Argument against flat grinds

He is entitled to his opinion, and if you agree, you are free to buy his knives.

It does explain why all my Bark Rivers have convex edges.

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kobold said:
That has more to do with the cost of production. The reason so few companies do convex edges is that it is not easy to do. I can remember only Fallkniven ATM.
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Not true, it's not hard for a maker, since it's done with a belt.
 
brownshoe said:
Not true, it's not hard for a maker, since it's done with a belt.
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If you go to the first page and watch the video that started this thread you will hear that the first step BRKT does is making the stock FFG. This is the point most other companies call it a day.
But it is only then when they start to convex, which is a two step process, and then they finalize by blending. These three extra steps amount to a significant cost increase relative to FFG manufacturers. Years ago BRKT spent $100K/year on abrasives alone. Today it should be more.
The real cost increase however, comes ofc from the man-hours needed for convexing all the FFG blanks. Don't forget to factor in the extra training hours needed either. I bet, creating a FFG requires way less skill at the grinder than making even the smallest and simplest convex blades. And it shouldn't go without saying, that a more skilled workforce deserves a better pay.
 
When I make knives without secondary bevels that have what people now are calling "zero grinds" I can't just run it on a belt sander and then heat treat the knife. Because the geometry is too thin to survive a heat treatment. So I have to complete 90% of the grinding and filing before heat treatment. Then the edge has to be left as thick as a dime. At this point of the production stage is where 99% of companies add the secondary bevel, post heat treat. But instead of grinding a quick secondary bevel. I then take the tempered knife and take it to the whetstones, which then takes 1-2 hours of hand sharpening to reduce the dime thick edge until it has thinned out to a zero grind.

If you try and take your hard blade back to a belt sander and grind off a zero bevel all the way to the edge, with how thin the stock is there it will burn and overheat. You can manage a scandi grind with thick stock if you are careful not to burn it. But you aren't taking a 1.5mm thick blade with a zero grind down to the absolute edge on a belt sander. it's too paper thin. I have to do all of mine by hand with whetstones.
 
I don't care if a blade is FFG, convex, scandi, or concave, after a few minutes of me freehand sharpening one of my knives it turns into my custom SNAFU grind which I could describe and show pics but then you all would steal my idea.

But my knives cut soft butter.
 
A knife is a wedge. The thinner the wedge, the less force required to cut. A thick wedge is strong, a thin wedge is weak.
A good knife is a balance between strengh and cutting ability.
This can be acheived by using straight lines or curves when forming the bevel and or cutting edge. Convex adds material and strength. Hollow removes material and strength. Straight lines are in the middle.
The variations and combinations are infinite.
Welcome to knifemaking....
 
Londinium Armoury said:
When I make knives without secondary bevels that have what people now are calling "zero grinds" I can't just run it on a belt sander and then heat treat the knife. Because the geometry is too thin to survive a heat treatment. So I have to complete 90% of the grinding and filing before heat treatment. Then the edge has to be left as thick as a dime. At this point of the production stage is where 99% of companies add the secondary bevel, post heat treat. But instead of grinding a quick secondary bevel. I then take the tempered knife and take it to the whetstones, which then takes 1-2 hours of hand sharpening to reduce the dime thick edge until it has thinned out to a zero grind.

If you try and take your hard blade back to a belt sander and grind off a zero bevel all the way to the edge, with how thin the stock is there it will burn and overheat. You can manage a scandi grind with thick stock if you are careful not to burn it. But you aren't taking a 1.5mm thick blade with a zero grind down to the absolute edge on a belt sander. it's too paper thin. I have to do all of mine by hand with whetstones.
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You absolutley can grind a zero grind post heat treat on the belt grinder. Even with thin stock. Just have to use fresh abrasives.

Honestly the far greater danger than burning is an overgrind
 
Nick-D said:
You absolutley can grind a zero grind post heat treat on the belt grinder. Even with thin stock. Just have to use fresh abrasives.

