I've been thinking about sharpness testing lately. We talk about whittling, HHT, finger print separation, violining, and paper slicing etc etc. We all know hairs aren't uniform. I can't help but approach problems scientifically, its my nature. Now, I understand that this is completely obsessive and only necessary because I am completely obsessed. But I've been thinking of making a machine lately. I want to measure sharpness with a number that can be precisely compared blade to blade. I picture something like this: the knife is held in a vice blade down, a uniform cutting medium like plastic q-tip sticks or maybe toothpicks are suspended from a scale (a scale that holds the maximum reading), and the scale is pulled slowly upwards along a track until the medium is cut. I'm wondering if anyone has any thoughts or ideas on making this. Or if such a tool already exists.
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Sharpness Testing
- Thread starter Ryan J
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I have a few things I do at work to test sharpness.
I roll about a few sheets of parchment or wax paper, then wrap with about 10 feet of plastic food wrap, and cut it on the cutting board without smashing it (think of it as a straw).
Most knives will not cut even with power pressure, I'm not happy until I cut it with light pressure and perfect Os.
I roll about a few sheets of parchment or wax paper, then wrap with about 10 feet of plastic food wrap, and cut it on the cutting board without smashing it (think of it as a straw).
Most knives will not cut even with power pressure, I'm not happy until I cut it with light pressure and perfect Os.
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Someone had posted about this device (EdgeVue) a while back, and it's obviously expensive; but, it might provide some inspiration as to how to go about testing in a more controlled manner. They utilize both hardware (fixtures, pressure sensors, etc.) and software to record the force exerted in making a cut through the 'test' materials (paper cards, it looks like; maybe other materials). Some pretty interesting videos at their site:
http://www.edgevue.us/Videos/Videos.html
David
http://www.edgevue.us/Videos/Videos.html
David
I experimented cutting thread (although you could use something else like fishing line). The thread is tied into a loop and put on a knife set edge-up. The loop goes around the edge vertically. A paper clip is put on the loop and washers are added. This provides the weight, pulling down on the thread. Add washers until the thread is push-cut. There are lots of ways you could modify this, too.
Dave
Dave
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But then you get into edge geometry and blade profiles. Is it that this knife is sharper? Or that is has a thinner grind? Or is it that it's convex ground instead of hollow? Or is it the carbides sawing the medium instead of cleanly slicing it on a microscopic level?
And then the same argument can be found all over the place.
And then the same argument can be found all over the place.
The problems are-
-it is hard to make a machine that will provide accurate measurements
-it is hard to find a material to cut that is uniform from one sample to another
-it is hard to find a material to cut where you are measuring the actual cutting and not the friction of the sides of the blade going through the material
David Martin
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Yes, the blade profile, edge grind, steel used and heat treat do come into play during cutting tests. DM
These simple set-ups are still useful to compare specific knives, despite the differences in angle, thickness, etc.
I guess it should be called something like "cutting ability tests"
They would show specifically how much force is needed to go through the same medium and nothing else.
I think testing specifically for sharpness would require precision measurement instruments and a very meticulous process to have good results.
I guess it should be called something like "cutting ability tests"
They would show specifically how much force is needed to go through the same medium and nothing else.
I think testing specifically for sharpness would require precision measurement instruments and a very meticulous process to have good results.
We get to caught up in the definition of sharpness. Yes if an edge is fully apexed and the burr removed it is sharp. A sharper knife cuts better imo. As far as variables such as geometry and convexing then my test would show which cuts easier. So i dont see that as a problem really. Guess i should of been more specific.
Well, if you have two of the same knife and put a different grind on one then yes, you can compare geometries.
But if it's two knives of different thickness and steel it goes back to my last comment saying it would only show the differences in cutting ability for those two setups.
The exact same edge grind on my Leek would cut much better than my Esee4 using the same profile, just clarifying what I meant.