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 a novel one for this blog. It’s from the Ukrainian company “PT.tools” (also known as PDT or Poltava), which are a manufacturer of abrasive tools. It uses a bronze bond, and the grit chosen (3/2 µm) is perfect for polishing, according to the manufacturer.
Let’s take a look under the microscope!
Optical micrograph of the PTD diamond 3/2 µm. Instrument: Leica Emspira.
The stone is very firm, showing a dark grey colour, that slightly reflects reddish/bronze coloured when the light hits it. Under the microscope, a very even structure is visible. Individual grits are near impossible to make out, because the bronze binder is so reflective.
For a better look, I’ve put the stone into our ultra high resolution scanning electron microscope.
SEM micrographs of the PTD Diamond 3/2 µm. Instrument: Zeiss GeminiSEM560.
The bond is very typical of a dense, highly sintered bronze bond. At the topmost surface, some plastic deformation of the matrix is visible, in deeper recesses some porosity from sintering, but generally speaking this is one dense bond! I typically encounter such tools in my dayjob for precision grinding of glass. The super low concentration of the abrasive also highlights this.
EDS analysis confirms what the manufacturer stats -small diamond grains in a bronze binder. The larger particles visible appear to be Silicon carbide, I’d guess embedded from the dressing process?
EDS analysis of the PTD Diamond 3/2. Instrument: Oxford Ultim Max ∞ 40mm2 EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.
Under the focus variation confocal microscope, a relatively smooth surface, dominated by the metal binder and dressing process is visible. This stone will likely create an immense amount of cutting pressure.
Instrument: Bruker Alicona µCMM, 50X objective lens, 3×3 FOV high resolution focus variation scan. Data is leveled and outliers removed (0.25%).
The surface parameters do mirror this finding – a smooth stone with a relatively low surface roughness, and generally dense material ratio (Sdc).
ISO 25178 parameters of the PTD Diamond 3/2 µm.
In order to evaluate the sharpening performance 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 finished with the PTD Diamond 3/2 µm. Deep, regular scratches are visible that were created by the stone.
The sharpening result of this stone was abhorrent. My regular preparation with my own, DrMarv Scientific Sharpening stones leaves a near mirror finish, with a super high gloss at 10 µm. Only by varying the light, some very, very fine scratches can be made out. With the PTD stone, even after just 2 passes, the whole surface turned matte and super dull, with lots of visible scratches. The SEM pictures show this very clearly – with carbide matrix fractures near the apex, and prow formation. The blade tested to a value of 201 BESS. It barely did shave, but was easily felt that it’s more tearing and less cutting.
I’m unsure what the issue is here. I would guess that the low concentration and embedded larger SiC particles, combined with the very hard binder mar the surface of the blade. From my professional day job, dressing such a bond is very difficult, requires a quick dressing spindle and low engagement. Nothing that is done easily or cheaply. While grinding with such bonds and concentrations on a milling machine, immense cutting pressure and heat is generated. I wonder why it is made with such a fine grain. If the concentration was bumped by a factor of 10, and large grits were used, it would likely be a fantastic, very long lasting sharpening stone, if the manufacturer was able to integrate some self sharpening properties.
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.
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 a very famous, well known brand. Naniwa is a Japanese brand, that has been making sharpening stones for over 60 years. Their homepage says they deal in all things abrasive. I like that! The stone I have bought is from the chosera line, with 5000 grit. It is, according to diverse homepages, an alumina-oxide stone with a magnesia binder. Let’s take a closer look:
Optical micrograph of the Naniwa chosera 5000. Instrument: Leica Emspira.
It has some marbeling to it, with a fine and smooth surface. Zooming in, individual particles and grains become visible. For a closer look, as usual, we take a look in the SEM!
SEM micrographs of the Naniwa Chosera 5000 stone. Instrument: Zeiss GeminiSEM560.
At low magnifications, the stone appears to have a smooth cover above the abrasive grit, covering about 80% of the surface. Zooming in further, one starts to identify cubic, small abrasive grits, but also that the covering “film” actually consists out of an uncountable amount of sub-µm particles, that are slightly rounded and longish. This is an interesting stone! To identify this, we will employ EDS analysis – check out this segment of the blog to understand the SEM metrology better. I mentioned before, that things get… tight once you employ the full suit of sensors. Because this stone is non-conductive, but we need a lot of acceleration voltage to get a reliable EDS reading, I’ve employed our low vacuum mode. With the aid of a small orfice, it is possible to increase the chamber pressure, but leave all sensors functional. For this, a diode-type BSD sensor with the small aperture is inserted pneumatically into the chamber. The EDS sensor meanwhile is shaped like a pen, coming in from the other side. To show you how unbelievably tight and confusing everything gets, I snapped you a shot of the chamberscope:
View from the chamberscope. The stone is visible diagonally from lower left to upper right. The EDS sensor is the pen shaped object coming from the right upper corner. The low-vacuum aperture sits below the pyramidal pole piece, and has been inserted from the left side of the picture. Instrument: Zeiss GeminiSEM560.
The EDS analysis reveals the chemical composition:
EDS analysis of the Naniwa Chosera 5000. Instrument: Oxford Ultim Max ∞ 40mm2 EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.
There’s a fascinating mix of chemical elements up there. The old truth “you can find the whole periodic table in ceramics” hold’s especially true. Very interesting is the large particle, with flaky composition. Let’s zoom in a bit more on that one:
SEM micrograph of a flaky particle, found in the Naniwa Chosera 5000 stone. Instrument: Zeiss GeminiSEM 560.
Elemental analysis of the flaky particle. Instrument: Oxford Ultim Max ∞ 40mm2 EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.
