Kitchen knife convex edge

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

  1. Scaniaman


    Jun 15, 2012
    I found some felt localy, 5mm thick 0.44 gcm. So also trying that soon.
  2. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    His description of doing the hollow grind is very similar to my (one) experience grinding a ura on my yanagiba. It actually was surprisingly easy to control.

    I would kind of worry about doing this on thin stock though ... like he said, it might make the blade thickness too thin... ???
    FredyCro likes this.
  3. FredyCro

    FredyCro Basic Member Basic Member

    Jan 11, 2019
    Great vid. Another great tutorial for an S grind with a wheel (Vachon knives calls it "diamond grind") can be seen on Vachon knives Instagram page. You will have to search for it yourself though, sorry.
  4. Richard338

    Richard338 Gold Member Gold Member

    May 3, 2005
    FredyCro and Hubert S. like this.
  5. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Richard338 likes this.
  6. Hubert S.

    Hubert S. Gold Member Gold Member

    Dec 14, 2019
    I tried the felt on a 5" petty knife made from 0.06" AEB-L today and it is a huge improvement over using the slack belt for creating a convex edge. I did not want to use the koolmist system with the felt and was a bit concerned about burning the edge, but the felt does not seem to generate near as much heat as the regular platen. I first used the flat platen to grind the edge down to about 0.025", then switched to the felt and the edge is now about 0.005". The last belt I used was an A60 Trizact before I switched to hand sanding at 320 grit with a sanding block made from a piece of leather glued to aluminum. That seemed quicker than usual and only took a few minutes, maybe the soft backing is more forgiving and hides mistakes better.

    Thanks again to Robert for suggesting the felt. For reference, I used 1/4" thick S2-32 grade felt from McMaster, product number 8759K82 and glued it to the platen with double-sided indoor/outdoor carpet tape.
    Robert Erickson and Scaniaman like this.
  7. samuraistuart

    samuraistuart KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Dec 21, 2006
    May I ask, with the convex grinds and "S" grinds that some of you are using, what geometry are you using for the actual edge/apex itself? Does your convexity go all the way to a "zero" edge, or are you putting a more traditional "V" shaped edge/microbevel? I ask because not many of my customers sharpen their own knives, much less know how to maintain a convex edge. So for that reason, I stick with full flat grinds that are just slightly convex and a traditional "V" shaped edge. I've been watching some of "Virtuovice" vids on YT and he really likes Bark River and their convex grinds, and I have been meaning to try convex geometry myself, not necessarily with kitchen knives quite yet. He maintains those convex grinds, which go to "zero", on flat waterstones, with a rocking motion. I find that interesting.
    FredyCro likes this.
  8. FredyCro

    FredyCro Basic Member Basic Member

    Jan 11, 2019
    I think the convexity that most talk of starts before the apex, usually in the last third of the width or so. You could sharpen that traditionally IMHO, but you will need to thin down the convexity (thickness BTE) sooner then with a flat grind. Murray Carter has also a great vid on thinning down, sharpening convex edge on a stone. But on the stone I think it is more of a convexity to make a stronger cutting edge. I might be completely wrong about all this though, its just my opinion.
  9. CallumRD1


    Jan 10, 2020
    I always finish with a normal flat edge but I grind extremely thin behind the edge, so the height of the edge is nominal relative to the size of the blade and doesn't impact food release at all. This also makes it much easier to sharpen and maintain the edge.
  10. Hubert S.

    Hubert S. Gold Member Gold Member

    Dec 14, 2019
    I have been sharpening them like a full flat grind with a "V" shaped edge and plan to do the same for the new one. I use a stone, guess at the angle and go, nothing fancy. I'll probably start with a 400 grit stone and then go to a 1000 grit stone and then strop. On the petty knife I ground today, the convexity is not really visible until you put a straight edge on the bevel. It is much less pronounced than on an Opinel, for instance. The edge is also much thinner and I can see a dimple when I run it over my fingernail with just slight pressure. While the angle has to be steeper at the edge than a full flat grind, I am not sure if I will notice a big difference in maintenance and it will likely take many years before I have to thin the edge. I've read some people use sandpaper on mouse pads for sharpening convex grinds, similar to the felt on the platen I guess. I am very interested to hear what methods people use, this is all pretty new to me and I'm just experimenting with it.
  11. Bigfattyt


    Jun 23, 2007
    I've been using comvexgrind knoves for 20 years or so.

    They are easy to maintain.

    I can do full regrinds if needed, but have not really had to.

    I maintain them with ceramic Spyderco sticks and a loaded strop.

    Typically every so often I will sharpen/remove a bit behind the edge bevel lightly, then strop that area too.

    Convex grinds are dead simple to maintain. I have a rubber strike pad and lay a sheet of 600 grit wet dry on it and poof.... blended convex and wicked sharp edge.

    Just a bit of elbow grease is all it takes.
  12. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Hmmm ... so you are basically thinning by hand with that 600 grit?
  13. Nick-D


    Apr 17, 2017
    Tried a hard rubber as a platen backing. Yeah nah don't do that, now I have half burned rubber everywhere.

    Need to find some of this felt locally....

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