Microscopy of the Tormek honing compound PA-70 etc

[wootz]

I happened to have micrographs of the Tormek honing compound and Autosol metal polish in the same scale.
Now we can compare their grain size.

Tormek honing compound PA-70 (microscopy by Anthony, USA):


Autosol metal polish (microscopy by Iliya, Australia):


To my eye, the particles in both are of similar size, in the range of 3 to 10 microns (not taking into account the conglomerates).
What do you see?

They have similar honing ability, but in my experience the Tormek PA-70 does better at slow RPM, while the Autosol at high RPM.

Next image shows a mainstream kitchen knife sharpened on a coarse wheel of #200-300 and then deburred (polished) on the Tormek leather wheel.
Very good result telling us that we can do the majority of mainstream knives and common woodworking tools without a fine grinding wheel. A coarse and medium wheels can do the job, thanks to the honing compound working so good.



What the 2nd image also shows us is the wire edge or feather burr seen all along the apex after the honing.



We see this picture all the time, off the Tormek leather wheel, and off the paper wheels - and it tells us that the root of the burr is still there.
That is the reason we do one more step of deburring that we call "de-rooting" the burr, or "de-wiring", to get a strong clean apex.

[wootz]

Now let us think about this: Can we mirror finish an edge with the Tormek honing compound?

The visible light wavelength range is from 380 to 700 nanometers.

For us not to see scratches, the human eye must stop seeing light reflected by scratches, and for that the scrataches must be less than 380 nanometers wide. In microns it is less than 0.4 micron.

The honing compound grit and the size of the scratches it causes are related by about an order of magnitude, i.e. in order to get scratches under 0.4 micron wide, the honing particles must be <= 4 microns in size.

The conclusion is that the Tormek honing compound with its particles of 3-10 microns in size, can give near mirror finish, but somewhat "cloudy".
For true mirror polish we should use a finer honing, and this is done with the Tormek Japanese SJ wheel, which has grains of 2-3 microns.

[Dutchman]

... in order to get scratches under 0.4 micron wide, the honing particles must be <= 4 microns in size.
...

Can you explain that? Because with a 1mm marker I can make 1mm scratches.

[wootz]

Scratches left in steel by an abrasive particle are always smaller in width than the size of that particle.
In order to form a scratch, sufficient pressure must be exerted by the particle to exceed the yield-strength of the steel, and the abrasive particles never fully go into the steel.
The scratching is done by a small contact area of the particle.

SEM studies have shown that in fine honing relation between the size of the abrasive particle and the width of the scratches it forms is approximately 10:1