Very poor edge retention when cutting cardboard

Guy McVer said:
I don't think he talked about that, but he does discuss how the steel is "fatigued" from the factory grind, and that it takes several sharpenings to get to the good steel underneath the area which was ruined at the factory. Basically it's the same thing as I mentioned earlier: the factory grinding process can ruin the heat treat at the edge, and you need to remove the ruined steel by sharpening the knife until it's all gone.

I feel like I should get a medal for watching that whole video...
Click to expand...
That wasn't the video I originally heard it in. But I was in a Cafe with the sound down and took a punt.

I have heard it mentioned a bit.

Here at about 4:30 he mentions how he goes from 20° to 17° and gets better edge retention.

There has been a couple other videos where reviewers have mentioned it in passing.

Do the cut test. Sharpen it do the cut test again and get better results.

It isn't something I know much about.
 
Last edited:
Drop bear said:
That wasn't the video I originally heard it in. But I was in a Cafe with the sound down and took a punt.

I have heard it mentioned a bit.

Here at about 4:30 he mentions how he goes from 20° to 17° and gets better edge retention.

There has been a couple other videos where reviewers have mentioned it in passing.

Do the cut test. Sharpen it do the cut test again and get better results.

It isn't something I know much about.
Click to expand...

I'll play the devil's advocate by suggesting that the increase in performance may have been owed to the fact that he put a better edge on the knife than it came with from the factory, and not due to the change in edge angle which he guessed was originally 20 degrees per side without actually verifying it. The actual change in the angle may have been smaller.
 
A lower (more acute) angle absolutely improves cutting ability and edge retention ... so long as the blade in question has sufficient edge stability to support the lower angle. Generally speaking, the harder the steel, the higher the edge stability.

Larrin Thomas has demonstrated this in his testing, and he generally recommends sharpening to a low angle and testing to see if the edge holds up (no rolling or chipping). If there's insufficient stability for the angle, go up one degree, and so on, until you achieve the optimum result.
 
Guy McVer said:
I'll play the devil's advocate by suggesting that the increase in performance may have been owed to the fact that he put a better edge on the knife than it came with from the factory, and not due to the change in edge angle which he guessed was originally 20 degrees per side without actually verifying it. The actual change in the angle may have been smaller.
Click to expand...
It's possible.
 
Blade Lab said:
A lower (more acute) angle absolutely improves cutting ability and edge retention ... so long as the blade in question has sufficient edge stability to support the lower angle. Generally speaking, the harder the steel, the higher the edge stability.

Larrin Thomas has demonstrated this in his testing, and he generally recommends sharpening to a low angle and testing to see if the edge holds up (no rolling or chipping). If there's insufficient stability for the angle, go up one degree, and so on, until you achieve the optimum result.
Click to expand...

It depends on the application. For straight cuts, it is advantageous. Kitchen knives for example. However for tougher material and twisting, the more acute edge angle is less stable and will be more prone to rolling and chipping.

For EDC, I like a thin blade with a 20 degree per side edge angle. It's kinda like getting some of the advantages of both. Swiss army knives are a good example of this, and I EDC one most of the time.
 
Use toothy edge,check for burrs,sharpen at low angle and you shouldnt have problem...also not every cardboard is same.
 
I recall reading a woodworking book where some carpenters recommended using cardboard as an emergency fine strop, because it is so abrasive. I used to use a box cutter (with a single edge razor blade) for cutting up boxes. Now, I prefer the Milwaukee utility knife. The blade retracts and it has a good handle grip.
I would only use a pocket knife for cutting cardboard if I couldn’t get to a utility knife or box cutter. If I were to use a regular pocket knife, I’d reach for a knife with a blade steel in M4 or ZDP-189 - and I would expect to spend some time sharpening. Personally, I like these sorts of steels because I don’t want to sharpen that often. Otherwise, I could make do with a low grade stainless or a carbon steel in 1070 or 1095.
 
I have a pair of Benchmade Mini Griptillians CPM154 that I sharpen on a WE100 to a polished 17degrees. I have absolutely no issue cutting cardboard with them even as they not at there sharpest.
 
Artyh said:
I recall reading a woodworking book where some carpenters recommended using cardboard as an emergency fine strop, because it is so abrasive.
Click to expand...

