Thread: Weight On a String sharpness test

Thinking of ways to quantify or measure sharpness, I came up with this contraption. I have not actually built it yet.

Basically it is a weight on a string and a razor, all held on a plank. The plank is pivoted. The razor is held stationary in relation to the plank to prevent scraping action on the string.
As the plank is turned, the pressure of the razor on the string will increase. At some point, the razor will cut the string. That location is recorded and used as a measure of the blade's sharpness.

The test will have to be calibrated for that particular string, weight and geometry, but after that should be fairly consistent.

A good consistent string that somewhat resembles human hair may or may not be a mono-filament fishing line.

This test could be useful to compare sharpness between different razors. Or use the same razor to compare different stones or honing techniques. The test is less subjective than some of the other sharpness tests.

YMMV

Clever concept but I wonder if it will work as you expect. If your increments are related to hones, 12k is not necessarily much sharper than the lower grits tho of course smoother.
Look forward to your results.

Some similar ideas have been proposed here and on other fora, I don't know what happened to the other contraptions or if anyone has ever even built one. If I remember correctly though the monofilament was found to not be as consistent as previously assumed or as stated by the manufacturers. I don't know if monofilament versus fluorocarbon would make a difference, but I also don't know if the tests run on the mono was on a quality product or store brand.
What I do know is that a final razors edge has to be both sharp and smooth. I don't believe that any tool could measure the smoothness like a human face. Now if someone found a contraption or calibrate one like yours to work as a test for the bevel set, that might be the key, as the hardest part of honing to learn, this might help some newb honers and veterans with a serious case of hone mange.

Originally Posted by onimaru55

Clever concept but I wonder if it will work as you expect. If your increments are related to hones, 12k is not necessarily much sharper than the lower grits tho of course smoother.
Look forward to your results.

Yeah, I was just wondering about that. Micro serrations and/or a wire edge after 1K could cut the string just as easily as a 12K finish. Something to think about...

Yes, those divisions were supposed to indicate stone grits.

Yeah this is on here probably 20 times in the past and all over the Knife forums, in fact they have actual machines that do this very accurately...

http://www.catra.org/pages/products/kniveslevel1/st.htm

The weakness in using it for razors is that it doesn't tell any more than sharpness, which a thumbnail or arm hair will also tell you quite accurately too...

Sharp is good enough for just about every other cutting tool, but when you start dragging that tool across your face the definition changes to sharp and smooth...

Here is a way to test the sharpness-hone it to the best of your ability ,shave with it ,and if you think its ready,sent it to a honemister you respect and get thier opinion on it. THAT will let you know how sharp it is-for sure.

Originally Posted by deighaingeal

Now if someone found a contraption or calibrate one like yours to work as a test for the bevel set, that might be the key, as the hardest part of honing to learn, this might help some newb honers and veterans with a serious case of hone mange.

The bevel is certainly a big challenge.
Everything has limitations in the sense that sharpness tests cannot replace magnification & vice versa but as with the HHT any calibration or personalisation of a system is VIP.

I would only need the string to be consistent in each spool, from beginning to end, not necessarily between spools. There is no trusting different spools. One spool should last a long time.

I wonder if dental floss is harder to cut with a rough blade vs a smooth blade. It would make it better suited for this test.

Don't forget, a lot of synthetics, mono especially, stretch a lot. Human hair doesn't stretch as much. You can get small nick in mono that won't tear through till they see a specific amount of weight. You also have to factor in micro serrations. They will cause cuts to happen faster.

Not all that long ago as time travels, there were martial artists who tested for higher ranking by having to stand on naked sword edges. While this sounds scary, and was discontinued as a practice, it is possible.

The principle would be the same with this device. As long as the string made perpendicular contact with the edge and did not slide laterally the string will not cut. Blade edges are most efficient when they move laterally through the material. A slicing motion if you will.

If you have the opportunity to see the Catral device in action, it slices, it does not only push through the material being cut.