Argument against flat grinds

[Londinium Armoury]

I grabbed something to show kobolds point about the brk process because it's similar to mine.
This knife was ffg and the edge left about a penny thick. Then the edge was zero blended from.spine to apex convex.
I tried to take a picture where the light glints on the apex. You can see where my ceramic rods touch it and leave marks from honing it. There is no secondary bevel set on it.
The ffg is the foundation or first stage of this process. Which can be done by robots or jigs, the next blending and comvexing stage has to be done freehand because tilting motion and rounding occurs where as a Jig can only run on rails straight unless you develop one with a pivoting frame.

Zero ground convex clip point Clay Tempered

https://imgur.com/a/cY6nNe0

This one is clay tempered 1095 using Yaki ire and Yaki modoshi

 

[brownshoe]

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.

Sorry, BRKT and it's staff has a long history of lying and telling half truths. A BRKT video justifying their prices is not really believable.

 

[singularity35]

So what are scandi grinds?

 

[Sonnydaze]

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. 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'll bet you produce some excellent blades....

 

[Londinium Armoury]

i'll bet you produce some excellent blades....

They are improving week by week, to a point where I now prefer to use my own knives over high end production knives.
Here's a scandi I made recently.
Jute Scandi

https://imgur.com/a/8PL9Zqw

 

[The Grendels]

I own a lot of different knives: different grinds, different blades, different steels, different designers, etc. What I can say is that I really like knives. That and it all comes down to right tool for the right job, because there isn't one knife that is perfect for every job and situation.

The perfect bushcraft knife for one person can be useless for the next person or less useful to the same person on a different day, because they use them differently to do different tasks. It depends where it's being used. I got my Joker Ember F (flat grind) just to balance out the kinds of grinds for my recent bushcraft knives, not because I don't like scandi grinds, but because I was already getting a puukko at the same time and had ordered in another scandi.

 

[A.L.]

Polished full flat convex blade is one of the most pleasing and efficient grinds for me as long as the blade stock is thin enough.

 

[Cobalt]

see them sparks fly

 

[kobold]

Another description of the convex that BRKT makes:

 

[Mikel_24]

I have only owned two bark rivers and I don't have them anymore, so I can't check them out. However, lets say you take a 1/4" thick, 2 inch wide blade and give it a full flat grind, then convex the edge. The only way to make that blade a full convex is to grind away a large amount of material from the edge. A flat ground blade is not as thick in any part of it's cross section as a convex blade. So that same blade might lose half an inch or more of it's width and it will lose the original edge. New edge would need to be put on it. Not sure why anyone would do that. But I am not a knife maker so....I guess I am missing something here.

What you state would be true... if you were to grind them flat in the first place to a zero edge. That is, full flat from spine to the apex... Then, if you want it convex, then you have to remove a LOT of steel. However, if you do your full flat grind but do not apex it (say you go from 7mm at the spine to 3mm at the edge area... then you have wiggle room to convex and blend those 3mm into zero...

At least that's how I understand it (and how I have made a couple knives like that myself).

Mikel

 

[Cobalt]

What you state would be true... if you were to grind them flat in the first place to a zero edge. That is, full flat from spine to the apex... Then, if you want it convex, then you have to remove a LOT of steel. However, if you do your full flat grind but do not apex it (say you go from 7mm at the spine to 3mm at the edge area... then you have wiggle room to convex and blend those 3mm into zero...

At least that's how I understand it (and how I have made a couple knives like that myself).

Mikel

Yeah, It was my confusion. I thought they were fully convexing the whole blade profile.
I think the last video explained a bit better than the first.

 

[herisson]

see them sparks fly

In my book, sparks flying is not good. I sharpen all knives way under 60 °C, when they get hot on my fingers I let them ly around for a while or dip them in ambient temperature water. I'm far from impressed by Bark River's marketing blurb. It's just that. If it works, great for Bark River. But it's mainly BS. Especially when sparks fly like that. I mean, I'm not just a hater, but look it up how (relatively) low temperatures can modify a heat treat. The scene in Seraphim Falls with the red heated Bowie knife is solid bullshit as well (even with low carbon steels, come on...).

 

[kobold]

Here is a video addressing those sparks at 5:25.

 

[herisson]

I call that "quick and dirty" and it makes sense, of course, from a professional point of view. But it's not "good".

 

[skyhorse]

We often discuss blade steel and grinds etc but imho when you get right down to the nut cuttin sharpening skills trumps all .

 

[Natlek]

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.

You should try chisel hollow grind .Stronger then double hollow grind thinner then FFG and BTE remains same long time .Winner !

 

[Natlek]

There is nothing wrong with convex grinds for certain uses. Yes, they typically hold an edge well when used for harder tasks. BUT.....

I do not agree with Mike saying they are "better" than a full flat grind. That is ridiculous. It depends what you are cutting. If you are doing general knife cutting stuff, or food prep, or heck - just whittling, you aren't going to find a better grind than FF (or arguably hollow ground). To say otherwise just shows either ignorance, or the total lack of desire to offer blades with more than one grind option.

I want my axe to be convex - but I have never in 50 years of owning a knife said "Jeez, this would cut a lot better if it was convex." Never. NEVER.

English is not my first language but I agree whit what he say in that video .Full flat grind without secondary edge wont hold edge at all , it will be too fragile.Next he say that FFG with secondary edge will hold edge much longer which is also correct .About convex.......If I understand the way they do convex , that is right way and that would cut like hell and will hold edge . I saw a lot of different convex blades, some well done, some not so good.
Here is how in Bark River grind convex blade as i understand it how he explain that .Drawing on left side would be Bark River , right side also convex but look and will cut like AXE ...Do it right and convex is best grind in my book .And one more thing , he is also right that cost and time to make that convex grind is much more then to grind full flat blade.
They grind first flat part which is red color and then they grind blue color part .......and grinding that blue part on slack/without backing behind/ belt is not funny at all , especially if it was steel full of carbide in question.

 

[Natlek]

Again, as I stated earlier.....never in 50 years of owning and using knives had I ever wished for a convex grind. NO convex grind ever cuts like a scalpel, or scalpels would have convex grinds.

Wait for it.........

Scalpels are FLAT GROUND.

Do you ever thought that scalpels are flat ground maybe just because it is easy and cheap way to grind and because it just meets the requirements for task ?

 

[Natlek]

That video is ridiculous, full flat grinds are fine and hold carbide no different than a convex edge.

“Those edges feel sharper; they’re not”

I don’t even know how to respond to such nonsense. That’s like ordering a bowl of soup at a restaurant and the waiter tells you “it may look like soup, but it’s actually a sandwich”.

You should watch that video again .He say that full flat grind will not hold carbide and he is right about that .Full flat grind without secondary edge would be too fragile . Then he say that full flat grind WITH secondary edge will HOLD edge MUCH longer which is correct .

 

[Natlek]

This knife was ffg and the edge left about a penny thick. Then the edge was zero blended from.spine to apex convex.

It is impossible to do that ! If you do that the spine will be thinner and you will lose a little width of blade from edge side ...........