This is really fascinating! we can pick out what we expected – Mg, O, Al, but also massive amounts of silicon. This is the moment where I am really happy, I haven’t spend more time studying minerals, because I don’t even want to imagine what this could be. Nevertheless, I went on a literature deep dive for you folks. There’s a couple of possibilities this could be – a paper I found had something similar to the flakes we are seeing, but was writen by geologists1. They stated that the flakes they are seeing could either be: Anortit – CaAl2Si2O8; Albit – NaAlSi3O8; and Paligorskit – (Mg,Al)5(Si, Al)8O20(OH)28H2O. The nice thing about geology is, pretty much every mineral has decent SEM pictures online. Albit2 has a matching appearance3, but the excited reader might now ask, where is our Sodium (Na) at this point? Well, it’s pretty exchangeable with Calcium (Ca), which we found in our spectrum. I have no idea what this is called, and I am quite unsure at this point what we found. Structure wise, it should be a triclin crystal latice, and it consists out of the chemical elements Si, Mg, O, Ca. If anyone has studied geology and wants to supply the solution here, reach out. If not, I now declare this to be something like Albit. It doesn’t really matter – it just shows they sinter these stones at quite the high temperature, and there’s cool structures hidden in the microcosmos! All of these oxides are of similar hardness – quite a bit harder than steel, not much harder than carbides.
Let’s take a look at the surface composition!
Instrument: Bruker Alicona µCMM, 50X objective lens, 3×3 FOV high resolution focus variation scan. Data is leveled and outliers removed (0.25%).
It’s a smooth stone, without a large amount of bearing surface. Roughness is not exceptionally smooth, but there are also no super deep recesses. This is a finely made stone, and if you scratch along the surface with your fingernail, there’s nothing catching it. The feedback, because of the relatively rough surface is noticeable. This stone doesn’t glitch over your knife edge.
ISO 25178 parameters of the Naniwa Chosera 5000 stone.
In order to evaluate the sharpening performance 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 stone was only splashed with water, not soaked (in accordance with the website I bought it from).
SEM micrographs of the blade finished with the Naniwa Chosera. A slight cross hatch pattern is visible, which stems from me changing hands during the sharpening. The edge is burnished at some parts, whereas other parts show fractures. Overall, the appearance diminished a bit compared to the 10 µm resin stone.
The edge shows no burr, but some cracking near the carbides, brittle failure of the edge and larger scratches are visible. I think the stone struggled a lot with the very hard (65 HRC!) high carbide steel, but also the fact that on a guided system, you can only splash it with water – it doesn’t build up a slurry. Seriously? I think this might be a fantastic stone for freehand sharpening and lower hardness steels. On this guided system, with the minimum amount of water I was able to apply, I am not a super large fan. A BESS reading I took showed a score of 153.
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.
I will try to revisit this stone in the future with a softer steel.
References:
Paper: Cvetković, Vesna & Purenović, M.M. & Jovićević, Jovan. (2006). Change of water electrochemical characteristics in contact with magnesium enriched kaolinite-bentonite catalyst substrate. CHISA 2006 – 17th International Congress of Chemical and Process Engineering. ↩︎
This is part of an ongoing blog series about metrology. It explains physics, principles and use cases of modern metrology devices.
TL;DR: Explains how a SEM works. Deep dive into the electron-beam interaction, showing how every sensor gives a different picture and what they could be used for. Lot’s of solid state physics, but in the fun “look at how amazing nature is” way, not in the “equations of horror and despair” way.This should be a fun read and easily understandable, even if you haven’t thought about physics since school.
From the amount of scanning electron microscope (SEM) pictures in this blog, you can guess that I’m a huge fan and heavy user of these wonderful devices.
Brief historical overview& resolution limit
The basic idea behind a SEM is the Abbe diffraction limit of resolution. Ernst Abbe was a pretty cool dude – he lived in Germany during the late 19th century. He defined the foundations of modern optics, had a very impressive beard and is credited with owning Carl Zeiss for some time and the creation of Schott AG. In precision engineering, he has had a lasting impact, mostly for his definition of Abbe Error Compliance (Measurement device in axis of movement is more precise than parallel to axis), but also the Abbe diffraction limit.
It basically states, that the minimum resolvable feature size d is a function of the wavelength of your radiation λ divided by 2 times the index of refraction of the immersed medium n (for example air) times the half-angle subtended by the objective lens θ. The numerical aperture NA describes the resolving power of a objective lens, and is the product of n * sin θ. Thus we have for our system resolution:
d = λ / 2 NA
If you have air between your objective lens and sample, NA can only ever be below 1. Very high quality, large magnification objective lenses can for example have 100x/NA 0.95, coming very close to this theoretical limit. This means, at absolute best, our smallest, resolvable feature is about half the wavelength of the radiation. If you have a nice, confocal microscope, your system might use a green LED at 532 nm, thus your systems resolving resolution is in the range of 0.25 µm. There’s a couple of techniques to get around this limitation, but with visible radiation, you are not going to get massive improvements in lateral resolution. But: the wavelength of radiation is inversely proportional to the energy of the radiation:
E = h*f and: λ = c/f
Visible light typically has an energy of 0.5 – 3 eV, a WLAN signal about 5 µeV. X-Rays start somewhere around 1 keV, and most SEM have their resolution sweet spot at 15-30 keV. Modern tunneling electron microscopes TEM are in the range of 200-300 keV. Sadly, we do not have a TEM at Kern Microtechnik GmbH. *chicken scratches one onto the “Dr.Marv purchase wishlist”*
Now, the actual resolution of a SEM isn’t as close to the theoretical limit as optical microscopy has, because it is surprisingly difficult to compensate all beam and lens (magnetic field) errors. Aberration error correction is something that is only now really hitting the market.
Nevertheless, even a small, entry level desktop SEM like our Thermo Fischer PhenomXL spots a datasheet resolution of smaller than 10 nanometre. Typically, this is achieved as the distance between gold nanoparticles on carbon. Very conductive, maximum elemental contrast and clearly defined boundary edges. It goes without saying, that this is the easiest possible image for a SEM!
SEM micrograph of a very dirty, hydrocarbon contaminated resolution test object. What you see is gold nanoparticles on carbon, at a very high magnification (500kX) and very low accelerating voltage (1 keV). Analysis has shown that our instrument is within specification, even here: 0.7 nm @1keV. Taken with the magnificent Zeiss GeminiSEM560.
