Lowest Possible Edge Angle?

BluntCut MetalWorks

BluntCut MetalWorks

Knifemaker / Craftsman / Service Provider
Joined
Apr 28, 2012
Messages
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Question is about lower limit of edge angle with sharp/strong-enough apex, not about sharpness (apex radius). No micro bevel, convex, etc.. hence as flat/true V angle as reasonable

This edge must/still able to smoothly slices phonebook paper and splits orange/apple/(pineapple a bonus) when dropping on it from 24-30" height

E.g. Razor&Surgical edge angle are around 15-20 degrees (7.5-10dps)
 
There are probably 20 major parameters that would affect that. No real answer can be given.
 
Lots of factors at play. Knife grinders Australia has a small book on deburring that talks about the lower limit of stable apexes being 12 degrees perside. They mostly work on kitchen knives. In bushcraft maybe 14 dps but you’re giving up a lot of durability. I personally like 18dps it strikes a nice balance.
 
Not what you are asking for, but I hand sharpen on stones for final edge, so convex.

The way I was taught. The way that comes natural to me. The way that I do it, I've tried to measure my approach and angle of attack with a digital protractor, and it seems like I hold around 12 degrees per side.
Which explains why the knives cut so good. and explains why some steels (like 3V recently) seem like Meh/not great to me. I'm having less success with steels that don't support strong, fine, thin edges.
 
Thanks for your comments.

Rephrase my question of 'Possible...' - Using whichever best knife steel(material & ht), can it support 5dps or less edge? Given this edge passes tasks/tests mentioned above.

Obviously this type of edge is more or less a novelty. Did you or know anyone produced edge with angle near the lower limit of steel capability? I know, sub 5dps edge is possible.
 
I think it's more difficult to get single digit degrees per side than people realize.

There's a lot of convexity that's not being measured or accounted for making it impossible to discuss on the Internet unless a picture of the angle reflection with a laser goinometer is shared.


Usually most folks are closer to 20dps at the actual apex as the edge bevel convexes from the shoulder to the tip over the apex.

Which is why we run into
"mY 10dPs Is SuPeR tOuGh"

Well, not if the convexity and microconvexity is removed.


I found 6 dps is the limit of the BESS tester. I find angles tested near that dps and lower will buckle under the test media.

z34MM61.jpeg

6zFN9Em.png

NATNxaX.jpeg
 
DeadboxHero said:
I think it's more difficult to get single digit degrees per side than people realize.

There's a lot of convexity that's not being measured or accounted for making it impossible to discuss on the Internet unless a picture of the angle reflection with a laser goinometer is shared.


Usually most folks are closer to 20dps at the actual apex as the edge bevel convexes from the shoulder to the tip over the apex.

Which is why we run into
"mY 10dPs Is SuPeR tOuGh"

Well, not if the convexity and microconvexity is removed.


I found 6 dps is the limit of the BESS tester. I find angles tested near that dps and lower will buckle under the test media.

z34MM61.jpeg

6zFN9Em.png

NATNxaX.jpeg
Click to expand...
Wow, I can't imagine how slick that thing must cut???
 
After 800 grit belt zero-ffg sub 5dps edge on grinder and now I am quite bored(takes too long and not done) at flattening using a 1K grit diamond plate.

Dropped from 30" height - Lemon seeds micro-rippled WIP edge - either from edge too thin and or wired edge. Cleaned up edge now slices phonebook paper but with some noise instead of whisper.

f5OCBQ1.jpg



Edit: I'll try to take a closeup/macro pic of the edge - naked-eye it's quite flat but nifty sure can't get rid of subtle convexity
 
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TFt4zlQ.jpeg


Here it is an example of microconvexing at the apex.

From a macro view this edge would appear to be an 18° per side bevel.

However, under the microscope we can see more convexity at the apex which can also be picked up in the laser goniometer and measures ~28°per side.

So, if somebody uses this edge as an example of an 18dps, the durability will behave more like a 28dps edge.
 
DeadboxHero said:
TFt4zlQ.jpeg


Here it is an example of microconvexing at the apex.

From a macro view this edge would appear to be an 18° per side bevel.

However, under the microscope we can see more convexity at the apex which can also be picked up in the laser goniometer and measures ~28°per side.

So, if somebody uses this edge as an example of an 18dps, the durability will behave more like a 28dps edge.
Click to expand...
I’m assuming a guided sharpener would result in less micro convexity
 
Thescrawnylumberjack said:
I’m assuming a guided sharpener would result in less micro convexity
Click to expand...
That thin would always bend the tip and create a wire until it breaks of and had to start over. So the sharpener has to be firm and straight and the tip has to be supported. Only in a lab. And that edge goes too fast.
It's better to thin the edge and sharpen with a useful angle. Maybe go down to 0.05mm before sharpening and sharpen to 10-12dps convex. Microconvex would be probably 15-ish so it's kinda durable in good hands.
 
DeadboxHero said:
I think it's more difficult to get single digit degrees per side than people realize.

There's a lot of convexity that's not being measured or accounted for making it impossible to discuss on the Internet unless a picture of the angle reflection with a laser goinometer is shared.


Usually most folks are closer to 20dps at the actual apex as the edge bevel convexes from the shoulder to the tip over the apex.

Which is why we run into
"mY 10dPs Is SuPeR tOuGh"

Well, not if the convexity and microconvexity is removed.


I found 6 dps is the limit of the BESS tester. I find angles tested near that dps and lower will buckle under the test media.

z34MM61.jpeg

6zFN9Em.png

NATNxaX.jpeg
Click to expand...

Out there on the frontier.
 
OT - I discovered a new catalog to test sharpness, recently, that really, really doesn't like to cut. It's the "Sportsman's Guide Spring Master 2024".
If you have one, try it. If you think you are sharp, get one and try it. I can cut phonebook and other catalogs all day long. This one is challenging.
 
From scratch pattern - very little convexity at edge. Edge was damaged from lemon seeds. Face of the blade (bevel) lay flat on 1000 grit diamond plate and metallic bond 8K CBN plate(try to de-wire).

WZ8Fs1X.jpg


Also from previous edge pic - a little trigonometry - edge angle is sub 4dps.

Edit: rescaled DBH/Shawn's pic above to 500 microns

TFt4zlQ.jpeg

Convexity is clearly seen...
 
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I bet a buck that if you microbevel it only 0.2mm@10dps slight convex, it will cut better. Reasoning is that 3dps is too flexible and there is a loss of force at impact because of the initial wiggle and it would prevent any rolling. Choosing steel with more compression strength is advisable.
 
JoeBusic said:
I bet a buck that if you microbevel it only 0.2mm@10dps slight convex, it will cut better. Reasoning is that 3dps is too flexible and there is a loss of force at impact because of the initial wiggle and it would prevent any rolling. Choosing steel with more compression strength is advisable.
Click to expand...
Easy win - here is a buck :)

Perhaps this video adds more context about my research. Same (ht, oven/batch) 64rc O1 at 20 dps doing something which I didn't seen done before
 
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