Honestly the far greater danger than burning is an overgrind
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I don't like risking it on the new batch of knives i'm currently doing. they are 1.5mm and 2mm thick at the spine. The tips are literally paper thin at the edge, it will turn blue just from looking at the belt. It will work when making thick BTE knives, like Spyderco Chapparel thickness and above, but you go down below opinel geometry and it's just so easy to ruin the blade. It's like putting a sheet of paper on the grinder, blink at it will vanish.
MAybe if I used big metal jigs or magnets to soak up some of the heat. But freehand grinding a 1.5mm zero grind down to the edge, it's just asking for trouble.
 
Londinium Armoury said:
I don't like risking it on the new batch of knives i'm currently doing. they are 1.5mm and 2mm thick at the spine. The tips are literally paper thin at the edge, it will turn blue just from looking at the belt. It will work when making thick BTE knives, like Spyderco Chapparel thickness and above, but you go down below opinel geometry and it's just so easy to ruin the blade. It's like putting a sheet of paper on the grinder, blink at it will vanish.
MAybe if I used big metal jigs or magnets to soak up some of the heat. But freehand grinding a 1.5mm zero grind down to the edge, it's just asking for trouble.
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Honestly it's not bad man. Most my stock is 2mm or under and I take pretty much everything to zero (or very close to it). I take it to about 15 thou and convex it in on a leather backed platen. The last few thou may get a tickle on the stones or disc but this only takes a few minutes.
 
Londinium Armoury said:
I don't like risking it on the new batch of knives i'm currently doing. they are 1.5mm and 2mm thick at the spine. The tips are literally paper thin at the edge, it will turn blue just from looking at the belt. It will work when making thick BTE knives, like Spyderco Chapparel thickness and above, but you go down below opinel geometry and it's just so easy to ruin the blade. It's like putting a sheet of paper on the grinder, blink at it will vanish.
MAybe if I used big metal jigs or magnets to soak up some of the heat. But freehand grinding a 1.5mm zero grind down to the edge, it's just asking for trouble.
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Nick-D said:
Honestly it's not bad man. Most my stock is 2mm or under and I take pretty much everything to zero (or very close to it). I take it to about 15 thou and convex it in on a leather backed platen. The last few thou may get a tickle on the stones or disc but this only takes a few minutes.
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Guys, some extra info on powered sharpening in case you haven't seen it: https://knifesteelnerds.com/2019/04/08/does-sharpening-with-a-grinder-ruin-your-edge/
 
brownshoe said:
I have a Sunfish Forge with a flat grind & a convex edge. It's O1 at 61Rc and it holds an edge better than a flat grind. Not sure if its the grind, the steel, the edge or all 3. The maker, Don Hanson, said it was all 3 :) The knife was made for a truck driver to cut belts, hoses, tires...It works great.

Most people don't like a convex grind because they don't know how to sharpen it and maintain the edge. I do as Don told me 400-600 grti sandpaper on leather or cardboard. I've had it for many years and never put it on a stone.
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I would be honored to have a fixed blade made by Butch...preferably 3.25 in blade, 7.25" OAL, thin stock for casual use! but, he's a busy guy these days.
 
Nick-D said:
Honestly it's not bad man. Most my stock is 2mm or under and I take pretty much everything to zero (or very close to it). I take it to about 15 thou and convex it in on a leather backed platen. The last few thou may get a tickle on the stones or disc but this only takes a few minutes.
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That I am fine with, I have done quite a few convex knives like that. It's fine if you are just going to blend and apex it appleseed style. But when i'm trying to go for a thin V grind zero ground it's not the same. Because I need to put the entire flat of the knife to the belt and that is just too aggressive at that thin geometry. I have no issues convexing an edge and bleding it to the apex, but that only requires me to kiss the belt with a small portion of the steel at a time. If I want 100% flat V grind akin to Japanese zero ground geometry, I can't do the last 5-10% with machines. That's why the Japanese use giant industrial water wheels to grind their thin zero ground knives. They don't use 2x72 belts, they use 4-6 ft waterwheels laid sideways.
If using a 2x72 was efficient at producing such knives the Japanese would save money and adopt them. They use the giant waterwheels for a reason.
 
