Tests of sharpness

[John Fenna]

How do folk test the sharpness of their blades?
I hve heard of various tests - shaving the hair of your arm is an old favourite - and slicing typing paper or newspaper that is hanging free seems popular.
I have recently been challenged to slice a sheet if typing paper (or is that printer paper these days)......that is cutting little curls from the THICKNESS of the paper (lay the paper flat and cut across the paper to remove curls without piercing the paper all the way through).
Most of my working blades will now do this - they will also slice ciggy papers in half.
This level of edge does not last too long once in the field but is reasonable easy to strop the blade up again.....
I guess this is pointless fun realy, but what tests do you folks use?

 

[Andyre]

I guess the bald patches on my arm give it away,
Once i had been shown how to sharpen my blade my arm looked like a chess board

 

[the interceptor boy]

i am the same at the moment i dont have any hairs on both arms, and also slicing curls off printer paper's.
i do not know any other way!
the interceptor boy.

 

[robin wood]

I use the thumbnail test. Some folk get freaked by it for some reason I don't know why but it seems to have a similar reaction to hearing polystyrene squeaking on glass. It is not a test for ultimate sharpness but for a good working edge and will help identify any parts of the blade that require attention. I rest the edge very, very gently on the back of the thumbnail edge facing away from flesh (towards end of thumb) with bevel resting on nail. Now just feel if the blade slides or grips on the thumbnail with the slightest pressure, you can test along the length of a blade like this and it will identify anywhere that is not sorted. This I can do in the field or in the workshop or anywhere, that is why I use it. If the blade does not grip can tiilt it up to a slightly higher andgle and see if it grips there, this would tell me that I have a sharp edge but a secondary bevel or rounded that is keeping the edge away from the nail when resting on the primary bevel.

The other test I use when sharpening at home is the slicing through a piece of A4 one but I do it quite slowly with a very gently slicing motion, this will identify any sections where I have not sharpened all the way to the edge or have remaining burr.

Personally I do not subscribe to the theory that sharper is always better. I could sharpen a blade to a 15 degree bevel which would shave nearly as well as a razor (they tend to be about 12 degrees) but it would edge roll at the sight of anything harder than a tomato. If I want to shave I use a razor.

 

[JohnC]

HAirs on the back of the arm here, If I've made a knife or got a new one, I go with Graham S's idea of making a spoon, to try a few different cuts, and see how the edge holds...

 

[C_Claycomb]

A sharp knife should be able to remove the type from a sheet of newspaper, without cutting through to the other side. However, there is no point in trying if you can't slice said paper in the normal way. Arm hair is a good test, but if you have much sharpening to do you quickly run out of test material I also have various bits of seasoned hardwood around that I use for testing.

Manila rope is very good to test edge holding and slicing ability.

 

[John Fenna]

It does seem that a bald left arm is the mark of a "knifey"
I have tried the newsprint test and the knives I have sharpened to fillet printer paper will also remove newsprint.....
To look at edge retention I carve JuJu sticks - a varient of Wood Spirits - whittle away on well seasoned hardwood and produce a plucking of feathersticks as well as batton the knife through various bits of wood.
The newsprint trimming edge does not normally last out these tests but is soon stropped back to sharpness....

 

[gregorach]

I often test using rolling papers. Back on the farm, I used to test the sharpness of my favourite long handled reaping hook by trying to cut a grass stem thrown in the air.

 

[shep]

I have to try the newsprint thing!

I usually just run it across my thumb pulp as if trying to 'shave' the worls off. Of course you don't remove any skin, but if you can feel it 'catch' nicely it's sharp enough for most uses. If you then see if it shaves, you can quickly learn what a shaving edge feels like when run across your thumb and you don't end up with silly-looking half-bald arms.

Another trick is holding it up to the light, you can often see areas that have dulled significantly as they catch the light. This is a good indication that the coarser stones have to come out.

You can also sometimes feel a burr when an edge has rolled rather than dulled. Supposedly this can just be reset on a steel, but I have had limited success with this and usually just resharpen it.

 

[Bushcraft4life]

I run my thumb across the blade (not along it!!), as Shep said, you can feel a nice catch on it if its sharp enough.

I also test on thick printing paper, if it goes through then i know its sharp enough

 

[sam_acw]

I tend to cut things with knives to see how sharp they are! Not quite as facile as it sounds, I often try making feathers on matchsticks or slicing paper.

 

[Chevin]

Like Jamie, I run my thumb across the edge as the first test. You can tell if it's getting sharp from this and without wishing to go 'all zen', it makes a different sound, somehow.

Also shave my forearms and look down the edge. If it's really sharp, you can't actually see or focus on the edge - all you see are the bevels.

 

[Wayland]

I skive a piece of leather.

My leather knives are kept sharp as scalpels and I know how they feel when cutting so that is my benchmark.

 

[gregorach]

You disappoint me Gary - I would've hoped your first test would be to try and cut through an anvil, and the second test would be to wade into a stream, throw a lock of wool upstream, and see if it falls asunder went it meets the blade. Some dragon-slayer you are.

 

[dommyracer]

I try cutting whatever it is that I am actually trying to cut.

If it doesn't cut easily, it's not sharp enough, if it does, then it's sharp enough.

I will occasionally do the thumbnail thing if checking out someone else's knife.

 

[weaver]

Shaving will impress most people. I test rather like Robin, checking on my thumbnail to see that the blade has an even edge and no burr. All my planes, draw knife, chisels and most of my knives are good strong cutters not thin scalpels. I have a select few knives that are real slicers.

For a truly sharp, sharper than a razor test try cutting a tissue. Any slight imperfection in the edge will tear the delicate paper.

 

[Dave Budd]

Simple. If it cuts what I need it to cut, then it is sharp enough. If it doesn't then it's not sharp enough

I don't bother testing to see if it's sharp after sharpening it up coz I KNOW it will be If it's somebody elses knife/axe/etc then I assume it is sharp until I have tried it, then I will go and sharpen it for them (with permission of course )

 

[Wayland]

You disappoint me Gary - I would've hoped your first test would be to try and cut through an anvil, and the second test would be to wade into a stream, throw a lock of wool upstream, and see if it falls asunder went it meets the blade. Some dragon-slayer you are.

I've always been rather fond of dragons, I think they are just misunderstood.

 

[andy_pevy]

I've always been rather fond of dragons, I think they are just misunderstood.

You have not met my mother in law then......

Andy

 

[Warrigal]

I find there can be big differences in knives that will shave hair. Some will scrape others the hair will jump off in fright as you wave it over. So my standard is.....

Carl