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.

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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.

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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.

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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.

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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.

An interesting idea!
I would have wanted something to tell me when I was at "shave ready" so bad when I first started honing.

I never did find anything though, except 2 things.
One was the TPT, which to me is the best method for assessing while honing. The thing, of course, was to calibrate it. Gain experience if you will:)
The second was the arm hair test. That too, took quite a while to get the right feel for, but now it is of value to me, and tells me what I want to know.

I'm looking forward to see if this concept gets to a usable level and how you find the consistency of it!
As the others have noted, I'm not sure this can be used to assess the smoothness, but we'll see when you get it done what you find
Good luck!

I'm not sure of how a strand of monofilament is constructed but IIRC a human hair is segmented if you look at it microscopically. A couple of years ago someone figured out that if you hold the strand of hair with the root outboard the edge is more apt to catch between segments and cut the hair more easily than if it is held with the root inbound. In that case the hair's segments will slide over the edge. Cutting hanging hair, monofilament, dental floss ..... there is a vid wih Mastro Livi cutting up a feather ..... is all well and good but in the final analysis the question is always "how does it shave." :)

I tried a few strand-cutting designs and got some to work pretty well, but I eventually gave up on them. Even though fairly consistent results can be achieved, you get more (and more useful) feedback from your tactile senses, like how the razor feels on a hone, or 'stickiness' on the thumb pad test. Other than shaving, those are about all you need, and they're quick 'n easy.

Fun to mess around with, though.

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Originally Posted by Mike Blue

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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.

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If you mean this machine here:
Sharpness tester

The web page says this:

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The test utilises the constant cut depth method in which the blade is pushed normally without longitudinal travel into the test media The cutting force is recorded as a measure of the sharpness, which means the lower the force the sharper the blade. The test media is either 8 mm square or with a 3 mm wide side bead silicon rubber which is bent around a 20 mm former and the cut is made into the outer periphery of this bend. This causes the rubber to open up the cut as the blade penetrates, thereby reducing the point of contact of rubber and blade to the tip of the edge only.

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It looks like they are saying there is no slicing motion involved.

I wonder how much that machine costs to buy AND operate. That silicon test media can't be cheap.

On the other hand, this design costs close to zero to build and close to zero to operate. One inch or less of string per test. Much better suited for hobbyist use.
And if properly calibrated, I would argue that it is every bit as accurate as the high dollar one.

I suppose it is better suited for knife sharpening or bevel setting on a razor rather than polishing the edge. I intend to find out. :D Might take me a while, I will have to find me a razor to restore.

I also agree that honemeisters have no need of it, it is more for beginners' use.

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Originally Posted by JimmyHAD

I'm not sure of how a strand of monofilament is constructed but IIRC a human hair is segmented if you look at it microscopically. A couple of years ago someone figured out that if you hold the strand of hair with the root outboard the edge is more apt to catch between segments and cut the hair more easily than if it is held with the root inbound. In that case the hair's segments will slide over the edge. Cutting hanging hair, monofilament, dental floss ..... there is a vid wih Mastro Livi cutting up a feather ..... is all well and good but in the final analysis the question is always "how does it shave." :)

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I agree the HHT is easier with the root outboard... Ironically on the shave test the cut is reversed :) Just an observation.

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Originally Posted by onimaru55

I agree the HHT is easier with the root outboard... Ironically on the shave test the cut is reversed :) Just an observation.

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I hadn't thought of that before you mentioned it but it is very true. Maybe that accounts for our ongoing struggle with comfortably removing those pesky whiskers that just keep coming back. :)

Mono filament is extruded. It is generally extruded vertically starting as a liquid and hardening as it is exposed to the environmental change after the die. It is unfortunately not a very accurate process, if I remember correctly they utilize gravity to force the extrusion process. This causes the mono to form in a smooth slightly undulating pattern. The measurement listed for diameter isn't even the size of the die, but the experimental average from that size die.
When I mention inconsistencies there will be inconsistencies within the spool.
It has been some time since I've researched this so it may have changed and I may have remembered slightly different, but this should give you an idea.