Dr. Marvin Groeb – Abrasive Solutions

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  • A brief study on sharpening stones – Part 18 – Venev OSB 2 resin stone – 3 µm

    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.

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

  • A brief study on sharpening stones – Part 17 – Nano Hone 3 µm resin stone

    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 the Nano Hone 3 µm one. Nano Hone is an American company created by a former Shapton employee (?), Harrelson “Hap” Stanley. They say he draws from 10 years of experience to manufacture sharpening products under the Nano Hone company now. Their homepage shows that they have a plethora of artificial, very neat looking products!

    A note on this stone: Finish and manufacturing on the blank holder, but also the resin patch is superb. The anodising, laser engraving and actual shape are top notch! Kudos from a manufacturing enthusiast.

    Let’s take a look at the resin under the microscope!

    Optical micrographs of the Nano Hone 3 µm resin stone. Instrument: Leica Emspira.

    The actual resin patch is very thin on this stone, without having measured I’d guess it at 1 mm. It looks to me like it’s glued to the holder. The surface is very smooth, some scratches are visible on the resin. The resin feels a lot softer than other resin stones. Because it is so thin, this is hard to judge and impossible to measure with my trusted Shore D hand measurement device. No distinct particles can be made out, but there is a certain sparkle to it – maybe the diamond?

    SEM micrographs of the Nano Hone 3 µm stone. Instrument: Zeiss GeminiSEM 560.

    A first look at this stone reveals a massively different composition. All resin stones we have reviewed so far appeared to be resin stones made from thermoplastic resins such as a phenolic base. This is the regular abrasive used in the industry – for example for resin bond grinding wheels. This one appears to be a cast, probably epoxy based resin? At the same time, the surface is super porous, with lots of voids. I am unsure how this was created – either the resin a large amount of micro bubbles, or maybe it is being extruded? Very curios!

    The SEM micrographs show some larger particles (in the size range of 10 µm), that are a lighter colour. This typically points towards a heavier element than carbon. If you take a closer look at the medium magnifications, you will make out a couple of diamond grains, although they are stuck deep in the resin and are very few. Before I speculate on this, let’s identify the large grains and look for other elements on this stone. This is done via EDS – if you are interested, I’ve written previously about SEM micro analysis and explained all of the techniques there.

    EDS analysis of the Nano Hone 3 µm resin stone. Instrument: Oxford Ultim Max  ∞ 40mm2 EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

    Surprisingly, the large, lighter coloured particles are aluminium oxide! I would expect that these stem from the manufacturing process, as they only seem to be in the top layer. The EDS analysis also reveals a couple of diamond grains that are just below the surface, as the interaction volume for EDS is much deeper than for imaging. We can see in the carbon channel, that the concentration is low, with a large tendency to agglomerate. I would expect that the finishing process that creates the smooth surface is also tearing out the diamond. The reason nearly no liquid-resin stones exist, is that the grain retention is super low on those resins, and we can see this exact thing happening here.

    Let’s take a look at this super smooth surface under a 3D optical profiler!

    White light interferometry height map of the Nano Hone 3 µm sized stone. Instrument: Zygo Nexview NX2, Objective Lens: 20X. Stitched overview of 3×3 images.

    We can see that the aluminium oxide particles sit just on top of the stone, and some deep scratches are visible. The rest of the surface is flat and shows some micro roughness. This is also reflected in the ISO 25178 parameters, that show a remarkable low roughness (Sq, Sa) for an abrasive stone:

    ISO 25178 parameters of the Nano Hone 3 µm stone.

    Let’s take a look at how this stone sharpens a blade!

    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 sharpened with the Nano Hone resin stone. Instrument: Thermo Fischer PhenomXL.

