Wire Edge and Chipping on the same blade, is this hard to explain?

[Fancier]

I've got a knife made of O1, it exhibits both chipping and wire edge. I've always thought that a wire edge was due to the knife being soft enough to be ductile, and chipping to be due to higher hardness to the point where the type of failure changes from plastic deformation to fracturing.
Is it likely that these two different types of edge flaws are found on the same knife due to different stresses being applied to different points on the knife?
I've been whittling with the knife (although it is ground pretty thick) and sharpening out the defects with a diamond hone about four times.
I've had to be very careful when sharpening to remove the very fine but persistent wire edge, and yet it will still show small chips the next time I sharpen it.
This is a 5" by 1" by 3/16" blade of forged O1 and it was ground very thick as a "survival" type knife. I put primary bevels of about 15° per side on it when I received it.
I'm going to increase the bevel angle to see if I can reduce the chipping, but it still needs a fine polished edge to remove the wire edge each time.

 

[retzius]

Your edge is too thin for the applications you have in mind. I would recommend at least a 20 degree edge and start there. When the edge is thin and you have a wire edge, it is easy for pieces of steel to be pulled out and damage the edge when it is stressed. The only knives that I would be willing to put a thin (15 degree) edge and use them for those tasks would be some steel with a much higher hardness (not toughness) like S30v etc.

 

[chiral.grolim]

I've got a knife made of O1, it exhibits both chipping and wire edge. I've always thought that a wire edge was due to the knife being soft enough to be ductile, and chipping to be due to higher hardness to the point where the type of failure changes from plastic deformation to fracturing.
Is it likely that these two different types of edge flaws are found on the same knife due to different stresses being applied to different points on the knife?
I've been whittling with the knife (although it is ground pretty thick) and sharpening out the defects with a diamond hone about four times.
I've had to be very careful when sharpening to remove the very fine but persistent wire edge, and yet it will still show small chips the next time I sharpen it.
This is a 5" by 1" by 3/16" blade of forged O1 and it was ground very thick as a "survival" type knife. I put primary bevels of about 15° per side on it when I received it.
I'm going to increase the bevel angle to see if I can reduce the chipping, but it still needs a fine polished edge to remove the wire edge each time.

Your edge is too thin for the applications you have in mind. I would recommend at least a 20 degree edge and start there. When the edge is thin and you have a wire edge, it is easy for pieces of steel to be pulled out and damage the edge when it is stressed. The only knives that I would be willing to put a thin (15 degree) edge and use them for those tasks would be some steel with a much higher hardness (not toughness) like S30v etc.

1) Is this a "Scandi"-grind? If not, then the edge-bevel is the secondary bevel, not the primary.

2) Wire-edges are the result of sharpening technique and have little bearing on the hardness of the material, ductility, etc. To eliminate the wire-edge, try improving your sharpening technique, plenty of tips around the web.

3) The chips you observe could be the result of edge tear-out initiated by the fragile wire-edge - stressed material will fracture where a fracture is already present, i.e. propogation. But are you sure that you are observing chipping rather than compression? If the edge is compressing, then it is ground too thin for the hardness. Leaving more support metal behind the edge - after eliminating the wire-edge - should reduce edge degradation.

4) S30V is not innately harder than O1 and certainly does not make a better steel for "whittling". I would recommend O1 well above S30V at 60 Rc. for whittling as it presents more than twice the toughness to resist fracture from twisting and prying with a fine edge - S30V is brittle in comparison and would present much more damage from the same use.


Something you might also consider is your whittling technique. Using a blade so thick and wide for such a task is unwise as your leverage against the edge is pronounced. Whittle with an SAK or other small blade instead. I have never had a problem with 15-dps and even lower on such blades in such use. Or, as recommended above, put a more obtuse and cleaner edge on your knife. My $0.02.

