Dr. Marvin Groeb – Abrasive Solutions

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  • Sharpening Mechanisms – Part 1 – Katocut Nowi Pro

    This is the start of a new blog series, where I try out sharpening mechanisms. I’m not yet fully sure about the format – I will write about things that matter to me, such as build quality, capability to sharpen, but also very subjective things like how it feels to sharpen with this. If I was you, I would expect this to be a rare blog segment. The reviews will be independent from the manufacturer, without control over what I test or write. I am not paid nor do I receive anything from the manufacturer if you decide to buy one.

    If you make a sharpening device and you want me to test it, feel free to reach out.

    KATOCUT Nowi Pro

    This sharpening mechanism is made by the Austrian engineer Alexander Hackl. He operates an engineering company under the name KATOCUT. The exact model for this post is the “Nowi Pro Black Edition”, which at the time of this review retails for around 1600 Euro, including VAT.

    A close-up view of a Nowi PRO device featuring a black arm, attached to a sturdy base with an olive-green component, designed for precision tasks.

    The sharpening mechanism is based on what is typically called a “Bogdan” principle. This means the knife is held at the desired angle by fixing that degree of freedom, while leaving most other directions free to move. I’ll dig deeper into this later on, but basically this means the angle is not dependent on the knife geometry or the height of the sharpening stone – which is also a principle, much in contrast to guided rod sharpeners, where every point along the curve of the knife later is sharpened to the same, precise angle.

    Basic configuration to put the Katocut together with the clamping mechanism. And a very pretty custom Shard from Roman Kasé in Rex 121.

    The Katocut comes in a very high quality, solid case with a precise foam cutout. The baseplate is heavy, 8 mm thick steel that looks powder coated. The vertical rod is a 25 mm steel rod with a brushed finish. The arm is black anodised aluminium, with a (vertical) thickness of 20 (first link) and 14 mm (second link). The kit includes different mounting options, such as a clamp as well as a large and small magnet. The vertical guide rod features the angle-adjustable mechanism and there is a spring to adjust preload / weight compensation of the apparatus.

    A digital angle meter as well as all needed tools plus some food safe oil to lubricate the bearings and mechanism is included. No stone holder is included, but I would guess that you already own one, so that’s not a large issue.

    Build Quality

    The build quality of the black edition is very high. All parts are nicely anodised or coated, with no rack marks visible. The parts are made well – good straightness, no machining marks and homogeneous chamfers really create a high quality appearance. The 8 mm steel baseplate in combination with the 25 mm steel vertical rod give the whole mechanism quite some weight, further increasing the qualitative appearance. The threads are well machined, and everything fits together nicely without major play or struggles. The high price of the device is mirrored in the build quality, much more so than on other sharpening mechanisms. The machinist in me can only enjoy this!

    Close-up of the Nowi PRO adjustable arm with metallic components, showcasing the branding and features.

    A couple of shots from the Nowi Pro.

    Working Principle

    Close-up of a mechanical arm joint and support structure, showcasing metal components and an adjustable lever.
    The angle adjustment mechanism. This constrains the angle of the blade, relative to a horizontal surface. Note the secondary swivel bearing below the mechanism.

    The idea behind any of these “Bogdan-Style” sharpeners is that a mechanism locks the angle of the blade, relative to the stone. On this system, this is achieved via a series of swivel joints and a threaded part of the rod. By setting a reference, for example via a digital level box, the angle can be adjusted very finely. Afterwards, the two screws are locked around the angular joint via supplied wrenches.

    Close-up of a digital level box displaying an angle of 17.0 degrees, mounted on a flat surface.
    Bevel box sitting on the parallel ground spline of a production Shard – if you have a fully ground blade, you need to compensate for the blade bevel angle.

    The reason this principle works so well can be put down to the principle of “constraints”. Every mechanism that moves has some degrees of freedom. Imagine a linear rail: you can move it back and forth, but not sideways or up and down. It is therefore constrained in 1 dimension.

    What happens here on the Nowi pro is similar – in that our system is also constrained – by the linkage joint shown above. This angular constraint makes sure that our knife only ever touches the stone at the angle we want:

    Illustration showing an angled tool in contact with a surface, with an angle 'a' indicated.

    This angle will stay constant, even if we rotate the vertical rod – it will just shift the contact point somewhere else along the stone! This is also true for moving the blade back and forth, or up and down – the angle won’t change, as it is constrained.

    Diagram illustrating the movement of a pivoting component above a flat surface, showing the angle 'a' and directional arrows to indicate motion.