    This stone was quite surprising. Initially, the glossy surface turned matte within a couple of strokes. After about 30 strokes, some gloss reappeared on the surface, but didn’t reach the level of the previous, Dr.Marv stone created, preparation. The SEM shows a multitude of super fine scratches – they are in a cross hatch pattern, as I sharpen first at about 30° until the complete previous surface finish is gone, and then I move the stone in the opposite angular direction. This makes sure, that the surface we look at is created by the reviewed stone. Here we can see that the micro scratches disappear the closer we get to the surface, and a very polished, I would even say burnished surface was created. This looks very much like the surface improvement if you strop on an unloaded leather strop.

    I would guess that the initial, matte surface is created by the aluminiumoxide particles embedded in the top layer. After a couple of passes, these are either pushed in deep, or become loose and accumulate on the blade with the arbasive debris from the cutting action, and the diamond starts cutting, creating a glossy finish again.

    The final surface is glossy and regular to the naked eye:

  • A brief study on sharpening stones – Part 16 – Boride 1000

    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 stone is an artificial silicon carbide sharpening stone manufactured by BORIDE, a US company that specialises in polishing stones for mold work. This is the CS-HD type, according to the manufacturer a green silicon carbide rock that excels at polishing up to 63 HRC.

    Let’s take a look under the microscope!

    Optical micrographs of the Boride CS-HD 1000 stone. Instrument: Leica Emspira.

    The manufacturer printed the grit size onto the stone, which is visible at large magnifications as black dots. I would expect this to be printed, as it looks like ink leaked into the small cracks of the surface. The overall stone material is a mix of different coloured particles.

    In order to make out more details, and look into the chemistry of the stone, we will do electron microscopy analysis. If you want to know more about this, I’ve explained the techniques in detail here.

    SEM micrographs of the Boride CS-HD 1000 stone. Note at high magnifications how the grains have grown into each other. Instrument: Zeiss Gemini 560.

    The stone shows a nice grain size distribution, with very regular shape. Green SiC is generally harder, but more brittle than black SiC. The BORIDE stones at higher grits show that green colour, at this size it is more an off-white colour, which stems from the particle size. At higher magnifications, the tendency to solid-phase sinter becomes apparent: the grains are interconnecting, which looks like they are melting into each other.

    EDS analysis of the BORIDE CS-HD stone. Instrument: Oxford Ultim Max  ∞ 40mm2 EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

    The EDS analysis shows that this artificial stone is mostly SiC – the oxygen we see is probably surface oxidation, and the minuscule amounts of aluminium are probably aluminium oxide impurities. This is expected of every SiC, as typical purity for green SiC is 99%. No large, impure particles can be found, which speaks for proper abrasive hygiene at the manufacturer!

    Instrument: Bruker Alicona µCMM, 50X objective lens, 3×3 FOV high resolution focus variation scan. Data is leveled and outliers removed (0.25%).

    Analysing the surface via focus variation microscopy, we can see that the matte, smooth appearance is mirrored in the surface roughness. The stone is unremarkable, with no distinct material ratio or deep voids. This is also reflected in the ISO 25178 parameters:

    ISO 25178 parameters.

    Let’s take a look at how this stone sharpens a blade!

    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 blade sharpened with the BORIDE CS-HD stone. Instrument: Thermo Fischer PhenomXL

    The boride stone created a matte, homogeneous surface. Under the SEM, lot’s of micro scratches as well as some deeper scratches with burr formation are visible. Near the apex, small foil type burrs can be found.

    The stone provided a very regular feedback – it felt like every position on it is identical, with a smooth, even friction feedback. The blade surface showed a lot of scratches, some very horizontal – I could imagine that this stems from me wipping down the blade and rubbing a particle across it. I would ignore those!

    Optical micrograph of the sharpened blade. The fine micro scratches, but also larger and deeper scratches are easily visible. Compared to the 5 µm resin stone, the surface visibly deteriorated.

    I think this is an OK stone. 1000 grit is not super fine, so I expected the surface to deteriorate. The stones are not super expensive, and I would guess with enough skill, they would present you with a fantastic edge. I just don’t see the appeal in a SiC based abrasive stone, when there are super abrasives out there like CBN or diamond, or fantastic natural stones like the yellow Belgian coticule.