Argument against flat grinds

[Natlek]

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

If you do that way you will change the thickness of the spine and probably you will lose some width on edge side.It is impossible to convex V grind without to change dimension of blade .You can t insert convex inside V grind without to do that .
number three is you way ..........
Number one is right way to keep dimension same .........

 

[Londinium Armoury]

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 ...........

No you start at the edge and work back to the spine, havent you ever done a zero grind before without secondary bevel? I can show you demonstrations if you need assistance.

 

[shane45-1911]

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 ?

No, because if there was a better tool to operate with, the medical profession would be using it - or at least demanding it.

 

[tinfoil hat timmy]

see them sparks fly

sparks mean burning
☄

 

[Cobalt]

sparks mean burning
☄

 

[mb>]

sparks mean burning
☄

But if you’re good, you can identify the steel when it’s mislabeled by the color of the sparks.

 

[Natlek]

No you start at the edge and work back to the spine, havent you ever done a zero grind before without secondary bevel? I can show you demonstrations if you need assistance.

This is your words , right ?

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

Show me how would look your convex on this drawing , please .
You start with this and then you make it convex???

 

[Natlek]

@ Londinium Armoury
Let clear something here ........If we start with same piece of steel , full flat grind blade would always have thinner cross section then convex grind in same piece If we keep spine thickness same , always .So you can not regrind FFG in convex without to change dimension of blade ! Impossible mission !

 

[Londinium Armoury]

This is your words , right ?


Show me how would look your convex on this drawing , please .
You start with this and then you make it convex???

yes around 1mm thick at the edge, then you start again and apex the middle of the 1mm and begin grinding and blending all the way back, so there is a slight rounding and appleseeding as each degree is blended. It would not be an absolute straight V under a microscope up against a engineered flat surface, it would be blended as though it looks V to the naked eye at a glance..

 

[TC]

No, because if there was a better tool to operate with, the medical profession would be using it - or at least demanding it.

I believe Natlek is right on this (was going to post similar). Scalpels are single-use, disposable items. Their task (cutting soft tissue) is not particularly demanding. They are made in the cheapest way possible - take some thin flat stock and put an edge on it. (One of my clients makes high-end surgical instruments and also lower-end stuff like scalpels - I asked.)

Also, check out this take on scalpels (pretty much the same):

 

[Natlek]

yes around 1mm thick at the edge, then you start again and apex the middle of the 1mm and begin grinding and blending all the way back, so there is a slight rounding and appleseeding as each degree is blended. It would not be an absolute straight V under a microscope up against a engineered flat surface, it would be blended as though it looks V to the naked eye at a glance..

We don't seem to be on the same page Are you are talking about convexing just edge ?? But then you say .............blending all they way back ???
My friend , which part of my post you don t understand ? You can not modify full flat grind bevel in convex without changing major dimension of blade .Do you understand that ?
Here is your FLAT grind and the only possible way to make it convex is a red line !
But we are now deep off topic , this is other subject ............

 

[Richard338]

N Natlek what L Londinium Armoury is trying to describe is possible since I have done it many times. Your pictures have unrealistic proportion and make it difficult to demonstrate.
If you start with a flat grind going from spine to a relatively thick edge (say 0.04"), then it's possible using a taut slack belt to convex the lower part of the bevel to a fully sharp convex edge. At no time do you reach or grind near the spine. You do however "walk it up" a little to blend it. Analysis of the geometry of the bevel once completed would show that it starts flat at the spine and slowly becomes more convex towards the edge.

 

[Natlek]

N Natlek what L Londinium Armoury is trying to describe is possible since I have done it many times. Your pictures have unrealistic proportion and make it difficult to demonstrate.
If you start with a flat grind going from spine to a relatively thick edge (say 0.04"), then it's possible using a taut slack belt to convex the lower part of the bevel to a fully sharp convex edge. At no time do you reach or grind near the spine. You do however "walk it up" a little to blend it. Analysis of the geometry of the bevel once completed would show that it starts flat at the spine and slowly becomes more convex towards the edge.