    By arranging a second bearing, and this one after the constrained angle, it is possible to tip the blade from side to side – which will allow you to sharpen every point of the blade, even the tip, at this specific angle.

    A diagram showing a cutting tool in operation, illustrating the movement angle 'a' and the cutting edge against a workpiece surface.

    What this means is that the system is pretty robust in terms of knife geometry (length or width of the blade does not matter!), but also height of the sharpening stones. Where on other systems you have to fiddle and adjust if your sharpening stone progression has different heights, this system by design and constraints always has the same angle.

    Sharpening Process

    The use of this device is pretty straightforward: Clamp your knife, either in the supplied centering clamp, or attach it to one of the magnetic bases. The adjust the angle of the joint mechanism via the digital level box, make sure the screw nuts are tightened, and start sharpening!

    A digital level box displaying a reading of 0.0, positioned next to a knife on a green surface.
    A close-up of a digital level box displaying an angle of 17.0° on a green screen, positioned on a work surface.
    Adjusting the angle of the blade – first by setting the reference (“zero”) on the stone, and then adjusting the joint mechanism. This Kasé shard was then sharpened to 17 DPS. Note that this blade features a parallel ground section on the spline where the measurement is easy – if you have a fully ground blade with no parallel section, you need to account for the blade angle as well.

    The sharpening action itself is – and I have to say this is of course very subjective – wonderful. This is what I think sharpening should feel like: relative movement between the blade and the sharpening stone, with no fiddling, no adjustments. Just you and the movement!

    When I started sharpening over a decade ago, I probably bought the same entry level stones everyone has lying around – some whetstones that you had to soak. The sharpening action on those was mostly defined by my skill – if I held the knife at the wrong angle, or wobbled, the result was a dull knife. But the freehand experience seems to scratch some primal itch, it is, for lack of better words how a knife should be sharpened.

    This mechanism fixes this issue in a big way: skill is not really needed here. I find this to be super true, as the first knife I ever sharpened on this mechanism probably was my sharpest knife to date… and it has only gotten more impressive with a little bit of practice. Check the action out below:

    Sharpening on the Nowi Pro – note the swivel mechanism of the clamp.

    Conclusion

    There is a lot of fantastic things about this mechanism. I absolutely love the way the sharpening movement happens here – if you ask me, this is how sharpening should be. It’s the freehand experience for those of us who lack the skills to sharpen freehand.

    The build quality and packaging of the device is stelar, as one would expect at this price point. Pair this device with a set of high quality benchstones (for example, Dr. Marv’s Scienitfic Benchstones), and you will have fantastic edges:

    A close-up of a sharp knife held above a black promotional card for Katocut sharpening systems, featuring a logo and an illustration of the sharpening device.
    A Kasé Shard (NitroX) sharpened on the Katocut Nowi Pro. Benchstones used: Dr. Marv’s Scientific Benchstones in 180 – 40 – 10 – 2.5 µm progression.

    I’ve had the Nowi since November of last year. It has replaced all other mechanisms and devices I own to sharpen my own knives. I don’t think I can give any higher praise.

    Moreover, this device will enable me to expand the blog reviews on sharpening stones towards benchstone sized ones – look out for some cool new reviews coming!

  • A brief study on sharpening stones – Part 44 – PDTools Diamond Vitrified 100 grit (Vitrified, Diamond)

    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 PDT. After I was super disappointed in the much hyped CBN vitrified, and equally in the even more hyped silver, I thought: why not spend more of my money on another PDT stone. At least this time, it contains my favourite abrasive, diamond. Diamond is only metastable, meaning at around 680°C, it becomes graphite. Making a vitrified stone, where ceramic components need to at least achieve a glassy phase, below that temperature, is quite tricky. Let’s take a closer look!

    Optical micrographs of the PDT Vitrified diamond stone. Instrument: Leica Emspira

    These are some chunky diamonds! But also, lots of other particles we can peek here. This will be an interesting stone under the SEM!

    SEM micrographs of the stone. Instrument: Zeiss GeminiSEM 560.

    We can see lots of coarse, abrasive particles inside a brittle matrix. This looks a lot like their previous vitrified stone – but in this case, with diamond as the abrasive. One question here would be: did they manage to stop the diamond from becoming graphite? This is quite hard to detect, a first hint can be given by switching sensors back and forth. For this, I used the InLens detectors of our fantastic Zeiss SEM – switching the detected electron type, and also energy filtering. Especially the EsB sensor is very sensitive, graphite shows up in a different brightness than diamond.

