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Best Steel (and Angle) for Cardboard Cutting

Discussion in 'General Knife Discussion' started by Sharperthansticks, Dec 18, 2019.

  1. Sharperthansticks

    Sharperthansticks Gold Member Gold Member

    Sep 19, 2017
    I've been in the knife game for about 3 years now, and I've heard about and collected several, though certainly not all, of the new generation of steels -- the "supersteels." I have what many of you own: S30V, S35VN, S110V, S90V, and CTS-204P/20CV/M390. In watching videos and seeing how sprint runs are gobbled up and then resold on the secondary market, I've seen how Shabazz, Cedric and Ada, and everyone else bows to the triplet CTS-204p/20CV/M390.

    Here's my issue: I do a lot of e-commerce, so I use my knives to cut down boxes that contained packages. (I also cut down thick boxes that were used at Costco to hold my purchases.) After cutting only a few feet of cardboard, even my best steels are noticeably duller. What's my methodology for knowing that? I test the knife against the short edges of those Valpack coupons that I constantly get in the mail. So I take my S35VN or M390 (or D2 or whatever) and strop (using green compound) about 50 times on each side so that my knife is back to its previous sharpness, as measured by ease of cutting the coupons. I just did this a little while ago after cutting down one small box with my Wayfarer 247. Once small box dulled it!

    Is there a steel that will retain its edge against cardboard so that I won't have to constantly do these touchups? Should I be using Maxamet or Rex45 or something else, entirely?
  2. DeadboxHero

    DeadboxHero Triple B Handmade, Custom Knives Knifemaker / Craftsman / Service Provider

    Mar 22, 2014
    Gotta rule out the sharpening.

    Sounds like there may still be the base of the burr sticking straight up like a false edge and folding over in use making prematurely dull.

    Also have to rule out using proper abrasive on steels that have hard Vanadium carbide so you don't fatigue the edge.

    Also edge finish is a big one.

    To answer your question of course a steel like rex 121, Maxamet, K390 will kill cardboard.

    But the edges on any steel also get gunked up with glue from the cardboard and you'll have to stop and clean the edge to keep cutting.

    Last edited: Dec 18, 2019
  3. Sunyata


    Mar 27, 2014
    Maxamet, Rex121, or K390.

    Sharpen and strop using diamonds
  4. Danke42


    Feb 10, 2015
  5. bikerector

    bikerector KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Nov 16, 2016
    S110v with a course-ish edge is fantastic for cardboard. Some of the high hardness steels don't take to a really keen, polished edge as well as other steels, but they hold that very slightly reduced sharpeness for a very long time.

    I think if I had a ton of cardboard to break down, an S110V manix or PM2 might be the ticket because of the handle ergos. I like the native 5 lightweight in S110v or UKPK in S110V, but the handle could get a little uncomfortable after a while if you're cutting a lot. Hollow grinds and full flat grinds have treated me the best. The S110V models are readily available.

    I also prefer to touch up the edge on a fine diamond rod instead of stropping. Just a couple strokes will do it. I like Buck's edgetek flipstick for portability, or the full-size option for a full sharpening. I've never had great luck stropping the high hardness steels, but I don't strop with diamond either.
    Dangerously, Dean51 and Smiling like this.
  6. Gamecocks84


    Dec 9, 2019
    I also recommend sharpening with diamonds, going no higher than 600 grit or so.

    I get the best cardboard cutting edges by using very thin edge angles and coarse edges. I aim for about 10 degrees per side when I set the bevel freehand, and tend to touch-up at about 12 degrees per side. The edge I get off a DMT X Coarse or diamond sharpmaker rods is ideal for this application.

    Geometry plays a role as well. A moderately dull Opinel will keep slicing for a while. I have an old slipjoint in D2 from Queen and its a great combo of thin geometry paired with a wear resistant steel.

    If you're trying to push cut it with polished edges, you'll have to sharpen frequently. If you slice with a toothy edge and use a wider part of the edge, it will take longer to dull.

    Lastly, slice it at an angle, rather than perpendicular to the cardboard. I couldn't tell you the science behind it, but many have noted slicing cardboard is easier when you use a 45 degree angle.
  7. Sharperthansticks

    Sharperthansticks Gold Member Gold Member

    Sep 19, 2017
    I welcome answers like this as a chance to learn more, but I also dread answers like this, because I'm not sure where to even start the conversation. I'm adept at using both the WorkSharp Ken Onion with blade grinder, and the KME. These days I mostly use the KME, though, and I mostly just use the 1500-grit diamond stone. It produces a burr easily on just about all of my knives. I might use some lapping films after that, but maybe not, since I've never really been comfortable with them. Mostly I use my strop with green compound to maintain the edge, after. My knives get sharp enough to shave arm hair. More than that is probably beyond my skill level. I also check my knives regularly under a lightbulb to see if the edge has rolled or knicked, though, with my eyes, I cannot tell which of the two ha happened; I can just see a glint, as I rock the knife up and down under the light. I call the glints "edge deformations" to subsume both the concept of edge roll and the concept of edge rupture (chipping). That being said,
    • Since I flip from side to side on my KME, I'm not sure how a false edge would remain, though I suppose it's possible.
    • Not sure what you mean about "proper abrasives." I use diamond plates, and almost exclusively 1500-grit plates, like I said (followed by lapping films or stropping).
    • I am not sure what to make of the term "edge fatigue" nor how I would fatigue the edge, though I think I've heard this term with regard to over-stropping.
    • "Edge finish is a big one." Hmmm. Meaning?
    Thanks for the recommendations regarding the three steels to try. They will certainly be on my radar. I also plan to see if my 4V Shaman does any better.
  8. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    First of all, for that kind of cutting you'll want to use a fairly coarse stone to produce an aggressive slicing edge. Often those boxes probably have fiberglass reinforced gummed tape on them, and that destroys most edges pretty quickly, and they're often chock full of silica and aluminum oxide dust from sliding around on the aluminum floors of delivery trucks. That'll blunt just about any edge. In my experience a regular ol' box cutter is the way to go, and I use one of my American Mutt pocket stones to keep it in good working order. I've found that stone makes for a more aggressive cardboard-slicing edge than I've gotten off of any other stone.
    Mecha, Smiling, craytab and 2 others like this.
  9. DeadboxHero

    DeadboxHero Triple B Handmade, Custom Knives Knifemaker / Craftsman / Service Provider

    Mar 22, 2014
    Here is your first assignment, dump the green compound stropping. Make the best edge you can with just the 1500 kme.

