This is part of a series of blog posts – looking into the appearance and composition of commercially available sharpening stones. If you are interested in the previous episodes, check out the archive for them.

If you have some suggestion on what I should look at next, or want to share your super secret DIY stones, I could be persuaded to open the bag of analytical devices… hit me up on Instagram under @marvgro for that.

Disclaimer: I’m not for sale. Every review you see on this blog is bought with my own money. I have no affiliation to any manufacturer.

Review

Today’s sharpening stone is another Venev stone. I’ve previously looked at their double sided one, but the resin and actual bond type was a bit weird under the SEM. Some very nice people messaged me and suggested I should order a specifically OSB2 declared one – which is apparently a very novel, high-tech bond, specifically designed for sharpening! That’s interesting for sure!

Optical micrographs of the Venev OSB2 Resin 3 µm stone. Instrument: Leica Emspira

Something that immediately hits is that this stone seems to have a mix between light regions, dark regions and dark particles. I fear for the worst…so let’s take a look under the SEM to identify what it is!

SEM micrographs of the Venev OSB2 resin 3 µm diamond stone. Instrument: Zeiss GeminiSEM 560.

We can make out several, very large particles in the top surface layer. The diamond concentration looks to be higher than on the other Venev stone we review, but agglomerates to small nests. The resin itself is flakey and very fine! No bubbles or larger porosity is visible. The surface topography is quite uneven for an artificial and factory dressed stone though.

Let’s look at the chemical elements! For this we are going to use an advanced SEM technique called EDS. If you want to know more about this, I’ve written extensively about SEM microanalysis here on this blog.

EDS analysis of the Venev OSB2 Resin stone. Instrument: Oxford Ultim Max  ∞ 40mm² EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

Surprisingly, there’s a massive amount of silicon carbide and magnesium oxide to be found in the composition of this sharpening stone! Basically all larger particles are foreign particles. Because it’s two different species, I hesitate to attribute these to the factory dressing process. I think one of the two is a filler to make the abrasive matrix harder, but also lower cost by requiring less diamond powder.

3D surface height map of the Venev OSB2 stone. Instrument: Bruker Alicona µCMM, 50X objective lens, 3×3 FOV high resolution focus variation scan. Data is leveled and outliers removed (0.25%).

The previously seen large height differences in the topography can be seen under the confocal focus variation microscope, too. A height difference of several microns make this the most uneven stone we’ve had so far on the blog, by far beating out all natural stones! This is also reflected in the ISO 25178 parameters, where large values for Sa, Sq and Smc dominate:

ISO 25178 parameters.

In order to evaluate the sharpening performance and material removal mode of this stone, a blade was sharpened with it. I am using a standardised testing procedure, read about it here. Nevertheless, it’s 65 HRC M398, and sharpened to 17 DPS with resin bond diamond stones down to 10 µm. Afterwards, the tested stone is used, first in a back and forth movement until the surface becomes homogenous, and then alternating strokes (5-5-3-2) on each side, for a total of 20 strokes towards the apex per side. No pressure is applied but the weight of the apparatus.

The edge is then analysed in the electron microscope for breakouts and morphological appearance.

SEM micrographs of the edge finished with the Venev OSB 2 resin stone. Instrument: Thermo Fischer PhenomXL SEM.

The edge has a smooth, regular appearance with a couple of deeper scratches. While sharpening, the stone has quite a bit of feedback – with this I mean resistance. It feels a bit sticky and shows a surprising amount of friction. The edge is slightly blunted in some sections, and some cracking can be observed. The stone barely removed any swarf. This edge BESS tested to 124.

Optical micrographs of the edge finished with the Venev OSB 2 resin stone. Instrument: Leica Emspira

Sharpening disclaimer: I use a standardised approach to sharpening, which basically follows how most manufacturer of guided systems tell you to use this system. I am very aware, that every stone could perform much better than this, in terms of sharpness, but I want a comparable approach. The sharpening segment mostly shows the material removal mechanism – is it burnishing? is it cutting? is the cutting pressure too high so that carbides crack? Is there massive burr or prow formation? The BESS value definitely doesn’t highlight the ultimate sharpening performance of the stone, but was an often requested information. Over time, this blog will show BESS values for different edge morphologies, but by the holy endmill – don’t read it as a „this is the max value this stone can achieve“. I would also suggest to familiarise yourself with the works of Immanuel Kant, it’s absurd I need to write such a disclaimer here.