Knife Geometry / Anatomy

[notaguest]

Hey,
so after finally deciding on which knife to buy and getting a grasp of everything, my current goal is to be fluent with knife terminology.
However, I feel like I'm stuck a bit and would like to be sure I got things right!
Please let me know if everything is correct.

[aname=microbevel]Microbevel[/aname] – A bevel that is very small, and never the primary bevel.

[aname=primarybevel]Primary Bevel[/aname] – The bevel that makes up the cutting edge. A primary bevel is sometimes a microbevel.

Don't these contradict eachother? (with question marks in graphic)
Does this mean you count Micro bevels or not?

Now for my specific case: this Yoshikane 240

When I first looked at it, it seemed like it wasn't quite 50/50. After tracing it out and checking online again, it should be 50/50 grind. Is this correct?

Furthermore, what am I supposed to sharpen this to? Right now, is it a full flat grind?

So this would be the optimal geometry, without a tertiary bevel? (red = micro, black = secondary, yellow-ish = Face)

Thanks for helping!
When I'm sure everything is correct, I'll edit/add any missing information and re-upload it.
Thanks!

 

[Redwax]

The primary bevel is not usually the "cutting edge". It is the main (first) grind from the original blade stock. eg. for a cheap mass produced gyuto/chef's knife you have a primary bevel which is a full flat grind from the spine to the edge and a secondary bevel which is the "cutting edge". You might also add a micro-bevel which would technically be a tertiary bevel, not that anyone really refers to it as that.

Another example: a scandi grind that you see in Mora's and other bushcraft style knives has a primary scandi bevel and sometimes has a micro bevel added for a bit of strength. Technically the micro bevel is the secondary bevel, but is normally just called a micro bevel. If the micro bevel is sharpened enough to the point that it is the size of a proper secondary bevel it could arguably be considered a sabre primary grind.

So basically in your diagrams you have the primary and secondary grinds/bevels in the wrong order. The secondary bevel in a general sense is where the apex is unless you have added a micro bevel.

 

[Just a DK]

If you want to see the grind of your knife use business card and put it against your knife. Will help see the grind.

Choilshots and lines drawn on pics wont really tell you the grind…

 

[mengwong]

When I got my Spyderco Sharpmaker the terminology they used was “back bevel” (30° inclusive) and “edge bevel” (40°).

 

[daveb]

"Primary" gets kicked around a lot and I don't think consensus has ever been found as to which bevel it refers to on kitchen knife. I use the context and not the term.

Your Yoshi should look like your middle diagram. It's claim to fame is being very thin behind the edge with flat profile. It will likely be closer to 70/30 than 50/50 and that's a good thing. If you're new to this (and even if you're not) you may want to have it professionally sharpened so you have a "go by" for subsequent maintenance.

 

[KasumiJLA]

Whatever the number of bevel, the apex is the meeting of the two angles which forms the cutting edge. So in this case in red it's the secondary bevel (or micro bevel) is what will make contact to cut your food. This is the part you should sharpen and the angle is roughly between 12°~18°. You can't really go wrong with a Classic 15° on each side.

Your main bevel in black (primary) is what dictates the geometry of your knife. As @Just a DK suggest, you can use something flat like a card and gently move between the hira (flat spot at the end of the shinogi line, yellow on your drawing) and the beginning of the cutting edge. You should see a slight convexity, or not, depending on your knife.

The choil view gives a good idea of the geometry but it is not 100% accurate as the last 2~3mm of the knife can be a bit thicker. If you really want to geek out, I personally use a calliper to measure different thickness along the entire length of the knife. For me the first 15mm behind the edge (usually referred as BTE in short here) is the most important part for the initial cut and feel of your knife. Then the geometry of the main bevel will continue to do his job by slowly pushing the food away with the help of the knife shoulder.

A convex grind will ensure that the penetration into the food will be done gradually with a slight separation effect. On a flat grind it is the same thing, but depending on the geometry and thickness of the main bevel, there will be a little less restriction but the food will tend to stick more to the blade. That's why geometry is so important. It's all about the little details from a good grind and an ok one.