    SEM micrographs of a diamond, comparing it’s appearance between the SE1 (InLens) and EsB (Backscatter InLens) detector. Looks very homogeneous! Instruments: Zeiss GeminiSEM 560.

    I did not find any difference here, even at lots of filtered energies – a good sign!

    Let’s look at the chemical composition! 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 stone. Instrument: Oxford Ultim Max  ∞ 40mm2 EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

    We can immediately identify the diamond, and also in a decent concentration and distribution! The matrix is a standard vitrified bond, consisting of different oxides. I find the addition of titanium quite curious – this probably gives the bond some tensile strength when used in CNC applications? I’m now very excited to try this out!

    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 stone. Instrument: Thermo Fischer PhenomXL SEM.

    The stone itself feels ultra coarse. There’s a massive amount of vibration/feedback, and one can really see how it removes material. It also stinks like no tomorrow. This is something I find with a lot of eastern stones – I’m unsure what they do to these, and when I use them they have been thoroughly cleaned and survived high vacuum inside the SEM. Nevertheless, the stone quickly removed a lot of material. The hype about this stone is in some part understandable – after just a few stroks, one can feel something akin to a burr! Taking a closer look under the SEM, this “burr” is revealed not really as a burr, but as a massive, deformed apex. I generally sharpen without any pressure but the weight of the aparatus, and the whole bevel is bend at nearly 45°, forming a super wide apex of > 10 µm. Brittle spots where the matrix cracked and individual carbides are visible can be identified. I’d say that without a high resolution optical microscope, it can be easily mistaken for ultra quick burr formation. But what we typically look for in a burr – a properly formed apex, isn’t visible here. Instead, massive plastic deformation prevails, which will probably make it harder to achieve superior sharpness later in the process.

    I’m really disappointed – I was hoping for a long lasting, bevel setting coarse stone. My guess is that the very hard vitrified bond pushes against the steel matrix and thus mostly deforms and pushes the material.

    Moreover, the bevel shows very deep, coarse scratches. I think this could be an option if you are a knifemaker and really need to remove a lot of material before forming the first apex, but for every knife that already was sharpened before, I find this stone to be more of a “wreck your steel” than “prepare that bevel” solution.

    Optical micrographs of the bevel sharpened with the PDT Vitrified stone. Note the large breakouts and folded over bevel. Instrument: Leica EMSPIRA 3.

    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.

  • A brief study on sharpening stones – Part 43 – Shapton Pro Ha-Nu-Korumaku 1000 Grit (Aluminiumoxide)

    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 a japanese whetstone – the Shapton Pro Ha-Nu-Korumaku at 1000 grit. It’s a coloured alumina oxide stone. Shapton has a stellar reputation in the sharpening world. The 1×6″ version I bought was purchased through a German online shop.

    Let’s take a look under the optical microscope:

    Optical micrographs of the stone. Instrument: Leica Emspira

    We can see some larger, very white particles in an orange matrix. The white particles are most likely the aluminium oxide – the purer, the whiter it becomes!

    SEM micrographs of the Shapton Pro stone. Instrument: Zeiss GeminiSEM 560.

    I’m not sure about you, but I am not surprised at this point! It’s exactly what one would expect: AO particles of the correct size in a hard, brittle matrix. This is not surprising, as it’s a japanese stone and they have a reputation for honesty and hihg quality products. I’m curious though, what the chemical composition is like!

    Let’s look at the chemical composition! 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 stone. Instrument: Oxford Ultim Max  ∞ 40mm2 EDS sensor. Note that our EDS sensor doesn’t show elements lighter than boron.

    The EDS analysis shows it’s a mix between different oxides – mostly Al2O3, MgO and to some lesser extend CaCO3 and SiO2. It’s quite tricky to make any oxide ceramic ultra pure, and probably also not needed for this stone. I think it’s therefore save to declare that it’s Al2O3 particles as the main abrasive, in a matrix of other, softer oxides that make up the bond design.

    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. As this is a water stone, I’ve used water instead of the typical oil.

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

    SEM micrographs of the edge finished with the stone. Instrument: Thermo Fischer PhenomXL SEM.

    The stone struggled quite a bit with the M398 steel I use for the tests. The apex was rounded over a little bit, and overall during use, it felt like the stone looses more than the steel edge I’m trying to sharpen. Moreover, some larger particles introduced pronounced scratches. Overall, I think the blade got noticeable duller due to the preparation with this stone. But from it’s composition, general well made quality, I would guess that this is an exceptional (and very affordable!) stone for less high-tech steels.