Secondary bevel / Shinogi location design decision

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Cushing H., Aug 15, 2019.

  1. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    so, here is a question ive been meaning to post for a while. Over the years i have spent a lot of time obsessing about bevel angles (and relationship to steel type / hardness). Mostly, though, that has been focused on the primary bevel (the cutting edge). With regard to the secondary bevel, how do you make your design decision? Do you decide on an angle, then do the trigonometry to decide on where the Shinogi will end up ... or do you just decide based on looks where the shinogi will be, and let the secondary bevel angle fall wherever that makes it be? Too shallow (acute) will be a problem, especially for less-hard steels - how do you avoid that?
  2. Stacy E. Apelt - Bladesmith

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

    Aug 20, 2004
    You can use an online triangle calculator ( or do the trig) to decide the grind angle. For instance a blade .125" thick will have the shinogi .5" from the edge with a 14.5 degree edge angle. If you wanted the shinogi 1" up the blade, you would grind an edge angle of 7 degrees. Those are inclusive angles, BTW.

    In practicality, none of that matters. Distal taper of the blade will change the placement of the line if you are using a fixed angle. Even tiny angle changes will move things.

    Just grind the bevel to put the shinogi where you want it. Then put on the final edge at the desired angle. I usually draw on the shinogi with a marker and grind to that line. It isn't rocket science ... unless you want to make it so.
  3. Jason Volkert

    Jason Volkert

    Nov 25, 2018
    What I would do is grind the knife some, sharpen it, and test it. Then use it. If it cuts like an axe and its a skinning knife. I would go grind more, sharpen, and test it. Keep doin that until it so sharp it will cut your taxes in half. :)
  4. Stacy E. Apelt - Bladesmith

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

    Aug 20, 2004
    Good advice, but he isn't determining the edge angle, but where the shinogi should fall on a Japanese kitchen knife. The edge is done last and is usually a tiny facet at a low angle.
    Jason Volkert likes this.
  5. Natlek


    Jun 9, 2015
    I make design decision based on steel I use and type of knife I want to make .If I work on kitchen knife in 1.2519 steel /1.5-2mm thick/ I don t care about any trigonometry......First I just decide what thickness I want on edge before sharpening and I start to grind , adjust grinding angle if necessary till I get thickness I want on edge and Shinogi where I want ....
    Last edited: Aug 15, 2019
  6. Alex Topfer

    Alex Topfer

    May 1, 2019
    I mostly do it by where it would look good. Which usually means around a third of the way in from one edge, maybe a bit more. I don't want it right down the middle. I then do some trig to double check that the angle isn't too large, and mostly for the sake of recreational trigonometry :p

    Thin blades give you a lot of leeway on this: a 2mm thick blade with a 10mm deep asymmetrical bevel gives you a ~10 degree angle. 10mm is a tiny bloody bevel.
  7. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    I asked because those small knives i am working on for my wife i calculated out 15 degree bevels.. and they just ended up looking too small for the blade. Mind you, the geometry of the blade makes wider bevels problematic, but i still look at them and keep thinking i should widen them. Will post pictures tomorrow.
  8. GoldSkula


    Jun 14, 2018
    Are you sure you've done your calculations right mate?
  9. Stacy E. Apelt - Bladesmith

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

    Aug 20, 2004
    Are you mixing up the edge angle with the bevel angle. The bevel is rarely more than 10° on any kitchen knife. A camp knife in 1/4" steel would only have a 15° inclusive angle with a 1" high shinogi. A camp knife in .25" steel with a 2" blade and a FFG has a 9.5° bevel angle.

    The edge angle is put on after the main bevel to the shinogi is added.

