Polishing Wide Bevel Kurouchi Knives?

[hukdizzle]

I was curious if any of you had tips on polishing/kasumi wide bevel kurouchi knives? I have a Tanaka Kyuzo Kurouchi that needs a slight thinning in some areas and after doing so I would like to polish up the bevels. My concern of course is going too high up the bevel and starting to remove the kurouchi past the shinogi. The knife has a very distinct and clean shinogi line between the kurouchi and polished wide bevel. I had thoughts about taping the kurouchi but I figure that would not work as the tape would prevent the knife from properly laying down on the stone and polishing near the kurouchi line. Is the answer here just to go really slow and be really accurate with my pressure? Finger stones?

https://strata-portland.myshopify.c...a-020b1k-06-fa240?_pos=1&_sid=47b1ea879&_ss=r
That's the actual knife above, the kurouchi finish on these is known to be very thin.

 

[user 16756]

I was curious if any of you had tips on polishing/kasumi wide bevel kurouchi knives? I have a Tanaka Kyuzo Kurouchi that needs a slight thinning in some areas and after doing so I would like to polish up the bevels. My concern of course is going too high up the bevel and starting to remove the kurouchi past the shinogi. The knife has a very distinct and clean shinogi line between the kurouchi and polished wide bevel. I had thoughts about taping the kurouchi but I figure that would not work as the tape would prevent the knife from properly laying down on the stone and polishing near the kurouchi line. Is the answer here just to go really slow and be really accurate with my pressure? Finger stones?

https://strata-portland.myshopify.c...a-020b1k-06-fa240?_pos=1&_sid=47b1ea879&_ss=r
That's the actual knife above, the kurouchi finish on these is known to be very thin.

in my personal experience keeping the shinogi ultra straight when you have a bevel that you want to really even out and didnt start that way is quite difficult.

I actually think keeping the shinogi tight/crisp is easier with stones if the stones are adequately hard and flat. if you dont care so much about it remaining ultra straight, you can just use hard stones and be careful not to push down north of the shinogi.

 

[hukdizzle]

in my personal experience keeping the shinogi ultra straight when you have a bevel that you want to really even out and didnt start that way is quite difficult.

I actually think keeping the shinogi tight/crisp is easier with stones if the stones are adequately hard and flat. if you dont care so much about it remaining ultra straight, you can just use hard stones and be careful not to push down north of the shinogi.

Yeah, I thought about that as well. Keeping a small contact surface with the bevel allows you to have a lot more control. I guess it's kind of like using an ultra fine sharpie compared to a normal sharpie. I typically like to dish the stone a bit to provide a bit more contact/convex and then maintain that as I polish but this may be the best way to approach.

 

[tripleq]

It is quite surprising how uneven bevels can be. They look great out of the box, but many are dismayed at how wonky they are once put on a flat stone. This is especially true with KU knives. Makers have various techniques to make the bevel look flat and even. Mostly by using some kind of material that will grind stone grit or engineered particles into the low spots. As you grind or polish the wide bevel your KU line will typically become wavy as the bevel is flattened. Most KU (like the one you linked to) is synthetic so there are remedies if you want to restore a crisp line. Gun bluing is a good way to go. You can experiment with different products and building up layers to approximate the KU very closely. Many times exactly. Restoring a straight line is just a matter of masking it straight.

 

[iandustries]

Would love to hear what you finally decide to do and see the result! I have the exact same knife with a blonde horn, and will need to do the same thinning some day.

 

[Pie]

Tape it off! The shinogi will most likely show some waviness when all is said and done, if you’re going for flat bevels. @tripleq said it, some careful detail work can do it, but I’ve resigned either to a wonky shinogi or funky ku in the name of performance and ease of polishing

 

[ian]

Yeah, I thought about that as well. Keeping a small contact surface with the bevel allows you to have a lot more control. I guess it's kind of like using an ultra fine sharpie compared to a normal sharpie. I typically like to dish the stone a bit to provide a bit more contact/convex and then maintain that as I polish but this may be the best way to approach.

