Best Steel (and Angle) for Cardboard Cutting

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.

 

Maxamet, Rex121, or K390.

Sharpen and strop using diamonds

 

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.

 

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.

 

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.

 

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.

 

Toothy edge has worked best for me regardless of blade steel.

 

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.

https://www.bladeforums.com/threads/vintage-artus-flex-knife.1689441

 

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.

 

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*

 

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.

 

I prefer a folding utility knife, but a box cutter is made for the task

 

a setup like the lansky crock sticks or spyderco sharpmaker is great for those touchups when breaking down boxes

 

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.

 

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.

 

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!