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Boattale said:
Pretty sure this is a convex blade. And I am here to tell you it is SHARP.


View attachment 1626525
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And then today, I decided to put a simple leather lanyard on it and the fargin bastage bit me right on the pad of my thumb. Took only the slightest bit of an error. I hate that POS non fitting non retaining sheath that BRK provides. A proper sheath is on the way made by Harry Savage. Had the knife been in that sheath, my thumb would not be wearing a bandaid.

I usually only cut myself prepping food. Done some good ones that way. Carpal tunnel and numb clumsy fingers will do it for you.
 
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Londinium Armoury said:
That I am fine with, I have done quite a few convex knives like that. It's fine if you are just going to blend and apex it appleseed style. But when i'm trying to go for a thin V grind zero ground it's not the same. Because I need to put the entire flat of the knife to the belt and that is just too aggressive at that thin geometry. I have no issues convexing an edge and bleding it to the apex, but that only requires me to kiss the belt with a small portion of the steel at a time. If I want 100% flat V grind akin to Japanese zero ground geometry, I can't do the last 5-10% with machines. That's why the Japanese use giant industrial water wheels to grind their thin zero ground knives. They don't use 2x72 belts, they use 4-6 ft waterwheels laid sideways.
If using a 2x72 was efficient at producing such knives the Japanese would save money and adopt them. They use the giant waterwheels for a reason.
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I've also ground ffg this way, although I prefer some convex for food release. Most Japanese knives aren't a ffg anyway usually a compound.

Do you have a variable speed grinder?

At the end of the day its your process and your time, but you absolutely can save some time and get that knife safely much closer to zero before hitting the stones and save yourself hours of your life.

The Japanese culture is interesting in that they don't always choose to do things the fastest or most efficient way. Its one of the reasons they make such excellent artisinal products.
 
Well, one argument that I can think of against flat grinds is that as you sharpen, the BTE does get thicker. Though, in use, the secondary/edge bevel just gets wider and I don't think there is that much of an impact on cutting performance. As far as EDC use, I think CRK's style of hollow grind makes sense since there's a straight section of the primary bevel where the BTE remains constant. Main issue with that is the need for precision machining. I think hand grinding a knife consistently like that would require some serious skill and, likely, a special platen.

As far as "they [blades with a flat secondary/edge bevel] do not hold an edge," I thought that was categorically false (it's not even a defensible opinion). Isn't there already data (CATRA or "use" testing [rope cutting]) that as the DPS gets more acute, the edge retention is higher? E.G. S35VN with a 15 DPS will out cut itself with a 20 DPS, everything else all the same (BTE doesn't seem to have as great of an effect on edge retention as DPS of the edge bevel, though, obviously, a thinner BTE will feel better in use). Most of the the edge testing that's available uses knives with a secondary/edge bevel (at least, that's what it seems like to me, correct me if I'm wrong). And, yes, I understand that for some steels that have rather high carbide content (40%+), a more acute DPS can result in worse results since there really is no support for the shear volume of carbides and the edge can literally distingerate. However, for steel that have under a 20% carbide content, the lower DPS, higher edge retention still follows.

Also, the process of blending the primary and secondary bevel removes material. Wouldn't that technically reduce the edge cross section? Even the process that's described in the video (flat grinding first, convex an edge, then blend the the two together) would still have a thinner cross section than just flat grinding a primary bevel and setting the secondary/edge bevel to whatever. If they took the edge down to, let's say, 30 thou before convexing and blending an edge, they're removing a shoulder and hence material; the BTE will be lower than 30 thou. If they ground to 30 thou, then set a secondary bevel, the shoulder material is still there; the BTE should actually be a litter higher since the shoulder will be above the point where they ground to 30 thou.

While, the convexed edges on BRKTs are fine for use, other makers have shown that you can still maintain sufficient strength with thin BTE and have a secondary/edge bevel with no microbevel through proper material selection and treatment. I'll stick to those since the ease of maintenance and sharpening is real AND they do, in fact, hold an edge.
 
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