When is a knife sharp enough, and how to you test?

I usually stick with 600 grit on my EdgePro, decent polish.

For bigger knives I take an old phone book and see how the knife carves it up, plenty sharp when you go more than halfway down a side in one slice, not exactly science but it works for me.
 
hardheart said:
a push cut is when the knife cuts the paper instead of crumpling it. There is no drawing/slicing motion.
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I would love to see this in a video, for some reason a lot of people do a lot of paper slicing videos on YouTube, but none have ever done a push cutting one :confused:

This is a video of sort of a push cut But I don't think it really counts, because he is holding both the knife and the paper at an angle.

A "real" push cut, to me, should be holding both the paper and the knife horizontally and at a 90 degree angle to each other. The speed of the cut should also be 1 tenth of the speed showed in the video.

Am I being to picky here, or ................
 
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Push cutting newspaper is good, yellow pages tend to be more uniform. My best is around 4 inches from point of hold, some forum members can go out to 6 or so. That's impressive.

If I'm just checking for edc sharpness, if it can shave the hair off my wife's back, I'm happy. :D :eek: :D
 
Hawkings said:
I would love to see this in a video, for some reason a lot of people do a lot of paper slicing videos on YouTube, but none have ever done a push cutting one :confused:
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I can do a video of push cutting newspaper for you, but it'll take a few days because someone borrowed my camera :(.
 
hair popping is as sharp as I could ever see myself needing. I'm not looking to do any cataracts surgery or anything,
 
My usual way of testing sharpness is fingers along the edge and the what angles catches on the hair on the back of my head, but I agree with the previous poster who said the best way to find out what edge works best for what you do is to cut what you normally cut.

Here are a few pushcuts. This is a very thin and sharp M2 blade (and thin helps to do it), but thicker edges can be made to do it too. I often cut kydex with this little knife.



 
CWL said:
A general rule-of-thumb for testing "working" knives is to place the edge against your thumbnail at an angle. If it is sharp enough, it will catch against your thumbnail and not slide, but if it isn't sharp-enough, the knife will slip.
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That is also my minimal level. If the whole edge hangs to the nail from bouth sides its sharp enough for everything. The rest is just for the own good feeling.

Bosse
 
Needs to split a hair off my fiancees hairbrush. I like a polished edge, and strop on my belt grinder after use.
 
Doing hand bookbinding and leatherworking for many years I needed a variety of blades sharpened in various geometries for the purpose. In bookbinding I'd cut paper all the time, leather, too, and bookboard (very high quality cardboard) and sometimes even wood.

Paper can dull a blade as fast as almost anything. For testing sharpness, I use the thumbnail test, and I'd also get a sense of sharpness from stroking my thumb lightly over the edge.

Another way I'd test. Take a spool of thread, unwind a bit and let it hang in the air. Can you slice the thread? (Ultra sharp.) Or do you need to swipe at it in a sword like action (usually sharp enough). Of course it also depends on the thread, is it cotton, linen, a synthetic, or mix? But this was my test, then I'd go on to cut the papers, leather, etc.
 
I'm still trying to get a knife sharp enough. Straight razors don't satisfy me. I'm looking for nuclear fission.
 
I'm for arm hair shaving-I have little to no hair about 6"X2" straight up my left arm most of the time.

It should at least be able to scroll a design in copy paper holding paper with one hand and not catch.
 
to me knife is enough sharp when it can cut regular paper without tearing it... Of course that really depends on knife. Larger fixed blades may require different method of testing.
 
I do the arm hair trick as well as cleanly slicing paper towels on the corner.I also slice a little bit of skin of my fingers.With light pressure it should take a shallow chunk out.
 
Broos said:
My usual way of testing sharpness is fingers along the edge and the what angles catches on the hair on the back of my head, but I agree with the previous poster who said the best way to find out what edge works best for what you do is to cut what you normally cut.

Here are a few pushcuts. This is a very thin and sharp M2 blade (and thin helps to do it), but thicker edges can be made to do it too. I often cut kydex with this little knife.



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Thank you for posting the video.
That is a sharp knife, no quastion about it.

Can you do it by holding the paper between 2 fingers and not bending it?
I often see people saying that they measure the distance from their fingers to the start of the cut. Some will claim that they can make the cut 3 or 4 inches from their fingers.
Bending the paper at the bottom will stiffen it somewhat. making the cut easier to preform.
 
I got my camera back, is this how you want it?

[youtube]9RhxwNQLW8k[/youtube]

There is a little draw in the cut because its not easy trying to cut something while looking through a 2" viewfinder.
 
Jeff Clark said:
I'm still trying to get a knife sharp enough. Straight razors don't satisfy me. I'm looking for nuclear fission.
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I have the same feeling. You are much closer to that level than me though, but hopefully with practice I can improve.

Mike
 
I like to try to get them sharp enough that if somebody is looking at it and is stupid enough to run their finger down the blade they cut themselves. Yes, this has actually happened.

In general push cutting newspaper or slice cutting paper towel are my tests though. Shaving hair on the arm or leg or just feeling the edge with my thumb or pointer are generally good indicators as well.
 
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