    After you set the bevel to a small burr each side, use VERY light touch and alternate sides each pass until you can cleanly cut paper, there should be no raggedy cuts.

    Deburr with alternating passes with light touch for as long as it takes.

    If you have confirmed you have a burr before deburring than you can rule out that it's the b residual that is the only reason why its not sharp rather than questioning if it's been apexed. If you you light touch at the same angle you can also rule out that you're not crushing the apex or rounding it over.

    Now use that edge and compare.

    Next step is to do the same thing but with the 600grit KME stone and compare.

    Last edited: Dec 18, 2019
  10. skyhorse

    skyhorse Gold Member Gold Member

    Jan 30, 2010
    Toothy edge has worked best for me regardless of blade steel.
    115Italian and FortyTwoBlades like this.
  11. kwackster


    Dec 23, 2005
    My best cardboard knife to date is this vintage Artus Flex knife, mainly because the blade is just under a millimeter thick, but the Becut steel with lots of niobium carbides in it is no slouch either.
    This knife just keeps devouring cardboard even when the apex is well beyond armhair shaving sharp.
    Think a boxcutter with a bit flexible 5 inch blade made from wear resistant steel.

  12. ferider

    ferider Gold Member Gold Member

    Jun 20, 2018
    I know I'm a snob and a box cutter would work too :)

    Still: these days I use a 20CV XM-18 Wharncliffe, that thing just goes through boxes like butter, even after loosing some sharpness. Plus, I (hand-sharpen) it rather coarse, on a 600-800 grit stone. Not the hardest steel but the geometry rocks for box cutting purposes.
    Last edited: Dec 18, 2019
  13. chiral.grolim

    chiral.grolim Universal Kydex Sheath Extension Knifemaker / Craftsman / Service Provider

    Dec 2, 2008
    Hmm, what about that cemented carbide blade folk have been reviewing, the Sandrin TCK (2.0)? https://usa.sandrinknives.com/
    It's only ~$300.

    Or use a 10cent box cutter and replace/sharpen as needed *shrug* :D
    Last edited: Dec 18, 2019
  14. Stumpy72

    Stumpy72 Gold Member Gold Member

    Jul 5, 2018
    Best knife for cutting cardboard: Stanley 99E (~$5USD). Replacement blades come in bulk packs of 100 for $10 and you can get a pull-through sharpener for ~$5. A $20 bill will give you countless work hours of cutting cardboard.
    Last edited: Dec 18, 2019
  15. I prefer a folding utility knife, but a box cutter is made for the task
  16. Sharperthansticks

    Sharperthansticks Gold Member Gold Member

    Sep 19, 2017
    There's various information here to consider, and I thank you all for it. There seem to be three major strains of thought:

    * Use a boxcutter.
    * Use an even super-er supersteel.
    * Use a less refined (i.e., toothier) edge.

    The first solution makes me sad, because the majority of my knife use is for cutting boxes. I don't hunt or skin animals or use my knives all that much for food prep at the office, and I'm not a leather worker or nautical rope cutter or wood whitler, so, it's mostly boxes. If I moved to a cheap boxcutter, my knives would get even less use and become little more than show pieces.

    The second solution is reasonable, though of course it makes me wonder what to do with all of my existing knives.

    The third solution presents a way for me to continue using my knives, so maybe this is for me the best solution.
    Mecha likes this.
  17. l1ranger

    l1ranger Gold Member Gold Member

    Jan 27, 2017
    a setup like the lansky crock sticks or spyderco sharpmaker is great for those touchups when breaking down boxes
  18. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    To be clear, you still want a crisp edge. Not ragged or with any sort of a burr on it. You'll have to grow accustomed to producing a clean, burr-free edge using stones that run coarser than you may be used to. A quick check you can use is to rest the edge on the back of your thumbnail and gently tug it side to side. You want it to grip and resist sliding in either direction. If it bites in one direction but skates in the other, the gripping side has a hooked-over burr and you'll need a light stroke on that side to true up the edge. If it slides both ways it's just flat-out dull. :)
    jpm2 and Sharperthansticks like this.
  19. Lesknife

    Lesknife Platinum Member Platinum Member

    Mar 31, 2018
    My Buck vantage pro 20cv does really good with a micro toothy edge. I use a fine 600 diamond stick for final edge finish. It’s kinda like micro serrations. To me it seems that a polished edge has more friction and builds heat at the edge and maybe that’s why it gives out sooner. Where as a toothy edge has less surface area contact at the edge.
  20. SpyderPhreak

    SpyderPhreak Rocketman for hire Platinum Member

    Apr 13, 2004
    I love Maxamet for cardboard! Like the Energizer bunny, it keeps going, and going, and going. I use a Spyderco Mule, sharpened with 3M diamond film belts to 9 Micron (~ 1,800 grit), with a convex edge at ~mid-30's inclusive. I then strop with green chrome compound, which makes the edge scream!

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