What really dulls your knives?

[Dorito Monk]

Most folks are probably familiar with edge retention tests where someone makes hundreds of consistent cuts through manilla rope, cardboard, or some such material to test how long a certain steel will hold its edge. Recently, though, I've been questioning the relevance of those tests to my particular knife needs,.

Something I've noticed about using my knives at work is that my knives rarely ever get dull from making repeated clean cuts through a consistent medium. Instead, it seems that my knives get dull almost exclusively from brushing against, say, a staple that I didn't notice, a knot or old nail in a piece of wood, or some sand and dirt that had worked itself into a piece of rope.

This realization caused me to question my need for a steel with really exceptional edge retention - For me, it would seem that it doesn't matter too much whether a steel can make 50 or 5000 passes through a sheet of cardboard before getting dull. Practically speaking, it seems like there always comes a point where I run into one staple or other unseen obstacle and my knife's edge gets dull, no matter how fancy the blade steel. Thus, while I notice a major difference between low end steels (420, 8c13 etc.) and mid-to-high end steels (14c28, 154CM etc.), I don't think that I personally would benefit from the added edge retention capabilities of super steels like CPM-M4, Bohler M390, ZDP-189, etc.

This is just something I've been thinking about over the past couple of weeks, but I'd like to hear your thoughts. For your applications, do you folks find that there is a point where you no longer see a real benefit to more advanced steels, or do very high end steels have real practical benefits for you?

 

[jimnolimit]

based on what you said, i think you would benefit from a steel like CPM-M4. it's pretty tough so the edge really won't chip. if done right, it's hard (around 62-63HRC) and it shouldn't deform. it's very wear resistant, so it will hold and edge for a good while. pretty much the only draw back is that CPM-M4 isn't stainless, but it won't rust/tarnish as fast as a basic carbon steel. for example: if i have some cardboard cutting to do and staples might be a problem, i would break out my CPM-M4 manix2. there are other steels that will also suit your purpose, but another major factor it blade geometry. blade geometry will drastically effect the performance for any steel under specific situations.

the way i look at is like this: you should pick the steel and design to fit the purpose. there are usually trade-off's when looking for specific qualities.

 

[upnorth]

Generaly I find the cheaper (within reason) steel lower priced production knife easy to sharpen, but needs it more often. Higher end needs sharpening less often and holds the edge longer. I have both and like both. I find myself looking more at grind angle these days as a deciding factor. I don't mind touching up AUS8 on a FFG blade as it's usually a quick job.

 

[Noctis3880]

Given that I make an effort to avoid nails and staples when cutting cardboard, I find I enjoy not needing to sharpen my knife for over 3 months rather than every other week with the lesser 12C27.

Still, the reason why it doesn't matter whether I'm using S30V or S90V is more because I don't go through enough cardboard during my day job to be able to tell the difference.

And have you noted whether your edge is chipped or rolled when you run it into a staple? Because it sounds like CPM-3V might be better suited for accidental run-ins with metal.

 

[hiwa]

Good post topic DM.

I really have no problems sharpening on a regular basis so extreme edge holding and having super tough steels that are more difficult to sharpen to me is not something I prefer. I'd rather have a knife that cuts pretty decently through most stuff , but is not a pita to sharpen.

I find cardboard dulls my knife quickly ; so does anything with dirt on it. This includes dirty sticks in the bush. Carpet , drywall , thick plastic ...those sorts of things. Hitting a piece of metal is something I really try to avoid unless I'm doing it with a knife specifically for a reason. Then I know the edge will definately suffer. I'll only do it with a beater knife if I can help it ( opening a can , sheet metal , etc..)

