No light reflected, but still not sharp

light reflected means you are not sharp
not reflecting light does not mean necessarily that you are sharp. but you are getting closer.
I strop with a the same angle and very light pressure.

somebody mentioned you are juggling many plates in another thread, and I seem to agree.
I also believe you mentioned you have a fixed angle sharpening system on its way.....this is good in my opinion.
having, using, and learning a fixed angle system really helped me to understand sharpening.
 
Bo, what's your exact technique for detecting reflecting light? Once it stops reflecting light, it should cut paper with ease, no matter what.

i wear a H1 and hold the knife against a black/dark background and also avoid scattered light to reach my location. Then i try to see the reflected light which gets 180degrees reflected from the H1 right into my eyes.

It is challenging to see reflected light from a sharp edge. You cannot do it by any means with sunlight. That's why i use the H1.
 
115: got it, thanks!

Bgentry: okay so it doesn't mean it's sharp just because it doesn't reflect light. Makes sense. What's the 3 finger sticky method? I've never heard of it. I have a head lamp I can use, would that work for the reflection test? Thanks for the advice, Brian.
 
kreisler said:
Bo, what's your exact technique for detecting reflecting light? Once it stops reflecting light, it should cut paper with ease, no matter what.

i wear a H1 and hold the knife against a black/dark background and also avoid scattered light to reach my location. Then i try to see the reflected light which gets 180degrees reflected from the H1 right into my eyes.

It is challenging to see reflected light from a sharp edge. You cannot do it by any means with sunlight. That's why i use the H1.
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A good advice well put.
No one can change physics of the light wave - its wavelength is 0.4-0.7 micron, and a reflective surface less than that will not reflect it.
When I sharpen ceramic knives which produce no burr at all, cease of the light reflection is the main check telling me the edge should be moved to a finer grit.
Edge under 0.4 micron is sharp enough to slice paper even if not fully apexed.

B bucketstove - sorry, I don't understand why you referenced to the "lower limit for a human eye to discern an object (≈ 2×10^-4 m ) "
We can't discern a single photon, but we look for reflected light of zillions of them, and the reflected light is by orders wider than the light wavelength thanks to scattering.
Blunt is an edge 1 micron and over, and it sure reflects lots of light.

Light reflection cease, as many have stressed above, does not necessarily mean the edge has been apexed.
 
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What's the 3 finger sticky method? I've never heard of it.
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It's a technique popularized by Murray Carter, who is a sharpening guru. I own his digital video series and found them to be very valuable. The 3 finger test is one of the more dangerous tests of sharpness. Here's Carter discussing and demonstrating the technique:


Brian.
 
I have Murray's dvd's, but haven't watched them in years now.

I have a set of five of his Muteki kitchen knives I purchased years ago while he was still living and working in Japan.

But my claim to fame with Murray is that I convinced him to make his first neck knife. (I have, I believe, the second one he made after he convinced himself that it was a great concept...and one fancy one that he brought to the Blade Show when he was going for his master smith rating.)

Muteki.jpg

Carter2.jpg Carter.jpg
 
wootzblade said:
B bucketstove - sorry, I don't understand why you referenced to the "lower limit for a human eye to discern an object (≈ 2×10^-4 m ) "
We can't discern a single photon, but we look for reflected light of zillions of them, and the reflected light is by orders wider than the light wavelength thanks to scattering.
Blunt is an edge 1 micron and over, and it sure reflects lots of light.
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For comparison, so you can click on it and maybe search about it.
Here is another
Comparisons as diameter:
≈ ( 0.3 ≈ 1/4 ) × diameter of an average human hair (≈ 80 µm )
≈ wool fiber diameter (≈ 20 µm )
≈ 2 × typical cotton fiber diameter (≈ 10 µm )

I can see cottons threads if I get them close to my eyes, they catch the light, no way I'm trying that with a knife :) there is no need.

What is limited is the eye’s resolution: how close two objects can become before they blur into one. At absolute best, humans can resolve two lines about 0.01 degrees apart: a 0.026mm gap, 15cm from your face (26 micron 15cm from face). In practice, objects 0.04mm wide (40 micron, the width of a fine human hair) are just distinguishable by good eyes, objects 0.02mm (20 micron) wide are not.

Assuming the closest distance an adult can focus (~100 mm) and an average maximal acuity of 1 MAR, the smallest visible size boils down to 29 microns. A young child can focus at distances down to ~50 mm, and can have a visual acuity of 0.4 MAR, which yields 6 microns.



When visually inspecting an object for a defect such as a crack, the distance (d) might be around 12 inches (30.48cm). This would be a comfortable viewing distance. At 12 inches(30.48cm), the normal visual acuity of the human eye is 0.00349 inch (88.646micron, 0.088mm). What this means is that if you had alternating black and white lines that were all 0.00349 inch (88.646micron, 0.088mm) wide, it would appear to most people as a mass of solid gray.
 
Kreisler: I stand below and in front of a light source and I angle the edge so it's facing me. I then move it around until I do or don't catch a glimpse of light off the apex. Thanks, those are good tips, but what's an H1?

Bgentry: wow that seems like a great test! Thank you.

Blues : those are really nice knives, thanks for Sharing them.

Bucket: thanks for the math lesson :) a bit beyond me as of right now, but I always enjoy learning that stuff. How much I remember has yet to be seen.

Thanks guys,

Bo
 
The usual number for "the smallest particle you can resolve" is something like 25 microns, but we don't need to "resolve" the edge of the blade, just detect the scattering of light from the blunted apex.

As an analogy, you can easily "detect" 1 micron dust particles in beam of sunlight because they scatter enough light to be "visible."
 
ToddS said:
The usual number for "the smallest particle you can resolve" is something like 25 microns, but we don't need to "resolve" the edge of the blade, just detect the scattering of light from the blunted apex.

As an analogy, you can easily "detect" 1 micron dust particles in beam of sunlight because they scatter enough light to be "visible."
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Thank you Todd, that's what I was trying to say but couldn't get through.

@Bo-dacious you will see that tiny burrs and glimpses of light from the edge apex sometimes are better seen under an artificial light rather than daylight, H1 stands for Halogen lamp
 
bgentry said:
Blues Blues that's neat! I have quite a bit of respect for Carter, but I don't own any of his blades. Yet.

Brian.
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Well, if you ever make your way to the mountains of western NC, give me a holler.
 
Bo-dacious said:
Thanks, those are good tips, but what's an H1?
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I don't like the company (marketing, distributors, retailers, products) and i certainly don't support them, not even in my mind, if not with my actions. That's why i didn't mention any further details re "H1". But i must admit that their headlamp product (with name "H1 ****") is exceptionally likable, probably the smallest 1xCR123A power LED headlamp on the market, even smaller than Zebralight headlamps. My H1 sports a CREE XM-L2 NeutralWhite LED, not a Halogen bulb.

I refuse to say the company name out loud. As mentioned, apart from the H1, i am no fan of that Chinese manufacturer for various negative reasons.
 
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