How do you know sharp?

[Blues]

The great thing about threads like this is that they prove to myself (and my wife) that I'm not OCD at all.

 

[Wowbagger]

I just hold the knife in one hand and the rod in the other

That's good for general sharpening.
PS: I wouldn't call the Sharpmaker rods crappy; they are really useful.

I do need to get an xtra coarse diamond stone.

The advantage of the bench stone for reprofiling is one can get some downward pressure on the blade and that speeds things up.

For some reason my hair is very difficult to whittle whereas if I borrow a hair off a friend it whittles fine.

Keep in mind that if you are trying to whittle your hair while it is still attatched (arm or beard) that going root toward the tip is more difficult than holding a hair n hand and dragging it across the edge while held by the tip. Check out a micrograph of a hair and you will see the "scales".

If your hair is super fine that can be more difficult to whittle. My hair cutter has such fine arm hair she can't really whittle it with one of my edges which whittles my arm hair easily.

 

[Lapedog]

That's good for general sharpening.
PS: I wouldn't call the Sharpmaker rods crappy; they are really useful.

The advantage of the bench stone for reprofiling is one can get some downward pressure on the blade and that speeds things up.

Keep in mind that if you are trying to whittle your hair while it is still attatched (arm or beard) that going root toward the tip is more difficult than holding a hair n hand and dragging it across the edge while held by the tip. Check out a micrograph of a hair and you will see the "scales".

If your hair is super fine that can be more difficult to whittle. My hair cutter has such fine arm hair she can't really whittle it with one of my edges which whittles my arm hair easily.

Yeah I know you are supposed to whittle towards the root.

I don’t find the sharpmaker rods themselves crappy. I rather find the sharpmaker system itself crappy.

Lots of people love it though so that’s just personal pref.

 

[bgentry]

There are lots of objective tests for sharpness that you can use. Hair whittling is certainly one, but I think that level of polish is just showing off. It's neat and it requires a good bit of skill to get there. Don't get me wrong. I just think it's not terribly practical for a knife.

Start with the basics on your blade:

Thumbnail test: When lightly and CAREFULLY cutting the blade into the top of your thumbnail, does it "stick"? If it slides, it's probably not as sharp as it could be. Though some super polished blades will slide with this test.

Phonebook paper: Can you cut at 90 degrees to the paper? No tilt of the blade in any direction. Perfect 90s in all 3 dimensions. Yes? Awesome. Now rotate the paper 90 degrees and try again. Many blades will cut with the grain of the paper, but not against the grain of the paper. Make sure you use push cuts. No sliding or pulling the blade. If your blade can do this test all the way, it's very sharp. Even a relatively coarse edge can do this quite well, as long as it's fully apexed.

There are home made jigs for testing sharpness with thread and a scale. Then off course there are the straight razor tests of "hanging hair sharpness". Look that one up and you'll find a full scale of "HHT1" through HHT[some number], where HHT means Hanging Hair Test.

For me, if a blade will cleanly cut phonebook paper with no snags, along the whole edge, it's done.

Brian.

 

[kwackster]

Even extra coarse edges done on a Rubber Wheel coated with 170 grit diamond powder & wax get checked on the ability to whittle a chest hair from root-to-tip.
They do it a bit differently when compared to highly polished edges, but they sure can do it.
BTW: i just use it as an initial check to see if i did things right, not as a test to end all other tests.
A high initial sharpness is always good, but edge longevity is even more important.

 

[Mr.Wizard]

Thumbnail test: When lightly and CAREFULLY cutting the blade into the top of your thumbnail, does it "stick"? If it slides, it's probably not as sharp as it could be. Though some super polished blades will slide with this test.

If the edge slides the apex has been rounded off. A sharp edge will stick even when mirror polished.

 

[Bob6794]

I use some methods already posted so here is a new one.

If you can accidentally cut yourself and not feel it. One of the memorable ones was a new Buck knife that I cut a huge chunk out of my thumb while flipping it open. I saw what appeared to be skin on my desk and a big piece of flesh missing on my thumb but no blood, so what did I do. I poked it... 40+min latter the bleeding slowed down. I didn't feel the cut.

I have far exceeded that factory sharpness since than. But that story I still laugh about it today and it happened over 10 years ago.