Precision Sharpness Testing Device

[Willy]

I got the book, thank you very much!

I also got a knife from Werner, which he sharpened using your method. Indeed, there is no increase in the cutting force with the number of cuts to cut the BESS thread with the knife. He also gave me a couple of Feather razor blades. These were not better than Wilkinson razor blades in my tests and again showed an increase in cutting force with the number of cuts ...

I usually sharpen knives with a cutting edge angle of more than 40° (more than 20 dps). But now I wanted to see which sharpness I can achieve and ordered a Viktorinox "flower knife" (little and easy to sharpen). I sharpened this with a 20° cutting edge angle. The measurement results are:

   

At the second position I finally saw a micro-dent after cut 28 that looks similar to your last picture in post #9 :-)
But nothing can be seen at the other positions, although the cutting force increases.

> BESS test line diameter is about 0.22mm, and under the same load it exerts 
> more pressure per point, than the fishing line of 0.25mm diameter.

I had ordered fluorocarbon fishing line with 0.25 mm, as my measurement on the BESS thread showed 0.24 - 0.25 mm. In fact, according to my measurement, the fluorocarbon line is 0.26 mm. This should not be due to the caliper, as it shows the correct values with feeler gauges.

[KnifeGrinders]

Very interesting. I should also thank Werner for providing you a knife sharpened by our methods for testing on your tester.
"Indeed, there is no increase in the cutting force with the number of cuts to cut the BESS thread with the knife."  tells us that the edge apex has been cleaned of any metal deformed by grinding, and is strong.

Have you started thinking of a de-rooting method in your sharpening process?

We remove the root of the burr on a rock-hard felt wheel with 1-micron diamonds.
If your grind on Tormek or Scheppach - this is a well-proven method. But mind that the German-made 0.9 g/cm3 felt wheel does not remove the root of the burr as well as the rock-hard felt wheel of 0.6-0.7 g/cm3.

But if not, then you need to adapt the de-rooting method we describe in the Knife Deburring book to the sharpening equipment you have.

Werner is Dr. in physics, worked on development and production of first scanning electron microscopes in Germany.
At the same time he is an advanced sharpener. Do you know many people who sharpened microtomes? - Werner used to.
We are truly blessed that my book was translated to German by Dr. Werner. He has the same deep insight into the burr.

[Willy]

Hello, I have some new findings. 
KnifeGrinders asked: "Have you started thinking of a de-rooting method in your sharpening process?"
Yes, I did. De-rooting at the Victorinox Knife (# 3.9050) was done at an angle of 2° above the previous sharpening angle with the 12.000 Naniwa Superstone which was moved only with the cutting edge. After 3 - 4 diagonal pulls, each about half the length of the blade, the other side was processed and this was done 3 times for each side. Finally, the blade was stropped a few times over cotton fabric. After this procedure, no scattered point reflections could be seen on the foremost cutting edge under a microscope with 60x magnification. The visual impression was now the same as with Werner's knife and the cutting force with the BESS thread was in the same range. The cutting edge angle is 30° this time (same as Werner used) and no longer 20°. 

   

In order to be able to recognize any micro-dent, photos were taken: An old 24 mm wide-angle lens from Tokina with a Canon FD connection was attached to a Sony full-frame camera using a retro adapter and 3 intermediate ring sets (150 mm in total, lined with black D-c-fix velor film on the inside). This results in a 7.5 times magnification, i.e. 4.67 mm of an object are mapped onto the 35 mm sensor width. Since the sensor has a width of 6000 pixels, object structures down to a minimum of around 780 nm can theoretically be displayed. This means that the physically possible limit (Abbe limit = light wavelength) is almost reached.

   

After 5 cuts through the BESS thread, a spot can clearly be seen on the blade. The cutting forces increased only slightly, but continuously: 108, 109, 115, 120 and 121 cN. The red point (Edding pen) was used to find the cutting position under the microscope and for the photos.

   

Back side of the blade. The spot can be seen clearly too. And there is definitely no micro-dent. Maybe a nano-dent below the resolution limit. 
I think the increase in cutting force is also related to how rough the grinding is. Except for the foremost front edge (0.05 mm or so), my grinding is significantly smoother than Werner's.