Hiromoto Gyuto second bevel angle?

Hello!

I'm knew to the world of Japanese cutlery and sharpening. I've recently acquired a Hiromoto AS Gyuto 210mm. I understand that this is a double bevel 60/40 edge. Is it correct to assume that the two bevels in question are the ones depicted on the picture with arrows? Does the 60/40 ratio apply to the bevel closet to the face of the blade, or to the bevel closet to the cutting edge?

I also noticed that the patina extends further up on the right side of the blade (as shown on the picture) than on the left side of the blade. Is this because of the 60/40 ratio?

I had some instructions that came packaged with the knife but unfortunately they were in Japanese.

Thank you!

60% of the total edge angle is on one side while 40% is on the other. What you are seeing in the picture is the lamination line. It's where the soft stainless jacket meets the carbon core. One side of the knife looks higher or lower than the other is because of the asymmetry in the blade face grind.

ThEoRy:

I think I get what you mean by 60% and 40% of the edge. More metal has been ground on one side of the blade, even though both sides may still have the same angle, aka, asymmetrical.

Then, the question is, what should be the angles of the two bevels?

I know Japanese knives are narrower that their western counterpart, ie., 10-15 degrees. I assume this applies to the bevel where the soft stainless jacket meets the carbon core, and that the cutting edge bevel (whether it is called the primary or secondary or micro bevel) is roughly 45° to give it strength?

It's hard to find a clear source of information as everyone seems to have a different opinion. Seems to be more of an art than a science.

With the Hiromoto out of the box the relief bevel is at a few degrees, with microbevels at 10 degree on the right side and 15 degree on the left one. Follow the existing geometry and you don't have to care about the numbers. Start at the lowest angle you're comfortable with -- so you're abrading fairly above the bevel -- and raise the spine little by little until you reach the very edge and raise a burr. Do the same on the other side. Verify with the sharpie trick or the scratch pattern.

http://www.kitchenknifeforums.com/showthread.php/5656-Asymmetry-–-The-REAL-DEAL

The cladding line is not usually a seperate or defined bevel. this can be seen when looking at a kuro Uchi knife. Approximately 2/3 of the blade face are covered with the black oxide finish. Then the polished/ground section starts. Which is pretty much the secondary Bevel. The lamination line is usually a further 2/3rds of the way down that section. With the final 3rd being the core steel. The same principle applies to your Hiromoto although the two planes are blended (convexed) which makes it harder to see. people usually then grind in the primary bevel with an inclusive angle of around 20-30 degrees. if you feel the edge needs to be strengthened you can then grind in a micro bevel ( say at 30-45 degrees. its usually only necessary to do this on one side. The right side for a right hander. And just deburr the left side.) alot of people dont take much notice of specific angles, as long as when you are grinding your primary bevel you are hitting the edge, it doesnt really matter what angle it is ( within reason)

The important thing to remember is that if you remove material from one side of the knife, you must balance that out by removing a similar amount of material on the other side. Neglecting this will eventually result in the knife steering.

I hope this makes sense and is helpful

Your explanation of the kuro Uchi knife was great! I was confused between the different lines.

Just to reiterate, from top to bottom of the kuro Uchi:

1- face covered in black oxide (for 2/3 of face)
2- face *not* covered in black oxide (for last 1/3 of face)
3- begin secondary bevel (polished/ground surface)
4- 2/3 after secondary bevel line, lamination line
5- 1/3 of secondary bevel is exposed carbon core
6- last millimeters is the primary bevel (also referred to as micro bevel?)

I'm still struggling a bit with the Hiromoto. All I can see from the picture:

1- face
2- lamination line (first arrow)
3- exposed carbon metal
3- primary bevel (second arrow)

Are there really a primary and a secondary bevel? I understand, as you mentioned, the faces are convex thus both planes blend in, still I cannot seem to see the second one. Is it above or below the lamination line, or is it not even perceptible?

I just might have a go at it and follow the angles and see with the burr.

There is only one bevel on the hiromoto pictured. It's just the primary bevel, there is no secondary bevel here. Look at the newer konosuke Fujiwara blue steel gyuto for an example of a knife with a proper primary and secondary bevel. It has a big wide blade road and a shinogi line. You'll know it when you see it.

I tried to look up Fujiwara blue steel gyuto but couldn't find a close up of the edge. But I see what you mean, I definitely could see it with the kuro Uchi.

Is it just an illusion or the left side of the primary bevel seems to have more metal shaven off than that of the right side? Shouldn't it be the opposite with a right-handed knife?

Have a look at the choil and you will see that the edge is off-centered to the left and that the left face is flatter than the right one.

From further reading and from what you guys are saying, I think that: There is indeed only one bevel, the primary bevel, but the reason why the lamination line appears to be higher on the right side than on the left of the blade (hidden on the picture) is because the *blade* itself is asymmetrical, not just the bevel!

Benuser---I think I see what you mean by the edge being off-centered to the left... I agree that the left *bevel* does seem flatter, in the sense that the bevel angle is less pronounced and longer than the right one.

FiGii said:

I tried to look up Fujiwara blue steel gyuto but couldn't find a close up of the edge. But I see what you mean, I definitely could see it with the kuro Uchi.

Is it just an illusion or the left side of the primary bevel seems to have more metal shaven off than that of the right side? Shouldn't it be the opposite with a right-handed knife?

Click to expand...

My mistake, I meant to say Konosuke Fujiyama. Apologies.
Here is what I meant.


The primary bevel is just the portion along the very edge. The secondary bevel starts at the top of the primary bevel and continues up to the shinogi line. The space inbetween is the blade road.

haha very clear indeed!

FiGii said:

6- last millimeters is the primary bevel (also referred to as micro bevel?)

