How do you test sharpness?

Klesk

Klesk

Gold Member
Joined
Jan 5, 2003
Messages
1,105
How do you test if your knife is sharp enough? Can you tell if parts of the blade are sharper/duller than others?

What I've been doing is lightly tapping/sliding the tip of my finger across the blade, starting at the choil and working my way to the tip. If the knife is really sharp, I can feel the blade biting in to the top layer of skin. If a portion of the blade is duller, then my finger just skips over that part, without getting cut. The problem is, over the years, the tips of the fingers on my right hand have toughened up to a point where I can no longer tell if a blade is sharp using that method.

Just tonight, I worked on my Sebenza for about 5 minutes, then touched the blade with my finger. It didn't feel sharp, but when I ran the blade over the back of my forearm, a clean, hair-free patch appeared, with very, very little pressure exerted. So the knife is sharp, but my normal test did not reveal this.

What do I do now? My right forearm is already bald; my dad can always tell when I've been going through my EDCs and sharpening them. On top of that, it seemed that the "touch test" was able to discern between really sharp, and really, really sharp in a way that shaving is unable to do.

Any suggestions? :confused:
 
I too have bald spots all over my arms. My other test is to hold up a piece of computer paper, and start the knife at the top of the paper and work my way down. If you have to stab the paper in the middle and then drag down, its not sharp enough. But if you can start at the top edge of the paper and cut down, then you have a sharp knife. This is the only way I know, but I am pretty new to the knife scene.
 
I've done a ton of knife grinding and also have the bald spots. :D

We only used the "skin slicing" technique to determine if there were any hangups. This would indicate that the blade had burrs.

The best test, IMHO, is to get a sticky note and hold it on the side with no glue in your left hand.

Then hold the knife at the center of the spine with your right.

Do not "slice", as even a dull knife will slice paper, but "push" cut the note.

The further away from your finger you can do this the sharper the knife.

The reason we always used a sticky note is because different kinds of paper have different properties. The properties of the sticky notes always stay the same.


Hope this finds you well-
 
John Juranitch of Razor Edge Systems sells a patented tool that's been in use for some time. It's the size of a pencil, made of some special material.

In one use, you hold the tool at a 45 degree angle and then rest your knife blade on it. If it slides down, your blade is not sharp. In the other test, you hold your knife edge-up and then run the end of this tool along the edge, where you get tactile feedback as to any pits and stuff present anywhere along the blade edge.
 
Yeah, Juranitch's Edge-Tester and its instructions are great. Actually, most soft-plastic (as opposed to the hard, transparent plastic) ballpoint pens will work about the same and cost less. If you slide the edge across the barrel of the edgetester, the friction you feel will tell you how dull the knife is. Holding the edge at an angle and letting gravity push the edge into the edgetester (do this for every half or quarter inch of the edge on both sides) double checks the method of sliding the blade across the tip and sides of the edgetester. You could theoretically have a completely flat edge which would slide almost effortlessly across the edgetester, but the other test would catch that fact when the edge doesn't catch on the edgetester.

Best $8+s/h ballpoint pen-shaped dohickey I've ever bought.
 
Shaving arm hair, running the edge lightly over my left thumbnail to check for irregular edge. Cutting the items that I want to cut with the knife.
Use to check whether the knife slides or catches on my nail at a 45 angle.
 
First, if you can actually SEE the edge, it's not sharp enough. Beyond that, I simply run the edge across my thumbnail. If it digs in across the entire edge with no pressure, it's fine with me.
 
I see how much pressure it takes to shave hair off of my arm, see it if cuts into the top layer of skin, and see if it grabs my thumbnail.
 
Lots of ways, seeing how it cuts a piece toilet paper folded in half, believe it or not TP will tear on a dull edge while a sharp one will pass right through.

Seeing if it dig into or slides across my thumbnail, cutting Styrofoam peanuts, or a Styrofoam cup will do.

How about trying to cut the glue off of a cigarette paper while holding it in the air.

Try cutting a foam ear plug, these will flatten out unless the blade is hair poppin scary sharp.

I like to hold a piece of paper and make the slices so thin and so close together the little slices curl up like hair.

See if it will fillet paper, only a sharp blade with good edge geomotry will do this.

See how many pages of newspaper it will slice thru,(be careful doing this, as the newspaper has a tendancy to shift while you cut, meaning you might end up cutting where you didn't expect to cut):eek:

Shave your significant other with it.:eek:

See how it slices a tomato or some othe soft skined veggie, a dull knife will smush before it cuts, a sharp one will dig in and cut easily.

Send it to me, if it's sharp I'll cut my self for sure, ain't never been cut by a dull knife yet, got a nasty bruise from one once though.:(
 
the test I most often use is the bald spot on the arm.

sometimes I take a rubberband and hold it between my fingers taught then lightly drag the blade over it, if it popps at the touch of the blade it is sharp enough for me.

also I use magazine paper if it makes a clean slice then it has a good edge.
 
I too do the arm test. Once, I did the test on the side of my right leg, but that was a long time ago. I am better now.


Cerberus
 
I'm happy. On a day to day basis that means opening the mail, cutting the packing staps on the cases of printer paper, sharpening pencils for sketching (electric pencil sharpeners don't expose enough lead) and maybe a bagel, apple or banana. I don't try to get my carbon steel Lightsabre sharp because I know the packing straps will kill the edge. I'm happy with a working edge. YMMV

Frank
 
I don't keep all of my knives razor sharp. Most of them I sharpen up very good and let them degrade down to a good working edge. Then I use them until they don't work anymore for what I want them to cut. No sense in KEEPING every knife shaving sharp - never had to shave a carboard box or anything.

On my edc knives, I use them until they won't easily cut plastic packaging anymore. That's a pretty good indicator. When I sharpen them back up though, they are razor sharp! I test for razor sharpness by shaving hair, cutting paper, and dragging it across my nail without catching.
 
Lay the blade at a very shallow ange against your thumbnail. Slide back and forth as if trying to shave a small slice of nail. Gradually lift the spine of the blade and steepen the angle as you do this. The sharper the blade the shallower the angle at which the blade will 'bite' and begin slicing the nail. I've got the feel for doing this test now and find it a very reliable guage.

I've got all my arm and leg hair and have had for 12-months.
 
You must log in or register to reply here.
Back
Top