At lower energy, the electrons are also much slower, thus experiencing more extraneous influences such as magnetic stray fields or vibrations from body or acoustic noise. A high resolution SEM will have sub 1 nanometre resolution over the entire energy range.
General working principle of a SEM
We have defined that instead of using a beam of visible light, an electron microscope uses a beam of electrons to look at matter. At minimum, an electron microscope consists out of an electron source, some condenser, scanning and focusing “lenses” (which are actually coils with a magnetic field), an aperture, a vacuum chamber with the sample as well as a sensor to detect the signal.
Below is a schematic view of the column design of our ultra high resolution, Zeiss GeminiSEM560.
Schematic cross section of a high resolution SEM column. Pictured detector is a SE2 Everhart Thornley type.
At the electron source, electrons are generated. There’s two typical ways: thermionic emitters, where either a tungsten or a LaB6 filament is heated until free electrons are emitted. The second option is a field emission gun (FEG), where a small filament is heated, but the electrons are removed via a strong electric field. FEG are typically more stable, have less noise and a narrower energy spread. They are more expensive and set higher requirements to the vacuum system.
The electron beam is then accelerated via an electric potential, and then shaped and focused via condenser lenses. The beam current is regulated via an aperture orifice. The beam is then focused and scanned across the sample in a regular pattern via the objective lens. This scanning is not a continuous process, but instead the beam dwells for a short amount of time at every “pixel” position. A detector simply counts the signal emission at every point, thus creating a black and white picture from the sample – electron beam interaction.
It is a very basic principle, but the interaction of the beam and the sample is very complex, and many sensors exist to detect different types of signals. What is really nice about this scanning and way of detecting a picture compared to having a high resolution sensor with many pixels is that all sensors have the same focus point – so you can typically seamlessly switch between sensors and don’t have to refocus.
Electron – Matter – Interaction
In order to understand the different pictures and data created from a SEM, we need to take a quick detour towards high-energy electron beam interaction with matter. When matter is hit with fast electrons (the primary electrons, PE), a couple of possible interactions can happen. The below schematic shows the 4 dominant types, mainly back-scatter electrons (BSE), secondary electrons (SE, type 1 and 2) and x-ray emission (hv). The interaction volume depends on beam energy, but is typically in the range of < 10 nm for SE1, 1-50 nm for SE2, 50-1000 nm for BSE and 1-10 µm for hv. Because of scattering, the interaction volume is shaped a bit like a pear.
Schematic beam interaction with matter. The 4 main emitted signals are shown: BSE, SE1, SE2 and hv.
The interaction volume depends on beam energy, but is typically in the range of < 10 nm for SE1, 1-50 nm for SE2, 50-1000 nm for BSE and 1-10 µm for hv. Because of scattering, the interaction volume is shaped a bit like a pear. To show this interaction, I’ve prepared a small Monte-Carlo scattering simulation highlight this interaction volume, and how deep the different species might reach. This is for a high energy beam in a light material.
Interaction volume of high energy electrons in a light material. SE are highlighted in green.
We will have to dig a bit deeper into the creation of each of these, but also how they change the picture and what data and conclusions we can draw from them. For this, I’ve put a very used, nearly broken carbide end mill into the SEM.
First/left picture: The used endmill, before being inserted into the SEM chamber. Second/Right picture: the inside of the chamber, with the visible polshoe, SE2 detector and illuminated chamberscope. A couple more complex sensors are visible in the background.
After pumping the chamber empty of air, activating the SE2 sensor and focusing, we can generate an overview image of the tool. Because the SEM flares the field at the objective lens, we get a much larger FOV, but heavy distortions. This is mostly useful for navigating and finding a feature (or even: where the heck am I currently!).
SE2 overview picture of the inserted endmill. Instrument: Zeiss GeminiSEM560
Secondary Electrons
Sometimes, when the incident electrons interact with an atom, they do so through inelastic scattering with the shell electrons. This ionises the electron, via ejecting a shell electron, the so called secondary electron. If it’s the primary electron, these SE are called SE1, and are very surface sensitive and detected via a SE detector inside the electron column. If it’s created by backscatter electrons ionising the atoms, they are called SE2 and are detected via an in-chamber detector. These are very sensitive to topography, so the resulting picture is a good representation of the shape and surface of the sample. Because they are created by BSE, the interaction volume is a bit deeper, and the signal can’t resolve very fine surface detail. This sensor is very susceptible to static charge up on the sample.
Schematic depiction of the SE creation process. Note that the incident species can also be BSE, and not only SE.
The SE2 sensor is very fast in it’s readout speed, and typically, especially at longer working distances (distance between the pole piece and the sample) exhibits a strong signal. If the sample is non-conductive, this is my first choice in focusing the picture and for navigating. Because it is at an angle inside the chamber, the sensor gives a very good depth representation of the sample. Pictures look plastic and 3 dimensional.
SEM micrograph of the cutting edge. Signal A = sensor used, in this case the chamber SE2 type. The picture has depth, and nicely shows the morphology of the grinding marks, the coating and particles on the tool.
Switching to the InLens SE1 detector, the picture changes in it’s appearance:
SEM micrograph of the cutting edge. Signal A = sensor used, in this case the InLens SE1 type. The picture has lost some depth, but gained some detail on the surface structure. Besides the grinding marks, the micro-roughness of the coating is now visible.
Because this sensor has a very small interaction volume, it shows fine surface details. Whereas the SE2 sensor mostly showed the grinding path along the tool cutting edge, this sensor shows the micro roughness of the coating, and highlights different sections of the build up edge through finer detail. At the same time, some depth perception is lost, resulting in a flatter picture.
Back Scatter Electrons
Back scatter electrons are created from elastic scattering (reflection) with the nucleus of the atoms. Because of this, the electrons have a lot of energy. The chance for elastic scattering depends on the mass of the nucleus, thus heavier elements give you a brighter signal. Therefore, the BSE signal gives you a material contrast.
