Japanese Kitchen Knife Edge Geometry Question

i4Marc

i4Marc

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Oct 19, 2011
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This is a question for the guys with experience making Japanese style kitchen knives. I am making some kitchen knives. These are not going to be fully convexed from the spine all the way down to the edge. I'm going with a 50/50 grind with wide blade roads. My question is, on this style knife, do the blade road bevels meet at a zero edge or are the roads typically convexed or shouldered near the edge? So, is it A or B? If it is B then how thick or thin should it be just behind the edge?


 
depends on the knife style/ use and the user and how much stiction they want to deal with
i liek slight convexed edge on my kitchen knives (not on sushi knives from me less its a deba) parers used to be flull flat ground to almost nothing but i have been usig nates 48 inch platen and leaveing a hair more at the edge thickness still with great proformance but wi a slightly stronger edge
 
You don't say exactly which kitchen knife you are after here. I am guessing Gyuto?
Apologies for posting as a newbie on this but I just got my steel yesterday (52100 and AEB-L) and am about ready to try my first on this style too.
I am researching blade geometry on this as well, so your post is very timely for me.
I found this pic this morning on edge geometry and there appears to be quite a selection to choose from, so it would seem it depends on the performance you are after.
What do you think of these?
 

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B works very well for a suji, I would also "covex" or blend the shoulder.
 
butcher_block said:
depends on the knife style/ use and the user and how much stiction they want to deal with
i liek slight convexed edge on my kitchen knives (not on sushi knives from me less its a deba) parers used to be flull flat ground to almost nothing but i have been usig nates 48 inch platen and leaveing a hair more at the edge thickness still with great proformance but wi a slightly stronger edge
Click to expand...

jdm61 said:
B works very well for a suji, I would also "covex" or blend the shoulder.
Click to expand...
Thanks for asking this question Marc!
Butch and jdm61, for your kitchen knives what edge thickness to you go to before starting the convex grind? Do you use a rotary platen?
Thanks
 
Additional information:

I am making a Gyuto at approximately 253mm, a western style Deba at approximately 210mm, and a petty which will be right around 140mm. The Gyuto will be ground with a long taper to the point for a light, quick feel in the hand and cutting performance. The Deba will be a constant thickness (3.1mm) along the spine to retain a bit of weight for the heavier chopping tasks. The Petty is tapered to the tip and ground thin for the more delicate cutting tasks. I am using 0.10" AEB-L. I don't have exact HRC numbers but they should be at 61.5-62HRC.
 
On the ones that I have done where I went for a complex grind, the top "flat" is not flat. If i am using say a 2.7 mm piece of stock, I do a full flat grind and bring the "edge" down to about 1mm, I then do the second flat grind and bring it down kinda thick, perhaps like .030. i then convex up from there maybe as high as 3/8 of an inch on a wider blade and then thin out behind the edge with EDM stones, etc. as needed. I have also used Nathan's 72 inch platen to hollow out under that shoulder near there top and then blend everything, That gives me an "S" grind of sorts. on the simpler grinds, I just leave out the hollow part and blend everything else, which says they are not actually all that simple.
rcetroy said:
Thanks for asking this question Marc!
Butch and jdm61, for your kitchen knives what edge thickness to you go to before starting the convex grind? Do you use a rotary platen?
Thanks
Click to expand...
 
Cool Marc.
I am curious of you are doing traditional Wa handles, or western style?

i4Marc said:
Additional information:

I am making a Gyuto at approximately 253mm, a western style Deba at approximately 210mm, and a petty which will be right around 140mm. The Gyuto will be ground with a long taper to the point for a light, quick feel in the hand and cutting performance. The Deba will be a constant thickness (3.1mm) along the spine to retain a bit of weight for the heavier chopping tasks. The Petty is tapered to the tip and ground thin for the more delicate cutting tasks. I am using 0.10" AEB-L. I don't have exact HRC numbers but they should be at 61.5-62HRC.
Click to expand...
 
I'm doing a mix of styles. The blades will be pretty standard Japanese shapes with a bit of emoto and generous blade road. The handles will be a Yo or western style handle with a nod to Japanese aesthetics.


So, on a typical Japanese made Gyuto with flat sides and 50/50 bevels, are they convexed at the edge or do the roads meet at a zero edge? If convexed what is a common thickness behind the edge?
 
Chances are that if you have in mind to let them meet at a zero edge, sharpening by hands on the whetstones you'll end with the perfect convex grind as it's supposed to be done.
 
if i speced a nakiri you woudl be wrong on a gyuto or a slicer so at that pooint im not able to give you a number (also because you need to know the type of user and how thin you can push things for that one person)
no one set number will cover you
 
Yeah Butch, that's the problem. The person who commissioned these knives will not be the end user. She is gifting them to somebody else. I don't know the end user's height/build, hand size, the grip they use, the kinds of foods they prepare, how rough they are with their equipment, the surface they'll be cutting against....nothing. At this point I just want to make the best performing blades I can (in an ideal setting). I want the Gyuto to slice like a laser, the chopper to have a robust edge but still cut effortlessly and the petty should be light and nimble with a very sharp edge. I guess I'll figure it out as I go.
 
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