 

[ryxlyx]

For what it's worth I have a small O1 patch knife that I assume has a bad heattreat cuz the edge turns completely over after cutting just a few small twigs-- like 3/16" dia max. Edge too thin on this one? No, it's plenty stout-- I fully convexed it.

Perhaps possible in your case as well?

 

[Fancier]

Thanks for your input, this knife is kind of an experiment for me. It is not Scandi ground (it is not a "zero bevel" knife) but rather the knife is ground to a fairly thick edge and then I've placed a single bevel on each side of it. Since I'm free handing the sharpening there is a limit to how precisely I can sharpen it, so obviously it is not perfectly beveled. I have knives and machetes in other low alloy steels, and other knives in very high alloy steels, but this one I think was heat treated by an enthusiastic amateur so I've been experimenting with it to see what it can do. It is entirely possible that what I'm calling a very small chip could be a compression deformation, I'm inspecting with a 10x hand lens and the flaws are too small for me to resolve clearly.
I am seeing more tendancy to wire edge while sharpening this knife than anything else I own, but I must admit that I don't inspect the edges on my machetes this closely. My Mora wood carving knives sharpen much more easily and do not exhibit these sorts of edge failures while performing similar wood carving tasks.

 

[chiral.grolim]

...I have knives and machetes in other low alloy steels, and other knives in very high alloy steels, but this one I think was heat treated by an enthusiastic amateur so I've been experimenting with it to see what it can do. It is entirely possible that what I'm calling a very small chip could be a compression deformation, I'm inspecting with a 10x hand lens and the flaws are too small for me to resolve clearly.
I am seeing more tendancy to wire edge while sharpening this knife than anything else I own, but I must admit that I don't inspect the edges on my machetes this closely. My Mora wood carving knives sharpen much more easily and do not exhibit these sorts of edge failures while performing similar wood carving tasks.

It is entirely possible that the HT is flawed - chipping means insufficient austemper, compression/folding means excessive austemper - but eliminating other possibilities first is a good way to go.

If you are polishing to a fine edge, tear-outs & chips are less likely when simply carving wood, compressions & fold-overs would be more common but should be visible to the naked eye along the edge using the "glint" technique. I cannot see it so cannot help you there.

The Mora's sharpen easily and cleanly because a) they are correctly hardened to ~60 Rc and b) they are very thin, light, narrow blades. Since they are so thin, less material needs to be removed to re-establish a worn edge; and since they are narrow, it requires more user force to impart significant lateral stress on the levered edge; and being light makes the user more aware of the force they are imparting on the edge.

The thickness of the edge of the problem-knife may also be part of the reason you notice the wire edge - more metal being moved means a more prominent wire-edge after grinding each side. I have hatchets and machetes made of the same steel, and the hatchet definitely forms a more prominent 'wire' during sharpening despite higher hardness. *shrug*

Again, I am not saying that the HT isn't the problem, just that there are other possibilities that one might eliminate first. O1 is great carving steel, never let anyone tell you different

 

[Fancier]

Let me see if I'm following your logic because I've never tried this out. Would you expect a Scandi ground knife (with a long single bevel being sharpened) be more likely to show a more noticeable wire edge during sharpening than the same knife with a second (less acute and shorter) bevel added to it?

 

[Grease]

I've got a necker made of O1 with a really thin edge, and whittling has never left a mark on it before...

Heck, I had a friend try to saw through wire with it yesterday eek and it didn't hurt the edge beyond a bit of normal dulling.

Regardless of what is causing the problem, your steel definitely has a problem.

 

[ryxlyx]

Since I'm free handing the sharpening there is a limit to how precisely I can sharpen it, so obviously it is not perfectly beveled.

I freehand as well. Since we both are unable to duplicate the angles exactly w/ repeated strokes we end up w/ a "domed" bevel in cross-section-- as opposed to flat (and of course, concave physically impossible). That means we by definition end up w/ a stouter edge. Perfect beveling (LACK thereof) not the issue here.