I'm not a pro in geometry, in fact I'm starting to get much more interested in this aspect. But one thing I know is that no matter what anyone can advise/suggest, it's up to you to find what really gives you pleasure and then adjust the result on your knife according to your taste.

 

[notaguest]

Thanks for all the help!
Updated Version

The primary bevel is not usually the "cutting edge". It is the main (first) grind from the original blade stock.

As @daveb mentioned there seems to be some discrepancy and with the first version, I went with the second method https://www.kitchenknifeforums.com/threads/primary-secondary-bevel-discrepancy.2231/

It is the main (first) grind from the original blade stock. eg. for a cheap mass produced gyuto/chef's knife you have a primary bevel which is a full flat grind from the spine to the edge and a secondary bevel which is the "cutting edge".

Does "cutting edge" always refer to the last "real" bevel or does it refer to the micro bevel if one is present?

If you want to see the grind of your knife use business card and put it against your knife. Will help see the grind.

Waiting for it to arrive atm!

Your Yoshi should look like your middle diagram. It's claim to fame is being very thin behind the edge with flat profile. It will likely be closer to 70/30 than 50/50 and that's a good thing. If you're new to this (and even if you're not) you may want to have it professionally sharpened so you have a "go by" for subsequent maintenance.

I'll send another pic with it against a flat card as soon as it arrives. What's the easiest way to determine if it's 70/30? Feel?
When ordering I added an initial sharpening (which was free if that matters) so I have somewhat high hopes for it OOTB.

So in this case in red it's the secondary bevel (or micro bevel) is what will make contact to cut your food. This is the part you should sharpen and the angle is roughly between 12°~18°

Pardon me for questioning you, but isn't the microbevel usually at a way higher angle? Like 20+ deg? So in Knife 3, the primary would be given by the manufacturer, the secondary would be 12-18 (as you mentioned) and the micro bevel something like 20?
And if the primary is well done by the manufacturer, I don't have to touch the primary at all (atleast for a long time), right? Would that be called thinning?

 

[KasumiJLA]

Pardon me for questioning you, but isn't the microbevel usually at a way higher angle? Like 20+ deg? So in Knife 3, the primary would be given by the manufacturer, the secondary would be 12-18 (as you mentioned) and the micro bevel something like 20?
And if the primary is well done by the manufacturer, I don't have to touch the primary at all (atleast for a long time), right? Would that be called thinning?

Some can make a micro bevel at higher angle like 20° if the geometry is super thin BTE. There's nothing wrong against it.

A zero grind is basically the primary bevel that is your cutting edge, without any micro bevel. Micro bevel is actually there to help for maintenance and to give some strength of your cutting edge. There's no need to make 3 bevel on your knife.

You are right and it's called thinning. After sharpening your secondary bevel several times, your knife will start to get thicker behind the edge. At some point the performance will degrade and the cut will no longer be pleasant. This is usually where you need to thin the primary bevel to get back to the original performance. Then you can make a new secondary bevel.

 

[Benuser]

A helpful tool to avoid all concerns about figures, angles, proportions etc. is using a sharpie and follow the existing configuration. You'll need a loupe to verify whether the paint is really gone, even on top of the bevel, and not some microbevel is there — or the bevels simply don't meet and you're accumulating debris on top of the old edge, and there's a line of black swarf on top of the bevel, you only see with a loupe (10-12X).
Therefore, start your sharpening on one side, clearly behind the edge and raise the spine only little by little. Check your progress by looking at the scratch pattern. Go on until you've raised a burr. This does not mean the bevels meet. Check with your loupe and go on until you have an entirely clean bevel.
That's the moment to do the same at the other side. Again, behind the edge, etc. Deburr with every stone in the progression.
This works if you're fine with an existing configuration.
Be aware some knives come out of the box with a minimalist edge, only meant as a service to the end so he doesn't have to remove a lot of steel. Edges of 6 or 8° per side won't hold with chef's knives who will encounter a lot of board contact. That said, you may change it with only a few strokes.
Most factory edges are weak and won't last. Produced with a few very coarse strokes and a lot of buffing to polish and deburr. Looking nice, but it's fatigued steel that should be removed. A good reason to perform the first stone sharpening with a relatively coarse grit, say 500.
This is different of course if the maker or retailer has given it a stone sharpening.