I wouldn’t think about it like an ultra fine sharpie. If you have flat stones, and you make sure via finger pressure that some part of the bevel is contacting the stone, the geometry of the knife will prevent the stone from contacting above the shinogi. This is because nothing above the shinogi is in the same plane as the bevel. You’ll only hit above the shinogi if you lose contact completely with the bevel and start riding the shinogi line, and going over it. So keep your stones flat and there will be no problems. (Caveat: if you let mud build up on the stone that can polish the ku a bit right near the shinogi.)

If you want to keep your shinogi straight (assuming the thickness at the shinogi is roughly even) don’t work too much on one part of the blade. Thin the blade evenly.

 

[tripleq]

I wouldn’t think about it like an ultra fine sharpie. If you have flat stones, and you make sure via finger pressure that some part of the bevel is contacting the stone, the geometry of the knife will prevent the stone from contacting above the shinogi. This is because nothing above the shinogi is in the same plane as the bevel. You’ll only hit above the shinogi if you lose contact completely with the bevel and start riding the shinogi line, and going over it. So keep your stones flat and there will be no problems. (Caveat: if you let mud build up on the stone that can polish the ku a bit right near the shinogi.)

If you want to keep your shinogi straight (assuming the thickness at the shinogi is roughly even) don’t work too much on one part of the blade. Thin the blade evenly.

That holds true on a single-bevel (most of the time). On a double-bevel reality is that shinogi are usually not that defined and there is usually a variation in thickness so as you grind your wide bevel the shinogi gets ground unevenly causing waviness. It is a very common problem when thinning KU double-bevel knives.

 

[ian]

That holds true on a single-bevel (most of the time). On a double-bevel reality is that shinogi are usually not that defined and there is usually a variation in thickness so as you grind your wide bevel the shinogi gets ground unevenly causing waviness. It is a very common problem when thinning KU double-bevel knives.

Yea, I included the “assuming even thickness” proviso for that reason. If you’re on stones, I wouldn’t try to keep it straight if the thickness is uneven, but what do I know.

The double bevels I’ve tried have had fine shinogis, at least. Not the crispest, but defined enough that I wasn’t worried about f-ing up the KU. I guess it’s true though that sometimes a bit of raised KU can poke over and hit the plane spanned by the bevel, and then you hit that when you sharpen.

Do you often see knives with uneven thickness at the shinogi that have straight shinogis to begin with? I’m guessing it’s possible to do that on a belt or a wheel, since you can better control the grind in different sections of the blade, but it just sounds like it’d be super difficult to get that right while having the bevel be even.

 

[tripleq]

Yea, I included the “assuming even thickness” proviso for that reason. If you’re on stones, I wouldn’t try to keep it straight if the thickness is uneven, but what do I know.

The double bevels I’ve tried have had fine shinogis, at least. Not the crispest, but defined enough that I wasn’t worried about f-ing up the KU. I guess it’s true though that sometimes a bit of raised KU can poke over and hit the plane spanned by the bevel, and then you hit that when you sharpen.

Do you often see knives with uneven thickness at the shinogi that have straight shinogis to begin with? I’m guessing it’s possible to do that on a belt or a wheel, since you can better control the grind in different sections of the blade, but it just sounds like it’d be super difficult to get that right while having the bevel be even.

Well, with a double-bevel you can never assume even thickness. Especially with KU. There is a lot that goes on at the production level that makes things look nice and clean, but grinding tends to be very rough. Even on high-end knives. That is why there are so many threads about people getting into trouble and worrying about their KU when they get into thinning. Low spots compound the problem. I see uneven shinogi in height and thickness regularly. When getting a wide-bevel completely free of low-spots I have yet to see a shinogi that remained unwavy and crisp.

If you don't believe me, take it from the master...

https://www.kitchenknifeforums.com/threads/wide-bevel-sharpening.20070/

 

[ian]

Well, with a double-bevel you can never assume even thickness. Especially with KU. There is a lot that goes on at the production level that makes things look nice and clean, but grinding tends to be very rough. Even on high-end knives. That is why there are so many threads about people getting into trouble and worrying about their KU when they get into thinning. I see uneven shinogi in height and thickness regularly. When getting a wide-bevel completely free of low-spots I have yet to see a shinogi that remained unwavy and crisp.

