Kitchen knife convex edge

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Hubert S., Feb 16, 2021.

  1. Hubert S.

    Hubert S. Gold Member Gold Member

    753
    Dec 14, 2019
    I typed it into units and got 0.68 g/cm³, but I might have made a mistake. Here is the calculation:
     
  2. Scaniaman

    Scaniaman

    666
    Jun 15, 2012
    I see, it is supposed to be gcm2 not gcm3 I'm pretty sure
     
  3. Hubert S.

    Hubert S. Gold Member Gold Member

    753
    Dec 14, 2019
    From what I've seen, they specify the density in Europe whereas McMaster has the weight per square yard. Take a look at this page, it has a table with the densities and corresponding hardness ratings (you have to click on the gray button labeled "more" in the bottom right to see the table). The hardest felt specified is H5 and it has the same density I calculated for the one from McMaster.
     
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  4. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    I guess I have mostly in mind the “naive” user who does not know much about sharpening. If there are professionals you sell to (or are using it yourself), and understand (and can seek out) the need to sharpen appropriately and to thin periodically in order to maintain performance, that is a totally different story. I’ve just seen too many users where their idea of “knife maintenance” is to throw it into a drawer along with the other knives, and MAYBE periodically take it to the local store that had a sign saying “we sharpen knives”. (Shudder...)

    Hubert ... not sure about the granton edge thing. I only have the one, and it’s not perfect, but definitely better on some vegetables (esp potatoes) than others... but I just don’t have any other comparison.
     
  5. Hubert S.

    Hubert S. Gold Member Gold Member

    753
    Dec 14, 2019
    I could be wrong, but if somebody spends a few hundred dollars (or more) on a knife, they probably either know how to sharpen or have a place they can take it to, or maybe send it back to the maker for tune up periodically. My mom has a knife sharpener gadget (that does not work at all) and she always pulls her knife through it a few times before she starts cooking. I think it would damage a knife with a thin hard edge pretty badly.
    The one I have is the worst of both worlds. It has a 3+mm spine and wedges badly so that the potato might crack before you cut all the way through it, but the off-cut still attaches firmly to the side of the blade. I think it was $30 and I bought it when I got a water stone as a practice knife. Sadly, my wife likes it better than the knives I make and keeps using it.
     
  6. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Sadly (or scarily?) that has not been my experience. A lot of the commercial knives run several hundred dollars each .... and often they are sold, and bought, based on "image" - not based on understanding of how they will perform. I have seen thousand-dollar sets of knives just put in a pile in a drawer (and are so dull I was very hard pressed to "cut" through a carrot - more like having to "hack" through the thing). I have seen expensive Shun knives haphazardly thrown into the dishwasher after using. I have also seen moderately priced knives appropritely stored in a block - but never sharpened, and incredibly dull. In my life I have found one, and only one, cookware store that sharpened knives, and actually used a wetted-stone system with accurate control of angles - but they stated most of their customers were chefs (and there are only so many of them). I might be wrong here, but my impression has long been that the vast majority of knives out there are not maintained, or are actively abused (like - left out dirty on the counter overnight, or thrown into the water in the sink and again left overnight).

    sounds like with at least some of the professional chefs they are very aware of and concerned about performance, and are willing to return the knives to custom makers for appropriate tune up. If that is who you can make/market to and maintain the "return to me for tune-up" relationship, that is good!

    Even for me though - I am not sure if I would regularly take the time to appropriately sharpen a convex edge. I do all (or most) of the cooking here .... and by the time I am in the kitchen working and notice that a knife is no longer sharp enough, I do not have the time to go down to the shop to sharpen it right then.... different markets for the products I guess....
     
  7. FredyCro

    FredyCro Basic Member Basic Member

    650
    Jan 11, 2019
    I have been following this topic closely. For me (as a home cook with a couple of years of experience in restaurant kitchens) the food release problem is a bit exaggerated. I do most of my precise cutting (like 90 %) with the top third of the blade and the food will release from the narrower area of the blade even with a FFG. I would rather have a knife that glides effortlessly through onions then one that will wedge or be too thick from the very start (in general and BTE).

    As a hobby knife maker I am really interested in performance of a well convexed edge. I think it might have its uses in heavy duty knives meant for cutting hard food (pumpkins, opening lobsters, cutting fish bones and similar cross my mind). If food release is the primary goal (after cutting performance of course) I would rather look into S-grinds. Over on the kitchen knife forum one maker introduced a grind called J-hook, have a look at that as well.
     
  8. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Freddy - do you know how well a concave (hollow) grind releases? The edge is more delicate, but if you aren’t going near bones, that should not be much of an issue?
     
