What causes an edge to roll?

S

Squashfan

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Jun 6, 2012
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Finished sharpening a new to me knife yesterday. It was a Gerber Blackie Collins Bolt Action. I did most of the reprofile on the fine side on my AlumOx stone. BTW, it cut a lot faster than I thought it would. Then I went to my Medium and Fine Spyderco ceramic bench stones. They were both used with oil. Finally, I stropped it on a black then green copypaper strop over stone. I had to work really hard to eliminate the burr because I raised to large of a burr. Elimination took many light passes on the ceramics and strops. (I bet you guys can see where this is going...) Carried the folder to work to try it out. The edge preformed well on light duty plastic bags. Then, I tried some plastic straps. Plain ole plastic straps. I have a Camillus electrician's knife(sharpened by me) that has been cutting these straps for a lllooonnnggg time. Several months, that is. One cut with the Gerber generated a large bur/roll in the spot being used. I am not kidding either. I looked like the burr from a file or a very coarse stone.

What on earth caused this. I could see a small roll from a little remaining burr but this was out of proportion to any burr that would have been left. All I can think of is that I overworked the apex and it collapsed under strain. What do you guys think?
 
My 2 cents:

1. Burr wire edge that wasn't completely removed.
2. Improper heat treat.
 
I very seriously doubt that it is a bad heat treat unless the previous owner overheated the edge with a grinder. And afterwards started using a pull through. At least it looked like a pull through. It is possible that the ceramics generate a burr that is too small for me to feel/detect.
 
I agree with others on 'wire-edge'.

I suspect, you removed the gross jagged burr but leave behind the burr base = a large wire-edge. Perhaps during last few sharpening stages, you test cut printer or newsprint paper (at least 4 cuts), which would reveal whether your edge is clean or not.

Initially, I concur with Martin/HH on possibly too acute of an angle for hard-use. However recall from my experiences fragile edge usually chip or deform more than rolled.

Squashfan said:
Finished sharpening a new to me knife yesterday. It was a Gerber Blackie Collins Bolt Action. I did most of the reprofile on the fine side on my AlumOx stone. BTW, it cut a lot faster than I thought it would. Then I went to my Medium and Fine Spyderco ceramic bench stones. They were both used with oil. Finally, I stropped it on a black then green copypaper strop over stone. I had to work really hard to eliminate the burr because I raised to large of a burr. Elimination took many light passes on the ceramics and strops. (I bet you guys can see where this is going...) Carried the folder to work to try it out. The edge preformed well on light duty plastic bags. Then, I tried some plastic straps. Plain ole plastic straps. I have a Camillus electrician's knife(sharpened by me) that has been cutting these straps for a lllooonnnggg time. Several months, that is. One cut with the Gerber generated a large bur/roll in the spot being used. I am not kidding either. I looked like the burr from a file or a very coarse stone.

What on earth caused this. I could see a small roll from a little remaining burr but this was out of proportion to any burr that would have been left. All I can think of is that I overworked the apex and it collapsed under strain. What do you guys think?
Click to expand...

edit:
bad ht - not likely and ppl should get off this band wagon.
burnt edge - usual symptons = can't get a sharp edge or edge will dull if you breath on it.
v pull through - won't damage beyond visual for soft steels anyway.
 
Squashfan said:
I very seriously doubt that it is a bad heat treat unless the previous owner overheated the edge with a grinder. And afterwards started using a pull through. At least it looked like a pull through. It is possible that the ceramics generate a burr that is too small for me to feel/detect.
Click to expand...

Ceramics work great for the finer work, they (IMHO) do not have enough abrasive potential to remove burrs well off the finer grades. They tend to roll or stand up, better to eliminate as much as possible at a medium grit, in this case on the AlumOx stone, before moving on to the ceramics. Am not sure using them with oil is best practices either - might be better to use them dry and clean 'em off later.
 
A wire edge is a solid burr structure that is as solid as the rest of the knife. They are typically large and caused by excessively grinding one side with high pressure.

Burrs are more of a soft structure easily deformed and hanging from the apex.

bad ht - not likely and ppl should get off this band wagon. every time I hear "it's a bad heat treat" it becomes a instant facepalm moment. I agree people really need to get off that wagon.


My opinion to the OP, the steel is soft and you sharpened too to fine of a level for the hardness of the steel. Personally I'm not surprised by the outcome.
 
Squashfan said:
Finished sharpening a new to me knife yesterday. It was a Gerber Blackie Collins Bolt Action. I did most of the reprofile on the fine side on my AlumOx stone. BTW, it cut a lot faster than I thought it would. Then I went to my Medium and Fine Spyderco ceramic bench stones. They were both used with oil. Finally, I stropped it on a black then green copypaper strop over stone. I had to work really hard to eliminate the burr because I raised to large of a burr. Elimination took many light passes on the ceramics and strops. (I bet you guys can see where this is going...) Carried the folder to work to try it out. The edge preformed well on light duty plastic bags. Then, I tried some plastic straps. Plain ole plastic straps. I have a Camillus electrician's knife(sharpened by me) that has been cutting these straps for a lllooonnnggg time. Several months, that is. One cut with the Gerber generated a large bur/roll in the spot being used. I am not kidding either. I looked like the burr from a file or a very coarse stone.