But sometimes the knife you have on you is just pressed into a needed situation and you just do it no matter what the medium is. I'd much rather chew up an edge that I can easily restore , compared to some super steel that will take me hours on the stones ( or worse , blow a big chunk out of the edge) Just my .02

 

[jimnolimit]

i got to thinking, i wonder how CPM-M4 would handle hitting a staple. then i decided to kick it up a few notches and see what would happen to CPM-M4 under worse than just a "hit a staple" scenario.

i used my M4 manix2 for testing. the bevel is around 15-18 degrees per side, sharpened on a 1500-2000 fine ceramic stone and lightly stroped with 2-5 micron white buffing compound.

for the test i used the bottom of a coffee can and decided to cut through the rim.

it took three tries, i changed the angle while i was cutting it. as you can see i used a lot of pressure to cut through the rim, much more than anyone would ever hit a staple with.

here is the edge before cutting (375x)

here is the edge after cutting (50x)

here is the edge after cutting (375X)

here is the edge after i gave it 30 swipes on the fine ceramic (15 per side) and 20 strokes on the strop (10 per side). re-sharpening took maybe 30-40 seconds.

at 50x

at 375x

the knife shaves stubble off my arm and push cuts thin newspaper after sharpening.

 

[Reeek]

Sometimes I feel like my EDC gets dull from air. Literally, when I strop up a folder to hair popping sharp and I test it again a week later with no use, it doesn't feel as sharp as it did after the stropping. Maybe the edge rolls from temperature flucuations. Who knows.

 

[EricV]

For me I think I've found a balance with Spyderco's s30v if we're talking plain edge, and their old 440V if we're looking at a serrated knife. The s30v is easy to touch up with a pocket diamond stick/plate but holds a good edge even through the silted up rope I cut thats hell on an edge. The 440v in SE is just a beast for rope/fabric/anything soft and gritty but it'll chip a bit if you try cutting something harder and tougher (like the stainless cable ties I sometimes cut with my para2 )

 

[Joshua J.]

For most of my life my knives usually did dull on some horrible, un-cuttable thing. In the last year or so I have been doing much better though, I have effectively separated my knives into "beaters" and "cutters", and I think I hit some sort of critical mass where I always have a beater handy for stuff I don't want to risk my sweet thin edges on.

 

[jimnolimit]

i decided to baton the M4 manix2 through the coffee can rim. so after plunging the knife through the steel and batoning it, the CPM-M4 still cut through thin newspaper.

here is the edge at 50x

here is the edge at 375x

i re-sharpened the blade, 30 swipes (15 per side) on a the fine ceramic (1500-2000 grit) and 16 strokes on the strop (2-5 micron white compound), i can't find any evidence of what i just did.

here is the spot at 375x

 

[knarfeng]

I dunno. I test alloys because I am curious about the differences, not because I need extreme performance in my daily usage. In my daily use I am happy with any number of alloys, everything from 420HC to M390, and I sharpen them as necessary.

 

[stabman]

Fiberglass insulation.
That stuff will dull your knife up really well. It shows what steels have better edge retention--and which manufacturers do a better heat treat--in a hurry.

 

[jbmonkey]

Fiberglass insulation.
That stuff will dull your knife up really well. It shows what steels have better edge retention--and which manufacturers do a better heat treat--in a hurry.

Yes Sir. Cutting a more dense fiberglass medium like ductboard used in ductwork for heating\air conditioning will kill a razors edge no matter the steel in allot less cuts than most would expect.

 

[ocnLogan]

I really like this thread, especially the photos of the edge of the blade after cutting through the can (props for that, I found it very interesting). I also agree with the comments about how anything dirty, or that contains fiberglass really dulls an edge.

That said, I unfortunately still EDC a gerber paraframe right now, so pretty much anything dulls it, no matter what .

 

[Alberta Ed]

The worst medium I ever found for dulling an edge was dirty, gritty animal hide: moose and bear, specifically.

 

[Bill1170]

Cardboard and fiberglass insulation do a real job on a fine edge, but often my work knife gets dulled by the need to cut right next to tile or steel, etc and the edge bumps the hard stuff. Old carpet is awful, but I never need to cut it with my folder, use a utility knife instead.

 

[generallobster]

Cutting sandpaper to resharpen the knife that's cutting it.

 

[Ankerson]

I cut mostly cardboard, and it will and does vary a lot in how abrasive and tough it can be.

 

[JPD1998]

Yes cardboard and some heavy fabrics like canvas or carpet backing will dull a knife pretty quickly.

 

[singularity35]

Yep, I dulled my knife peeling 5 pounds of potatoes. That dirt really did a number on my edge.