How Do You Test Knife Sharpness?

Why can't you shave arm hair with you serrated blades? They should be able to do so if you want to get them sharpened in that manner you just need to polish to the necessary grit size.

Anyway, the three tests I use for sharpness are:

1) see if the blade will catch on my thumb nail if pulled edge wise down across it (blade held perpendicular to direction of pulling)

This tests for a nice thin edge and makes sure no burr is formed (on one side the knife will grip well on the other side it will slip)

2) run the blade across a rough section of my hand to see how it bites

This makes sure that the edge has the required smooth microserration pattern I am looking for

If the sharpening is to a suficiently high grit then I'll try a shaving test just becuase its cool, if it passed the above two it will not fail this anyway.

These tests can be done very quickly while sharpening then once they are passed I proceed to the final test.

3) try to cut suitable materials

These test can be done on serrated blades as well with slight modifications, for example I have a hard plastic dowel that I use intead of my thumb nail on serrated blades.

-Cliff

 
I generally test sharpness by slicing a thumb or finger.
Thanks for all the suggestions. I knew there were better ways
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Bill
 
You topo Bvioll?. Dfamn basndsages!2

(translation: You too Bill? Damn bandages!)

Sdhadews
(Shades)
wink.gif

 
I usually do it by accidentally slicing the hell out of something: My finger, my pants or shirt, etc.

Spark
 
Thanks, everybody, for your feedback. I'm trying out some of the methods you all (or y'all) posted. I work at a marina so we have a lot of line in our yard and shop but I normally sharpen knives at my desk so I can't be dragging around a spool of 3/4" nylon and getting pieces all over the carpet. I do open a lot of UPS shipments but we never seem to get them when I'm doing any sharpening. I must be doing something right though. I sharpen knives for most of my crew and they're happy with the results. Thanks again.
 
Hello,

I have seen many time Fred Perrin
checking the edge on the back of
one nail. To see if the blade bites.

Personnaly I tests my blade on my Mother In Law ...

JM

 
JM,

That made me laugh out loud.
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Does she dull the blade fast?

Blues
 
This is sorta like the newspaper test but harder (softer?) to do. Take a peice of toilet paper about 6 or 8 inches long. I generally use Scott brand. It is not as thick as some others. Hold it up and stab the knife through it at the top next to where you are holding it. Now see if you can push cut down the length. I admit that I am still a novice at sharpening. I can get my blades to cut through, but they bind and tear a little along the way.
 
If it will cut paper without riping it or you having to push it in without any hard effort-- it is a sharp knife. Also, if it will cut thin plastic paper without going over it again --it is a sharp knife. I know because I work retail and have to open boxes and unload trucks.

Yours Truly,
 
I always get the "what the heck are you doing?" question when I check for sharpness by running the blade at an angle on my head. If the edge bites my hair, then it's sharp.
 
I've cut so much stuff it's not funny, one of the ways that I tell if the edge is there yet is to see if it can cleanly slice through paper towels or kleenex tissues since the fibers are so soft they tend to move out of the way and only a very sharp knife can cut it. Also I have a ritual, when in the bathroom sitting on the magazine reading chair/toilet and the toilet paper roll is empty leaving only just the paper spool that is begging to be cut off, I test all my knives to see if I can make one cut lengthwise on the spool and then insert the tip to pull the spool of the holder and drop it in the wastebasket. Weird uh? for some reason my wife doesn't follow this procedure...

Others I have heard do the back of the head test, if the edge can catch hair then it's sharp enough, (works for those that have hair there of course, mine has either turned gray or turned loose lately)

my .02 or .03
 
My left arms bald, I won't put anything that sharp to my own throat, the wife won't let me shave her legs, my sons arm is bald too.
A piece of scrap leather works, I just shave a paper thin piece off the flat surface.
P.J.
YES, it is sharp, just keep your fingers out of the way!
 
I NEVER shave my left arm completely bald, that would look stupid! DOH!
Actually, since hearing all the negative thoughts about this, I've decided to test all my knives by shaving my dog's butt. Sure, it'll make him look stupid, but HE doesn't CARE!
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BTW, Why DOES Frank have to shave his fingernails? Does Minoxidil work that well? Has anyone told Bald1 or Doc?
HEHEEE! My wife says I am a BAD man!BAD! BAD!
At least she doesn't make me go lay down in the corner!

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I cut it, and I cut it, and it's STILL too short!

 
I found long ago, when both arms were bald and I was still trying to perfect my sharpening technique, that my leg hairs were even tougher to cut than my arm hairs, so I now use those. Living in shorts much of the year helps. Also, my wife no longer sees bald spots on my arms, so she is happy.

pat
 
Also, all of my Clipits, reguardless of serration patterns, have shaved. Turned me on to THEIR serrated edges for the last 5 years. Currently rethinking that tho
pat
 
There is a lot more to the type of edge you put on your knife than many think. People on these forums aside, most people have no clue about the different kinds of edges you can put on a knife.

Anyway, when sharpening the knife, I run my thumb along it to see if the edge is keen enough to catch on the ridges of my thumbprint. Once I think I have it and there is no wire (it catches evenly on both side of the edge), I grab a piece of newspaper, let it hang freely, and swipe the blade through it. This tells me if the any portion of the blade is not right, because it will TEAR when the paper catches that spot, rather than slice. Just because you got one protion of the edge right does not mean you got it all.
Cutting lightweight newspaper tells me that I got just the right edge I want: not too smooth, but not too jagged. I don't want my edge to be TOO smooth, or it will not slice fibrous material well. I have my own "secret" technique for getting the perfect edge, and it involves a DMT diamondstone and a japannese waterstone. Like many other here, I am very proud of the edge I can get and researched many different techniques before I got the one that works in real world cutting tasks.

I also like to trim a small steak of flesh off my finger callouses to make sure the knife really gets through flesh efficiently, but this only tests a small portion of the blade to make sure I got the right type of edge. The newspaper slice tells me if the edge is uniform.


James Keating says that a knife should "seek bone" if it has the proper edge. Ernest Mayer of Black Cloud Knives taught me the "bump test". But alas, it is only for plain edge knives, so it doesn't apply in this thread.

The newspaper slice should work on a serrated knife also if you sharpen it completely uniformly, which is a tedious task. The teeth should glide through the newspaper without tearing. This is very difficult to achieve because the serrated edge has so many facets that you only have to miss one facet of one tooth and it will catch on the newspaper. It you really put some sweat into it, and want a perfect edge, a serrated edge should also glide through newspaper without catching. It usually takes me some sweat on my brow and patience to get this edge by hand, but it can be done.


thaddeus
 
I sharpen sometimes as many as 15 blades a day, so shaving is not really an option anymore. I'm not that hairy to begin with. I check the sharpness almost entirely through feel, either by feeling the edge, or by slicing paper. How easily the edge moves through paper can tell a lot, and eventually you can feel different degrees of drag. For quick testing-good 'nuff testing-I touch the edge to my thumbnail to see how much it sticks. My left thumb is all grooved now, but I keep it shallow enough that I can file them out. I use the pads of my thumbs and index fingers, as well as the side of my index finger, because it's less calloused. there's so much scar tissue on my fingertips that they're not 100% reliable anymore. I've got as many horizontal lines as circular ones on my prints.

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A flute with no holes is not a flute, but a donut with no holes, is a danish.
 
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