Very poor edge retention when cutting cardboard

Z

Zenturio

Joined
Aug 7, 2017
Messages
171
Hi folks,

at the moment, I am a little desperate about the performance of my knives when cutting cardboard.

Please note that I am not a sharpening novice, I am very experienced.

Normally, I sharpen most of my knives 15dps bevel and 20dps microbevel. Things like burr minimization, edge destressing etc. are included in my routine.

When I get a new knife, I will test the factory edge and after that I will do my normal sharpening routine (mostly guided system with diamond plates 220#, 600# and 1000#, burr minimization and microbevel freehand with a 1200# diamond plate; Sometimes I use the sharpmaker brown rods). After these steps, all knives will easily shave armhair in both directions, sometimes hair whittling is not a problem. I want my edges quite toothy but exactly done.

In particular, I tested my Spyderco Shaman S30V yesterday (sharpened as said above). After a few meters of cardboard, the knife was extremely dull. Even had a microchip. I did another 2 sharpenings, but nothing was improved.

So I did the test with a Para 3 in S45VN and a CS Recon 1 Tanto in CTS-XHP. I had very similar results.

I repeated the test with the Para 3, but I used Cliff Stamp's Plateau Sharpening method instead. No improvement.
After that I sharpened the Para 3 freehand with a DMT 600# plate, did bur minimization (was able to shave armhair cleanly off the plate) and stropped with 5µm diamond emulsion. The edge was agressive but also push-cutting-telephonebook-paper sharp.
Even with that method I gained no improvement. After let's say 5-10 meters of cardboard the sharpness decreased to about 30% of beginning sharpness.
__

I did also edge stability tests before the cardboard test to check for burrs and chips. All knives passed those tests (cutting through very hard wood, even with twisting into the wood and cutting/twisting through heavy zipties). All knives did not chip and did not lose any sharpness. And that is the point where I do not understand what is going on exactly.

Do I have problems with micro burrs or is the cardboard I got extremely abrasive?


Maybe you can help me out ;)

Thanks in advance and BR,
Oliver
 
I have not been impressed with Spydercos S30v. Is is possible that some of these knives still have the burned edges from factory sharpening? Or maybe your expectations are off. Try some M4 and see how it does.
 
Thanks for your quick answers.

eveled eveled : That really could be. Maybe because of worldwide saving politics/recycle politics the newer cardboard contains more abrasive media; I really do not know.

D DMG : I do not think that the edge is still suffering from overheating. Production Date of the knife is November/2023.
S30V may not be the best edge retention steel, but from experience and what I have seen from others, it should do better, same counts for the other knives tested.

K ktataragasi : I have a 15X loup; I will try to take a picture after the next sharpening and share it with you. But I do not understand why all knives pass the edge stability tests.


BR,
Oliver
 
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I don’t do any science and angle stuff but you can forget all the edge retention princess stuff with cardboard. I use AUS 8A and it works fine for week or two in active use depending on how sharp I want the edge to be or how lazy I am to sharpen. Then you just sharpen quickly in about five minutes and get something else to do.
 
I'm not familiar, personally with your steels, but I cut A lot of cardboard....

I agree with DMG with trying M4.

I haven't tried it yet, but I use M2 often and it screams through paper and cardboard all day, no issues....... And M4 is "supposed to be better"
I can't imagine how awesome it must be.

*also I sharpen to much more acute angles. Less than 15
M4 should be able to handle it
 
Zenturio said:
Thanks for your quick answers.

eveled eveled : That really could be. Maybe because of worldwide saving politics/recycle politics the newer cardboard contains more abrasive media; I really do not know.

D DMG : I do not think that the edge is still suffering from overheating. Production Date of the knife is November/2023.
S30V may not be the best edge retention steel, but from experience and what I have seen from others, it should do better, same counts for the other knives tested.

K ktataragasi : I have a 15X loup; I will try to take a picture after the next sharpening and share it with you. But I do not understand why all knives pass the edge stability tests.


BR,
Oliver
Click to expand...
One thing I was just thinking about. Have you done a cut test right off the sharpening system? I saw that you do a few passes freehand and you may be creating a burr at that step. It's just a thought.

I have done freehand as well as systems and I have a much harder time with burrs freehand.

