Poor edge retention / apex stability

[supergrind]

Hello community!

For a while now, I noticed something when sharpening my knifes: I can get them shaving sharp, down to about 80 - 100 Bess. When I make a quick cut test through cardboard (20 straight cuts against the grain), I loose the shaving sharpness and the edge deteriorates to a Bess score of around 250 - 300. This raises some questions. Maybe that deterioration is perfectly normal because cardboard is just very abusive, or, I could have a micro burr on the edge that initially gives me a low Bess reading, but then folds over when cutting.

The problem is, that I don't have any kind of reference because on Youtube, so many only test the newly sharpened edge but not how it behaves after some stress.

What do you guys think about this? Is this kind of deterioration in the normal range or do I have a problem?

My background:
I sharpen on a Tormek T8 with CBN wheels and deburr on a felt wheel with 1 micron diamond paste, then manually on a natural leather strop. I check sharpness on the Bess machine and the edge angle through a Goniometer. Also I just got a digital Tomlov microscope for visual reference.

 

[115Italian]

What blade steel is the knife? Have you tried cutting the cardboard then stropping the blade and testing it again?

 

[supergrind]

What blade steel is the knife? Have you tried cutting the cardboard then stropping the blade and testing it again?

I tried different steels like D2, Sandvik, VG10 and others. I can strop it back up almost to where it was after the initial sharpening. But I'm not experienced enough to interpret that behavior. Maybe it's perfectly normal that edges behave that way after 20 cardboard cuts, but maybe I have a problem and there is room for improvement. That's what I'm trying to find out.

 

[Obsessed with Edges]

Cardboard can definitely be abrasive. I wouldn't expect most any blade to retain shaving sharpness after cutting much cardboard at all. But it's also possible there's a wire edge (burr) that's folding over too. That would explain why you're able to strop it back to nearly as sharp, as the stropping is likely realigning the folded wire/burr at the edge.

If you couldn't strop it back into shape, that would point more to abrasive damage done by the cardboard, blunting the apex. It would take regrinding of the edge to get it back.

 

[Twindog]

Obsessed makes some good points, but it's difficult to tell how much cardboard you're cutting. 20 cuts seems like a lot more than a test. And I tend to be skeptical of Bess tests.

Another possibility is that you're leaving what Dr. Vadim Kraichuk [Knife Deburring: Science behind the lasting razor edge] calls a "root burr." You may be removing the more malleable top of the burr, but leaving the lower root. The edge-trailing burr removal at high speed tends to create a taller burr that is malleable at the top but more attached to the apex. The method you're using to deburr is more likely to leave an apex that is formed from the root burr. That kind of apex won't last as long as it should.

You might try to deburr your machine edge with some very light edge-leading passes on a hand stone with a high grit. Don't make long passes, because you'll just create a new burr. And alternate passes from one side to the other -- one on one side of the edge, then one on the other. Lighter and lighter, shorter and shorter strokes. Use a jig to hold the angle, unless you're very good at that from muscle memory.

Then finish with a light manual stropping -- just a light stroke or three at edge angle to refine the apex.

Then try your test.

 

[Obsessed with Edges]

I'd also 2nd the above^ suggestion to deburr with very, very light edge-leading passes on a fine stone.

I like to use a ceramic hone for that - I use a Sharpmaker with either the medium or fine rods according to preference. I also raise the angle slightly to create a very minimal microbevel in no more than a couple light passes per side, also done at the lightest touch I can manage. That goes a long way toward improving edge strength and stability while also narrowing the apex width a little bit for fine cutting. That's my favorite edge-finishing method. I prefer it over stropping with compound, in fact. Any stropping I do these days is just on a bare leather belt, essentially for cleaning up any light, fragile remnants of burrs still barely clinging to the edge.

 

[cudgee]

Any stropping I do these days is just on a bare leather belt, essentially for cleaning up any light, fragile remnants of burrs still barely clinging to the edge.

Stitchawl used to say the same.

 

[SwissHeritageCo]

Cardboard kills a keen edge pretty quickly.

