BESS values for various burrs

[Cyrano]

These are recent results using a Tormek T-8 system on a fixed-blade Mora. In each case, the BESS value shown is the average of three measurements. 

After sharpening on the Tormek DC-250 coarse diamond wheel, BESS = 582: 

d

After sharpening with the Tormek SG-250 standard wheel graded to 220, BESS = 589:



After sharpening with the Tormek SG-250 standard wheel graded to 1000, BESS = 416:



After one set of stropping passes on the Tormek standard leather honing wheel, BESS = 208:



After a second set of stropping passes on the Tormek standard leather honing wheel, BESS = 208:



Discussion:

* I was surprised at the BESS values associated with the burrs before any stropping (582, 589, 416). I expected values much higher.

* I was also surprised at the BESS value associated with the results of the first set of stropping passes (208). Given the presence of visible residual burr, I expected a higher value.

* My second set of stropping passes appears to have been effective at removing all residual burr.    It also appears to have been effective at rounding the edge. 

[Larrin]

Very nice! What microscope did you use?

[EOU]

That's good stuff Cyrano and an excellent tutorial! All of your edge measurements before and after burr removal seem very much in-line to us and track with your photographs as well. We haven't spent a ton of time measuring edges before any attempts have been made at removing the burr but we think that your measurements fall very much within the expected zone. Dependent on the grinding circumstances, we've seen 350 and we've seen 700. Of course, we're not attempting to accurately measure the sharpness level of a burr edge. First and foremost, we're simply trying to detect the presence of a burr. The point is that neither number, 350 or 700, is acceptable for most skilled sharpeners and that burr removal activities need to commence. 

We think that your last two pictures point out the advantage of using an edge tester in conjunction with a microscope. We know that if 50% of the edge contains residual burr and if 50% doesn't that there must be a 50/50 chance of getting a good/bad reading with any of our edge tester models. This information may be gleaned with an edge tester alone by taking multiple measurements but the way that you did it, utilizing a microscope, seems much more efficient and informational. So much so that this is the way that we do it.

So here is our takeaway from your experiment; you are well on your way to having established a well documented sharpening process. Using the same knife, and under the same set of grinding parameters, a double session on the leather wheel should yield the edge seen in your last picture. If you repeat the experiment with similar results then you might be able to chisel this one in stone.

One last comment here and not on your sharpening efforts but on ours. Those little blobs of burr remaining after your first burr removal effort sent chills up our spines. Fortunately, it appears that all of yours were removed with just an additional session with the leather wheel. With our past sharpening efforts, we've seen them where they couldn't be removed with a stick of dynamite. In our case, the problem turned out to be too much grinding pressure during the last couple of passes. Our's were just too gnarly and robust to stand back up so that they could be removed.

This was a great post so thank you.

[KnifeGrinders]

Cool illustration to what we know, Cyrano.

We know that diamond crystals leave behind deep narrow scratches while aluminium oxide shallow - you show that;
we know that the burr worsens BESS reading rather than the coarse apex - you show that.

You've put the right accent where those new to BESS tend to misinterpret the tester readings - a bad BESS score is more often indicative of a burr rather than of a not refined edge. Now I know that the BESS score of 350-700 I get on repeated sharpness tests of the same edge is indicative of the feather or foil burr, but when I was only starting to use the sharpness tester, I thought I hadn't thinned the apex and aimed my efforts to refining the edge where I should have to deburr it better.
Nowadays when I see a BESS reading of around 200, I read it as the wire burr.

"* I was surprised at the BESS values associated with the burrs before any stropping (582, 589, 416). I expected values much higher." - I'd suggest this is thanks to the decent steel in your knife, in the lower steels the burr gives higher readings.

"* My second set of stropping passes appears to have been effective at removing all residual burr.    It also appears to have been effective at rounding the edge.  " - love this part, but the reading you see does not necessarily mean you've rounded the apex - it is rather expected, and I explain why.
Using Tormek honing paste which particles average 3 micron in size, and Todd Simpson's observation that "grit size and the scratch size are related by about an order of magnitude" (scienceofsharp.wordpress.com) we shall expect edge refinement to 0.3+ micron which is around 150+ BESS.

From my experience, I get better sharpness when honing with the Tormek paste by not applying the fresh paste and thus honing on the "worn" paste known to break down to smaller particles (they say down to 1 micron); also the leather wheel diameter differs by a few decimals on the same wheel in its different points and to avoid rounding the apex I hone at an angle little shallower than what the edge has been ground at.

[Cyrano]

Very nice! What microscope did you use?

These images were created using a Dino-Lite AM7915MZT.

[Jan]

In the attached image you can see grains of fresh Tormek Honing compound at magnification 500.

   

Jan