    A photo would help, also blade thickness, width, and shinogi height desired.
    Last edited: Aug 16, 2019
  10. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Always a good question . I believe so ... but will post calcs and photo as followup to Stacy’s response. I think what i am seeing is consistent with stacys example of a 1/4” thick camp knife ... but other factors constrained me to a less acute secondary bevel - which results in kind of a weird look. Hopefully will make more sense when i get those photos posted...
  11. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Ok Stacy - here you go. I am not mixing up the edge angle and the bevel angle (also am not confusing the single-sided angle with the full two-sided angle). The concept here is this: my wife discovered that she likes using some of our old, cheap, tinny, overly light,, butter knives as a "dinner knife".

    Her hands are small, so the small handle works well for her, and the blades on our regular dinner knives really are quite long and unwieldy. I thought I would make something for her that is more hefty, sharper, easier to hold ... so we sketched out something that was better contoured for her hand, but yet retains the basic blade shape/geometry of the cheap originals. She was also quite clear that she liked the rounded blade tip, AND liked to use that extreme curve on the tip as part of the cutting edge. So ... this is what we came up with:
    (this, and its 3 partners, are still a work in progress - need to finalize the blade finish, and finish-sand, pin, and oil the handle - also, in a lot of ways, these blades are part of a couple "learning" projects - so there are imperfections I am well aware of :-( ). My target was to not make this blindingly sharp, but rather with an edge robust enough for daily usage against ceramic plates (dont scream - these are dinner knives after all.. :) ). Hence I am targeting 15 degree secondary bevels, and an edge angle of 25 degrees.

    Here are the calculations (and blade dimensions) to determine the Shinogi location given that 15 degree bevel:

    Not sure if you want to wade through the calcs, but I have double checked them, and the final shinogi location (my dimension "a") of 0.16" from the edge is what was achieved on the ground blades. (given the relative thicknesses of this blade versus your "camp knife" example, I think this is pretty consistent with your example)

    So ... here is the issue: going back to the photo of the actual blade, but zooming up on the tip:

    I would have "liked" (for looks) for the bevel to go further up the blade (1/3 - 1/2 of the way), but with the significant curvature of the blade relative to thickness, where on the blade would I make that determination of shinogi versus blade width? Also, a shallower (lower angle) bevel presented two concerns: it might not be robust against daily usage against said nasty ceramic plates, AND trying to continue that shallow bevel (& shinogi) a significant way around the rounded tip would have resulted in a really weird looking tip - and even maybe the possibility of the shinogi "doubling back" on itself while going around the curved tip (also would be really challenging, at least for me, to actually do that...). Given all that ... my only real answer was to settle for the 15 degree bevel and just go with it (based on performance and execution needs).

    BUT, that gave rise to this bevel that is ground to (or close to) the criteria I targeted, but is nevertheless rather funky looking (I DOES look alot like a "smiley face"....... ). Hence my original question: do you typically decide on shinogi location based only on "looks" in terms of the overall knife ... or do you decide on what angle you want on the bevel to be based on function and go with that? IN this case, using the latter gave rise to something a little more funky than I wanted (but still functional). The only other thing I can think of is to have tried to define the shinogi that looked good, then try to execute a grind that gave a variable bevel angle depending on where you are on the blade, in order to achieve the pre-defined shinogi location.

    How would you have dealt with the conflicts here and proceeded on this???

    (btw - this is not an idle question: my intent was/is always to make a final set out of stainless damascus, and use these as a learning process. Also, one of the "mates" of this knife has a brass bolster - and we both agree that the bolster gives a much better "look and feel" to the knife - so the final versions (if/when I get around to them) will all have bolsters.....)
    Last edited: Aug 16, 2019
  12. Stacy E. Apelt - Bladesmith

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

    Aug 20, 2004
    You are overthinking this. Just grind the bevel to put the shinogi wherever you want it.

    I don't understand why you used half thethickness in your angle calculations?isn't the back flat?

    I see the stock was .085. Using 1" as the average blade height, the shinogi you want is .3" up the side. That would make the apex (edge) 16.5 degrees. 1/2" high would be an angle of 9.8 degrees.

