Convex edges: Are they really practical?

Discussion in 'General Knife Discussion' started by J.Davey, Jan 10, 2018.

  1. marcinek

    marcinek Gold Member Gold Member

    Jan 9, 2007
    Good question. I don't remember what I have. At least 3 or 4 grits.

    Thing is, once you get the edge established (if it doesn't come with one), you rarely have to go back to the sandpaper. Frequent (after every use) use of a loaded strop hone (black emery and chrome oxide) maintains the edge a long time.

    Even with stuff like 1095 or AUS-8 or SAK steel (I forget what that is...)
     
  2. marcinek

    marcinek Gold Member Gold Member

    Jan 9, 2007
    Which is another argument for the practicality of convex edges....making and maintaining them is cheap. 10 bucks of black emery and chrome oxide is going to outlive you. You can make a hone by gluing an old leather belt or scrap leather to a paint stirrer or chunk of 2 by 4. Wet/dry is cheap, maybe you load a hone with Flitz if you want shiny edges.

    50 bucks maybe sets you up for life.
     
  3. marrenmiller

    marrenmiller Basic Member Basic Member

    Apr 6, 2017
    I'm fairly sure I realize that, hahaha. That was poorly worded, I apologize.

    I simply mean the entirety of the secondary edge bevel is convexed rather than the shoulder transition, like with the green example posted before. If the edge itself was rounded, it would be dull. In the example with the green lined edge, that is an extremely poor cutting convex grind.
     
  4. marrenmiller

    marrenmiller Basic Member Basic Member

    Apr 6, 2017
    Oh, absolutely, I'm not arguing that this is how convexing *should* be done. Only that you need to agree on how it's defined before this argument rages on again and again.
     
  5. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    I'm just illustrating why it's necessary to use edge angle as the standard for comparison rather than visual bevel width. :)
     
    Caleb27, Mecha and marcinek like this.
  6. marcinek

    marcinek Gold Member Gold Member

    Jan 9, 2007
    The chances of doing one and not the other are small. Very very small.

    And I am out. We are going back down the rabbit hole.

    Go get a cheap slip joint, some wet/dry sandpaper grits, a piece of cardboard, and try to convex it. Eventually you will do it. Truly it's a marcinek-proof thing.

    Here, read this

    http://brkca.com/convex.htm

    Its the seminal piece on the process. Note that when they mention a hard mousepad, they mean hard. Dont use one of those squishy ones or, as they say in the page

    "...the abrasive will actually be coming back up in the wake of the blade and remove the edge, dulling the knife rather than sharpening it."

    That is, ROUNDING THE APEX. Or making a U like somebody claimed earlier. A convex edge isn't a U. Sheesh.

    And it doesn't have more steel behind the edge for a fixed angle.
     
    Armadew, Mecha and marrenmiller like this.
  7. 91bravo

    91bravo Gold Member Gold Member

    Jun 29, 2008
    I've used mousepads with great results as well. Just don't use too much pressure and check often to make sure you're getting the scratch pattern you want, and where you want it.
     
    MarriedTheMedic and marcinek like this.
  8. marrenmiller

    marrenmiller Basic Member Basic Member

    Apr 6, 2017
    Sure. But that doesn't mean that OEMs like lionsteel do a convex the same way you and marcinek are describing. You guys are describing a way to use convexing to make things cut better. But it doesn't seem like all people or OEMs do that.
     
  9. marrenmiller

    marrenmiller Basic Member Basic Member

    Apr 6, 2017
    I completely understand what you're saying a convex edge is, and I'm sure bark river does them the same way. But my point is that it doesn't seem like everyone does a convex that way, to improve cutting performance. Lionsteel appears to ship out knives with ludicrously chunky convex edges that appear to be more the other way, where the actual edge angle is waaay more than what is usually used for a normal knife (in other words, like the green example).This might be what a lot of people in the forums have experience with, and why these posts go on and on "into the rabbit hole". They think what you're describing is the other, worse way to do a convex edge.
     
  10. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008

    In such cases what they're essentially doing is bulking up the edge angle while keeping the region behind it at a reduced thickness compared to a V-edge of equal angle. So yes, they're still doing that. It would be even chunkier if the edge was flat-ground at the same angle. What you're describing is just a manufacturer putting a thick edge on knives.
     
    marrenmiller likes this.
  11. marrenmiller

    marrenmiller Basic Member Basic Member

    Apr 6, 2017
    Surely. But that brings up the problem I've been pointing out; the final edge angle isn't going to be comparable to other competing knives. As you noted, the apex angle matters here. The angles on knives like those from lionsteel are probably going to be much larger than the +/- 20° per side standard, and only look reasonable at a glance because of the convex nature of the edge. I don't think it matters here that a v edge would be chunkier; most manufacturers would have to be out of their minds to put a v bevel at whatever edge angle lionsteel is using in the first place. They seem to be taking the other track, which is using the convexing as a microbevel to strengthen an edge.
     
  12. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    Again, though, you're conflating the shape of the bevel with its angle. It's really almost irrelevant in the case you're describing that they used a convex. Yes, it's a convex, but that's not the chief influencing factor. However, they may be using the greater visual bevel width as a cheat to make it look thinner than it actually is, reducing grinding times. There are knives on the market with flat edge geometries that thick from the factory, though.
     
  13. Littlebabycarrot

    Littlebabycarrot

    56
    Jan 1, 2018
    I think it is possible to freehand a perfect V bevel. In theory if you can get a series of flat bevels the bio-mechanics are there. Once you have a flat bevel, if you find a stone with good feedback you keep just the thumb and (in fact i think the pad under my forefinger exerts atleast half the force)forefinger pressing down loose grip otherwise, and the wrist curls in while the elbow pulls back parallel to the body and out* it feels like it follows the bevel like that. Coarse diamond hones i still have trouble with.

    -as an aside before i got a worksharp a few years ago, id already had this technique down... then i had to learn how to freehand a convex bevel, got it down stopped freehanding and when i started again all i could remember was how to convex. Something like, 6 months of screwing around with various hones, folders and kitchen knives to relearn it.
    I cant state the bevels are unequivocally, truly flat but when i slice into carboard there is definite drag from material squeezing the bevels, so they must be flat somewhere along the length
    Im sure a lot of guys already do it this way, but i was thinking, it took me so long to figure this out again id point it out
     
    Last edited: May 26, 2018
  14. Littlebabycarrot

    Littlebabycarrot

    56
    Jan 1, 2018
    Okay im a changeable guy and realize the whole of the bevel will not be flat without some sort of guide. I just happened to read even the best free hand sharpeners still have a plus or minus 1 degree margin of error. Then i thought truly how many degrees there are and fractions beyond that. Mathematically impossible i suppose.
    Id still like to accomplish it some day
     

Share This Page