Tests of sharpness

[Tadpole]

My cheap Mora, is, to me at least, very sharp, the hairs pop/leap off my arm and even after making 20 tent pegs from ¾ inch dry hazel, and chopping up a couple of lofting boards (don’t ask ) it’s sharp enough to shave paper in to beautiful feather stick like curls. I think that is sharp enough. For a full time EDC user, I need a tool that is robust enough to do the job, and more to the point keep on doing it for hours/days at a time.
Is a knife that is capable of shaving the print off of a paper just a parlour trick? Would it not weaken the edge, to the point that a simple wood knot or a gritty bit of bark would roll it? I can understand the need for ‘scary sharp’ for, say, a fish filleting knife or a leather cutter, but a general work-a-day knife, I’m not so sure?

I'm not having a go at anyone, just trying to learn.

 

[Dave Budd]

tadpole, you are dead right mate A fine razors ege is great for carving but for many other things it's too fine, fragile and slippery. Often a less polished (not hair popping) edge is better suited to the job. Unfortunately people do rather enjoy seeing how sharp they can get their knives

 

[crazydave]

the americans have a thing about knives being beyond sharp but from experience its all pretty useless when you need it most. I used to shave my arms with freshly sharpened knives as a kid and I guess the novelty wore off now I know its sharp enough to do whats needed for as long as I need it to.

if I cut paper normally its cos I'm bored

 

[mariobab]

For butcher knives,I keep those shaving sharp,but all of my big outdoors blades(MOD,kukri,SP1...) need not to be that sharp,maybe blasphemy,but I mostly use chainsaw flat file and scythe middle coarse stone.Folders are razor sharp in other hand.

 

[British Red]

The saddo test for me is slicing a piece of tissue paper in half whilst its in free fall. As many say there is a balance between stupid sharp and edge retention.

Still fun though....I think sharpening is one of those things you go through and come and the other side back to "sensible"

Red

 

[John Fenna]

The saddo test for me is slicing a piece of tissue paper in half whilst its in free fall. As many say there is a balance between stupid sharp and edge retention.

Still fun though....I think sharpening is one of those things you go through and come and the other side back to "sensible"

Red

I have never got my blades that sharp!
"Shave my arm" sharp on a lightly convexed edge (for durability) does it for me for most uses.....
Anything less makes fine work need too much pressure and risks slips and a none to clean wound.
For rough work I will accept less than razor sharp - as long as I can be sure that I can keep body parts out of harms way

 

[British Red]

Why bother John? It can be done for sure but it makes for a very fragile edge. It all has its place but its a bit like "whats the perfect grind"? The only answer that makes sense to me now is "for what job"? I personally still like a zero ground scandy - but I'm sure thats because I usually carry a very sharp axe so my knife is for precision work. When I don't a flat grind and a lightly convexed secondary makes sense to me - but then I will also carry a larger knife as a rule. It wont slice tissue in freefall but it holds an edge a heck of a lot longer when chopping and being batoned. The tools that needs to be stupidly, madly, silly sharp for me are a scythe and a chefs knife. Everything else is generally a compromise. More and more I get bored with worrying about the tool beyond the act of not compromising the task.

Red

 

[John Fenna]

I totally agree with you Red!
Mind you a tissue slicer....hmmm...I wonder if I could.......it would be a challenge.....

Anyone got anymore interesting test methods that they use?

 

[Prophecy]

Usually I hold it on my skin on my left forearm, and using no pressure at all other than the weight of the blade, see if it nicks me or not. If I don't feel that, then it's obviously not sharp enough.

Other than that, I'll cut paper, or just simply just give the edge a feel with my thumb.

BTW John, there's a good thread over on BB called 'How sharp is sharp'? which is similar to this and may have a few different answers.

 

[markheolddu]

I use my thumb

 

[Armleywhite]

I use my thumb

Aye, me to. Sharpen, then drag my thumb across the edge. You'l know when it's sharp or not.

 

[ganstey]

The tools that needs to be stupidly, madly, silly sharp for me are a scythe and a chefs knife.

Sorry to take this slightly off-topic, but how does one sharpen a scythe (or a billhook for that matter)? I've used a cigar stone to remove nicks etc., but never worked out how to get them properly sharp. For my knives and axe I use waterstones following the RM technique.

Feel free to start a new thread if you think this is taking this thread off-topic.
Cheers
G

 

[British Red]

I use a stone and then wet and dry wrapped around a piece of drain pipe secured with laccy bands. Not pretty but it works.

Red

 

[ganstey]

I use a stone and then wet and dry wrapped around a piece of drain pipe secured with laccy bands. Not pretty but it works.

Red

Ah, of course I've got a load of plastic conduit, and I'm sure I've got a pack of wet n dry somewhere.

G

 

[mariobab]

Sorry to take this slightly off-topic, but how does one sharpen a scythe (or a billhook for that matter)?

Well,for billhook I do like any other chopper i.e. if it was not chisel grind.Scythe is other thing,before first use it edge usually needs peening,and repeat it from time to time,when metal become too thick.Some 20 years ago I worked in town greenery,and each day we had -can't remember exactly how long 1/2 or was it 45 min - some time for peening.When we was just learning boss would give us old scythe to practice.(Man,it was wavy kris edge on my first one,boss wouldn't believe what I managed to do with that blade.It wasn't fit for practice or anything else anymore).
And depends of grass scythe needs frequent honing.We used wet honing,we always carried some kind of sheath with water and stone immersed in it.After honing old ones would always wipe edge with fistful of grass,wouldn't know why,but I do it too now,at least it cleans the edge.