 

[ch_br]

Now for my specific case: this Yoshikane 240
View attachment 350873
When I first looked at it, it seemed like it wasn't quite 50/50. After tracing it out and checking online again, it should be 50/50 grind. Is this correct?

My $.02:

Look at the red line on the RIGHT, its off..

Technically its near VERTICAL originating out of the handle before the primary bevel was shaped...

Therefore, its angle is not equal to the Left grind

 

[aporigine]

To elaborate on the last post, that Yoshi choil looks like a right-biased grind. The knife is inverted from use attitude, so the shallow grind on the right in the image is on the left (toward uncut produt) in use. The side toward cut product is more convex, aiding in food release.

By convexing the right side more, an optimum is struck between release performance of the grind, and slicing performance that goes up with knives of thin geometry.

Think of it as the cutlery equivalent of a mullet haircut: business in front; party in the back. More directly, laser in back and workhorse (with its superior food release) in front.

A skilled sharpener (which in Japan includes setting the blade’s overall grind) does cool mysterious stuff to the edge-adjacent portion of the flatter left side to compensate for the steering effect that an asymmetric grind can display — while retaining the overall comparative flatness of the left face.

A knife ground for a left-handed user will be the mirror image of the above.

 

[mengwong]

Nice illustration work! Just footnoting some other classic diagrams and related threads—

After sharpening your secondary bevel several times, your knife will start to get thicker behind the edge.

it eventually needs a thinning

When sharpening you move the edge to a thicker part of the blade. If you don't compensate by thinning expect a rapid thickening behind the edge.

On the first frame below from https://scienceofsharp.com/2015/10/30/burr-removal-part-1/ note that the "high angle passes" that were effective at removing the burr were performed at only 20° per side (40° inclusive).

turn the black factory grind into the wine-color profile by grinding just above the shoulder of the edge bevel. This drawing is only the edge, not the entire blade height.

cool mysterious stuff to the edge-adjacent portion of the flatter left side to compensate for the steering effect

Figure 7. The differing size and angle of the bevels introduce deflection in the opposite direction of Figure 5, helping to cancel out any steering overall

Here's a little tip for thinning knives with slight asymmetry to the grind

This is different of course if the maker or retailer has given it a stone sharpening.

The keyword is “honbadzuke”.

This is how I understand Science Of Sharp's definitions of sharp and keen

I liked your sharp/keen in the first version, maybe the above post could help bring it back?

I don’t personally use the term “thin behind the edge” because there’s no general consensus

 

[blokey]

Tried lots of knives with similar looking grind but very different performance, now I think it is more of a divine providence

 

[Redwax]

Thanks for all the help!
Updated Version
View attachment 351029

As @daveb mentioned there seems to be some discrepancy and with the first version, I went with the second method https://www.kitchenknifeforums.com/threads/primary-secondary-bevel-discrepancy.2231/


Does "cutting edge" always refer to the last "real" bevel or does it refer to the micro bevel if one is present?

Thanks for that link, I haven't heard anyone use the reverse order for bevels/grinds. I guess it's not totally agreed upon as far as terminology. The only thing that strikes me as a little illogical in the reverse order is that if eg. you had a scandi(primary) grind and added a micro bevel you would then have to refer to the original scandi grind as the secondary bevel, whereas in the more common order it would always be the primary bevel. Then again I would guess that even that wouldn't be agreed upon by everyone.

I used "cutting edge" to mean the bevel which is apexed; I wasn't really using it as a definitive term. So yes the micro bevel would be the "cutting edge" if there is one.

 

[fortheloveofmoar]

What is eve try ones thoughts on how wide or long a primary bevel should be? I know we say 15 degrees and I’m sure that the size of the primary bevel will change depending on the thickness BTE, but is there a general rule of thumb?

 

[mengwong]

is there a general rule of thumb?

More seriously,

There’s a few guys on the forum who take both their edges and BTE thickness to increasingly low angles and then back off when they get chipping. But they’re playing with both edge angle and geometry.