Hope you get it figured out.
 
My EDC SAK holds up pretty well to cardboard with a 20 degrees per side edge angle. I have other knives that are made from budget steel and they do just fine too. I run 20 DPS on pretty much everything unless it's a scandi grind.

I'm reminded of a youtube video I saw with a woman complaining about how her brand new magnacut knife was having the same issue with cardboard. The edge just wouldn't hold up.

Long story short, after enough sharpening, the problem cleared itself up. The theory is that the heat treat along the edge was bad, and after enough sharpenings she eventually got down to some good steel. You may have the same issue.

I guess what can happen sometimes is that the heat treat gets ruined when they grind the edge on the blade because it gets too hot.
 
Cardboard is horrible on edges, and the blades that shine on them are the ones that are so thin that the edge geometry continues to cut after the apex is dulled.
Something like a SAK or box cutter will do well because of the thin blade stock.
The adhesive that is used in cardboard is derived from starch from what I understand and is full of grit. It is almost like cutting through a very fine sandpaper.
Cardboard makes a pretty good strop for this same reason.
I have stopped using my knives for Cardboard because I know it is just going to ruin the edge, I keep a Jiffi Cutter nearby for this purpose.
 
Thin blade geometry makes the most difference with cardboard. The edges can still get beat up by the dirt/abrasives in most heavy cardboard, much of which is notoriously dirty. So, what saves cutting performance in cardboard is more about how thin the steel is behind the apex, after the apex has been worn dull. This is why a box cutter blade works as well or even better than most EDC blades - because it's very, very THIN behind the cutting edge. They'll still lose shaving sharpness or other fine cutting abilities after use on cardboard. But the thin grind of a box cutter blade is what will keep it working. Cardboard binds up on the shoulders of thickly-ground cutting edges after the apex has dulled, and that's where cutting will cease with thick blades.

Of the EDC blades I have that've worked fairly well with cardboard, they're either very THIN grinds, or the thicker grinds have been thinly convexed & polished behind the edge, which helps the thicker grind sail through heavy cardboard without binding up. A shallow convex at a high polish helps the most, with a thicker blade.
 
They’re not putting anything new in cardboard that I know of. I buy tons of the stuff all day long and composition is heavily regulated, along with recycled content and recyclability.

The way I have seen some cutting cost on it is making it thinner or decreasing the thickness of the corrugated material, etc. Slightly decreases the edge crush test (ECT) value, but the composition does not change. The strength does.
 
chevyrulez1 said:
The adhesive that is used in cardboard is derived from starch from what I understand and is full of grit. It is almost like cutting through a very fine sandpaper.
Click to expand...

Interesting. I use a brown spyderco medium pocket stone to sharpen and touch up my SAK. I don't use anything with a higher grit.

Now I half-wonder if the cardboard is just polishing my edge. 🤣

Ah, but the tape gunk is another story. That stuff clogs my edge up in a hurry. Thankfully I made an awesome discovery a while back. "Odorless" mineral spirits are fantastic for getting that stuff off, and it doesn't dissolve the plastic scales on your SAK like isopropyl (medicinal alcohol, aka "rubbing alcohol") does.
 
chevyrulez1 said:
Cardboard is horrible on edges, and the blades that shine on them are the ones that are so thin that the edge geometry continues to cut after the apex is dulled.
Something like a SAK or box cutter will do well because of the thin blade stock.
The adhesive that is used in cardboard is derived from starch from what I understand and is full of grit. It is almost like cutting through a very fine sandpaper.
Cardboard makes a pretty good strop for this same reason.
I have stopped using my knives for Cardboard because I know it is just going to ruin the edge, I keep a Jiffi Cutter nearby for this purpose.
Click to expand...
When I was a little kid, my dad saw me cutting holes in a large cardboard box to make a play-fort out of it. He said “Don’t ever use your pocket knife to cut cardboard - you’ll dull the edge.”

Still solid advice some 50 years later :thumbsup::cool:
 
Box cutters exist.
Box cutters do not require sharpening.
Use a box cutter for boxes.
-This message brought to you by GenX.

Coming soon:
"I broke a knife batoning madrone."
Axes and hatchets also exist.
They're good for not batoning hardwoods with a knife, ya goofs.
 
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