Extreme sharpness?

jac_solar

jac_solar

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Sep 1, 2013
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I was wondering, is it possible to get a regular knife as sharp, or sharper, than a store-bought razorblade, or does a razorblade, more or less, represent the highest level of sharpness for steel? As in, to get a sample of how sharp it's possible to make a piece of steel, just walk into a store and buy a razorblade?
 
Sure, if you know what you're doing. And the meaning of "sharp as a razor" depends on the type of razor you're talking about. A utility knife "razor" blade is nowhere near as sharp as a shaving blade from say a Gillette Fusion or similar.
 
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You can get a knife that sharp, yes. However the edge would be very thin and not very stable, so not very useful in a knife you plan on using for daily chores.
Just for giggles I made one of my knives polished enough to shave my face with, but there is not really a reason to keep your knives like that (as I said above)
If you are cutting endless boxes or something similar then just buy a utility knife or be prepared to sharpen your knife very often.
 
The main thing that makes razor blades 'razor sharp' (for actual shaving) is the narrow edge geometry, which is very acute. The remainder is in how cleanly a razor blade's edge is apexed and finished (by machines operating within very tight tolerance, for consistency). In terms of making a knife as 'razor sharp', if you can get a crisp apex at the same thin geometry as a razor blade (and that's just dependent on the held angle), then a knife can be made just as sharp. Straight razors are obviously made to be at least as sharp as razor blades (and I'd bet many are sharper), and those are sharpened and maintained by human hands on a daily basis, by many.


David
 
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Blade thinness is what gives a razor blade it's abilities to cut well. Not so much how fine a grit it was take to. (double edge blades) Single edge straight razors are another matter.
There are gents who can really hone these. Learned skills that could have taken a year to master. Still, they have edge geometry for shaving not cutting various material. I don't think comparing a knife to a razor is a level comparison. DM
 
If I remember correctly, a straight razor is around 15 degrees inclusive or so. You can get a knife what I call stupid sharp without going that low but to get a comfortable shave you would want it fairly acute. DesertChris over on the buck knife forum shaves with his buck knives. But I think he has leather skin. :) I shaved with my endura once. Key word...... Once
 
I've done it by sharpening kitchen knives (decent ones) at 12-15 degree angles, but as soon as I actually used the knife to cut food it fell apart horribly. Chipped even. Same with regular knives although harder blades with thicker primary grinds helps a little more but it's pointless. My laredo bowie is crazy sharp, 20 some degree angle, used it to cut pizza and went through it and the pizza cardboard like butter with little effort, but it's not truly razor sharp, and for the purpose I'd use it it doesn't need to be (random cutting, wood etc).
 
This is oversimplified, but I'm trying to keep it short and mostly factual. There are essentially three things involved in perceived sharpness:

1. What angle the final edge is sharpened at.
2. The thickness of the stock behind the edge, and all the way to the spine of the blade.
3. What polish level was applied to the final edge bevel.

All of this assumes a properly apexed edge of course.

The first two seem to be bigger in cutting performance than the last. Razor blades and utility blades cut well because of their overall geometry: A very acute edge bevel and extremely thin stock behind the bevel and all the way to the spine. The lowly Olfa seems to outperform almost any "real" pocket knife I've tried for cutting cardboard. I still use a "real" folding blade because I'm in denial and I like good knives. :p

You can also get into very detailed discussions about point 3 above depending on what type of cutting task you want to do. Generally speaking, highly polished edges don't do well at slicing. Conversely polished edges do very well at push cutting. Like shaving hair. More coarse edges are bad at push cutting and good at slice cutting.

It amazes me that it's taken me *SO* long to figure out these simple truths! I should learn to listen to those that know.

Brian.
 
I shave daily with my Spydercos: Gayle Bradley, Resilience or Endura SB. The best shaver is 52100 paring by bluntcut.

So yes, it can be done, but that sharpness will be destroyed once you start using it for cardboard ... So it's either a working edge or a shaving sharp, user needs dictates what edge geometry & finish a blade is sharpened at.
 
If you go into a store that sells disposable type razors eg Gillete Fusion, etc and bring a 10x magnifier with you and actually look at the razor blades, you will be surprised to see just how coarsely they are ground. Thus their cutting performance is achieved by virtue of their thin geometry much moreso than edge refinement which you see with thicker blades like straight razors and knives that can achieve good cutting performance to produce an acceptable shave.

---
Ken
 
I thinned out a cheap $3 victorinox paring knife to being pretty thin and just putting roughly 12-17 degree angle on each side will bring that to scary levels of sharpness and makes my Opinel jealous in cutting performance. The thin geometry of the blade plays a very large role in this. It wouldn't surprise me if this thing is as sharp if not sharper than a scalpel in terms of cutting performance now.

As a side note I don't find normal box cutter razor blades to be anything special it's their blade geometry that plays a major role in their cutting performance especially when you start comparing it to the modern folders we have today which are overbuilt enough that they could pry apart a tank.
 
ksskss said:
If you go into a store that sells disposable type razors eg Gillete Fusion, etc and bring a 10x magnifier with you and actually look at the razor blades, you will be surprised to see just how coarsely they are ground. Thus their cutting performance is achieved by virtue of their thin geometry much moreso than edge refinement which you see with thicker blades like straight razors and knives that can achieve good cutting performance to produce an acceptable shave.

---
Ken
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Edges don't need to be very refined to shave either. Most of my knives will shave after the 300 grit oilstone. Hardly refined. The purpose of using super fine stones is one, it does get slightly sharper, but mainly a fine edge stays sharp a hell of a lot longer. Anyone whose chipped a knife edge knows once it's chipped it gets bigger and bigger the more you use it. Same thing happens on a micro scale.
 
yepimonfire said:
Edges don't need to be very refined to shave either. Most of my knives will shave after the 300 grit oilstone. Hardly refined. The purpose of using super fine stones is one, it does get slightly sharper, but mainly a fine edge stays sharp a hell of a lot longer. Anyone whose chipped a knife edge knows once it's chipped it gets bigger and bigger the more you use it. Same thing happens on a micro scale.
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Last night i scraped off some armhair after my 24 grit Nubatama. I wouldnt do that to my face but...

I also have a video shaving some armhair after a 140 Atoma.

My mother had an old carbon steel pairing knife. It never once in its life saw a stone. Still hasnt 20 years later. Its extremely thin and peels and breaks down potatoes just as well as when I was a kid. It wont cut you ,but being so thin its goes throw potatoes all day without breaking a sweat.
 
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