What on earth caused this. I could see a small roll from a little remaining burr but this was out of proportion to any burr that would have been left. All I can think of is that I overworked the apex and it collapsed under strain. What do you guys think?
Click to expand...

The bolded part is textbook, to me, for softish steels with relatively low carbon and relatively high chromium content; in other words, low-end stainless like 420-variety and similar steels. That goes hand-in-hand with other points mentioned about too-thin edge angle and/or likely burr retention, which seems to happen all-too-often in steels like this. These tend to be very 'gummy' in character, so burrs/wire edges are very hard to eliminate completely, and easily re-form if too much lateral pressure is exerted on the edge. I always ran into the same issues when sharpening steels like 420HC on ceramics, in particular. I've since had much better results using edge-trailing technique on wet/dry sandpaper, which leaves much less of a burr/wire in the first place, and also does a much more efficient job in cleaning them up when they do form, in just a handful of passes (2-5, usually).

(I underlined the "I bet you guys can see where this is going...", because it's really that familiar to me; no kidding. ;) )


David
 
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So, the ceramics were a mistake on this steel. I suspect that this knife is 440A. I am going to try to reapex it with just compound on paper over a stone. I will let you guys know what the results are. Oh, and I would say that the odds off getting a poorly heat treated production blade are probably about the same as being struck by lightning.

QUESTION: What steels DO respond well to ceramics?
 
Squashfan said:
So, the ceramics were a mistake on this steel. I suspect that this knife is 440A. I am going to try to reapex it with just compound on paper over a stone. I will let you guys know what the results are. Oh, and I would say that the odds off getting a poorly heat treated production blade are probably about the same as being struck by lightning.

QUESTION: What steels DO respond well to ceramics?
Click to expand...

Depending on the 'touch' (light or slightly heavy), most can be OK. The thing with these softer & more ductile (gummy) steels is, they're just not as tolerant of a heavy touch, due to the burring/rolling issues. Same could be said about steels at very high hardness, which would risk chipping instead of rolling. Other steels in the middle ground, between too soft/ductile and extremely hard, are more forgiving if pressure is just a little more than feather-light. For me, I've noticed that steels like 154CM/ATS-34, 440C, D2, VG-10, S30V and others with fairly high carbon content (~1% or more), at mid-high hardness (mid-high-50s to low 60s RC) all seem easy to get along with, on ceramic hones. Having said all this, ceramics do still demand a careful touch, and no steel I'm aware of will tolerate very heavy pressure on ceramics. It's also easier to regulate pressure by using only the flats of triangular ceramic hones, instead of the corners, which multiply and focus pressure into a very small contact area.


David
 
I would like to see a photo, it would tell us a lot. It could be a wire edge hanging about or it could be poor heat treat. I've seen it to many times to discount it in mass.
If you are in doubt, try the brass rod test. A well heat treated blade will have an edge that will roll under pressure and return. It is easily observed with the naked eye. If the edge chips its overly hard if it distorts without returning to its inline position the edge is not hard enough. Of the 6 knives I sharpened yesterday for my neighbor the two Bucks were fine, the Old Henry was really hard, one large gut hook blade :( carried the best edge of all, the last one marked rigging knife would sharpen but would not hold up during use, it was way to soft. Doing the brass rod test will give you a lot of info about most all knife blades.
 
This is a full size Spyderco benchstone and I didn't know that I needed to dial back the pressure on ceramics. That was causing some of my problems right there.

Man, there is so much good info in this thread. I could spend a couple of hours just pouring over it and asking questions.


EDIT: I might could do a photo tomorrow. It won't be pretty though. I chewed up the shoulder of the logo side of the blade. And I just cut myself figuring out which side of the blade is logoed. I guess the black compound strop did some good this morning...
 
I just rolled an edge on a 9" blade cpm 3-v. 1.5" wide. Hacked on a privit bush branch that was no larger than a pencil. Edge was/is extremely thin, made for kitchen slicing. I'd say your edge was too thin for the work.
 
IMO - brass rod test would reveals certain desirable ht outcome for many knife profiles & steel types & intended usage. However there are knives heat treated to leverage high alloy steels (e.g. s90v; zdp189) and ultra/upper-range high hardness for fixed-set of tasks (e.g. kitchen petty/gyuto), for these instances a brass rod test might damage the edge. Elasticity (part of toughness + of course geometry/modulus too) add versatility to an edge but makers/mfg may traded that for additional strength (high rc) & wear resistance (lot of carbides), plus even willing to pay coarser grain penalty.

Fred, you are an expert in this field, easy for you to determine ht quality. But for non-expert, please use brass rod with caution, when in doubt DON'T DO IT, better ask first.