 

[awestib]

Can only second "chiral-grolim". The wire edge is not a problem (I mean it is but ...), it's a product of sharpening and "left over" if not completely cleaned after grinding in a new edge. Now in regards to your chipping, you may be brave enough to try an edge flex test. The edge should flex and go back upon relief. Take a look into and at your chipps! Are they round and regular and is the grain of the chipp a dull gray color, not granular (not like sand)? Use a lupe. If yes, you likely "overused" it. There is a great youtube video from Murray Carterabout this very thing: http://www.youtube.com/watch?v=dU3ALY8OmZk

 

[Fancier]

I'll have to think about whether I'm ready to flex a 3/16" piece of hardened steel just to see what happens.

 

[chiral.grolim]

You don't flex the blade, just the edge. The video awestib posted is a great submission :thumbup: Here is an example of a poorly manufactured knife (over-tempered after hardening) subjected to the edge-flex test: http://www.youtube.com/watch?v=p4ss8NtqEkw

Now, if the edge of your knife is too thick (>0.05" behind a 1/8" bevel) then this test may not work for you... on the other hand, if your edge is that robust and is still compressing or chipping on wood, the steel is faulty.

 

[Morrow]

Moving to MT&E.

 

[Jason B.]

I freehand as well. Since we both are unable to duplicate the angles exactly w/ repeated strokes we end up w/ a "domed" bevel in cross-section-- as opposed to flat (and of course, concave physically impossible). That means we by definition end up w/ a stouter edge. Perfect beveling (LACK thereof) not the issue here.

Angle of the apex still rules.

Convex does NOT translate to stouter, stronger, or tougher. It's actually thinner.

 

[Fancier]

Okay, I just viewed those two videos and I must say they both made me cringe. I'll put my knife in my work bag so I can put a caliper on it tomorrow and see how thick behind the edge it is, but it is vastly thicker behind the edge than either of those. I also now have a new (much different) appreciation for how bad chipping can be. Yikes!

 

[chiral.grolim]

Angle of the apex still rules.

Convex does NOT translate to stouter, stronger, or tougher. It's actually thinner.

You KNOW that this is false, you are taking the idea out of context.

A convex edge is only thinner if you leave the apex intact, i.e. simply knocking off the shoulders during sharpening and pushing the secondary bevel much higher up the blade.
But the context here is maintaining the same bevel height. To thus accomplish a convex edge, the apex must be knocked back as well, just as if you added a tertiary microbevel to the blade (which is exactly what you are doing). You cannot add metal the edge, only subtract. The result of convexing the edge is that the thinner flat-ground edge is removed, replaced by a more obtuse convex edge, an edge with more support-metal behind it - "stouter, stronger, tougher", "putting more metal behind the edge" than was previously present by removing the thinner extension.
After establishing this stouter edge and maintaining the same bevel-height, resharpening convex means "leaving more metal behind the edge" compared to grinding it flat.


When comparing convex and flat bevels, bevel-height and shoulder-thickness must be maintained, otherwise you are not comparing similar geometries. If bevel height is not maintained, then you might as well be comparing completely different flat-ground edges, why bother bringing convex into it?

 

[Fancier]

The thickness behind the edge on this particular knife is 0.04" and I was not able to cause chipping by forcing the edge sideways onto a hard rounded plastic surface.
I think I'm going to call this a good educational experience and stop tormenting this knife. Thanks for all of the advice!

 

[Jason B.]

You KNOW that this is false, you are taking the idea out of context.

A convex edge is only thinner if you leave the apex intact, i.e. simply knocking off the shoulders during sharpening and pushing the secondary bevel much higher up the blade.
But the context here is maintaining the same bevel height. To thus accomplish a convex edge, the apex must be knocked back as well, just as if you added a tertiary microbevel to the blade (which is exactly what you are doing). You cannot add metal the edge, only subtract. The result of convexing the edge is that the thinner flat-ground edge is removed, replaced by a more obtuse convex edge, an edge with more support-metal behind it - "stouter, stronger, tougher", "putting more metal behind the edge" than was previously present by removing the thinner extension.
After establishing this stouter edge and maintaining the same bevel-height, resharpening convex means "leaving more metal behind the edge" compared to grinding it flat.