Schematic depiction of the SE creation process. Note that the incident species is either the PE, or a lower energy already back scattered BSE.
The same cutting tool we looked at in the SEM can also be visualised with back scatter electrons. For this, our GeminiSEM560 is equipped with two different one: the ESB detector, that sits very high up in the column, and a retractable diode type 4 sector BSD sensor that can be fitted exactly below the pole piece.
Because we can always activate it, let’s start with the ESB detector picture. We can see that the image is flattened a lot – this sensor is not really picking up any topography.
In column ESB detector SEM micrograph of the cutting edge. Note the lighter coloured structures – these are heavier elements than the darker coloured structures.
This sensor is quite “slow”, in the sense of it not getting a lot of signal. The above picture took a bit over 4 minutes to record.
The SEM is fitted with a diode type, 4 sector BSE detector, that can be retracted and inserted via a pneumatic cylinder. Because it is sitting below the pole piece, it is much quicker, and still shows some surface structure.
Chamber BSD SEM micrograph of the cutting edge. The picture has very little depth, showing only a minimal amount of surface structures. The BUE material is clearly distinguishable, showing 2 different materials via the inherent BSD material contrast.
This sensor is much quicker, and shows some topographic details. A bit more depth perception than on the ESB sensor is given.
X-Ray creation (EDS – Energy dispersive x-ray spectroscopy)
The PE are able to create x-rays. I find this absolutely fascinating, and one of my favourite tools inside the SEM. When the PE interacts with the atomic shell, sometimes an electron is ejected (the SE). If this happens at a lower shell, a hole (missing electron spot) is created. Because most systems strive to lower their potential energy, a higher shell electron will then drop down. Because the new orbit has a lower radius, there is now some excess energy. Through this energy, just like Einstein foretold, a particle is created, specifically a x-ray photon. Because the distance between shells is dependent on the weight of the atomic core and it’s configuration (proton number), the energy difference is unique for every element.
Schematic description of the x-ray creation process. An incident electron creates a hole in an inner shell through inelastic scattering (a SE is ejected). A higher shell electron drops down to fill the hole (blue arrow), because of energy conversion the lower orbit energy results in the creation of a x-ray photon.
By recording lots of x-ray photons, and sorting them by their inherent energy, we can identify and map an elemental distribution over our picture. This process is called energy dispersive x-ray spectroscopy. It doesn’t tell you “This is REX 121 steel”, but instead after several minutes you can say “oh, we have about 12 % chromium in our sample. Maybe. I hope. Pinky promise!?”. This is the part where TV shows have ruined science for us scientists. But if done right, at correct readout sampling rates, high beam energy, you get fantastic results.
What can we see on our tool edge? First and foremost the coating material – Ti, Al, N, Cr, resulting from a ceramic high tech multi layer coating applied to most modern tools. Build up edge and particles from aluminum, some stuck carbon, places where the coating has failed and tungsten carbide is visible through the coating. Pretty nifty, eh?
EDS analysis of the tool edge.
The real expertise in EDS is looking at the data and then making judgement calls and drawing from experience and know how. We once found a particle we wanted to analyse, and it contained bromine. People were stumped, because which part of the machine contains bromine? In the end it was the base of our powder coating, and the particle we found at a place it shouldn’t be was the powder coating from the machine enclosure that had flaked off. We managed to nail that down, because the only reasonable expectation of where bromine could be used was exactly that. Comparing a fresh piece revealed identical chemical composition.
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:
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.
Review Today’s sharpening Stone is a triplet of stones. These are from a German sharpening shop called “Schleifjunkies”. The stones are advertised under the name “resinbond”, and according to the manufacturer create high gloss and super sharp edges in minutes, not hours. Ok! Let’s take a closer look 🙂
The stones are well finished on the top surface, with a smooth, green surface. The side is raw and appears to be saw or maybe beam cut? They are actually glued down to the holder with some flexible foam tape, allowing for some flex between stone and aluminium holder:
Let’s take a look at each stone under the optical microscope.
Optical micrographs of the SJ Resinbond 6 µm stone. The scale bar is visible in the lower right corner. Instrument: Leica Emspira.
Quite a bit of colour is visible at higher magnifications. Green, translucent green (typically diamond), black, and some reddish-orange colour. I think this is going to be a very interesting stone to look at under the SEM.
Optical micrographs of the SJ Resinbond 3 µm stone. The scale bar is visible in the lower right corner. Instrument: Leica Emspira.
Optical micrographs of the SJ Resinbond 1 µm stone. The scale bar is visible in the lower right corner. Instrument: Leica Emspira.
The two finer stones show about the same colour – the translucent green particles do shrink in size though, most notably from 6 to 3 µm. I can’t really tell any difference in size on the other particles.
The stone was cleaned with IPA in an ultrasonic bath, rinsed and then blow-dried with compressed, ultra pure nitrogen gas before getting put into the SEM.
SEM Micrographs of the SJ resinbond 6 µm stone. Instrument: Zeiss GeminiSEM560.
The stone is a mix of 3 different, easily identifiable grains. There are larger, above 10 µm grains all across the surface, in a low conecntration. there is a higher concentration of smaller, blocky, fractured grains as well as a notable amount of rounded grains, that have some molten look to them. Between the grains, some areas are binder (matrix / resin) dense, whereas others are dense agglomerations of grains.
SEM Micrographs of the SJ resinbond 3 µm stone. Instrument: Zeiss GeminiSEM560.
The 3 micrometre stone shows the wide spread of grains, and also their diverse size:
There are some 10 µm sized grains, that are very long and narrow, interspersed with some more blocky, rounded grains that I suspect will be the diamond. On the upper left corner, one can make out the molten droplets in fine detail. These are also a bit lighter colour – typically a sign that they consist of a heavier element than the surroundings. I took a quick peak at the 1 micrometre stone, which looked nearly identical to the 3 micrometre one, but didn’t go through the trouble of recording the images, as I prefered to focus on finding out all it’s secrets – especially the 3 different grains that are visible! For this, I did energy dispersive x-ray spectroscopy (EDS) to create elemental composition maps over the SEM picture.
