Flat Bevel Grinding with Surface Grinding Attachment?

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by tkriz1027, Feb 17, 2021.

  1. tkriz1027

    tkriz1027

    3
    Dec 16, 2020
    This is a complete newbie question...can you use a surface grinding attachment for a 2x72 grinder to do full flat grinds on something like a chef knife? Obviously, you are in a fixed position relative to the platen and assuming you angle the platen (or surface grinding attachment) at the correct angle to achieve the bevel it seems like it would work for something like this. I'm sure I'm missing something as I have no experience doing this but thought I'd ask the experts.
     
  2. john april

    john april KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Feb 27, 2006
    i think you have to increase the bevel angle as you get nearer to the tip? if it was a flat edged lawnmower blade it would work if you could tilt the magnetic table.
     
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  3. HSC ///

    HSC ///

    Nov 7, 2012
    Could work for a nakiri
     
  4. tkriz1027

    tkriz1027

    3
    Dec 16, 2020
    I'm guessing that's because of the pointed tip of a chef knife vs. flat front profile of a nakiri?
     
  5. FredyCro

    FredyCro Basic Member Basic Member

    667
    Jan 11, 2019
    Yes. The grind has to follow the edge as you proceed to the tip. You would need to follow the curve which you couldn't do with sga.

    It's also how you can tell on some saber grinds that someone used (only) jig to grind a knife. The bevel gets smaller to the tip, because the grind doesn't follow the curve, so to keep your edge thickness the same on the tip the grind is shorter there.

    You can partially mask this if doing a full flat grind.

    It's one of those things that the easiest way to learn/understand by doing it.

    All this doesn't account for the distal taper. Here you would actually need to change (steepen) the grind angle as you grind toward the tip to keep the same grind height.
     
  6. Aidenag

    Aidenag

    298
    Apr 16, 2009
    Theres a video somewhere on youtube of Travis using the Tw90 surface grinder attachment to do chef knife bevels so thin that you could bend the last quarter inch of the edge. Was pretty impressive how precise he had it working.
     
  7. Hubert S.

    Hubert S. Gold Member Gold Member

    772
    Dec 14, 2019
    I remember seeing this old post by Don Nguyen from 2014 in one of my blade forum searches. Don has not been on the forums since before I joined, but I recently came across a youtube video by him about grinding bevels and he did not use a surface grinder, for whatever that's worth.

    I think it is possible to get a good start on the bevels with an SGA as shown in the thread linked above, but I have no personal experience with it. A full flat grind on any blade that does not have a straight cutting edge seems like a mathematical impossibility to me anyway, in the sense that you cannot have two planes intersect in anything but a straight line. A nakiri is close, but if you look at Don Nguyen's knife on the SGA, you can see how this might be helpful for many knives that do not have too much belly. But you'll still have to finish the grind by hand. The other thing that I cannot quite wrap my head around is how to do the second side of the knife because I don't really know whether the bevel or the remaining flat area would end up flat against the chuck. Maybe that's not an issue at all, I don't know.

    I'm a hobbyist, and even though I've made a few knives, I still consider myself very much a newbie at this. If you gave me a surface grinder today, I would not use it to grind bevels even if it eliminated 90% of the work. Part of it is because I want to get better at grinding and want to practice as much as I can. The bigger part is probably because the work that the SGA could eliminate is actually fun to me. I do most of my work on a computer so working on stuff with my hands and creating something tangible is very rewarding to me. Well, I am digressing, so as a fellow newbie I'll end this post with a famous quote in the field of computer science that may or may not be relevant to this discussion: Premature optimization is the root of all evil.
     
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  8. Natlek

    Natlek

    Jun 9, 2015
    Fredy my friend ..........I use jig and i have no problem to overcome that problem .If knife makers understand what are you saying there was easy solution to that problem :D THE GRIND will follow the curve in same angle IF you know what you need to do with jig when you grind belly/curve on blade :)
     
    Last edited: Feb 18, 2021
  9. 12345678910

    12345678910

    Jul 13, 2009
    You need to taper length as well as width at the same time.
     
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  10. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    I personally feel a jig is a poor crutch for doing bevels. Freehand the distal taper in and then grind the bevels. It takes a few knives to get the basics of it, but once learned it becomes easy and fast. Honestly, it takes me about two minutes to do the distal taper and a max of five to do the bevels.
     
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  11. tkriz1027

    tkriz1027

    3
    Dec 16, 2020
    Thanks for the comments, I was just trying to work out the geometry and I understand the limitations of the surface grinding attachment. I am just setting up my Ameribrade Fastback grinder and have Fred Rowe's Bubble Jig to start learning how to grind bevels. Hopefully by the end of the weekend I'll have my first blade worked out. I've been making handles for finished knife blanks and really enjoy that process but am a bit intimidated by the blade grinding but need to start makin blades!
     
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  12. Richard338

    Richard338 Gold Member Gold Member

    May 3, 2005
    I take a more flexible definition of full flat grind. I don't demand that the entire bevel be a plane, but only that a straight line connects each point along the edge with the spine. This allows the angle to evolve along the length.
    I'm with you on free hand grinding, I spend too much of my work day on a computer.
     
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  13. Hubert S.

    Hubert S. Gold Member Gold Member

    772
    Dec 14, 2019
    I think the way you describe it is correct, a full flat grind is not a single plane, but all cross-sections are lines. I did not really express myself very clearly and did not mean to define a full flat grind as two intersecting planes. What I meant to say was that you have to finish the grind by hand because it cannot be a perfect plane like you would get off an SGA, unless your cutting edge is a straight line. Hope this makes sense.
     
  14. Richard338

    Richard338 Gold Member Gold Member

    May 3, 2005
    Agreed.
    I will point out that talented machinists can program what you might imagine takes manual finesse. CPK has daggers with hollow grinds where the radius slowly increases towards the tip for added strength.
     

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