What I have noticed though, is that my convexed edges seem to have superior edge retention to my V edges. Could just be the geometry and lack of shoulders doing the heavy lifting, but it's a very noticeable difference to me.

 

[elevator man]

This is my experience. It matters how you sharpen and deburr. I was never happy with s30v on sharpmaker stones. Switched to diamonds was happier, but still not happy with it so I got some hard high wear resistance tool steel knives, sharpening on diamond. I had learning pains as I dealt with the best steels not living up to their potential. The problem for me was a burr and it failing, 1000x quicker than the edge should've. I eventually found a combination that works wonders for me is apexing by developing a burr on my coarse stone. Then I refine the edge on finer stones with edge leading strokes only. Then I finish deburring by stropping on a compressible substrate (for me denim) with diamond paste/spray. I believe the compressible part is the most important in deburring. I had constant burrs/edges failing when I stropped on balsa wood. I now look at stropping as a primarily deburring step. Now I can finish an edge, cut hanging hairs, and then pop zip ties, carve plastic, cut cardboard with nothing happening to my edge.

I will say I'm not sure about alot of steels. I am pretty sure I'm spoiled that my "normal" is a 65 hrc tool steel with roughly 17-23% vanadium. But my knives don't care much about cardboard and if I cut enough to loose some keeness a pass or two on the strop brings it back. I tend to loose edges by cutting real dumb stuff or alot of stuff. I think if your loosing that much sharpness after some cuts in cardboard it's either a burr or could just be a lower wear resistant steel. You could definitely take steps to rule out the burr part.

I found the articles at science of sharp helpful and changed my opinion on the reason for stropping by his info on using a hanging denim strop to deburr the razors he uses.

 

[RustyIron]

For a while now, I noticed something when sharpening my knifes: I can get them shaving sharp, down to about 80 - 100 Bess.
When I make a quick cut test through cardboard (20 straight cuts against the grain), I loose the shaving sharpness

Expecting to chop up cardboard boxes and then get a good shave is a bit optimistic.
Even Jon Snow had to hone his Valerian steel sword after chopping up whitewalkers.

 

[Alberta Ed]

Fine edges don't hold up to abrasive materials like cardboard. Game animal hides are also very abrasive due to sand/silicon embedded in the fur. Making the initial cut when field dressing can take the edge off the best steel.

 

[Gottagofishn]

I have found similar results in that edges sharpened to below 100 on the BESS don’t last very long. In the De-Burring book the late great Vadim stated that if there is a burr, wire or foil edge it should affect the results measured by the BESS as the media would crush the edge and result in a higher reading. I am not able to see a burr after sharpening with a microscope. Stropping restores the low BESS readings in my knives.
I suppose it could be the burr root… Has anyone used the process Vadim described in his book for removing the root and tested the results?
Al

 

[777 Edge]

Maybe that deterioration is perfectly normal

Yep, completely normal and to be expected, even for high edge retention steels. What happens after that initial drop in extreme sharpness, and how long it holds a usably sharp every day edge is where the big difference in steel types and edge types lie.

 

[777 Edge]

Game animal hides are also very abrasive due to sand/silicon embedded in the fur. Making the initial cut when field dressing can take the edge off the best steel.

Yep, I second that. Even my Rex 121 knives need a quick resharpening after only one whitetail deer.

 

[garry3]

I skinned and quartered my elk and half my partners this year with a knife in white steel no2. I carry a diamond sharpener for quick touch ups but never had to reach for it, I would have had I tried to do both elk by myself.

 

[chevyrulez1]

Cardboard kills a keen edge pretty quickly.

This has been my experience as well. Short of dragging your blade across a brick, cutting cardboard is one of the quickest ways to dull a knife. On the flip side, a good flat piece of cardboard makes a pretty good strop due to the abrasiveness of the material.
I no longer use my knives for cardboard for this reason and either use a utility knife or jiffy cutter for that. I will use my knife in a pinch but don't like to because of the dulling and getting tape, glue, etc. on the blade.