EDS analysis of the Schleifjunkies 3 micrometre resinbond stone. Instrument: Oxford Ultim Max ∞ 40mm2 EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.
The EDS analysis brings some clarity to this! Let’s take a closer look at the elemental mapping ,and what we can deduce from this.
The stone has some large, blocky, molten looking red areas, which are carbon rich. This is the resin used to bond the particles together. The smaller, red grains are also mainly carbon – most definitely the diamond grain. SJ seems to have used a more blocky, smoother grain shape here.
THe green grains are silicon, but by comparing the carbon intensity map, we can see that they also consist of carbon. This is silicon carbide, at about 3 times the size of the diamond grains. Silicon carbide is quite hard (2400-3000 HV, depending on the type), which is why it is often used as an abrasive on it’s own. The use in resin bond stones is typically to make the bond harder. The purple grains are actually copper – which explains the reddish grain we could make out in the optical microscope pictures. Copper is added to industrial resin grinding wheels to improve heat conductivity, and while this makes a lot of sense at high cutting speeds, and if your abrasive is alumina oxide (corundum) or SiC, diamond has a much better heat conductivity, and it’s the first time I’m seeing this on a diamond grinding bit. Frankly, here it can only be either a cheap filler, or the manufacturer took the same mix they use for AO grinding wheels and just added diamond. Trace amounts of chromium can be detected, as well as some oxygen, matching particles with the silicon map, so I’d suspect that the rare, white-ish particles we have seen in the microscope are SiO2 (quartz) particles.
Let’s take a look at the surface roughness and appearance.
3D height map of the 6 µm SJ resinbond stone. Instrument: Bruker Alicona µCMM, 50X objective lens, singe FOV high resolution focus variation scan. Data is leveled and outliers removed (0.25%). 2nd picture: area extract to show the grain.
The surface, similar to the SEM picture, has large, very smooth sections, where the grain is still covered in a bit of resin, and also irregular, smaller sections with voids and recessed grains. This matches the view from the SEM quite well.
ISO 25178 parameters of the 6 µm SJ resinbond stone.
The stone surface roughness (Sq) is very low, with a nice and tight control on the height of the surface bearing material ratio (Sdc). The kurtosis (Sku) is quite high here, a result of the very flat sections in combination with the very steep walls leading down to the voids. This smooth stone will glide quite easily along a blade, while providing little feedback. The pressure applied is spread over a large area, reducing the force acting on every grain.
3D height map of the 3 µm SJ resinbond stone. Instrument: Bruker Alicona µCMM, 50X objective lens, singe FOV high resolution focus variation scan. Data is leveled and outliers removed (0.25%). 2nd picture: area extract to show the grain. 3rd picture. ISO 25178 surface data.
The 3 micrometre and 1 micrometre stone do not differ significantly in their surface parameters. I believe the surface of these stones is dominated by both the filler grains (SiC & copper), but also the breakouts above large nests of grains in combination with the dressing from the manufacturer.
3D height map of the 1 µm SJ resinbond stone. Instrument: Bruker Alicona µCMM, 50X objective lens, singe FOV high resolution focus variation scan. Data is leveled and outliers removed (0.25%). 2nd picture: area extract to show the grain. 3rd picture. ISO 25178 surface data.
The 1 micrometre resinbond stone has a line through the center of the height scan, sitting quite a bit above the rest of the surface area. Maybe a missed spot on the final dressing of the stone surface?
In order to evaluate the sharpening performance of these stones, 3 blades were sharpened. In order to evaluate the sharpening performance 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. One blade was prepared with the 6 micrometre stone, the 2nd with first the 6 and then the 3 micrometre one, the last with all three stones.
The 6 µm blade tested to a BESS rating of 135. No stropping was undertaken.
SEM micrographs of the sharpened M398 blade. Finishing Stone: Schleifjunkies 6 µm. Instrument: Zeiss GeminiSEM560.
The 6 µm blade shows a slightly wavy edge. Some burr is visible, as well as some carbide cracking from the grinding pressure. Periodically, deeper scratches are visible.
The 3 µm blade tested to a BESS rating of 130. No stropping was undertaken.
SEM micrographs of the sharpened M398 blade. Finishing Stone: Schleifjunkies 3 µm. Instrument: Zeiss GeminiSEM560.
The 3 micrometre stone left a smoother surface with lower scratches. Near the apex, some cracking and a ghost burr are visible. Some deeper scratches are visible, similar to the 6 µm stone. The stone didn’t remove a lot of material, and mostly burnished the surface, which also explains why no significant sharpness improvement was visible.
The 1 µm stone felt very dull. I spend more than 15 minutes just on that stone, with barely an improvement on the blade. Because of the low material removal rate, I raised the angle by 0.1°, so that the edge was leading and we could be sure that what we are later measuring was created by the 1 micrometre stone. The blade tested to a BESS rating of 160.
Whenever I got a section to become smoother, a larger scratch appeared again. These deeper scratches are very similar to the other two stones. I would hazard a guess that it’s the SiC particles, which are similarly sized in all 3 stones.
SEM micrographs of the sharpened M398 blade. Finishing Stone: Schleifjunkies 1 µm. Instrument: Zeiss GeminiSEM560.
The blade got a bit smoother, but also rounded of the apex. The deeper scratches are very similar to the other two blades.
Optical macro shots of the 6 / 3 / 1 micrometre finished blade. Instrument: iphone 15 pro max with a 120x optical loupe macro addon. Note the improved surface finish, but general appearance of larger scratches.
I’m quite disappointed in these stones. I have two Schleifjunkies resin wheels for my Tormek T8, which do a better job. These stones feel to hard, with not enough of a bite. It feels like I am constantly burnishing the surface, and not removing a lot of material. The mediocre BESS tests and persistent scratches are of note here. I sharpened a much softer knife at 58 HRC with this, and had better results.
