CONVEX EDGE, why is it so popular?

Discussion in 'Custom & Handmade Knives' started by Transit, May 18, 2008.

  1. Transit

    Transit

    18
    Jan 22, 2006
    I have been a custom knife user for over 20 years. All my customs are forged carbon steel knives, the majority camp knives and bowies. These blades are mainly forged by ABS M.S and J.S., Hendrickson, Graham, etc...with flat grinds and convex edges.

    I do own a few sabre ground knives...Ruana and Randalls #1 and #14. To me the Ruana and Randalls I own may not have the chopping force of the convex blades (since they are smaller and lighter knives) but they excel in sharpness and are equally strong.

    My question is why does the ABS preach the convex grind so much when it seems the majority of convex camp knives and bowies cannot out perform a well forged sabre grind?

    I just don't see the performance advantage of the convex grind.
     
  2. David Schott

    David Schott

    Sep 27, 2004
    Im not sure what you mean. A proper convex edge will pretty much outperform most other edges other than very specific tasks. A sabre grind is basically a flat grind that isnt even taken to the spine, so really only excels in heavy chopping and durability since the edge is so thick. Pretty much all competiton cutters have convex edges as they geometrically excel at multiple tasks and with proper sharpening, and will not thicken behind the edge with repeated sharpening like a flat grind....

    [​IMG]

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  3. Keith Montgomery

    Keith Montgomery

    May 9, 2000
    What leads you to believe that the sabre grind excels in sharpness?
     
  4. ryan9977

    ryan9977

    Feb 16, 2006
    "and will not thicken behind the edge with repeated sharpening like a flat grind...."

    david...in all fairness if you sharpen correctly this will never happen....over time you need to thin out your knife so the bevel does not get thicker.....ryan
     
  5. David Schott

    David Schott

    Sep 27, 2004
    True, but thats reprofiling the main bevel, not sharpening. With a convex, this happens with every sharpening, not just when the knife is so thick behind the edge that you get frustrated. Point taken, though! :thumbup:
     
  6. ryan9977

    ryan9977

    Feb 16, 2006
    true david....it does happen every time u sharpen a convex edge......i consider reprofiling a part of sharpening....i'm lazy and just lump it under the same category.....for choppers i prefer a convex edge and think it holds up better than a flat edge....ryan
     
  7. rprocter

    rprocter Banned BANNED

    Jan 19, 2007
    Thanks David for the diagrams. this important aspect of a blade is often mis-understood, but here you clearly show what the terms primary grind and edge bevel (or grind) refer to. i believe i have seen many posts in which these terms are misused, leading to a lack of clarity. roland
     
  8. Ed Caffrey

    Ed Caffrey

    Jul 23, 1999
    I would assume that the ABS promotes the convex edge because most of us (ABS Smiths) have found that the convex edge provides nearly every aspect you could want in an edge. With a very fine convex edge you get that "scary" sharpness that folks speak of, and because of the extra couple of thousandths thickness just behind/above the edge you achieve much greater durability. The real key to the quality of edge that the convex provides is just that....its shape. A smooth radius means much less cutting resistance than something like the semi-hollow grind you see on many blades. (many of these blades have very obtuse bevels between the "hollow" and the edge, creating much greater cutting resistance) Most of us have also "tweaked" our heat treatment to compliment the particular grind we apply, which is another key element in producing a quality edge.

    I can't speak for other ABS Smiths, but I do not apply a full convex to my knives. About 80%-90% of the blade is flat ground to reduce weight, and the last 1/8" to 1/4" of the blade's edge is convexed (the amount of convex depends on the specific blade/knife) I believe that if you look closely at many of the ABS MS knives, you will find they are similar. They will all have some degree of edge bevels, but in most cases those bevels are also radisued rather than flat. It's the transition between an edge bevel and the main blade bevel that makes all the difference.

    I personally think that not enough attention is paid to cutting resistance in a blade. A dull blade that is setup/ground to reduce cutting resistance (as in one with a convex edge) will seem to cut as well as a different type of edge configuration that is freshly sharpened. In all actuality, that is why the convex edge shines in the cutting competitions....its not that it stays sharper any longer, its just that the cutting resistance is so low that even after many abusive tasks it still keeps going.
    And finally, if the Bladesmith/Knifemaker has done their job correctly, the convex edge will be simple and easy to resharpen once its dull. The convex edge, correctly applied, will be sharp, durable, and easy to resharpen..... Thats probably why most ABS smiths choose to employ it on their knives.
     
  9. muddy672

    muddy672 Gold Member Gold Member

    Jul 26, 2006
    Great thread! The edge pics are very helpful.
     
