Sciencing Sharpness – Part 1 – Predictions

I hope to use my new sharpmeter to get some knowledge about, well, sharpness. And since I am going to be playing at science whilst doing so, I have decided that I will write down the predictions for my tests. The tests will not be blind, because I will be doing both the sharpening and testing and there will still be some subjectivity to these tests, but nothing is perfect. I am doing these tests to gain some knowledge and I will share that knowledge for free but there will inevitably be bias.

The first test that I intend to perform is the influence of grit on edge sharpness. I think that after establishing the bevel with 180 grit the cutting force will go down significantly with the next steps, but it stops changing significantly above 400 grit. My reasoning for this is the fact that it is possible to get a knife shaving-sharp with ca 320 grit stone and at 320-400 grit usually the wire edge/burr falls off. I think that I have mentioned in the past in comments somewhere – either in Marcus’s place or here – that going above 1000 grit in sharpening makes little sense function-wise, although I cannot find the comment now. I will go up all the way to trizact A6 belt (the equivalent of 2000-2500 grit) in the experiment.

The second test that I intend to take is the influence of the sharpening angle. There was a heated debate between me and Marcus on this issue a while back -click-  and I really want to test it (caveat from the first paragraph applies doubly). I expect the force needed to cut the thread to rise exponentially, i.e. slowly from 10-25°, then some more for 30° and even more for 40° and again even more for 45°. I won’t test sharpening angles steeper than 45° because it makes no sense IMO since a 45° sharpening angle means a 90° edge. I know from praxis that knives sharpened at 15°, 20°, and 25° can be shaving-sharp. I do not know much about the 30° angle, since that is extreme and I only sharpen hatchets and axes at that angle and I never even tried to get those to shaving-sharp. They do cut paper though.

So, sometime this week I shall heat the workshop again, sharpen some steel offcuts (probably pieces of old hacksaws) and go measuring.


  1. dangerousbeans says

    What steel are you using? Carbide and grain size makes a big difference. Also if you are machine sharpening you need to make sure you’re not over heating the edge. A 2000 grit edge is very fine and can be over heated very easily.
    With my knives I notice a difference in actual use going up to 4000 grit (shapton), but 8000 seems to be no help. I use whetstones above 500 grit

  2. tuatara says

    In my experience my HHS edges do not benefit from anything finer than about 3,000 grit.
    In contrast, my japanese laminated white paper steel blades (chisels and planes) can not only take a much finer edge but the edges last longer if I take them to about 12,000. This is the grit of my finest water stone -- a natural stone -- that gives a fine polish to the edge.
    I never sharpen with a machine, only ever using water stones or diamond plates.

  3. tuatara says

    As for ‘sharpening’ a knife with a steel, in every restaurant I have worked in over the years most of the knives have been ruined by overzealous steel use.
    I used to sneak a knife home and spend a couple of hours reshaping and bringing the edge back with my water stones. The look of surprise on a ‘chefs’ face when a knife is properly sharp is very satisfying. I would usually only take the edge to a 6,000 grit at approx 12-15 degrees each side, so comfortably shaving-sharp. My own knives were much sharper than theirs because I would touch them up briefly with a good waterstone after every shift, and unsurprisingly they always wanted to use mine.
    Touching the edges up took about 2 or 3 minutes on each knife. Much easier than the 2 hours needed to restore an edge ruined with a steel.
    Please, don’t anyone think a steel can ‘sharpen’ a knife. It cannot, and is not intended to be used as such. A steel should only be used to quickly realign a dulling edge. Sharpening should always be performed with good stones, and a fine edge worked on a stone will have a long usefulness between sharpening.
    This is my experience at least, experience in which, over the years, I have only ever met one chef who used stones to sharpen their knives. Unsurprisingly to us, our knives were always in good condition and ready to go at the start of every shift.

  4. says

    @tuatara, I think dangerousbeans was talking about steel as in the material used for the testing cutting edge, not honing steel. Proper, old school honing steel should not destroy a knife because it has only minuscule abrasive capabilities. It mostly just realigns and slightly burnishes the edge and there is a point when it stops doing anything and whetstone has to be used. In our kitchen, we are using honing steel about once every two-three weeks and I sharpen the knives on my belt sander every six months or so when they start having trouble cutting tomatoes.

    Ceramic honing steels are very fine abrasive rods and they can allegedly maintain a blade slightly longer. I do not have an experience with those, however, so I can only relate what I read about them.

    A diamond-coated honing steel on the other hand is an abomination that does destroy knives because it has way too aggressive abrasive action. It is only slightly less bad than those drag-through “sharpeners” where a blade is scraped by carbide discs.

  5. dangerousbeans says

    I was talking about the material the blade is made from. The chromium and high carbon content in stainless steels leads to the formation of large carbides in the steel, which will break off before you can sharpen it to a fine edge. you can get a similar effect with an overly coarse grain structure (the size of the crystals in the steel).
    Something like Tuatara’s white paper steel chisels have smaller carbides and a very fine grain, so take a much finer edge before it starts crumbling.

  6. tuatara says

    Sorry my point about sharpening ‘with’ a chefs steel was more related to the video in the link, and the conversation therein. I understood that dangerousbeans was speaking about the material of the blade itself. That is why I referred to the Japanese steel blades that I have that take a much finer edge than the material from which many a chefs knife and most of the knives found in people’s homes are made.
    I still would never use a chefs ‘steel’ on any knives. I seldom need anything coarser than a 5000 grid waterstone to bring my edges back (I haven’t worked in kitchens for years now so it is just home cooking tasks they are required to undertake), and it only takes a few minutes to polish them up to last another few months.
    As for the Japanese blades, I do also have a Japanese santoku that takes a superb edge, but it is so sharp that I don’t use it for day to day work. It is actually frighteningly sharp so it mostly sleeps safely and soundly in the scented Australian Rosewood saya that I made for it. I check it often to make sure it is well and not lonely.

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