The Rule

 

[Benuser]

What is eve try ones thoughts on how wide or long a primary bevel should be? I know we say 15 degrees and I’m sure that the size of the primary bevel will change depending on the thickness BTE, but is there a general rule of thumb?

30° inclusive sounds perfectly reasonable, but that rarely means 15° per side. Symmetric and centered edges are rare. Most knives have a strong right biased — right side convexed, left one flat, edge more or less off-centered to the left. Allows better release of produce. Optimised for right-handers, as left-handers tend to be ignored, to be put it mildly.
With the off-centered edge, users who aren't familiar with it, will experience strong clockwise steering. To attenuate steering, it's common to rebalance friction between both sides. As the left side offers low friction, the edge may get a higher angle. The right side a lower one. Further, extra thinning at the right can be done, and make the bevel form a continuous arc with the convex right face, ending at a lower angle. So, you get e.g. a right angle ending at some 10-12°, while the left one, kept straight, at 15-20°.

 

[notaguest]

30° inclusive sounds perfectly reasonable, but that rarely means 15° per side. Symmetric and centered edges are rare. Most knives have a strong right biased — right side convexed, left one flat, edge more or less off-centered to the left. Allows better release of produce. Optimised for right-handers, as left-handers tend to be ignored, to be put it mildly.
With the off-centered edge, users who aren't familiar with it, will experience strong clockwise steering. To attenuate steering, it's common to rebalance friction between both sides. As the left side offers low friction, the edge may get a higher angle. The right side a lower one. Further, extra thinning at the right can be done, and make the bevel form a continuous arc with the convex right face, ending at a lower angle. So, you get e.g. a right angle ending at some 10-12°, while the left one, kept straight, at 15-20°.

Like this? The right one is with the resistance correction.

 

[Benuser]

View attachment 351184
Like this? The right one is with the resistance correction.

That's about what I meant. The straight left bevel is very small. I should add, that over time one gets used to steering, and compensating for it by very slightly turning the wrist clockwise. In that case the need for the correction with the edge becomes less pressing. If sharpening for myself I now convex and thin the left side as well — still ending at the much higher angle. It's quite a personal thing. Loosing the grip helps a lot, by the way. The craziest steering I've seen was by people fresh from our culinary schools here in the Netherlands where they learned a 'firm' grip with there Wüsthof or worse, holding it strictly perpendicular. Give them a simple Misono and it steers like crazy. With a loose grip and a little use you may cut straight with a honesuki or hankotsu, without even thinking about it.

 

[Benuser]

View attachment 351184
Like this? The right one is with the resistance correction.

You inverted the sides. Seen from the choil, edge upward, the left side should show the blade's right side. The right side as defined as when you handle the knife, edge down. Usually with Japanese knives the side with the kanji.

 

[Benuser]

I'm well aware this all seems a bit confusing. Don't worry. After a while it becomes rather simple. The right side is where the cut produce falls — or sticks. That's the reason to give it its convexity.

 

[Delat]

This photo/knife is a good example of asymmetry. You can see the core steel is offset to the right in the photo (left side in use). This leaves more cladding on the right side (in use) for convexity, which you can see in the photo - the left side in the photo is gently curved while the right side is almost vertical.

I never actually noticed steering with this knife OOTB but I sharpened it at 10/20 anyway for fun. The yoshikane in the photo also looks asymmetric to me - the right side in the photo actually looks almost concave as it approaches the edge.

 

[aporigine]

Tried lots of knives with similar looking grind but very different performance, now I think it is more of a divine providence

Knives are a divisive subject.

 

[fortheloveofmoar]

What’s a left handed user?

 

[notaguest]

Thanks yall for clearing things up!
I'll post the final pics + exported as pdf here if anyone wants to use it.
In case anyone needs the original file (I abused Word for this) or feels something is wrong, feel free to dm!
PS: The yoshi arrived, and it is indeed convexed! Will upload a picture tomorrow probably.