If you don't believe me, take it from the master...

https://www.kitchenknifeforums.com/threads/wide-bevel-sharpening.20070/

Hmmm, in Dave's thread it looks like he just thinned normally, so the shinogi line became kinda wavy, exactly in the way you'd expect it would given the initial scratch pattern, which is what I would do. I mean, yea, if the shinogi's uneven, then when you sharpen you'll "hit the KU" in the sense that you'll raise the shinogi more in some places than in others, but I took the OP's comment to be more about scuffing the KU accidentally. (I guess if the geometry of the knife is really uneven you could get like a hole of KU with a polished ring around it, i.e. the new "shinogi" doesn't have to even be a line.)

I guess maybe lots of makers go in there and like artificially straighten out the shinogi by polishing the low spots?

P.S. I believe everything you say! I just like the discussion.

 

[user 16756]

Hmmm, in Dave's thread it looks like he just thinned normally, so the shinogi line became kinda wavy, exactly in the way you'd expect it would given the initial scratch pattern, which is what I would do. I mean, yea, if the shinogi's uneven, then when you sharpen you'll "hit the KU" in the sense that you'll raise the shinogi more in some places than in others, but I took the OP's comment to be more about scuffing the KU accidentally. (I guess if the geometry of the knife is really uneven you could get like a hole of KU with a polished ring around it, i.e. the new "shinogi" doesn't have to even be a line.)

I guess maybe lots of makers go in there and like artificially straighten out the shinogi by polishing the low spots?

P.S. I believe everything you say! I just like the discussion.

I got the sense the OP wanted to keep the nice clean arc. afterall, it's a nice knife and once the shinogi starts getting all wavy you lose some of that IMO.

I dont mind it and Ive definitely got some knives that after having evened things out look fairly suspicious, but I can appreciate not wanting to have your nice knife look like that

 

[tripleq]

Hmmm, in Dave's thread it looks like he just thinned normally, so the shinogi line became kinda wavy, exactly in the way you'd expect it would given the initial scratch pattern, which is what I would do. I mean, yea, if the shinogi's uneven, then when you sharpen you'll "hit the KU" in the sense that you'll raise the shinogi more in some places than in others, but I took the OP's comment to be more about scuffing the KU accidentally. (I guess if the geometry of the knife is really uneven you could get like a hole of KU with a polished ring around it, i.e. the new "shinogi" doesn't have to even be a line.)

I guess maybe lots of makers go in there and like artificially straighten out the shinogi by polishing the low spots?

P.S. I believe everything you say! I just like the discussion.

In that thread the discussion is about aesthetics. In reality whether you want to flatten out all the low spots or thin it a bit at a time the basic problem still exists. You never know how the problem will manifest till you put that bevel on a stone and grind. Eventually you’ll scuff the KU no matter how careful you are. The bevel is uneven, the face of the knife is often uneven and the KU is sometimes cleaned up in consequence at the production level to make it look perfectly sharp. You might manage to avoid altering the KU line on the first go if you are lucky but it will happen eventually. In sticking with the OP concern there is no way to avoid it. Only ways to clean it up.

 

[ian]

This is all good info!

 

[user 16756]

I will say it all depends on the sharpener and how even you need your bevel, too. my iron clad Yoshikane still has more or less a perfect shinogi minus a bit near the tip on one side because the grind was already good enough. would it be that good if it were a 240 gyuto instead of a 165 bunka? not sure but maybe.

but on most knives for me Im going to have to take it to a point where it's more or less not consistent. but then that's part of the appeal to me.

I will say @hukdizzle Milan Gravier posted an excellent video on instagram about polishing I think is probably the best single source of information I can think of. it really covers all the stuff you need to know in one place IMO

 

[ian]

I will say @hukdizzle Milan Gravier posted an excellent video on instagram about polishing I think is probably the best single source of information I can think of. it really covers all the stuff you need to know in one place IMO

This one? (Thanks @milangravier!)