 

[Mike Ameling]

I use the simple thumb nail test. Set the blade edge down on my thumb nail, and gently slide it to either side. I then see how much it "grabs" the thumb nail. If it just skates across it, it's too dull. If it catches a bit, and even shaves a little, then I check it pulling in the other direction - to see if I just have a little "curl" on the blade edge to one side.

It's a simple/quick test for an edge on a "working" blade. "Razor" sharp is fine for SOME applications. The worst cuts I have gotten when using a knife have been with blades that were TOO SHARP for the type of work I was doing, or TOO DULL. So I go for an edge somewhere in between. But most of the time my cutting edges could use a little ... touching up. I'm kind of lax in sharpening them when I should. I'm much more concerned about them doing the task at the moment.

But we do have some very un-realistic expectations about blade sharpness and edge holding abilities on this side of "the Pond". We have lots of people who expect to sharpen their knife today, use it HARD for everything, and still have it be razor sharp a year from next Tuesday! That's pretty crazy expectation for a working knife, and they are constantly being disappointed by the knives they buy - and "bad mouthing" them when they fail to meet that un-realistic expectations. They just can't understand that it is a "working tool". And if you use that tool, you will have to touch up that cutting edge. It's a simple fact of life.

But I also know a number of people who "test" a cutting edge by holding a knife in the hand with the cutting edge up, and then running their thumb right down along that edge! And the people doing this seem to expect every knife they try to be as DULL as a butter/table knife! Yes, they cut their thumbs a lot. So much for learning from experience.

Just my humble thoughts to share. Take them as such.

Mikey - yee ol' grumpy German blacksmith out in the Hinterlands

p.s. I sharpen my hand sythe all the time with that simple "sickle stone" - tapered rectangular with a wood handle. Just a few drawing-type passes along each side - keeping the right angle between the blade and stone. But I don't go for a "razor sharp" or "mirror smooth" edge. Just a "working" edge. And I use that sythe for cutting everything - from grass to weeds to brush - with a short "brush" style blade. I only "hammer draw" or peen the edge on a sythe if I have a lot of grain to cut - and that's with a different style/shape long blade.

 

[Bogeyman]

I too used to try shaving my arm hairs, until i came across Murray Carter of cartercutlery.com and bought/watched his two DVDs (I'm not advertising, just pointing out!)

Watching his clips on you tube got me curious about this guy, because he really seems to know his stuff. He utilizes something he calls "the three finger test of sharpness".

He briefly does this in the following clip:

http://nl.youtube.com/watch?v=U3oUlfxWK6c

What he does is rest his thumb on the spine of the blade and gently put his three fingers of his same hand on the edge, then he very gently tries to slide his fingers sideways ( I know, sounds crazy, right! :werd: ) He repeats this at various points on the whole length of the blade.... What he's looking for is when the knife is (real!) sharp, it wants to grip into the skin and because he's moving his three fingers slowly, his fingers stop and won't slide along the edge i.e. the blade wants to cut into the skin.

By having your thumb on the spine, you'll be able to control the motion and the amount
pressure you apply to the fingers. Also because of our built-in survival instinct, the brain won't let you slice into your fingers, thus preventing you doing so.

A lesser (not just dull) sharp blade won't grip into the fingers and instead just glide along the length of the blade.

I don't think i can explain it more accurate than this, you should all just see him doing this. It really changed my definition of sharp!!

 

[woodfiend]

I use my thumbnail to test it, and it works pretty well. I thought I was the only one who did this but I guess I am wrong.

 

[mariobab]

Thumbnail test is what I use on most knives.I use also thumb pad to feel the edge.Or slide at back on my head.If blade is sticky to hair it is OK.For folders and butcher knives I shave hand.Hair splitting is useless for my needs,and wife and children was not impressed with that skill,so now I do normal sharpening.

 

[Dave Budd]

I too used to try shaving my arm hairs, until i came across Murray Carter of cartercutlery.com and bought/watched his two DVDs (I'm not advertising, just pointing out!)

Watching his clips on you tube got me curious about this guy, because he really seems to know his stuff. He utilizes something he calls "the three finger test of sharpness".

He briefly does this in the following clip:

http://nl.youtube.com/watch?v=U3oUlfxWK6c

What he does is rest his thumb on the spine of the blade and gently put his three fingers of his same hand on the edge, then he very gently tries to slide his fingers sideways ( I know, sounds crazy, right! :werd: ) He repeats this at various points on the whole length of the blade.... What he's looking for is when the knife is (real!) sharp, it wants to grip into the skin and because he's moving his three fingers slowly, his fingers stop and won't slide along the edge i.e. the blade wants to cut into the skin.

By having your thumb on the spine, you'll be able to control the motion and the amount
pressure you apply to the fingers. Also because of our built-in survival instinct, the brain won't let you slice into your fingers, thus preventing you doing so.

A lesser (not just dull) sharp blade won't grip into the fingers and instead just glide along the length of the blade.

I don't think i can explain it more accurate than this, you should all just see him doing this. It really changed my definition of sharp!!

Incase anybody tries this out,

DON'T BE SO BLOODY STUPID!!!!

I can see how it works and it obviously does for him, but I don't want to take the risk thanks.

just my opinion, of course