I've heard that stropping on the cut edge of cardboard is best. You know how when you cut a piece of cardboard, it has this zig-zag pattern between the two faces? Supposedly you should strop on that instead of the face.
 
Try a Japanese Canary DC-190F-1 boxcutter. Fixed micro-serrated blade edges with a round 'point' (but no sharp edges) and flourine coating. It would be very hard to cut yourself with this, you can grab it by the blade or moderately run it along your hand/leg without blood. Have done that multiple times. I use mine a whole lot in the warehouse to break down boxes for recycling. Good in the office too. The blade can get bent, but it bends back. Less than $10 online. I wouldn't recommend the retractable or shorty blades tho.
 
Brock O Lee said:
My first impression was that you probably still had a burr. A cleanly formed apex should not chip on a few meters of cardboard, unless perhaps if the cardboard was extremely gritty/sandy.

A few questions, if I may...

Did you perhaps have a perfectly aligned burr that was invisible to detect?

How did you check for edge stability? One test I know of is to push-cut monofilament fishing line on a cutting board. If you have a burr it would fold over and leave a tiny dent/chip in that spot on the edge. A clean apex will not be affected by cutting fishing line.



Does it continue to cut cardboard or paper after that? Is your standard for sharpness perhaps too high?

In my experience I lose the hair-shaving sharpness relatively quickly, but it continues to cut cardboard for a looong time after that. For instance, I've been using a K390 Endela wharncliffe to cut boxes for home recycling for over a year. I can go 2-3 months between sharpenings before it stops gliding smoothly through cardboard. No stropping in that time. I run a 17 dps edge with a 20 dps DMT Fine (600 grit) micro bevel, which is quite obtuse!

K390 is the best performer on cardboard so far in my experience. The stuff is magical.



I also found this flashlight trick to spot a burr useful, especially when checking in a dimly lit room. Make sure you shine light from behind onto the edge on either side. Kindly ignore if you know this already.

Click to expand...
I did a test sharpen on some S35VN and discovered it was noticeably sharper after running my stones parallel with the blade for a few swipes before moving on. I wonder if I impacted the burr in some positive way?? I saw a guy doing this on his Wicked Edge to remove scratches. Back on topic, knife makers and sharpeners use cardboard tests on knives for a reason. It's brutal. Now that we have box cutter designs rivaling EDC, I use one with Lenox Gold blades for the dirty work when I can.
 
What he said, cardboard can have basically clays and all sorts of minerals that are brutal on edges.

You can 3d print a sharpness tester, use some objective measure to test if you feel it's necessary or helpful.
Let me know if you want me to try and find the link or file to the one I had my buddy make on his 3d printer for me.
 
The point of the original post is not to find a tool to cut cardboard. Cardboard is the most commonly available test media for comparing knives.

Increasing edge holding in similar materials or slicing type uses is most easily done by lowering the edge angle and coarsening the grit used for the final edge. Drop to 10 degrees and finish with a Norton Coarse India stone or Black X-Coarse DMT stone. If that angle is too low, increase it until gross damage or deformation stops.

For a real eye opener, try a Coarse Crystalon stone edge on high hardness D2 steel at about 7 degrees per side. Keep cutting cardboard until it won’t slice standard notebook paper, cleaning the glue and such periodically. Get a LARGE supply of cardboard first. I cut over half a mile of cardboard with a cheap Chicago Cutlery kitchen knife and a Sharpmaker Medium grit edge and finally gave up.
 
me2 said:
The point of the original post is not to find a tool to cut cardboard. Cardboard is the most commonly available test media for comparing knives.

Increasing edge holding in similar materials or slicing type uses is most easily done by lowering the edge angle and coarsening the grit used for the final edge. Drop to 10 degrees and finish with a Norton Coarse India stone or Black X-Coarse DMT stone. If that angle is too low, increase it until gross damage or deformation stops.

For a real eye opener, try a Coarse Crystalon stone edge on high hardness D2 steel at about 7 degrees per side. Keep cutting cardboard until it won’t slice standard notebook paper, cleaning the glue and such periodically. Get a LARGE supply of cardboard first. I cut over half a mile of cardboard with a cheap Chicago Cutlery kitchen knife and a Sharpmaker Medium grit edge and finally gave up.
Click to expand...
How did they compare against a utility knife?
 
You must log in or register to reply here.
Back
Top