150 gf sharpness

[grepper]

Thanks Mr. EOU. That makes total sense.

Mr. EOU proclaimed, "To tell you the truth, we are very intrigued by the sharpness levels reported in single bevel edges. We do not doubt for a second that these edges are easily sharpened to that level because it is an edge commonly used in medical applications and we have seen reports of very similar successes before."

That is indeed very interesting.  I started a new thread:
http://bessex.com/forum/showthread.php?tid=167

[SteveG]

Truly fascinating! I'm still not entirely convinced, but can accept that the geometry might not be as big of a factor as I currently think.

Assuming that the media would only need to be severed to 25% of its diameter to fully separate, that's still over 60 microns. If an edge was at 30 degrees inclusive, and the edge width was less than a micron, the blade width at 60 microns penetration would be over 30 microns (i.e., the width at 60 microns "up" from the edge, which presumably would be in contact with the media to some extent). I have to believe this has some effect on the reading, but I can also accept that the total effect might be smaller than, say, the difference between using the test clips instead of the spool, and therefore doesn't explain the knife vs chisel paradox (another theory shot down by facts).

[Ken S]

I have a Chinese vegetable cleaver. I sharpened it with 15°bevel angles (30° edge angle) before I realized that the original angles were more acute. 

The next time I sharpen it, I will use 12.5° bevel angles and compare BESS readings with a single bevel 25° chisel.

Ken

[grepper]

If there is any detectible difference due to bevel angle, and EOU states that for all practical purposes there is not, it is insignificant when compared to the 20% variance of test clips.  If variance exists, it is not even close to 20%.
 
In theory you may be correct Mr. Steve, and I had some of the same questions at first.  One thing to consider however is that the impact of bevel angle on the sharpness reading is so miniscule as to not be detectible by the test apparatus so it is basically irrelevant. 
 
Another interesting observation is that we are measuring knife and tool edges which are really big, clumsy instruments as far as edges go.  Remember that EOU test instruments can measure differences between various DE razor blades, and our knife and tool edges are not even approaching the level of sharpness.  Even if some minute variance were to exist cleaving test media due to bevel angle, and we were actually able to measure it, that data, while it might be intellectually entertaining would be of little or no real world consequence.
 
If I sharpen a knife and see a 20 gf variation along the edge I’m generally completely satisfied because I know I won’t be able to detect that variance when chopping some kohlrabi or a piece of rope and I know that after one cut the sharpness will decrease at least that much anyway. 
 
I use the PT50B which has a resolution of 5 grams.  It is nowhere near granular enough to begin to measure any possible influence of bevel angle cleaving the very small diameter test media. 

That said, it is nonetheless certainly entertaining to consider exactly what is happening.
 
Over time I’ve gained total confidence in the equipment and sharpness readings even when it informs me that I just did a crappy job of sharpening or deburring!  

[SteveG]

Good points. I'll remain skeptical but accepting for the time being, unless I can figure out a way to reliably test it. I'm very interested in Ken's results when he sharpens the cleaver.

I just had a horrible thought: what if my 100 readings are just a nicely pointed burr due to single-bevel sharpening!? Practically it doesn't matter since they're cutting wood beautifully, but it sure would screw up my understanding of my results.

[grepper]

“I'll remain skeptical… “.  Truly, a man with an iron will, eh?    

“I just had a horrible thought…”.   I wouldn’t let it keep me awake at night.  Check this out.  Here is an image I took of a burr standing straight out from the edge.  The test media simply smashed it down to the nice clean edge when I took a reading.

   
 
Indeed, in some circumstances a sharp wire edge can cause an erroneously sharp reading, but more than likely a burr will cause a higher, not lower reading.  To avoid being misled by that, or to at least better understand what is going on, I generally take more than one reading on the edge.
 
Keep in mind that the test media is very small in diameter, and will definitely indicate if variations exist along the edge.  That can at once be informative, misleading and even frustrating.  Nonetheless, it is telling a truthful story about the edge.   I’m quite sure that after a while you will accept, trust and even delight in the readings along the edge.
 
Obviously, variation along the edge is more pronounced with a toothy grind than with a smooth grind.  For instance DE razor blades show very little if any variation.
 
If a polished edge chisel is showing much variation, I would suspect first burr, and second, uneven sharpening such as not actually reaching the edge when grinding.  From what you have posted you seem very good at sharpening, so in your case I would suspect burr.  A good light and magnification will more than likely resolve that question.

[SteveG]

Thanks for the input Mister Grepper.

I sometimes do take multiple readings, but on chisels/planes they're consistent. To clarify, my "horrible thought" was wondering if the edge-trailing strokes I do on the back of those blades might leave a nice, straight, fine burr pointing directly from the edge. I always thought they were removing the burr, but now I'm not so sure. I can test that, I think, by taking one shaving and then remeasuring - I'll try to do that tomorrow - I suspect the burr should then roll, giving a much higher reading.

BTW, I failed to comment on your earlier post that the practical differences in what I'm seeing are negligible - I totally agree, this is for fun and education. As long as my tools are doing their job then the rest is strictly for the joy of learning.