  9. CallumRD1

    CallumRD1

    136
    Jan 10, 2020
    Concave grinds are the absolute worst for food release. The food will suction into the hollow and stick horribly. The best food release grinds provide a minimum of surface area in contact between the food and the blade, so a convex grind has the blade back away from the food and an s-grind has a hollow behind the edge so the food never can come in contact with the middle of the blade.
     
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  10. Natlek

    Natlek

    Jun 9, 2015
    You should watch this video...............
     
  11. Natlek

    Natlek

    Jun 9, 2015
    And this video to ..............hollow grind, I can make better video if anybody want that :)
     
  12. CallumRD1

    CallumRD1

    136
    Jan 10, 2020
    What's the point you're trying to make? I've done such test myself and my results agree with the statements I made. (I got into knife making by the kitchen knife enthusiast and almost all the knives I've made have been kitchen knives.) Food (especially wet foods like potatoes) stick when a film of water is between the food and the blade resulting in a suction that's hard to release. The more rigid the food and the drier the food the less it will stick. The solution is to allow an air gap between the food and the blade. The most common way to do this is with convexity so the food is pushed slightly away from the flat of the blade. An s-grind does this by grinding back the middle of the blade so the food can't touch it there. This doesn't mean there aren't other ways of achieving the same result, but it is still true. My favorite knife to use for chopping large batches of vegetables is my s-grind nakiri that almost nothing sticks to. I can work so much faster when a diced onion or potato remains in it's exact shape after dicing and I can just pick it all up at once.
     
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  13. HSC ///

    HSC ///

    Nov 7, 2012
    I don’t test and cut enough to argue one way or the other but S grinds with hollows are hugely popular in the kitchen knife world

    kagekiyo is a Japanese brand with a slight hollow grind which Of course adds to it being very thin behind the edge
     
  14. CallumRD1

    CallumRD1

    136
    Jan 10, 2020
    I guess I should be more specific to avoid any confusion. When I say that concave hollow grinds are terrible, I'm referring to a tall hollow grind going most of the way up the blade. An s-grind with a hollow ground in the middle of the blade is a completely different grind style, performing far better. The tall single hollow pushes the cut piece of food up the concave surface not allowing for an air gap to form at all, leaving the food stuck to the blade. (Again, dry or more rigid food pieces will be much less susceptible to sticking.) An s-grind, even if the part of the grind right near the edge is also hollow ground, allows the food to release from the edge as an air gap is formed behind the food as it passes over the hollowed middle of the blade.
     
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  15. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    I had not heard about s grinds ... interesting. Maybe a new application fir my newly made radiused platen? :). Seriously ... maybe I will try that on a new nakiri (which is what I mostly reach for for potatoes, onions, and carrots)
     
  16. FredyCro

    FredyCro Basic Member Basic Member

    650
    Jan 11, 2019
    Sorry, never tried convex, but I am going to try S grind now that I have a contact wheel :)
     
  17. Natlek

    Natlek

    Jun 9, 2015
    My point ? If you watch that video you should see that some of used knife for test have convex blade and they all fall in that test . You simple can not make enough convex in 2 - 2.5mm thick and 2 inch wide blade to not stick , that is my point . I would like to see your convex grind knives how they handle potatoes :thumbsup:

    This is knives used in that test

    0:00 Mac Pro 8.5" Gyuto 2:08 Carter Muteki Funayuki (Jamison) 3:37 Carter Funayuki (reground from chef profile - previous video) 5:07 Asai Nakiri 6:50 Asai Gyuto 9:20 oooops..... 9:37 Kochi Gyuto 11:28 Kochi Sujihiki 13:04 Vintage Sabatier (another oops) 15:01 Moritaka Honesuki 17:05 Mizuno Tanrenjo Gyuto
     
    Last edited: Feb 21, 2021
  18. CallumRD1

    CallumRD1

    136
    Jan 10, 2020
    I don't want to drag this thread down into a pointless debate that's been carried out scores of times all over the internet. Feel free to do some googling to learn more yourself; I won't continue this debate here. I'm just going to conclude that I'm not saying a subtle convexity is the end-all-be-all of knife grinds that works perfectly on all foods in all situations. I'm merely suggesting that it offers an improvement in food release over a full flat grind or a concave hollow grind and I've presented the logic behind it.
     
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  19. Hubert S.

    Hubert S. Gold Member Gold Member

    753
    Dec 14, 2019
    That's all I'm after at the moment, an improvement. I might think about S- or J-grinds after I get better and more consistent at grinding.
     
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  20. Hubert S.

    Hubert S. Gold Member Gold Member

    753
    Dec 14, 2019
    I received the felt from McMaster today but was not feeling well so it will have to wait, hopefully not too long. Since the S-grind was mentioned in this thread, I thought I'd post the video below by @Salem Straub. He has been posting a lot of great videos lately. In the one below, he shows how to do an S-grind and makes it look real easy.
     

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