Testing Some Inexpensive Knives

me2 said:
I have several knives with very thin blades, less than 1/32". This test was set up in a way to minimize the effects of geometry and the sharpness test of cutting paper relies almost solely on the apex sharpness, not the geometry behind the very cutting edge. Those thin knives will still cut carrots when dull, but will not slice paper. My machetes will still cut thumb thick branches but cannot clip the top off a blade of grass or slice paper when dull. If you want to cut cardboard, rope, or some other standard and readily available material until the blades won't slice paper, nearly any steel will do it for a LONG time. Prep 2 or 3 days worth of meals on a ceramic plate and run the knife through the dish washer each time and no steel will stay sharp for long.
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me2, I am certainly not comparing a machete to your knife. I guess my point was that with a super thin blade, as you wear the edge down, you still have a cutting geometry. 1/32" is a very thin blade. But I agree, slicing paper is a whole different animal. So what do you think is the cause of this performance. Cardboard is a media that can dull knives quickly. In fact, you thought of going to rope, but the cardboard will wear an edge down faster in my experience. You cut 1km of CB. I don't know that I could do that with my spyderco made of 110V. But I haven't tried.
 
Absolutely. Cutting ability for those types knives continues after the sharp edge is gone.

I think the performance comes from 2 sources. First, a knife that will still slice paper isn't terribly sharp. However it is an easily repeated test and one that everyone is familiar with at least a little.

Second, I'm taking advantage of edge angle, grit finish, and easily sharpened steel. Common angles now are 20 DPS or more. I'm using a 12/15 DPS back/microbevel. See Hardheart's Catra tests that show roughly a 45% increase in edge holding for 3-5 DPS angle decreases.

Though I'm using the fine side of the stone, its still relatively coarse. I'm doing slicing cuts and testing by slicing paper. These 2 factors work together.
 
thin edge is good at cutting , that is not the latest finding , men.

my kitchen knives are relatively dull , with thin edge & narrow V cross section , but they are still cut well on Vegetables and frozen meat.
 
Cobalt said:
me2, I am certainly not comparing a machete to your knife. I guess my point was that with a super thin blade, as you wear the edge down, you still have a cutting geometry. 1/32" is a very thin blade. But I agree, slicing paper is a whole different animal. So what do you think is the cause of this performance. Cardboard is a media that can dull knives quickly. In fact, you thought of going to rope, but the cardboard will wear an edge down faster in my experience. You cut 1km of CB. I don't know that I could do that with my spyderco made of 110V. But I haven't tried.
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Is it possible that cardboard instead to dull this knive to sharpen them ? It is very thin blade and easy go trought cardboard / resistance on edge during cutting is small / end perhaps have more contact with the side of the blade edge than with edge ? What I think is ........at the same time while cuts to sharp ? Sharpening angle is small ... 12/15 DPS back/microbevel ??
 
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Natlek said:
Is it possible that cardboard instead to dull this knive to sharpen them ? It is very thin blade and easy go trought cardboard / resistance on edge during cutting is small / end perhaps have more contact with the side of the blade edge than with edge ? What I think is ........at the same time while cuts to sharp ? Sharpening angle is small ... 12/15 DPS back/microbevel ??
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Ha, I'm glad I'm not the only one to have this thought. I have some very inexpensive Enlan and M-Tech blades that I have reground to <0.01" behind the edge and lowered the edge bevel on. Running these on cardboard, I felt like sharpness would degrade to a certain point and then just level off, like the cardboard itself was keeping them sharp at some point.

The shaving edge was long gone, but they still slice paper and feel like they would keep cutting cardboard pretty much indefinitely, but I've never tried to quantify it and tend to resharpen them to a shaving edge more often than I need to just because it's so easy. I sharpen similarly to me2 on a Norton Economy most of the time, maybe with the addition of a few licks on a medium Sharpmaker rod.
 
Basically all dulling behaves the way you describe. The CATRA graphs on the link show the more rapid dulling in the beginning and the leveling off in the end. This is also one of the reasons I could cut so much cardboard with a $7 kitchen knife. Once the cutting is into the leveled off tail on the right of the CATRA graph, dropping a small amount in sharpness requires one to cut a tremendous amount of material.

http://www.catra.org/pages/products/kniveslevel1/slt.htm

Search around and you can find Buck's CATRA testing of their new Edge 2000, which is a lowering of edge angles and thinning of edges, though mostly edge angles. These show the trend in dulling very well. After the transition at the beginning (left of the graph) the cutting levels off and you can just keep on cutting. Every steel shows this, and every steel will hold a working edge like this.
 
I have heard of very thin edges acting like self sharpening edges on steels like D2, ATS-34, 440C, etc. The edge angle has to be very low (less than 8 degrees per side) and the stuff being cut has to be soft enough that the edge at that angle doesn't just fold.

I don't have much use for a knife in the later dulling stages. I just sharpen them. I've had to use a knife at work a couple times past the point I would have sharpened. While it was not my choice, the knives still cut and cut. I just sharpened them when I got home.
 
Yes, I am aware of the non-linear nature of blunting. It is easy for me to feel the edge loss in the first few dozen cuts on cardboard before it starts to level out. You are correct that is most likely all I am seeing.

I still wonder about the possibility that at some point the cardboard itself could begin to have a positive effect through its abravise nature. Polishing the bevel and maybe, just maybe, maintaining the apex at a certain level of sharpness. It at least seems plausible to me, but as you suggest, it may take a much thinner blade at very low angles to be significant enough to distinguish from the general long plateau where the edge stabilizes and additional dulling occurs more and more slowly.
 
I am curious about the quick loss you describe. While testing some knives, I've noticed the loss of initial sharpness, but it doesn't seem to be as fast as you, and many others, describe. It could just be differences in how we cut, but I wonder if there isn't something more. Many knives will hold an edge that is just below arm shaving for a LONG time. These edges will shave a few hairs off my arm, but not cleanly, and require a fair amount of pressure.
 
It's hard for me to say anything definitive, since careful testing isn't really my thing. I would say with confidence that I have noticed high initial hair-popping sharpness degrade quickly, but then still maintain a decent working edge on the lower to just below shaving area for a long time. There are a lot of factors that could be at play: the specific material or grade of cardboard being cut, speed & angle of the cuts, edge geometry, quality of the edge/sharpening, level of initial sharpness, etc... I wouldn't know where to start to sort it all out.

...and I guess somewhere in there the actual alloys and quality of heat treatment might start to matter :p
 
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