use the sub 4 with pine?
 
Additional question, since the carbides in the matrix being unsupported could he the problem, should I resharpen all of my vanadium carbide steels or is stropping with a more coarse diamond and working up the progression good?
 
dkb45 said:
So leather isn't the best choice even when it is 12oz+ saddle skirting? I used it to make armor for my larp, and it barely even needed hardening, cutting the blanks out for my demi-greaves completely dulled two box cutter blades. Honestly the firmest leather I've ever comes across.

That said, I ordered an assortment of diamond pastes, so I will be able to load up a few different MDF sticks with different compounds. I'd assume since it's coarse on its own, I shouldn't go below like 4 micron on it, and use the sub 4 with pine?
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Try the leather, if you want to. You might find a niche for it, in your sharpening scheme. I've never found any leather yet, that was quite as firm as something like basswood.

And for the mdf, I'd personally avoid using it for high-polish finishes, if you really want to avoid any visible scratching against a mirrored finish. By 'high polish', that generally starts around ~3 micron with diamond pastes, and maybe < 10 micron for other grit types, like aluminum oxide.
 
dkb45 said:
Additional question, since the carbides in the matrix being unsupported could he the problem, should I resharpen all of my vanadium carbide steels or is stropping with a more coarse diamond and working up the progression good?
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Assuming the apex has been weakened, I'd apex again with a diamond hone, perhaps preceding that by lightly drawing the edge vertically across the hone (as if cutting it), to scrub most of the weakened steel away from the apex. You don't necessarily need to go all the way back to the beginning of the progression, to do that. Might start with something like the Fine or EF (600 / 1200), and go from there, back through the finishing end of the progression.
 
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