 

[user 16756]

This one? (Thanks @milangravier.)

yeah that's the one!

I mean there are loads of excellent videos out there and I wont say that you cant learn a lot from Mutsumi Hinoura's sharpening, or Forty who is always so helpful, or any number of other good sharpeners, but if you were only going to watch 1 video about polishing I think you could do a lot worse than that one.

I mean even personally I learned something really cool from this video about when you wash your hands when you polish dont dry them off, just let them stay wet if you can to reduce the potential for lower grit contamination. I had never thought about that but what a great tip.

 

[tripleq]

It is a good vid. He goes into what I am talking about at about 16 minutes. He explains that the shinogi will be wavy even doing your best to keep it 'crisp' because it will follow the thickness of the blade. He demonstrates that the flat portion is not truly flat especially on a KU blade so the shinogi follows that geometry. Bottom line is you can't separate your KU line from the rest of the knife's geometry. As you thin, things change. As you grind into the KU it will follow the overall geometry. If your knife is perfectly ground you have the best chance to keep you KU line in tact, but I haven't met a knife with perfect geometry yet. Especially not a KU.

 

[tripleq]

Here is another thing to consider when thinning. As we know all J-Knives are asymmetrically ground, so you can’t expect results to be the same on the front and back. I am a proponent of thinning with every sharpening. That is to say whatever I do to the edge also gets done to the secondary bevel in order to maintain the original geometry. Here is a Nakiri that I’ve had for about 10 years. When sharpening or thinning it is best done with respect to the overall geometry, so development can differ quite a lot between front and back.

Front.

Back.

 

[hukdizzle]

Thank you everyone for the replies, I started to watch the video with Milan but it was very long and I could not finish yet. In the mean time I bought another Tanaka... This one with no KU. We will see how I like it compared to the KU version but initial comparisons seem to favor the migaki. I may not end up giving this particular KU knife a polishing go but I will be prepared for any future attempts.

 

[captaincaed]

This one? (Thanks @milangravier!)

This is a great vid, thanks everyone for posting!

 

[captaincaed]

I have a dumb question. What is the performance benefit of having super flat bevels (flat meaning ”without low spots”, not “full-flat grind”)? I know overgrinds are an issue for long-term knife life and holes in the edge. Otherwise, I haven’t noticed much performance difference comparing stone-flattened vs. machine-finished knives with notable low spots. Is this purely an aesthetic thing?

 

[nakiriknaifuwaifu]

I only briefly skimmed through stuff people said above, but yes you will probably need wa-powder or finger stones.

The sakai widebevels are almost always finished on waterwheels and the kasumi you see is from wa powder and not a crisp, off-the-stone finish. With wheels, you'll get a trough through the middle of the bladeroad, usually deepest at the heel.

Below is an example:

Black is areas where the bladeroad touches the stone, red is the trough that's left from grinding on a wheel.

So you can thin effectively from a performance perspective because you can raise the shinogi and decrease thickness behind the edge, but you will need to spend more time if you want to flatten the geometry and have a kasumi finish from just stones. Getting the bevels from concave to flat is some time, and if you want to go from flat to hamaguri/convex then that is another ordeal.

With these, I think it's best to just keep doing maintenance thinning and using fingerstone and wa powder for kasumi until the bladeroad is flat on its own. Otherwise you'll eat a few mm of height just to chase a stone-ready bevel.

 

[ian]

I have a dumb question. What is the performance benefit of having super flat bevels (flat meaning ”without low spots”, not “full-flat grind”)? I know overgrinds are an issue for long-term knife life and holes in the edge. Otherwise, I haven’t noticed much performance difference comparing stone-flattened vs. machine-finished knives with notable low spots. Is this purely an aesthetic thing?

Purely aesthetic imo. If anything, food release might be slightly worse if you flatten them. Flattening and then hamaguri sharpening is generally ok though if you want reasonable performance and pretty bevels.