Sharpness Chart

[wootz]

An easy and immediate remedy for edge retention is to use the right cutting board
https://forum.tormek.com/index.php?topic=3452.0

[cbwx34]

I've been thinking about this thread... and should modify my request... from "edge retention" testing to "burr/wire edge" testing.  One thing I've learned over time, is that some sharpening methods can create a wire edge that, as opposed to a burr, tests very sharp, but is very hard to detect.  Usually, however this wire edge won't hold up to much cutting.

One quick/easy way to test, is to make a slice thru a thin piece of paper (I use phonebook paper), then make a couple of cuts thru cardboard, maybe throw in a couple of cuts thru copy paper, or a single rope cut, then back to the phonebook paper.  To pass, the knife must make another clean slice.

You're not testing for "absolute sharpness"... in other words, it doesn't matter if the knife could push cut the paper, or pass a "higher level" test... but being able to make a clean slice thru phonebook paper before and after, has become a fast way to check for a wire edge.

Maybe give it a try?

[wootz]

The KN100 Operating Manual in the manufacturer library http://www.edgeonup.com/Library.html has speculations about the burr, and the wire burr in particular, accompanied by edge sharpness measurements.

[cbwx34]

The KN100 Operating Manual in the manufacturer library http://www.edgeonup.com/Library.html has speculations about the burr, and the wire burr in particular, accompanied by edge sharpness measurements.

Trust but verify.   

I don't think the answer is to use the same machine you're getting your sharpness results from, to tell you whether or not there's another reason for it.  (Especially when other options are available).

[Sharpco]

Wootz.

I have been told that the knife can be very sharp even though it has a very fine burr.

So I want to ask you.

How sharp is it that Burr is completely gone? In other words, what is the minimum level of sharpness that the burr can't exist?

[wootz]

These tests had been done by Mike Brubacher and described in that KN100 Operating Manual I referred to above, pages 39-42.
What you read there is in line with what Todd Simpson found out and illustrated by SEM images on his scienceofsharp.wordpress.com

A continuous wire burr is seen as a structural part of the apex, folding to one side of the edge soon after sharpening; "foil burr" is just another name for the wire burr.
When straightened by steeling or stropping, it is your sharpest edge.
Deburred completely by high-angle stropping, i.e. at an angle larger than the edge angle, the edge will be less sharp initially, but stay sharp for longer as no burr rolling occurs with the knife use (well, at least in soft food cutting on an edge-friendly cutting board).

In the KN100 Operating Manual, Mike Brubacher gives BESS scores for a knife edge in the 200-300 BESS range, and shows how the wire burr changes the score.

The BESS scores I get when I sharpen deliberately preserving the wire burr:
- immediately after sharpening 55-60;
- 2 houra later 80 - I attribute this worsening chiefly to oxidation, and to a lesser degree to the burr bending - the edge oxidation is known to worsen the score by 5-20 BESS;
- in 10 hours 115 BESS - due to the wire burr folding to one side.

By gently stropping this edge on a clean leather, after just 4 very light knife-weight alternating strokes, I get the sharpness score back to about 70-80 BESS - thanks to aligning the wire burr.
Mike B. says it takes 6-8 hours for the burr to spontaneously return to its rolled position due to the metal memory.

USB microscope image of the wire/foil burr

[wootz]

For comparison to the above, look at the same edge, but now completely deburred by fine honing on a paper wheel with a 0.5 micron abrasive at an angle +0.4 degree larger than the edge angle (e.g. honing a 15 dps edge at 15.4 degrees):



The BESS scores I get for the deburred edge:
- immediately after sharpening 65;
- 2 hours later 70;
- in 10 hours 70 BESS;
- next day 72 BESS - no deterioration with time.

You see now why almost every our sharpening protocol has a final step of fine honing on a paper wheel at +0.4 degree.
I've checked with the US Sharpeners Report when our study on this is published, and was told they couldn't make it into the December issue, but will for sure in February.
BTW the December issue has a very interesting and detailed article about a sharpening and knife rental service in Las Vegas.

Interestingly, when Judy, the Sharpeners Report editor, sharpened her knives at a local shop in Minnesota they showed her the BESS score before and after her batch was processed - similarly to how we do it in Australia.

[Sharpco]

Amazing post! Your knife sharpening technique seems to have reached the apex.

It is no exaggeration to say that knife sharpening is the process of making burr and removing it.


BTW, Tormek says no need honing after using the SJ stone and I understood it means SJ can deburr completely. However, according to page 26 of the "Experiments on Knife Sharpening -John D.Verhoeven", it's not true. SJ produce very small burr, so we need the next step(maybe it's a final).