I'm still struggling a bit with the Hiromoto. All I can see from the picture:

1- face
2- lamination line (first arrow)
3- exposed carbon metal
3- primary bevel (second arrow)

Are there really a primary and a secondary bevel? I understand, as you mentioned, the faces are convex thus both planes blend in, still I cannot seem to see the second one. Is it above or below the lamination line, or is it not even perceptible?

I just might have a go at it and follow the angles and see with the burr.

Click to expand...

Primary bevel and micro bevel are not the same thing, you add a micro bevel to your primary bevel. It should be minute in height, nearly invisible. This video by Jon Broida should help to explain it
http://m.youtube.com/watch?v=xwnFrjiAA_8

Because your Hiromoto is new, the convexing makes it hard to see, however as you use and sharpen the knife it will become thicker behind the edge and cutting performance will deteriorate. At this point you will need to create your own secondaary bevel. You can lay the knife flat on the stone and raise the spine slightly. With your finger pressure at or slightly above the lamination line you grind in a secondary ( also sometimes referred to as a relief bevel) go slowly at the start, and check the scratch pattern to make sure you are grinding on the right spot. Also you shouldn't be hitting the very edge at this point. You can use the magic marker trick to check this. You only need to remove enough steel to return the knife to its original geometry ( you can remove more if you think it needs it) turn the knife over and remove a similar amount of material from the other side (to maintain the assymetry) you can then slightly lower the spine and blend that new secondary bevel. next raise the spine further and grind in the new primary bevel ( making sure a burr is forming) and then decide if you want to add a micro bevel.

Depending on how you feel about aesthetics you may want to polish out the thinning scratches, this can be done with wet/dry sandpaper or a progression of finer stones. If you plan on doing this it is best to be done before you grind the primary bevel.

As far as I can see from your picture the blade has undergone some change since it came out of the box. What have you done exactly?

FiGii said:

From further reading and from what you guys are saying, I think that: There is indeed only one bevel, the primary bevel, but the reason why the lamination line appears to be higher on the right side than on the left of the blade (hidden on the picture) is because the *blade* itself is asymmetrical, not just the bevel!
.

Click to expand...

You can only see one bevel, but there is a secondary bevel. Unless the knife is completely flat ground, or a flat billet of steel.( which t isn't) Check out this thread by Will Catchside. Duri g the WIP you can see he grinds in the secondary bevel, but when polished you can't make it out.
http://www.kitchenknifeforums.com/showthread.php/15103-Stainless-ladder-damascus-san-mai-WIP

FiGii said:

ThEoRy:



I know Japanese knives are narrower that their western counterpart, ie., 10-15 degrees. I assume this applies to the bevel where the soft stainless jacket meets the carbon core, and that the cutting edge bevel (whether it is called the primary or secondary or micro bevel) is roughly 45° to give it strength?

Click to expand...

Your assumption is wrong. These 10-15 degree angles, FWIW, apply to the very, very edge. 45 degree inclusive might be suitable for soft stainless Germans, with Japanese blades this would lead no an unnecessary performance loss. More important though, applying a V-edge with such figures will result in a considerable waste of material. To put it crudely: you're throwing away the best part of your knife.
Is this what happened?

Benuser said:

Have a look at the choil and you will see that the edge is off-centered to the left and that the left face is flatter than the right one.

Click to expand...

I noticed that too and found it odd. I watched the KORIN sharpening vids and I am pretty sure the master sharpener said that the right face of the gyuto, with the 60 or 70% bevel part, should have a LOWER angle than the narrower 30 or 40% left face ...?

The left will often get a bevel at a higher angle to balance friction between both sides and avoid or limit steering. So, 15 degree at left and 10 degree at right as Korin proposes is a very common configuration. I wouldn't formulate a general method though as all will depend on the way the knife one handles has been grounded and sharpened before. When you're satisfied with its performance you may stick with the present configuration. Otherwise, you may change it more or less.

There was a misunderstanding I'm afraid. If the left face is ground flatter, that doesn't say anything about the bevel of the edge we are going to put on it.

It's difficult to explain without pics or better, drawings...

so, if both sides of the knife (gyuto for right handed user) are ground at the same angle, the bevel on the right side will be "wider" because it is ground with, say 7 out of 10 strokes and the left side only with 3 out of 10 strokes (for a 70/30 bevel) and the actual cutting edge will be moved to the left in relation to the middle of the spine.

But the right side will also be ground at a lower angle which will make the bevel on the right side appear even wider, but will not move the edge further to the left.

This is how I understood a gyuto should be sharpened.

Nothing wrong with that as a rule of thumb, but more often than not some adjustment is needed. See post nr. 109 by Geoff about steering and wedging.

http://www.kitchenknifeforums.com/showthread.php/5656-Asymmetry-–-The-REAL-DEAL/page11

And once you're fine with the existing configuration you won't matter about angles or proportions, unless you're the victim of some jig system seller. I start fairly above the bevel at the lowest angle I'm comfortable with, raise the spine little by little until I reach the very edge and raise a burr. Than I switch to the other side and do the same. I can verify the progression with looking at the scratch pattern or the disappearing patina on carbons.

Thank you all for the valuable info.

This is the blade as it was shipped out to me from the store, no sharpening has been done yet.

I will check out the video on microbevels, and read the thread on steering and wedging.

As I understand it, there are many rules than can be applied to determining angles and bevels (which I will definitely read upon), but one cannot go wrong by going with the stock blade geometry, and finding the proper angle by looking for a burr on the opposite side.

I don't think you will need a micro bevel on this knife. At least I never did on my Hiromoto and I beat the **** outta that thing. Just stick with the angle set from the factory and make tiny adjustments over time to correct the geometry as you go along.