The stones tested between 85 and 95 shore D at random locations. I took 5 measurements per stone. The measurements were taken at the sidewall of the stone.
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.
Lemma: Do sharpening stones become “finer” over time?
Looked at new and used galvanic grinding stones under the scanning electron microscope, comparing grain wear, swarf accumulation and tear out over time
Applied first principle thinking based on the metrology results from the stone to determine grain engagement, and then proofed theory via experiments:
Sharpened two edges, one with a brand new and one with a nearly used up stone
Compared visual apperance, but also took SEM pictures and 3D metrology of the blades, to compare roughness, spatial parameters and morphology
Results:
With continuous wear, the grains actually become wider, and more grains become active. This reduces the depth of cut, visible in the step height determination on the 3D surface data
The duller grain and lower engagement create a burnishing effect, reducing depth of scratches by >60%, lowering roughness by 27% and introducing a convex bevel and more pronounced, plastic burr at the apex. It also increases gloss. The result therefore looks like it is done with a finer stone, minus the sharpness and shape, which deteriorate.
Actual Science and long version:
This is part of a series of blog posts, where I try to apply my professional knowledge on how chip formation and material removal happen to knife sharpening. I think this could also be called: debunking myths. Because this probably will ruffle some feathers, and is likely to be denied by some people, let me state firmly here: everything you will see in this post is real, and repeatable. Because it is breaking with common misconceptions, I have done the below experiments twice, to verify it. For clarities sake and readability reasons, I only include one dataset below.
Something you can see on a couple of manufacturer homepages, but also often on the internet, is that galvanic stones become “finer” over time. You generally find two seperate statements about this, with a small difference in language, but a large difference in sense. The first is, like stated above, that with wear, galvanic diamond or CBN stones become finer. The second version is, that they behave like a finer grit after some use. Sometimes, you are also warned about a break in period, where they are supposed to be super aggresive.
Let’s take a look at a galvanic stone. You can either jump into the full analysis of the TSPROF Blitz F1000, or just take a peek at the following gallery.
SEM micrographs of the unused Blitz F1000 vom TSPROF. Instrument: Zeiss GeminiSEM560.
We can make out some grains that are deeply embedded, but also some that are nearly sitting completely on top of the galvanic bond. A good question here would be: How many of these grains are actually cutting at contact with a flat surface such as a knife edge?
In literature, this is called the difference between statistical edges (e.g., all you see above in the picture), and kinematically active edges. In order to clear up this point, take a look at the following diagram. It shows a typical grain distribution in a galvanic stone – actually, a pretty good one already. 90% of the grains are within 10% of their diameter variation. If you plot a straight line through these, you will see that only 4 out of the 10 grains are actually cutting into this imaginary straight line. I’ve coloured them red at their intersection. I like the colour red. It’s a professional thing.
Illustration of a decent height distribution of similar grains in a galvanic binder. A portion of the grains above a certain horizontal line is coloured red, to show how few grains are typically active in the cutting process.
Now, if we have a moving edge, the situation becomes a bit more complex. Because now, we don’t have a level, horizontal line of engagement. That would be the case of you lay your stone on top of a plate of steel, and becomes kinematically much more like lapping, with different material removal processes. Instead, what we have is a flat piece of metal (the knife edge), being dragged along the stone, and either by gravity or your hands being pushed into the material. If we imagine for a moment, that friction, elastic deformation & rebound are nonexistent, we can imagine that every grain basically removes the material to it’s very topmost, highest apex. But because the blade is moving, the “drag” behind it is finite, and a new portion of the blade is pressed into the grains and again thusly removed. I’ve illustrated this below. Please note that obviously, this is a very small section of the blade, and I’m not suggesting you should in any way be sharpening to a single sided edge.
Illustration of the removed material from the 4 kinematic active edges. The blade movement and force vector are resembled by the black arrow.
Now, here’s a couple of things we can deduce from this: the first is, the amount of grains that are cutting metal is actually pretty low. Secondly, because of the complex movement, the grains create some kinematic roughness in the blade. Our surface is not created by the highest grain, but by several of those, leaving a “ragged” surface behind. Nevertheless, the last grain leaves a track on the surface. With some use, these grains will wear first. In the space between grains, we will accumulate debris and swarf:
SEM micrograph of a used TSPROF Blitz F1000. Some flattened grains and swarf stuck to the galvanic bond are visible. Instrument: Zeiss GeminiSEM560.
Now, what does a very used galvanic stone looks like? For your viewing pleasure, and in the pursuit of the adventure of sharpness, I’ve sharpened edge after edge until my arms were sore and the stone was removing basically nothing:
SEM micrographs of a very used TSPROF Blitz F1000. This one pretty much didn’t remove any material at all, any longer. Instrument: Zeiss GeminiSEM560.
If we focus on one of the really flat grains, we can see how much is worn away, and how much swarf is embedded deeply into the galvanic bond:
SEM micrograph of a VERY used TSPROF Blitz F1000. Instrument: Zeiss GeminiSEM560.
Take a look at the grain directly above the red Kern logo (lovely, ain’t it?): This is pretty much completely rubbed flat, and level & even with the surrounding bond.
If we flatten the grains in our previous illustrations, and apply the same GEDANKENEXPERIMENT of a blade being dragged along it, it looks like this:
Illustration on how flattened grains are interacting with the material. For this, a horizontal line was drawn, but the removal of the material “simulated” via linear interpolation between the highest peak of a grain and the lowest portion of the next grain (kinematic distance between active grains).
Now, a good question here would be to ask: Dr. Marv, why did you draw the engagements of these grains so shallow? They were taking much deeper cuts beforehand!
