(How) Would You Re-Grind this Blade?

C

Cushing H.

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Jun 3, 2019
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So ... I have this commercially made Nakiri. It is a nice knife: good weight, Hitachi White blade. Wa ("D") handle with good weight and balance .... BUT it was always rather wide BTE. Echoing comments in the current thread by AustinS1234, as it has been sharpened several time, the edge (secondary bevel) has become noticeably wider, AND the BTE measurement has continued to increase considerably. At current, I measure the BTE at ~0.025" (yes, really). For a while I have been thinking of re-grinding the thing to correct that BTE, but there is a cool makers mark about 1.25-1.5" up from the edge.

First of all, does anyone think I should not re-grind this primary bevel? second, how to grind: flat grind up to the very very bottom of the makers mark (which will give only something like a 1.25" wide bevel, which I would like like a little wider), or maybe flat grind grinding out the very bottom of the makers mark and gain something like a 1.5" bevel. What do you folks think? (photos below)
upload_2020-2-17_14-2-37.png
upload_2020-2-17_14-3-1.png
 
Make a pass down the edge to clean it up and make it flat. Blacken the edge with a sharpie or Dye-Chem ( helps to see the thickness as you grind). Re-grind the bevels keeping the top where it is and thinning the edge until it is almost sharp. Add the secondary and you are done.
Don't get it hot!
If you aren't good at bevels and/or have a single speed grinder, do it by hand on stones.

TIP:
put a couple layers of tape on the upper bevels to protect them from stray grit and accidental bumps. Duct tape works well.
Tape the front part of handle with blue tape if you are concerned about bumping it.
 
This kind of knife is designed to have the bevels thinned. Unless you're really good with a belt grinder, start with coarse stones. You will need to be able to flatten your stones regularly, every few minutes. Coarse stones work relatively quickly, but they dish even faster. Adjust your pressure towards the edge or "shinogi" (where the bevel ends) to get the edge thickness or bevel height you want. Take note of the geometry of the grind. It will most likely be more convex on one side.
 
No problem with the grinder and flat grinding the bevels. Not so good at a dead-sharp shinogi ... but the original smith did not try for that - and I should have no trouble hitting basically that original quality. I have already checked the geometry - one side is pretty much dead flat - the other slightly convex (I will flatten that up as I regrind). I had not thought about taping up the upper flat of the blade (it IS flat - the only bevel is the one you see) - thanks. I do all my grinding post-HT - so again no problem keeping things cool (it the tips that can catch me - but no blade tip here :)

so Stacy .... I was thinking I would widen the primary bevel in order to lower the angle at the edge so as to keep that geometry as thin as feasible during repeated re-sharpenings. You would not do that here???
 
I'd start with a fine grit like four or six hundred and probably with a flat 9" disc grinder - not an angle grinder

VFD, Low speed, foot switch, wet
Put the blade against the platen, then foot switch it on - you will probably keep the angle you started with.
As said, use dychem or marker to see what you did


Plus, I'd skip the "So..."
It's a verbal tic, no need to write it down.
 
I presume it's convex on right hand side for right hand use?
Why flatten it?
You will just make food stick to the blade
I would flatten the flat side and convex the other,on stones
I wouldn't do it on grinder as it's easy to f up
 
When I said "bevels" I was referring to the main edge bevel on both sides (the shiny steel).
The kurouchi is what I was talking about protecting with the tape.
Regrind the wide edge bevel so the top stays where it is and the edge thins.
Once at a near sharp edge, a few strokes at a higher angle will put on the keen edge. I do the keen edge at around 10° per side.
 
John mc c said:
I presume it's convex on right hand side for right hand use?
Why flatten it?
You will just make food stick to the blade
I would flatten the flat side and convex the other,on stones
I wouldn't do it on grinder as it's easy to f up
Click to expand...

I agree that Japanese kitchen knives often feature a convex grind on the right side which is designed to help drop the cut food off the blade. Sometimes can be convex on both sides with greater convexity on the right versus left as majority righty users.

Depending on the maker and type of knife, J-knives can often have the cutting edge offset from the centerline of the blade. See this thread at Kitchen Knife Forums which is heavily populated with J-knife users: https://www.kitchenknifeforums.com/threads/a-basic-explanation-of-asymmetry.33951/

Here's a cartoon stolen from that thread of what John and I are saying:
JZ5O4mq.png&hash=7c510e1252b5c0f6ef7788a265a190f9


Not every kitchen knife from Japan is made like that, but there are many.
 
Huh - thank you. If it is intentionally convexed (on the right side) it is very subtle (I know it does not take much), and is definitely not consistent along the length of the edge. I usually have not convexed my edges (I view it as a maintainability issue), but no reason at all I can not try doing so on this blade.
 
A thin nikiri like the one shown would not have a convex grind. It will have a flat bevel to the shinogi on both sides. Any convexing that exix=sts is probably a result of the edge becoming thick and the edge "rolling" down in sharpening.
 
assuming this is a laminated blade, soft cladding, I would use the coarse stones as suggested above.
 
as far as I know it is not a laminated blade - solid white steel #2..... (unless the original selling description was misleading)
 
Actually, I take that back - even though the original description does not say so ... the blade is pretty clearly laminated. Out of curiosity - what would be the problems/challenges with the softer cladding using a grinder (with say 120/200 grit) to do the grinding??? What do makers do with fresh blade material while grinding such a laminated structure??
 
What do makers do with fresh blade material while grinding such a laminated structure??
:rolleyes:
I suppose they just grind like other steel :D
Just grind that bevels and be done with that , don t make science from simple task my friend :thumbsup: And be careful to not make mess ,look like nice knife :)
 
Natlek said:
Just grind that bevels and be done with that , don t make science from simple task my friend :thumbsup: And be careful to not make mess ,look like nice knife :)
Click to expand...
Actually - I was just planning to go at the thing with a 120 grit ceramic belt, then work up to finer gator finishes. My only real question what whether to march the grind line backwards. Some here appear to want to use stones. Not sure why - but thought I would ask.

It is a nice knife. I use it almost every day :) the wide BTE has just begun to bug me too much.....
 
I guess the stone advice is due to being less likely of doing a major mistake and move the line naturally at the already given angle. Also there is not much material to be removed. I would follow Stacey's advice. Find the bevel on the grinder and apply more pressure to the edge. You will probably be done in couple of passes on each side. You will be less likely to screw up the line if you use the work rest while grinding IMHO. Push stick or thumb on the edge to apply pressure. Job done.
Make sure to post results. :)
 
Why 120 grit belt , to easy over heat edge ? Take 40 grit belt , glue that knife on piece of square tube like this on picture and you will done job in five minutes with prefect bevels .Don t practice on this one :thumbsup:
o7gSg7j.jpg
 
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