When comparing convex and flat bevels, bevel-height and shoulder-thickness must be maintained, otherwise you are not comparing similar geometries. If bevel height is not maintained, then you might as well be comparing completely different flat-ground edges, why bother bringing convex into it?

No, If you convex a "v" edge it is thinner that it once was. I know exactly what I am talking about and thus the reason I made the comment, but, I've been in this battle before and know the direction so I will leave it at that and wish all the best.

 

[chiral.grolim]

For anyone confused by knifenut1013, here is a edge-bevel cross-section diagram for clarification:

Cross-section (A) shows convex- (violet) and flat-ground (gray) bevels with comparable (i.e. similar) geometries = equal height and shoulder width. One can imagine each profile being ground from identical billets. Note which profile leaves more metal behind the edge.

Cross-section (B) demonstrates how one would grind a comparable convex bevel (violet) out of an original flat-grind (pink). Again, the gray represents reducing the convex bevel back to flat while matching the geometry (height and thickness) of the original (pink) bevel. The gray and pink profiles are identical, the violet profile is comparable... and it is thicker than the gray profile from apex to shoulder, requires less removal of material from the original pink profile.

Cross-section (C) shows the original convex grind (white, violet-outline), reduction to flat-grind (pink), and further reduction to knifenut1013's thinner convex grind (violet). What knifenut1013 wishes to point out is that the violet edge is thinner than the pink at the pink shoulder. Quite so. However, 1) from apex until the orange line denoting tangential separation (~1/2 the height of the pink bevel), the violet convex grind is STILL thicker than the pink flat-grind (pushing the apex of the violet grind to match the pink would obviate this fact), and 2) the pink and violet bevels do not have similar geometries - the pink is as different from the violet as it is from the gray. As before, the true comparison is between the violet and the gray - bevels of equal height and shoulder thickness. If the pink and violet shoulders where at the same height, the entire violet blade would be thinner as well (assuming the same primary bevel angle and total blade height)!

If you are not measuring edges of equal height and thickness, what are you measuring? Convex apex angle?? Unlikely - No one does this. Instead, width of the blade and distance from spine-center to hone is measured, using a semi-flexible hone. Using the flexible hone, the convex apex (violet) will always be more obtuse than the correlated flat apex (gray), which is the entire point (pun intended) - a more robust edge for a given bevel height & thickness. One CANNOT thin from a flat bevel to a convex bevel without widening the bevel, i.e. establishing an entirely different bevel. Conversely, one CAN thin from a convex edge to a flat-edge while maintaining the same bevel dimensions, reducing the apex angle.

In practice, if you want a thinner edge, widen the bevel - lowering the spine-to-hone distance accomplishes this (creating a lower apex-angle). If you want a more robust edge, either reduce the bevel height (raising the spine-to-hone distance accomplishes this, creating a more obtuse angle) OR sharpen convex and maintain the same bevel height (same spine-to-hone distance).

 

[Jason B.]

Like the diagram shows, you can't add metal.

In practice, if you want a thinner edge, widen the bevel - lowering the spine-to-hone distance accomplishes this (creating a lower apex-angle). If you want a more robust edge, either reduce the bevel height (raising the spine-to-hone distance accomplishes this, creating a more obtuse angle) OR sharpen convex and maintain the same bevel height (same spine-to-hone distance).

So because when you sharpen convex you make the apex more obtuse due to held angle suddenly everyone sharpens convex in this way? If you change the angle you change many factors, if you simply sharpen convex while maintaining the same apex angle you only change the shape.

You are trying to factor in angle when we are only speaking of shape.