    What it actually is doesn't matter ... just grind the bevel to the line you draw that looks right.
    After that is done, the final edge is put on at the desired angle. You said 25 degrees was what you want, which will work fine (you might try 20 degrees).
  13. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    I am not sure that I understand your question. The trigonometry has nothing to do at all with the height of the blade.

    Sin(angle)=opposite edge / adjacent edge. The "adjacent edge" is the height of the shinogi from the edge. This is a double-sided grind, not single sided - so The "opposite edge" is one-half the thickness of the blade (assuming the "angle" being specified is the angle of the bevel of a single side relative to the centerline of the blade) (hence my use of one-half the thickness of the blade). (the right-angle for the trig would then be at some imaginary point in the middle of the blade, and at the height of the shinogi).

    I have always been taught that the "angles" we speak about on the bevels and edge are the angles per side. So ... if you were to talk about an edge angle of 15 degrees, that would be 15 degrees per side, giving a total included angle of the edge of 30 degrees. Should have nothing to do at all with the height of the blade. Are you thinking about the angles in a different way?

    In either case - it seems you have answered the question as - dont sweat the angles, just put the shinogi in the location you want, then pay attention to the edge angle. In this case I wanted to try 25 degrees as a more robust angle against the usage. I can always re-grind to a smaller angle if the 25 does not work....
  14. Stacy E. Apelt - Bladesmith

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

    Aug 20, 2004
    There is always confusion when talkiing edge angles. The edge is a complete angle, not two halves. Side A is the stock thickness. The two othetr sides, B and C, are the height of the blade on a FFG or the height of the shinogi on a partial grind. The edge angle is angle a.

    When sharpening you use the per-side measurement, which is half of the edge angle desired.

    Most of us use "inclusive" to notate that the edge angle given is the full angle, inclusive of both sharpening angles. When giving sharpening info, we use DPS to notate that it is only one side.
  15. Natlek


    Jun 9, 2015
    I hear how this knife is screaming to be convex . . . :D
  16. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Stacy - so if i understand you correctly, when you speak of the (secondary) bevel angle, you will speak of the complete (“inclusive”) angle, but when you describe the primary (“edge” or “sharpening”) angle, you will speak of the per-side angle (which is what i have always used)?

    BTW - i fear i am a trained and life long engineer - and am frequently accused of “over thinking things” :) . I have never, however, worn a pocket protector :)
  17. coldsteelburns


    Aug 2, 2010
    Last edited: Aug 17, 2019
  18. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Thanks Paul. I dont have any problem doing the math (been doing it all my life....) ... but i think that table would be really useful for a quick check on the resulting angle if you take stacy’s approach of “put the shinogi where it looks good” (to make sure the angle is neither too large or too small for the steel and the knife’s purpose...
  19. coldsteelburns


    Aug 2, 2010
    Ok I gotcha. Yea I just skimmed through the comments quickly and thought I saw what was maybe a bit of confusion on the angle formula, that's what I get for being lazy.

    And yep, I'd agree to go with what's aesthetically pleasing, it's what I've always done, although depending on certain factors it could alter cutting performance in addition to the edge thickness and edge angle, but generally I think it's safe to go for looks if your not making a competition cutter etc.

    Also, just wanted to add FWIW that those bevel angles in the chart are for a final edge thickness of zero, or a zero edge. I would say how to find out the angle for a given/final edge thickness, but it sounds like you're good to go there. :thumbsup:

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  20. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Yeah, i could do it ... but dont think i would bother? likely the difference between that and the “zero edge thickness” assumption is usually pretty small, no?

    I apologize that this thread went in a math-heavy direction: i meant the original question as a literal dichotomous choice of design based on “esthetics - shinogi location” versus “math - target bevel angle” ... never intending on getting in to how to do the math :-(. . I think the thread finally got there though - consensus really does seem to strongly favor blade esthetics versus concerns over bevel angle... ​

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