  10. Lorien

    Lorien KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Dec 5, 2005
    is there anyone out there producing knives that are hollow ground, with a convex edge? Some knives I own are like that, but only because I sharpen them that way. But it should be possible to produce a lighter knife by hollow grinding it, I would think. And if hollow ground, would that reduce friction, compared to a flat grind? How about a full flat grind that was really shallow, leaving a lot of material at the edge, followed up by a subtle hollow grind and finished with a convex edge?
     
  11. Transit

    Transit

    18
    Jan 22, 2006
    Keith,

    All I'm saying is that of the forged flat grind with convex edge knives that I own, most did not arrive with a servicible edge. These knives were made by ABS M.S and a few J.S. so I would expect the heat treat to not be a factor in the lack of sharpness. It is a big disappointment when one pays $600 plus for a knife and have a Randall or Ruana outperform it in most cutting.
    I do agree that some convex knives do cut well, however the ones that I have seen have a secondary bevel at the edge. These knives technically are not truly convex since they carry this secondary bevel. While I do believe that a convex knife make a strong and robust blade (especially suited to chopping) since it is based on an axe grind, I still think that what it makes up in strength it takes away in sharpness.
     
  12. DWinkler

    DWinkler

    218
    Nov 7, 2005
    Transit,
     
  13. flatgrinder

    flatgrinder

    Dec 20, 2005
    It also depends on how the blade has been sharpened. ;)
     
  14. DWinkler

    DWinkler

    218
    Nov 7, 2005
    Transit,

    What do you mean by "Sabre ground.

    Daniel
     
  15. Transit

    Transit

    18
    Jan 22, 2006
    Daniel,

    Sabre grind, while I do not have pics to post, is the grind given to Ka-bar knives, Randalls...etc.
     
  16. Transit

    Transit

    18
    Jan 22, 2006
    Sabre Grind

    According to Joe Talmadge's article "The Blade Geometry FAQ" at knifeart.com

    Sabre Grind-
    The sabre grind is a strong edge format. The bevel starts around the middle of the blade, and proceeds flatly towards the edge...
     
  17. Keith Montgomery

    Keith Montgomery

    May 9, 2000
    [​IMG]

    (1) Hollow ground—A common grind where a convex hollow is removed from both sides of the edge. It produces a very sharp edge but being so thin the edge is more prone to rolling or damage than other grinds. It is unsuited to heavy chopping or cutting hard materials. Straight razors are hollow ground. This grind is used extensively in mass produced knives.

    (2) Flat ground—The blade tapers all the way from the spine to the edge from both sides. A lot of metal is removed from the blade and is thus more difficult to grind, one factor that limits its commercial use. It sacrifices edge durability in favor of more sharpness. The Finnish puukko is an example of a flat ground knife. A true, flat ground knife having only a single bevel is somewhat of a rarity.

    (3) Sabre ground—Similar to a flat ground blade except that the bevel starts at about the middle of the blade, not the spine. It produces a more lasting edge at the expense of some cutting ability and is typical of kitchen knives.

    (4) Chisel ground—As on a chisel, only one side is ground (often at an edge angle of about 20 – 30°) whilst the other remains flat all the way to the spine. As many Japanese culinary knives tend to be chisel ground they are often sharper than a typical double bevelled Western culinary knife. (A chisel grind has only a single edge angle. If a double bevel has the same edge angle as a chisel grind, it still has two edges and thus has twice the included angle.) Knives which are chisel ground come in left and right-handed varieties, depending upon which side is ground.

    (5) Double bevel or compound bevel—A back bevel, similar to a sabre or flat grind, is put on the blade behind the edge bevel (the bevel which is the foremost cutting surface). This back bevel keeps the section of blade behind the edge thinner which improves cutting ability. Being less acute at the edge than a single bevel, sharpness is sacrificed for resilience: such a grind is much less prone to chipping or rolling than a single bevel blade. In practice, double bevels are common in a variety of edge angles and back bevel angles.

    (6) Convex ground—Rather than tapering with straight lines to the edge, the taper is curved, though in the opposite manner to a hollow grind. Such a shape keeps a lot of metal behind the edge making for a stronger edge while still allowing a good degree of sharpness. This grind can be used on axes and is sometimes called an axe grind. As the angle of the taper is constantly changing this type of grind requires some degree of skill to reproduce on a flat stone. Convex blades usually need to be made from thicker stock than other blades.
     
  18. I'mGatMan!

    I'mGatMan!

    Dec 13, 2007
    Thanks for this great info, people.
     
  19. xaman

    xaman

    Nov 27, 2005
    Lorien,

    Jerry Hossom (while a stock removal guy, not ABS) makes very efficient cutters which are hollow ground with convex edges :thumbup:

    I'm sure there are others, but he's one I know of for sure... In fact, (as far as production blades -- sorry I know we're in the custom forum) I'm sure Busse has done some in that configuration as well.
     
  20. Lorien

    Lorien KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Dec 5, 2005
    Thanks for engaging my question, Xaman! I thought for sure that somebody was doing that. It just makes too much sense.
     

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