How to tell if a edge is sharp

S

seanystrangle

Joined
Oct 1, 2009
Messages
374
What is a good test to see if an edge is sharp? Sorry this is prob been asked 1000000 times. Thank you in advance
 
Drop a silk scarf on the blade, if it cleanly cuts the scarf in half...:thumbup:
You are good...:D

Doug
 
seanystrangle said:
What is a good test to see if an edge is sharp? Sorry this is prob been asked 1000000 times. Thank you in advance
Click to expand...

Some;
Shave the hair of their arm and see if it shaves, pops the hair off or just scrapes.
Cut newspaper or any kind of paper,
Feel it with their thumb tip see if the blade "bites"

Those are a few ways.
 
Shaving hair-
Lots of people test sharpness by actual shaving hair, and in many different ways. Leg hair, arm hair, face hair, and some see whether the hairs “pop” off, whether they're cleanly shaved, “tree topped” ( the blade skims hair off without even touching skin), and there's probably a few others...

Whittling hair-
I think some would regard this as kind of a novelty test because the general consensus is an edge this sharp won't last much past two cuts or what not, but basically if you can hold your hair out between two fingers and slice off bits of it like you would a stick, it's hair whittling.

Hanging hair test-
There's another test popular amongst barbers with hair, which involves holding the blade up straight in the air ( so the edge is closest to the ceiling and you could drop a fruit onto the edge if you wanted to act like the guy in the Ginsu commercials ) and then placing a hair perpendicularly across the edge. A very sharp straight razor will part the hair in half under gravity, or by dragging the hair a little bit... Some people even report hearing a truly sharp edge “singing” when doing this.

Push-cutting/Slivering Paper-
Push-cutting, just pressing straight down when the blade with no linear “slicing” movement, and a lot of people like to push-cut straight down into paper, or carve off very small slivers ( think between .020” - .050”, or maybe even way smaller) by just pushing into the paper. Some people see this as a separate level of sharpness than doing this with “slicing” so it could be seen as “sharper” if you can do it with push-cutting.

Shaving/Biting your Fingernail-
A lot of people will rest the edge on their finger nail ( remember to do this with it pointing away from your finger) and see if the edge shaves or bites the fingernail. If it just glances off the edge is dull.

Skin-biting-
Murray Carter has his “three finger test” which involves draping your index, middle and ring against the edge ( very lightly of course) so see if it “bites” the skin or just rolls over. I think there's a few variations in which this can be done; personally I like to use the edge of my index finger because the skin is thicker there and you can literally see where the edge had entered into the dermal ridges. Some say this is dangerous.... Because well, you could sneeze and slice your finger open. On the other hand I think it's a fairly controlled and quick way to do it, and probably doesn't have much chance of going wrong, and because your finger is so much more sensitive than anything else, I think you can get a better feel for how sharp a particular edge is doing this than anything else. Typically I can tell the difference between an edge that will shave and one that will just be able to cut up paper, but it's not quite exact.

Bic-pen/EdgeTester
You can use a plastic, cylindrical tube to check the edge for bite and defects. Razor Edge Systems sells one called an “EdgeTester” that has machined tapers which are nicer for checking for burrs to me than a Bic pen is, but the overall idea is essentially the same in that you hold the pen/tester at an angle and see if the blade will bite into it under its own weight, or setting it on a table and running the blade across the shaft to see if you can feel snags, or just running the lip of the tube down the edge at an angle to detect small burrs or imperfects.

I think actually ordering these levels could be quite controversial, but in my eyes from sharpest to least sharp it goes...

Hanging hair test, hair whittling, hair shaving, push-cutting paper slivers, push-cutting paper, slicing paper-slivers, slicing paper, skin-biting, finger-nail biting. The tests with the pen or edge tester kind of depend on the plastic being used. I've found that with the edge tester, edges that would be indicated as perfect with it would only really shave hair.

So I think that's probably a good rough measure of the tests and their different levels. Personally I just go by the skin-biting feel and can kind of tell how well an edge will do, but generally speaking I think paper-slicing tests are the most useful in determining if your edge is sharp enough for practical use, but I guess practical use just kind of depends on what you use your knife for. I would say that for food prep and cutting plastics ( and of course papers ) paper slicing is "sharp enough".

I think tricky thing about these tests is that they're all pretty subjective. I mean, just the relative humidity will probably lead some people's experiences to be quite different. Ever tried to cut up soggy photocopy paper versus dry crisp paper? It's quite a world of difference, so I don't really think it indicates just how sharp an edge is, just that it may be "sharp enough", so you should use the test that best indicates that the edge is "sharp enough" for what particular task you need it for. My kitchen knife probably doesn't need to be capable of shaving, but on the other hand a knife a friend will use for skinning would probably benefit from being that sharp.
 
For me, it's
1.) Getting it to catch on a Bic.
2.) Catching on my thumbnail
3.) Leaving an acceptable cut on A4 paper, with a folded/ragged edge.
4.) Leaving a clean, smooth cut.
5.) Being able to use half a cm of the blade to smoothly cut A4 lengthwise.
6.)Shaving off arm hair.
7.)Being able to slice off thin fingerprints( as of now, my finger is missing a few splotches.)
8.)Pushing a hair against the blade and cutting it.
9.) Cleanly cutting tissues
10.) Hair- Whittling

Note that I've only reached the last 3 steps a few times. Most of the times I'm too lazy and quit at arm-hair shaving.
 
Can you ship me one?:rolleyes: I'm sharpening up all the kitchen knives this weekend and need to know when to quit. USPS, no insurance is fine, just be sure to overnight it Friday.
 
Thank you everyone and sorry for such a lame question I just want to see if I can get it sharper each time thank you all so much.
 
You must log in or register to reply here.
Back
Top