Sharpness testing...

[bushguy]

Happy New Year Everyone! :wave: I was just wondering with all the knives you guys have, what method y'all use to tell when your knives are sharp enough. Do you do the, shave the hair on the back of your hand thing? Anybody use the slice and glide thing on a sheet of typing paper? Maybe you try and see if it can cut through a 1/4" or bigger, hardwood dowel in one stroke?

For starters, I'm old school and I use an old ignition, point file and then any kind of hard steel handy for the finishing touches followed by a little stropping on my well worn (25 plus years) old leather belt on my pants. They are sharp when they can slice a clean snake-like pattern right through the whole sheet of typing paper without catching and tearing it. By that time, they shave my forearm hairs easily too.

How do YOU know when your knife is ready to go to work?

 

[Bloodnut]

Hi bushguy, welcome.

Your question is a good one. It's also one of those, "Ask 10 people, and you'll get 10 different answers..." kind of questions. I've gone round and round on how to sharpen and how sharp is sharp enough. I expect that your method using the file and finished with stropping leaves a toothy, but polished edge which is great for slicing fiberous material (rope, cloth, etc.).

Toothy edges are certainly wicked. A while back I read a comment stating that folks in the meat industry who slaughtered/butchered large quantities of meat daily prefer a smooth, highly polished edge. After I thought about it, this made a lot of sense. A smooth, polished edge should be very strong (given that it is applied to good steel with a proper (hard) heat treat), and it should therefore be very durable and easily touched up. Sooo, I have taken to sharpening with that goal in mind. I work my way up to an extra fine (grit unknown to me) stone. The edge shines like a mirror.

As for sharpness testing, I first inspect the edge visually and by feel to verify that the two sides of the "V" meet. Once this is accomplished I use the shaving hair test, fingernail test, cut cardboard, newspaper, and sometimes leather. Because it is winter, my fixed blade sees a lot of use creating fuzz sticks and shavings for firestarting. This is mostly from (very) hard oak. Talk about a sharpness test. If the edge is not *very* sharp, the blade will simply break the wood along the grain rather than shaving and shearing off little curly Q's. When the blade is repeatedly creating the curly Q's and the resulting finish on the main piece of wood is smooth as glass, I know I have a good edge.

My primary blade at this time (and for the forseeable future) is a Mad Dog BearCat. O-1 steel, differentially heat-treated with a ~62 rockwell hardness at the edge. It'll hold whatever edge you put on it. You can build a dozen big fuzz sticks and then go skin a deer with little loss of sharpness.

 

[greenstuffs]

if your knife can split paper then it should be sharp enough

 

[HoopleHead]

i always use the fingernail test. paper isnt accurate IMO and will dull the edge. with the fingernail (trying to shave a thin slice off the back of your fingernail) youll definitely know whats dull and sharp, and when it catches right away barely touching you know its really sharp.

 

[FlashSpyJ]

I use a Fallkniven DC4 its a diamond/ceramic shaperning stone. On big knives I use spydercos triangle sharpner. First I feel the edge with my fingers, gently stroking the edge away from the edge, and look at the edge to see If I can spot any nothces (correct word?). I try to gently draw the knife on my finger nail to se if the knife glides of, if all is good so far i try to shave my armhair. If the knife can easily shave the hair and not leave a burning itching feeling then the knife is sharp just the way I like it!
I usually try to cut a printer paper or some other paper, the thinner the better, but lately I have started to try the knife by attempting to cut a A4 paper in half in one stroke. Even a small knife should be able to do this. Push cuts on a paper are also a good way to test the sharpness!

 

[cutlerylover]

I try all kinds of methods...I have used the paper thing, as well as newsprint for extra sharp blades...I also use the fingernail test, as well as using a pencil or pen...But what I use most of all is cleany and easily slicing a rolling paper...thats thin enough that it will let me know my edge is super sharp and ready to go! I no longer smoke (have not for years) but I have a nice stash of rolling papers left that I now use to test my edges...

 

[LukeA]

I shaved some hair off of the back of my forearm. I looked like I had mange for two months.

 

[cutlerylover]

I shaved some hair off of the back of my forearm. I looked like I had mange for two months.

Hahaha, I use to shave the back of my hand at 1st, then when I ran out of hair there I would shave my upper leg, that way not many people, I learned this aftre about 2 years ago when a friend noticed I only had arm hair on my right arm, lol...

 

[ACMarina]

I used to do that thumbnail test until I sliced through the nail and drew blood. Then it pooled under the nail and I had to the "heat the nail and punch a hole" trick to relieve the presure. Now I just sharpen until it seems good enough and trust myself from there

 

[chmsam]

I caution people who borrow my knives not to run their thumb over the edge because I only carry so many band aids. Doesn't always stop them but at least they were warned. I may not have many knives but they are usually really too sharp (I myself am often none too sharp but that's a whole 'nuther thing).

I am a dumb old coot and so I still shave a bit of hair off of my forearm or run the blade very, very lightly over my thumbnail (if it catches, it's sharp). I know this is less than brilliant however. When I am in an intelligent mood I will take a free hanging piece of paper and slice into it. That is a much safer method and I should force myself to do that and not the other methods. Slicing free hanging toilet paper also shows that you have a seriously sharp edge.

One of the scariest moments I have had in carrying a pocket knife for over 45 years was when I was using a very small knife and I took a swipe at a piece of bailing cord. I expected to cut the cord easily but I did not expect to cut the free hanging strand that was about 1' to the left of it. I did cut it and quite cleanly and easily. Please understand that this knife weighs next to nothing and the blade is less than 2" long. It certainly wasn't the mass of the knife or the force used that cut the second cord, so maybe it was a tiny bit of Zen, but mostly I think it was that it was literally "scary sharp." This blade is one of a few I have seen that make the hair pop off my arm before it even sees the knife coming.

I have learned that some jobs require a certain polished edge (similar to a razor) and other jobs are much easier with a bit more rough finished edge that has more "bite." It's not always a good idea to have the 8000 grit water stone polish on a knife. I now only finish polish and/or strop some of the knives I have.

 

[RA40]

I roll up a piece of 22# photocopy/laser/inkjet paper and make a slice attempt perpendicular to it at an angle. If it will bite and cut into it, it's sufficiently sharp for my usual cutting tasks. YMMV
Lousy pic but to give an idea...

 

[Monocrom]

I have a "tester" that came with one of the sharpening systems which I've bought over the years. A blue rod with a pen-clip that one can use instead of a finger nail....

Still, I prefer the old shaving hair off the arm technique. Hair-shaving sharp with a bit of skin flakes is sharp enough for me. No flakes = even sharper! Now, hair-popping sharp is something I've only seen on some of the better knives out there, like Spyderco and Benchmade.

 

[bushguy]

Great stuff here boys. Thanks for all the fine feed back on this age old question. :twothumbs So, I guess the moral of the story here is that as long as you believe your knife is sharp enough, it doesn't really matter how you've achieved that degree of sharpness. Same goes for the testin' too, it appears.:thumbsup:

Later,