 

[nightslayer]

Hello you learned folk. I'm slightly struggling to understand how the grind of my knife affects its everyday function. I have two issues with this knife; wedging and produce sticking to the blade. The sticking I can slightly understand as it is a laser and apparently sticking is what lasers do, since there's not much material to convex. I have also discovered that the blade was ground with a left-bias and I am right-handed. I unfortunately can't get rid of the knife as it was my first good knife given by a close friend, also I have scuffed the blade by learning to sharpen with it. Am I needlessly inflicting suffering on myself if I continue using the knife right-handed? Also what's the best way to restore an even finish to a knife blade?

It is the wedging I cannot understand, by all accounts a laser should go through food effortlessly, yet this thing gets stuck in anything thicker than half a carrot and I cannot comprehend why. It will sink into a butternut squash about halfway down the blade and get hopelessly stuck after that point (pulling it out is difficult). Have I screwed up with sharpening or is there something about the grind I'm not understanding?

 

[Barmoley]

Hello you learned folk. I'm slightly struggling to understand how the grind of my knife affects its everyday function. I have two issues with this knife; wedging and produce sticking to the blade. The sticking I can slightly understand as it is a laser and apparently sticking is what lasers do, since there's not much material to convex. I have also discovered that the blade was ground with a left-bias and I am right-handed. I unfortunately can't get rid of the knife as it was my first good knife given by a close friend, also I have scuffed the blade by learning to sharpen with it. Am I needlessly inflicting suffering on myself if I continue using the knife right-handed? Also what's the best way to restore an even finish to a knife blade?

It is the wedging I cannot understand, by all accounts a laser should go through food effortlessly, yet this thing gets stuck in anything thicker than half a carrot and I cannot comprehend why. It will sink into a butternut squash about halfway down the blade and get hopelessly stuck after that point (pulling it out is difficult). Have I screwed up with sharpening or is there something about the grind I'm not understanding?

Does it crack carrots? What you are experiencing with wedging might not strictly speaking be wedging but a result of friction/suction, surface sticking and when enough of it touches what you cut it gets stuck. How polished is the blade?

 

[M1k3]

Hello you learned folk. I'm slightly struggling to understand how the grind of my knife affects its everyday function. I have two issues with this knife; wedging and produce sticking to the blade. The sticking I can slightly understand as it is a laser and apparently sticking is what lasers do, since there's not much material to convex. I have also discovered that the blade was ground with a left-bias and I am right-handed. I unfortunately can't get rid of the knife as it was my first good knife given by a close friend, also I have scuffed the blade by learning to sharpen with it. Am I needlessly inflicting suffering on myself if I continue using the knife right-handed? Also what's the best way to restore an even finish to a knife blade?

It is the wedging I cannot understand, by all accounts a laser should go through food effortlessly, yet this thing gets stuck in anything thicker than half a carrot and I cannot comprehend why. It will sink into a butternut squash about halfway down the blade and get hopelessly stuck after that point (pulling it out is difficult). Have I screwed up with sharpening or is there something about the grind I'm not understanding?

Flat bevels.

Why?

Because friction. 2 flat surfaces create a lot of friction and suction. If the bevels are convex, there's way less surface area for the produce to stick to and create friction.

 

[nightslayer]

Does it crack carrots? What you are experiencing with wedging might not strictly speaking be wedging but a result of friction/suction, surface sticking and when enough of it touches what you cut it gets stuck. How polished is the blade?

Slightly..? I.e. my usual is pull the blade across, it goes halfway through, then I have to press on the spine to get it all the way through and the last quarter/fifth or so usually cracks. I get less of an issue if taking slices off a carrot (i.e. the intermediate stage of a julienne, rather than cutting it in half). But this sticking also happens with softer produce (think aubergines) so that made me think maybe it's not wedging as you say!

Blade has got a hairline finish on the stainless cladding which I've scuffed with amateur sharpening..

@M1k3 is there anything that I could do about the bevels to reduce this issue? Seems odd to me that Wakui would grind something which is so user-unfriendly! I just assumed it was my poor sharpening that messed up the knife somehow. I have a shibata that doesn't seem to stick in the same way and that has even less material behind the edge than this does.