For this, we will apply critical first principle thinking. When you sharpen, what you are doing is WORK. And I mean this in the physics sense of the word. Now, we will postulate that you know what you are doing, so you are not pushing unevenly. Whether the stone is worn or not, you apply the same force and speed to it, thus the same work. The work we are doing while grinding consists of several components: friction (which generates heat), plastic deformation (which removes material, generates heat), elastic deformation (“bounce back”) and shearing action. If you have a good lubricated stone (for example, with oil), and are moving slowly, friction and heat are not that big of an issue*. Elastic deformation is generally only a fraction of what is happening here. So, we could equal the work being done to material removal. If instead of only a few grains, all of which are taking a larger cross section out of the material, if you have more active grains, these will all have a similar cross section (maybe a bit larger, as we are moving towards their center and therefore maximum diameter), your actual depth of cut will diminish.
*authors note: total lie here. Friction ALWAYS is a super big issue, and actually becomes worse, the duller your grain is. But for our Gedankenexperiment, it doesn’t change a lot. Just makes it less dramatic than my drawing. Trust me. I’m a doctor and I draw pretty illustrations. Also, I have stuff to prove this.
The following illustration is showing the new, much smaller intersection from the beforehand drawn kinematic active grains.
Illustration, highlighting the kinematic active grains and their active cross section in red. To see how much the grains are worn down, their full shape is visible with low opacity.
Now, what is the result of this? To prove my point, the above theory and showcase this, I’ve prepared two edges. One, with a brand new Blitz F1000. One, with the very much destroyed one. The steel used is M398 at 63.5 HRC, the edge was prepared with progressively finer galvanic stones (150-220-400-800) at 17 DPS.
Let’s compare the result from an optical perspective:
Optical micrograph of the same edge prepartion with two different usage states. Left side: brand new galvanic stone, right side: very used up galvanic stone. Instrument: iPhone 15 Pro with a 120x macro loupe, hence the distorted picture on the right.
This is a pretty drastic difference, the blade on the right side is much smoother, shinier, even glossy. It looks like a finer stone made this! …wait, what?
Luckily, I have access to better microscopes than my phone. Let’s compare what these two edges look like in the scanning electron microscope:
SEM micrographs of a sharpened blade, 250x magnification (FOV: 505µm). First/left picture: new stone, right/second picture: used stone. Instrument: Thermo Fischer PhenomXL.
SEM micrographs of a sharpened blade, 500x magnification (FOV: 505µm). First/left picture: new stone, right/second picture: used stone. Instrument: Thermo Fischer PhenomXL.
Now, this is a stark difference. The new stone created a sharp, uneven morphology. Lot’s of micro prows, deeper scratches and general uneven surfaces are visible. The used up stone created a much smoother surface. There are some scratches, especially closer to the edge. The surface further from the apex is very smooth and rounded, giving it a burnished appearance.
SEM micrographs of a sharpened blade, 1000x magnification (FOV: 505µm). First/left picture: new stone, right/second picture: used stone. Instrument: Thermo Fischer PhenomXL.
At higher magnification, we can make out a sharper apex from the new stone, but also more debris, burr and carbide cracking. The apex from the used stones looks more rounded and dull.
Now, while the SEM is a tool that is fantastic in spotting small details, it’s spatial (in the direction of the beam) resolution isn’t super good. To further analyse what we are seeing, I’ve used our Bruker Alicona µCMM to record some 3D data of the blade apex. It’s a very expensive, optical coordinate measurement machine that uses the measurement principle of focus variation to record height data over a surface area. Why did I use that one and not the Zygo interferometer? Well, the lovely zygo is currently at an exhibition, so I had to make do with what we had *crys in millions of metrology equipment*.
3D height maps of the two measured edges. Left/first picture: new stone. Right / second picture: Used stone. Instrument: Bruker Alicona µCMM, 50X objective lens, singe FOV high resolution focus variation scan. Data is leveled and outliers removed (0.25%)
Now, one thing is immediately visible: The new stone created a very flat surface, with deeper, and very direction scratches. The used stone created a slightly rounded of (convex) surface, with smoother roughness. The scratches are directional, but there are some deeper ones at a steeper angle.
With this height data, we can start doing real analysis. First, let’s take a look at the width and depth of the scratches. For this, I’ve filtered the micro roughness via a gaussian filter with a cutoff of 0.8 micrometre:
New galvanic stone blade: Above: filtered surface to remove micro roughness and make step height determination easier. Below: Step height determination. Software used: Digital Surface Mountains Map. <3
and extracted a profile perpendicular through the scratch: Step analysis shows a width of 11 µm, with a maximum “height” (or depth) of 1 µm.
Comparing this to the used stone, with identical workflow (filtering, extraction of profile, step height determination):
Used galvanic stone blade: Above: filtered surface to remove micro roughness and make step height determination easier. Below: Step height determination. Software used: Digital Surface Mountains Map. <3
We arrive at a similar width (10.5 µm), but a much lower maximum height (depth) of 0.38 µm. So, without question we can answer a lemma put up at the beginning of this post: galvanic bound grinding stones do not become finer over time. But because the grains flatten out, their actual depth of cut and the grooves they are creating are more shallow and smoother.
Let’s take a look at the surface metrology data we can extract. For this, I’ve extracted an area of the scan, leaving out the very fine apex of the blade, as we have some measurement artefacts on this one (“batwings”, basically diffraction light at a sharp and burry edge). For those of you working in the manufacturing world, feast your eyes on the ISO 25178 parameter table. This is how you state roughness: clear identification of the workflow, filters and parameter settings used, together with a coloured heat map of the surface recorded.
Surface heatmap and ISO 25178 roughness (S-L) parameters of the edge ground with the new TSPROF Blitz F1000 stone.
Now, what can we extract from this? The quadratic surface roughness Sq is a super fine parameter to evaluate surface roughness, as it is also the “power” of a surface, and therefore directly proportional to how shiny you experience this. We’ve achieved a value of 0.28 µm here, which is about what I would expect from this grit of galvanic stone. The kurtosis (Sku) is around 3, which is where “sharper” profiles start. This means the surface is more of a zig-zag instead of a well rounded sine profile.
