How sharp is sharp?

DeadboxHero said:
Alright I have to know,

Why do high vanadium steels work better with a coarse finish?

Whats the mechanism involved?
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Because vanadium carbides are very hard, and the finer grit you go the longer it takes to actually cut through the carbides to achieve that grit finish uniformly along the full length of the edge. This is assuming doing it by hand because anything with power sharpening equipment can be done much, much more quickly. To achieve a "uniform" (obviously not perfect) edge you have to cut through the carbides and not tear them out. Even with diamonds this can take some time when done by hand depending on the amount of material that needs to be removed. However, if the sharpening media is too coarse you can end up with carbide tear out because the carbides aren't abraded they're simply removed from the steel matrix. It's far easier to abrade the steel matrix than to wear down the vanadium carbides.
 
HeavyHanded said:
I have no solid idea on this. Ankerson's testing seems to show a clear correlation between (all else being equal) a rougher finish on super steels and edge longevity cutting Manila. This does not mean they cannot be taken to a bright finish and still give good performance, just that they seem to run far longer when started at a lower finish. It is also far easier to reliably achieve.

For D2 with the larger carbides, I find the RC plays a huge role (as it seems to with most steels, but especially D2). My Eskabar just doesn't run for long at higher polish, while my BCMW D2 takes a screaming edge at brighter finish.
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Edge retention has to do with the material being cut. If you aren't cutting material similar to manila then using manila as a basis for determining edge retention makes absolutely no sense and making edge retention claims without referencing geometry yields biased results.

At lower grit the blade will probably experience carbide tear out and at some point will "self sharpen" due to this. It all depends on the material being cut and the means of blunting, whether through slow wear, impact, etc.
 
Thanks to all for this great discussion - why I keep hanging out on the BF :thumbup:
 
Fanglekai said:
Edge retention has to do with the material being cut. If you aren't cutting material similar to manila then using manila as a basis for determining edge retention makes absolutely no sense and making edge retention claims without referencing geometry yields biased results.

At lower grit the blade will probably experience carbide tear out and at some point will "self sharpen" due to this. It all depends on the material being cut and the means of blunting, whether through slow wear, impact, etc.
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That's why I included the "all else being equal". When the geometry stays the same and the edge finish is changed, there are changes in retention based on cut strategy. And yes, cutting one type of material to get a baseline for retention is somewhat limiting, so is using any other singular material yet we have to start somewhere. Manila is also a readily available material that can be bought the world over.

Am not sure why lower grit values would encourage greater carbide tear out than a finer finish, I would suspect the carbides will have greater mechanical anchoring in a rougher finish, but may be absolutely no difference in this respect - at least with smaller carbides. At the least, the lower finish will allow greater surface area of carbides to get in on the cutting - distributing wear over a larger area. I would fully anticipate greater force needed to execute a press cut with this strategy, but considerably less when used with a draw.
 
Jens Schuetz said:
Would be cool to know how exactly you sharpen your D2 Eskabar since I got one too.
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I've used all manner of abrasive from SiC wet/dry to diamond plates, to Norton waterstones. The one constant I come across is the finer finish seems to degrade rapidly back to a lower level of aggressive cutting and stay that way for a long time. Stopping at a lower finish seems to produce much greater longevity and less maintenance. I normally go no higher than a 4k Norton or 600 grit wet/dry, or a fine DMT.

For going to a finer finish I use diamond lapping films and avoid stropping on anything with noticeable give.
 
HeavyHanded said:
I've used all manner of abrasive from SiC wet/dry to diamond plates, to Norton waterstones. The one constant I come across is the finer finish seems to degrade rapidly back to a lower level of aggressive cutting and stay that way for a long time. Stopping at a lower finish seems to produce much greater longevity and less maintenance. I normally go no higher than a 4k Norton or 600 grit wet/dry, or a fine DMT.

For going to a finer finish I use diamond lapping films and avoid stropping on anything with noticeable give.
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Thank you for taking the time.
So far I only sharpened everything up to 1000 grit on the edge apex pro. The next time with that knife I'll skip that last grit and see what happens.
Thank you!

BTW I just read the BK24 (D2 Eskabar) is being discontinued. :-o
 
Just wondering... would it be considered sharper if instead of curling a hair into two, it cuts it in half the second you start pulling on it no matter what trick or type of hair it is
 
nick_30 said:
Just wondering... would it be considered sharper if instead of curling a hair into two, it cuts it in half the second you start pulling on it no matter what trick or type of hair it is
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I think so yes, might be HH5, the ultimate in sharpness

can you cut arm hair without touching the skin?

can you do a push cut on newspaper of phonebook paper at 90 degrees to the paper, with no tilt or rotation to the left/right/up/down?
 
That was achieved long time ago. It is at a hole new level now from the .01m cbn. That's cool if it is indeed at that level. Btw, what is hh5. I know it is a sintific measurement of sharpness but what does it mean?
 
as far as the coarser is better for high vanadium steels, i'm not sure but i keep most of my knives at or near 2k at least and sometimes 4k always followed by a light stropping with diamond paste on leather...cutting involves cardboard, light plastics, sometimes cloth, and some field dressing/food prep when I am priveleged enough to make it down south to hunt...

steels used are 3v, 4v, 20cv and m4-maybe these are not super high vanadium but they have enough to qualify. i guess my point is that i have not noticed any problems with my edges even though 2-4k is refined compared to say 600.

i will definitely try a coarser edge next time though because i would like to know.

what a good thread this is!
 
EdgePal said:
A edge, on any edged tool, shall only be as sharp as it need to be for its purpouse. Not sharper then that - in my opinion.

If you are in a competition about the sharpest edge possible - the edge shall be as sharp as possible.

If you sharpen your hunting knife to razor knife sharpness - you have change your hunting knife purpuse to a razor knife. You cannot use it as a hunting knife any more. It is to sharp.

The small U shape on the edge close to the handle can kill you. If you shall cut your self free from a fishing net in cold water, the fishing ner strings fasten in that U all the time - and time is just what you dont have in that situation...

An edge, in my mind and experiance, shall only be as sharp it need to be for its purpouse - and the sharpness must allways be in balance with needed retention - that balance makes that you also can use your knife long time before you must sharpen it again.

If your knife are to sharp for its purpouse - it will be dull fast...

Thomas
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This quote is going to hang on my grinding room wall. Thanks, Thomas.
 
Cleanly slicing newsprint or phonebook paper all the way from edge to edge is good enough for me. It usually means clean apex with no burrs. If left slighty toothy it should slice toilet paper too. I like the aggressive slicing edge that medium grit diamonds and silicon carbide abrasive paper produce.
 
DeadboxHero said:
The sharper the better.

A good clean apex is sharp at any geometry.

Its the geometry that is task specific.
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Agreed. A 25-30 degree (per side) sharpened axe can still shave hair if sharpened properly. It's geometry simply lends itself to being more durable for cutting down trees. Yet a 17 degree single bevel Sushi knife with Urasuki will fail to shave hairs if the edge is not sharpened properly.
 
pathwinder14 said:
Agreed. A 25-30 degree (per side) sharpened axe can still shave hair if sharpened properly. It's geometry simply lends itself to being more durable for cutting down trees. Yet a 17 degree single bevel Sushi knife with Urasuki will fail to shave hairs if the edge is not sharpened properly.
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Hi,
What I read on the internet, 25-30 degrees isn't for felling trees, maybe a splitting maul for splitting rounds :)
 
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