I agree with that , to convex the lower part of the bevel .I thought we are talking about convex bevel from spine to edge ??
Something like this

 

[Londinium Armoury]

We don't seem to be on the same page Are you are talking about convexing just edge ?? But then you say .............blending all they way back ???
My friend , which part of my post you don t understand ? You can not modify full flat grind bevel in convex without changing major dimension of blade .Do you understand that ?
Here is your FLAT grind and the only possible way to make it convex is a red line !
But we are now deep off topic , this is other subject ............

I've got a batch of 7 honyaki knives to quench, If you don't understand what I have explained already then i can't help you,

 

[Richard338]

I agree with that , to convex the lower part of the bevel .I thought we are talking about convex bevel from spine to edge ??
Something like this

If the belt is loose or you aren't practiced at it, you may fairly abruptly convex only the lower part of the bevel. However, done correctly it is possible to chase it higher, blending up all the way towards the spine.

 

[Spears]

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

That does seem like a cool grind and I would certainly like to try one. If you got a maker or a recommendation, I'm all ears.

However, I'm not sure where you got the claim that doing a grind that way would be stronger than a double ground hollow with the same radius/same primary bevel curvature. The BTE would remain constant for the same distance up the width of the knife. Though, past that point, the thickness of the bevel will diverge to stock thickness faster on a double hollow because you have two radii going in opposite directions instead of one. In fact, because of the that, the primary bevel will end lower on a double hollow and you will maintain more stock width and have a wider flat section. This would make a single/chisel hollow weaker, not stronger because there would physically less material on a single/chisel hollow after the portion where the BTE remains constant compared to a double hollow.

My other main issues (and this is personal usage probably because I'm not familiar with wood chisels to begin with and chisel grinds in general) is not having a microbevel, or any bevel, on the flat. I just don't like having to mess with the entire flat bevel and messing with the finish to deburr. I know some knives have the flat hollowed out to make this task easier but it messes with my cutting as the cut itself tends to lean and follow the hollowed out portion.

 

[Cobalt]

N Natlek what L Londinium Armoury is trying to describe is possible since I have done it many times. Your pictures have unrealistic proportion and make it difficult to demonstrate.
If you start with a flat grind going from spine to a relatively thick edge (say 0.04"), then it's possible using a taut slack belt to convex the lower part of the bevel to a fully sharp convex edge. At no time do you reach or grind near the spine. You do however "walk it up" a little to blend it. Analysis of the geometry of the bevel once completed would show that it starts flat at the spine and slowly becomes more convex towards the edge.

That's what it seems like is being done by bark. However, that is not a true convex blade profile. That's just convex near the edge blended into a modified flat grind.

 

[Natlek]

That does seem like a cool grind and I would certainly like to try one. If you got a maker or a recommendation, I'm all ears.

However, I'm not sure where you got the claim that doing a grind that way would be stronger than a double ground hollow with the same radius/same primary bevel curvature. The BTE would remain constant for the same distance up the width of the knife. Though, past that point, the thickness of the bevel will diverge to stock thickness faster on a double hollow because you have two radii going in opposite directions instead of one. In fact, because of the that, the primary bevel will end lower on a double hollow and you will maintain more stock width and have a wider flat section. This would make a single/chisel hollow weaker, not stronger because there would physically less material on a single/chisel hollow after the portion where the BTE remains constant compared to a double hollow.

My other main issues (and this is personal usage probably because I'm not familiar with wood chisels to begin with and chisel grinds in general) is not having a microbevel, or any bevel, on the flat. I just don't like having to mess with the entire flat bevel and messing with the finish to deburr. I know some knives have the flat hollowed out to make this task easier but it messes with my cutting as the cut itself tends to lean and follow the hollowed out portion.

@ Mike Snody make knives like that one.
I should have expressed myself better......double hollow grind bevels with same height of grind like chisel one would be weaker, most likely unusable .

 

[Londinium Armoury]

Zero

https://imgur.com/a/cQYrZfS

Natlek you don't need to remove anything from the spine, just blend up to its level.
Here is diagram without your excessive matetial removal of the spine.

 

[Natlek]

That's what it seems like is being done by bark. However, that is not a true convex blade profile. That's just convex near the edge blended into a modified flat grind.

In my book that is Axe..............