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can you convex a hollow grind?

Discussion in 'Maintenance, Tinkering & Embellishment' started by joeyza, Apr 22, 2013.

  1. joeyza

    joeyza

    915
    Feb 27, 2013
    i recently got a sharpmaker which from what i understand should be able to put a nice convex edge on a knife. my question is if a knife has a hollow grind, is it then possible to put a convex edge on it? i was thinking that it would not be possible because the hollow grind already has more metal removed from behind the edge, metal that would need to be there in order for the convex edge to really be 'convex'. Am i right in thinking this??
     
  2. Any edge can be convex. On a hollow-grind blade, because the metal behind the edge is already very thin (this is the main attribute of hollow grind, which improves slicing in thicker materials), you wouldn't likely notice as much change in cutting performance as with a thicker blade (which benefits most from convexing). This is because not a lot of metal would be removed by convexing a thin edge anyway. The rounding and smoothing of the bevel shoulders will always reduce resistance to cutting, but the improvement would be less noticeable, assuming the edge angle isn't significantly changed in the process (from obtuse or very wide, to a more acute or thinner angle).

    The easiest (and usually best) way to convex an edge, especially a thinner one, is by using an edge-trailing ('stropping') stroke on sandpaper over a slightly forgiving backing (like a hard-backed leather strop). Stropping technique on somewhat soft backing (leather) will always tend to convex anyway, and using the same technique on sandpaper will simply do it faster, and remove metal more aggressively. Any freehand method, including use of the Sharpmaker, will result in at least some convex, simply because the human hand won't perfectly maintain a consistent angle on each and every stroke. More often than not, trying to deliberately convex on the Sharpmaker will more likely round over the apex of the edge, in addition to the bevel shoulders, which will just dull the edge. Great care must be exercised, to avoid rounding the apex itself. The Sharpmaker's setup is geared towards minimizing the 'user error' in angle control (just maintain the spine of the blade at vertical), so deliberately attempting to convex would sort of defeat the main advantage of using it. It's better-suited for V-bevels, in keeping them as flat and crisp as possible, without actually using a guide to hold the angle.

    One of the reasons I personally like convex, even on hollow-grind or other very thin blades, is because it can be maintained using exactly the same techique & stroke (edge-trailing), at every single step of grinding, honing or stropping. Only thing that varies is the grit at which it's done. That helps in a big way to refine technique and maintain consistency throughout the process. So, with some practice, sharpening gets very, very easy, from beginning to end. :thumbup:

    David
     
    Last edited: Apr 22, 2013
  3. joeyza

    joeyza

    915
    Feb 27, 2013
    thanks a lot, very helpful answer:) oh and i guess i did say sharpmaker, i meant to say worksharp. easy to see how i got those two mixed up haha, i have a sharpmaker aswell but just recently got the worksharp as I wanted to convex a few of my knives and just wanted a quicker way to sharpen. I definitely prefer convex as well from the little i have used them!
     
  4. Ah, good. There are at least a 'few' differences between those two sharpeners... :D

    Only thing I'll add, regarding using the WorkSharp. Go about it carefully; powered sharpeners will remove a lot of steel fast. Hollow grinds don't have that much steel to give up at the edge, before they're gone completely. :)


    David
     
  5. Swoop03

    Swoop03

    822
    Dec 1, 2012
    It can be done I've done it before to a few knives. (CRKT 16-01KZ, Kershaw Chill, Spyderco Kiwi) I don't have power sharpeners though so it does take a bit of elbow grease that way but I feel it is worth it sometimes. The kiwi isn't finished yet, a good portion of the hollow is still showing but the shoulders are all rounded with a convex edge on it.

    Just be careful with a power sharpener that you:
    1. Don't over heat the edge and ruin the heat treat, keep water handy to cool the blade if it gets warm.
    2. Take it easy, power sharpeners will eat steal like its free candy.
     

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