Opinions on an Edge Test

I have been trying a new edge test and I am iterested in opinions on whether it is an accurate indicator of sharpness.

Lay a standard sheet of Laserjet/Copier paper on a flat surface and slice a layer off of the surface without cutting all of the way through the paper.

My preliminary testing indicates that this is a reasonably accurate indicator of shaving sharp without the limitations of running out of hair or offending the spousal unit.

AKTI Member No. A000370
Sal Glesser of Spyderco uses this test as one method of checking sharpness in the SharpMaker 204 instructional video.

It's useful for the tip and belly of a blade, but it's not practical for the full length of most blades since they're curved, especially those with a recurve or serrations.

Knowledge without understanding is knowledge wasted.
Understanding without knowledge is a rare gift - but not an impossibility.
For the impossible is always possible through faith. - Bathroom graffiti, gas station, Grey, TN, Dec, 1988

AKTI Member #A000831

[This message has been edited by Codeman (edited 12-20-2000).]
Sep 3, 2000
I like standard newsprint as a medium to test for sharpness, sharpness over the full blade edge and to test for knicks on the edge.

It's a cheap and uniform standard medium that is very fibrous in nature and much less rigid than computer paper or notebook paper. A moderately sharp blade that will nicely slice computer paper will likely tear newsprint. Similarly, merely shaving-sharp edges will tear newsprint when encountering edge imperfections.

When sharpening after hard use of a blade, I find that I can detect edge imperfections with newsprint that I can't even see with a 30X optical scope.

After a few slices through newsprint, you'll find that you can not only feel the difference in sharpness but also hear the difference as the blade cuts through the newsprint fibers.
I keep saying that there has to be an objective, quantitative way to measure sharpness and nobody has an answer for me.

When the US Military buys an airplane, the contract doesn't say that the plane has to fly "very high" and "scarry fast" while carrying a "really big payload." No, the put numbers to these specs and they spell out exactly how the tests will be conducted so that when the planes are delivered, they can test them and, if they don't meet the test, can reject them.

I have to belive that when the US Military buys knives, they don't say they have to be "really long" and "scarry sharp." No, they specify how long in inches or centimeters and they spell out exactly how that length is measured. My guess is that they somehow specify how sharp and that there is a repeatable, objective, quantitative test.

For Christmas this year, a number of folks on my list are getting Brothers P-Touch label makers. I love mine. I made neat labels for all the Bill's Custom Cases that all my best balisongs are stored in so that I don't have to open them up and search through all them to find a specific knife. Anyway, if you haven't seen one of these things, it sort of looks like a baby typewriter with a little display. You type in what you want, edit it on the little display, and then press the big button and the machine generates an excellent quality label tape. When the machine finishes printing, you push down on a lever and it cuts the label off. Obviously, there's a little knife blade inside. I doubt very much that Brothers Corporation makes knife blades. Like many of the other parts in this product, they buy them from a supplier. Whenever you have two businesses in a supplier/buyer relationship, there has to be a contract that spells out exactly what the part in question is. The contract says that if the supplier makes parts that meet or exceed the specification, the buyer will buy at least a certain number of them at the agreed price. If the parts don't meet the specification, the buyer doesn't have to buy them and the supplier is stuck with them. If the parts do meet the specification, then the buyer has to buy them. So, the buyer must write the specification very carefully to be sure that the parts will meet his need. In the case of the little knife blades for these label makers, the blades must be at least some minimum sharpness. If they're not sharp enough, then they won't cut the label tape easily and cleanly and, therefore, they won't work in Brothers' product. To avoid being stuck with a bunch of useless parts they can't use and to assure that they get the parts they need to make their product, Brothers needs to specify the sharpness. On the other hand, the blade supplier needs a repeatable, objective, quantitative test that they can pass. If the contract says, "Hair poppin' sharp," well now it's a question of who's hair and how exactly you go about trying to shave it. Without a well-defined and repeatable test, the supplier can't be sure that Brothers will buy his blades. He could make the best, the sharpest blades he's ever seen and Brothers could reject them as "not sharp enough." Then, he'd be stuck with 'em.

So, there must be a well-defined, repeatable, objective, and quantitative test that they can use to define the supplier/buyer relationship.

Well-defined: both parties can understand exactly how the test is conducted. Both parties can independently and yet identically construct whatever facilities are necessary to conduct the test and can independently conduct the same test.

Repeatable: when the incoming inspector at the buyer tests a given blade using his equipment, he will get the same result within an acceptible and defined tollerance, that the outgoing inspector got at the supplier when he conducted the test using his equipment.

Objective: test outcome of the test does not depend on any biases of the person conducting the test.

Quantitative: the test results in a measurable quantity, not "scarry sharp" or "really sharp", or "The sharpest @#$! thing I've ever seen" type results.

Balisongs -- because it don't mean a thing if it ain't got that swing!