We have a low material ratio Smr (17%), so that means only a fraction of our surface is found at the top 1 µm of our height data. If this was a bearing surface (and during a cut it is!) it would have very few spots it would actually have contact with. The auto-correlation length Sal is the dominant spatial structure – here we can see that the fine scratches we see at a direction of 144° to the x-axis of our recording (compare parameter Std, texture direction) are spaced at 1.35 µm.
Surface heatmap and ISO 25178 roughness (S-L) parameters of the edge ground with the used TSPROF Blitz F1000 stone.
Comparing the used surface with the one above, we can see a significant improvement of the surface roughness Sq at 0.22 µm (27% lower), a much higher kurtosis (Sku, 4.45 µm). The material ratio Smr is also crazy high – 79% definitely point towards a “flattened”, e.g. burnished surface. The auto correlation length Sal didn’t really change, as did the texture direction (153° compared to 144°).
So, that’s it folks. I think this shows that galvanic stones do not become “finer” over time. Surface finish improves, as the grains are flattened, outlier grains are torn out or shattered, and a burnishing process begins. The shape of the blade seems to deteriorate – at least with my skill of sharpening and on a TSPROF K03.
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:
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.
Today’s sharpening stone is the Edge Pro Matrix Stone at 4000 grit, which according to the manufacturer equals 5 micrometre grain size. It’s their stone “made for modern super steel” and apparently self sharpening by loosening grains over time. 🙂
It’s a super smooth, very fine stone. Stroking it with your finger, it just feels barely sticky, while scratching it with your fingernail shows some resistance – but can also leave a small groove.
Optical micrographs of the Edge Pro Matrix Stone (4000). The scale bar is visible in the lower right corner. Instrument: Leica Emspira.
The microscope supports this picture. A very uniform, smooth surface. The corners around the stone are slightly beveled. At higher magnifications, grains start to become visible. Do we have a new king of agglomeration here? Let’s throw it into the SEM to check it out.
The first thing I saw in the SEM was…nothing. Because this stone is so smooth, and also because they really seem to use no fillers, additives or anything else, it immediately starts charging like crazy. The resin they are using is also covering the topmost layer, making it hard to distinguish between resin and diamond. Well, this ain’t a BEAST of a scanning electron microscope for nothing. We’ve equipped it with multiple sensors and it is a very versatile device. To make an image visible, I’ve bumped up the accelerating voltage. To explain why this is different to the other pictures you’ve seen in this blog before, I think I need to detour for a small moment.
In a scanning electron microscope, the image is created by using a beam of electrons, and moving that one in regular lines across the surface of a sample. At every point it hits the sample, interaction happens. This interaction is typically either an elastic reflection of the incident electrons (back scattered electrons, BSE), or the ejection of electrons from a shell around the atoms (secondary electrons, SE). The BSE are showing you mostly elemental contrast, whereas the SE show you a topographical (surface) contrast. Nevertheless, with good enough sensors, both show you a bit of the information of the other type. Now, the BSD (back scatter detector) is pretty robust, and works nicely at lower vacuum. Because the sample is non conductive, it will experience static charge. Lowering the chamber vacuum introduces moisture (H2O) into the chamber, and this is enough to reduce the static charge on the sample. Unfortunately, lower vacuum also means lower resolution, and the BSD doesn’t give us great surface morphology to begin with. A workable way to combat this is to increase the accelerating voltage. This will not only give you more signal, reduce noise, but also increase the interaction volume of the beam. Basically, you are now looking a couple micrometre deep into the material!
SEM Micrographs of the Edge Pro Matrix Stone (4000). Note that these pictures are BSD and at high accelerating voltage. Instrument: Zeiss GeminiSEM560.
We can see that this stone really only contains a matrix and the diamond grit. All grains are small with tight controlled size distribution. No fillers or other abrasives are visible. The matrix is relatively dense, and the atomic contrast of it is similar to the diamond next to it. This is the first stone I’ve looked at that contains no fillers. Unfortunately, with this comes two problems: Quite a bit of agglomeration is visible, with often 3 or more grains sticking close to each other. The second is the retention of the grains – we can see on this unused stone already, that nearly no grain is sticking out of the surface. Even the manufacturers dressing process removed the majority of all surface grains. I would expect this stone to be quite slow and soft. Because of the simple composition, no EDS was recorded.
The surface under the white light interferometer shows a smooth, regular and low roughness surface.
White light interferometry height map of the Edge Pro Matrix Stone (4000). Instrument: Zygo Nexview NX2, Objective Lens: 10X. Stitched overview of 4×4 images.
The overall height distribution is lower than for example on the similar grit Venev stone. The actual contact surface, at least brand new, should be relatively low, as it doesn’t show a lot of plateaus in the height map.
ISO 25178 parameters of the Matrix Pro Stone (4000).
The areal surface parameter support this observation. This is one very smooth stone, with very low roughness and material ratio.
In order to evaluate the sharpening performance of these stones, 3 blades were sharpened. In order to evaluate the sharpening performance 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. Then the Pro Matrix stone comes into play. The blade tested at 118 BESS. No stropping was undertaken.
SEM micrographs of the sharpened blade. Note that the last picture (2kx magnification) isn’t a center zoom of the one before, but slightly to the left of the FOV, as I identified some carbide cracking that I wanted to visualise in higher detail. Instrument: Thermo Fischer PhenomXL Scanning Electron Microscope.
The surface of the edge is much smoother than with the equally sized Venev sharpening stone. The edge shows a low waviness and no identifiable burr. This is certainly a statement to the heat treat of the steel (made by Roman Kasé!), but also to the stone. Some deeper grooves are visible, which could be because of the agglomeration, or a rolling grain that got loose. The low material removal rate gives a high cutting pressure, likely leading to the carbide cracking and edge breakouts at carbide-steel interfaces. This is a cool stone, with a nice feeling while sharpening, awesome result and very finely made. I like it. If only it was a faster stone!
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.
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