Fred.Rowe said:
I would like to see a photo, it would tell us a lot. It could be a wire edge hanging about or it could be poor heat treat. I've seen it to many times to discount it in mass.
If you are in doubt, try the brass rod test. A well heat treated blade will have an edge that will roll under pressure and return. It is easily observed with the naked eye. If the edge chips its overly hard if it distorts without returning to its inline position the edge is not hard enough. Of the 6 knives I sharpened yesterday for my neighbor the two Bucks were fine, the Old Henry was really hard, one large gut hook blade :( carried the best edge of all, the last one marked rigging knife would sharpen but would not hold up during use, it was way to soft. Doing the brass rod test will give you a lot of info about most all knife blades.
Click to expand...
 
As cylindrical object getting smaller, the larger the localized(due to small curvature) force on the edge. Hence small dry branches/vines/stalks are nifty damaging on your edge. I usually whack them using the spine.

sirupatespecial said:
I just rolled an edge on a 9" blade cpm 3-v. 1.5" wide. Hacked on a privit bush branch that was no larger than a pencil. Edge was/is extremely thin, made for kitchen slicing. I'd say your edge was too thin for the work.
Click to expand...
 
bluntcut said:
IMO - brass rod test would reveals certain desirable ht outcome for many knife profiles & steel types & intended usage. However there are knives heat treated to leverage high alloy steels (e.g. s90v; zdp189) and ultra/upper-range high hardness for fixed-set of tasks (e.g. kitchen petty/gyuto), for these instances a brass rod test might damage the edge. Elasticity (part of toughness + of course geometry/modulus too) add versatility to an edge but makers/mfg may traded that for additional strength (high rc) & wear resistance (lot of carbides), plus even willing to pay coarser grain penalty.

Fred, you are an expert in this field, easy for you to determine ht quality. But for non-expert, please use brass rod with caution, when in doubt DON'T DO IT, better ask first.
Click to expand...

Not an expert just someone with a lot of time invested. I agree about the high alloy steels or any blade for that matter. Some of them you can lean on, others must be approached with a much lighter touch. Experience does help to understand the amount of allowable pressure. Good associative post.

Fred
 
knife chop said:
How about power grinding? I've read that power grinding can over heat even an edge that has no burr.
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Correct. Its very easy to over heat an edge using a belt or anything moving at speed. The blade does not have to heat up; its the apex and just behind where the damage can be done. Example such as basic carbon steels, if you get the apex itself above 500 fh the hardness will begin to slip. Even if its only the surface of the edge that overheats you will end up having to remove this softened structure through sharpening before a true edge can be attained.
 
The blade steel for knives that have multiple production runs can vary by quite a bit. You might have gotten a blade with a softer temper. That with a finer edge, say 15 dps or less, and a bit of lateral pressure could cause the edge to roll. What angle do you have the edge at? What type of steel is the blade?
 
IMO, you set up a failure in the sharpening. Raising a large burr will leave damaged material under the burr. This will not be a problem for most, as they will remove the burr and continue refining and get past the damage. However, it appears you went too fine on the next step, and flopped the burr back and forth, exaggerating the issues with raising too large a burr in the first place. I cannot recommend reliance on stropping to remove burrs, except in the case of power stropping. I have not seen any advantage, and in most cases, the strop just doesn't remove them effectively.

To remedy the situation, try the following. Cut into a medium stone lightly 2 or 3 times to remove any damaged steel. Since the edge rolled, we know it's there, even if only in the spot you saw roll. Now sharpen on the coarse grit until the facet on the edge is no longer visible. Increase the angle considerably, nearly double, and make 1 or 2 light passes on each side using the Fine side of the Alox stone. The Spyderco medium stone might work ok too. This should remove any small burr that formed from the coarse grit. Now go to the medium stone and make a few passes with light pressure at the original angle or slightly above. Do this until the edge is sharp. Then repeat on the fine stone, and strop lightly if desired.

A sharpening problem should be easy to eliminate, so I'd try that first. If it's an overheated edge from the previous owner, you may have to rinse and repeat a couple of times to get past the overheated part. If the HT was blown, well, you're just stuck with it. If the hardness is too low, then there is nothing you can do to fix it short of rehardening the blade.

There are many who swear by it, but the brass rod test is another thing I've had no luck with on my knives. I've never had an edge chip, and only one knife has bent, and it was an experimental blade in annealed 1095 (HRc ~25). Every blade I currently use will pass, flexing visibly and returning to straight with no detectable damage.

Also, make sure you're Spycerco stones are clean. IMO (again) ceramic stones like this are best used for microbeveling. It will extend they're life, reduce loading, save time, and give a good edge that is quickly touched up.

The edge angle is, IMO, not that critical, as no matter the angle, there will always be some depth of steel that is thin enough to roll if you're getting a truly sharp edge. This is also another thing that's easy to check. It's pretty quick to increase the angle by a few degrees and try again to see if it helps. Lowering the angle is much more time consuming. I've made cuts on copper wire, heavy plastic (~0.06" thick), and old seasoned wood (70+years) with no rolling issues on a no-name stainless from Japan made in the mid 90's. The edge angle was 7 degrees per side with a 9-10 dps microbevel.
 
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