best degree angle for a knife bevel

[Obsessed with Edges]

A little more clarification. With clamped or guided angle sharpeners the angle indicated is usually degrees per side. That means that if the OP is setting his sharpener at 25º and it's degrees per side, his inclusive bevel with be 50º inclusive. Which is thicker than an axe bevel.

In going back and reading what you'd quoted from my earlier post, I think I see why you added that. My attempt was a bit ambiguous. Thanks.

(I edited my earlier description slightly, hopefully in the pursuit of clarity... )


David

 

[rogerxd45]

i wasnt saying a 25dps is better i just figured i should post that even high end manufactures use angles in that range

correct me if im wrong but are you saying a 15dps edge will retain its edge longer then a 25dps? i thought the more obtuse angles hold their edge longer since there is more material

 

[Obsessed with Edges]

i wasnt saying a 25dps is better i just figured i should post that even high end manufactures use angles in that range

correct me if im wrong but are you saying a 15dps edge will retain its edge longer then a 25dps? i thought the more obtuse angles hold their edge longer since there is more material

Knowing you're asking Jason (and I respect and agree with his views on it), here's my take:

In most normal uses, the thinner geometry behind the apex is what makes it work better, even after the apex has dulled slightly. Buck Knives reduced their target edge spec to 13°-16° per side (26°-32° inclusive) for that very reason, after confirming better performance via CATRA sharpness testing. The apex still wears at the same rate, which is characteristic of the steel itself, not the geometry; but the thinner grind behind the apex will allow it to keep working longer. It can also be said that a thinner edge grind requires less force/pressure into the apex when cutting, which also helps to preserve the sharpness of the apex.

The ONLY thing working for a 40°+ inclusive edge is a perfectly-crisp apex. When that apex wears even slightly, either by dents/deformation or by abrasion, cutting performance drops off a cliff, because the backing geometry is so wide & blunt. A 30° inclusive edge and lower will still retain some cutting effectiveness in most normal uses, after a similar amount of wear at the apex, because the thinner grind behind the edge allows it. In essence, the cutting edge is just a 'wedge' after it dulls; the only thing left to make any difference in how it'll work is how wide or narrow that wedge is.

A wide-angled edge can definitely retain it's basic shape longer, being less susceptible to rolling or chipping. But by itself, the geometry (shape) of an edge that wide won't ever allow it to cut very well in the first place, and virtually not at all if the apex isn't always in perfect condition.

Manufacturers have long been very, very conservative with their edge grinds; I suspect it's due to their knowledge that a lot of people will essentially abuse it as a cutting tool (prying, 'screwdriver' use, etc). And assuming that sort of use, at least a very thick edge is less prone to severe damage (and subsequent warranty returns) caused by that abuse. Even if they put thicker edges on by design (and most do it accidentally), almost any modern steel or blade can do so much better, if actually used properly as a knife.


David

 

[chiral.grolim]

...The apex still wears at the same rate (which is characteristic of the steel itself, and not the geometry), but the thinner grind will allow it to keep working longer. It can also be said that a thinner edge grind requires less force/pressure into the apex when cutting, which also helps to preserve the sharpness of the apex...

I would add a couple quick things to David's post:

"The apex still wears at the same rate" he means that the same amount of material is worn away from the sides of the bevel-faces that form the apex, with the result of a widening apex-diameter (thickness of the very edge), but the edge with the larger apex-angle widens more rapidly, reducing its ability to penetrate and so cut effectively. Maybe the schematic of edge-angles below will help. Also, remember that the force/pressure required to complete a cut is due to an equal&opposite force from the material being cut. The force it takes to complete a cut is force being directed against your edge and bevels - wedging - the precise force that results in abrasion and edge deformation. By reducing the edge-angle you thin the blade and so reduce wedging-forces and thereby reduce abrasion and lateral stress on the apex - a thinner blade with sufficient strength and higher wear-resistance!

Now, there is a limit to how thin you make your edge before it folds/crumbles under the resistant forces being applied at the apex that depends on how you use your blade, i.e. what stresses you subject it to. A concrete jack-hammer bit sustains heavy forces to the apex and so requires a sturdy geometry and does not require a thin apex-diameter to keep working. But for comparison, most chainsaws and chipper-blades do benefit from a shaving-sharp apex, and many of those are ground at ~30-inclusive or 15-dps. Will your knife be subjected to greater or lesser stress than a chainsaw or gas-powered wood-chipper? But i would add to this that even hand-powered wood-planar blades, designed to maintain a razor's edge slicing thin curls of wood, are sharpened no lower than 15-dps, otherwise they suffer chipping and edge-wear beyond what is acceptable. So the same angle is used for heavy-force wood-cutting and low-force wood-cutting.

But angle is less important than edge-thickness. You can have an edge that is 25-dps and does last longer than an edge 15-dps and also cuts better! But you'd need the thickness behind that 25-dps edge to be much thinner (2-4X) to equalize the wedging-forces sustained by each, and remember that thinning the blade can compromise its integrity if taken too far or subjected to heavy stresses (a 2x decrease in thickness = 8x decrease in strength). The stresses against which a 15-dps apex would fail and a 25-dps apex would survive are limited... more limited than stresses against which a 25-dps edge that is ~2X thinner (to equalize cutting performance) would fail vs a 15-dps edge at normal thickness. With the stouter apex, you may gain some durability under specific conditions but you would lose in either cutting performance or overall strength... Is it worth the trade-off?

 

[Jason B.]

You gentleman have it covered.

 

[singularity35]

In going back and reading what you'd quoted from my earlier post, I think I see why you added that. My attempt was a bit ambiguous. Thanks.

(I edited my earlier description slightly, hopefully in the pursuit of clarity... )


David

David, it's very rare for me to to have something to add to your posts. It just happens I asked for the same information early on in my sharpening sojourn and at the time, I too, wanted an unambiguous answer.

Your posts are a wealth of information for the starting and the advanced sharpener.

i wasnt saying a 25dps is better i just figured i should post that even high end manufactures use angles in that range

correct me if im wrong but are you saying a 15dps edge will retain its edge longer then a 25dps? i thought the more obtuse angles hold their edge longer since there is more material

Yes, it sounds counter intuitive but it's really true. Check out Chiral's post. Personal experience and my own unscientific experimentation have convinced me of that.

Additionally, most modern knife steels will be more than capable of 15 dps angles. Even my $2 kitchen knives with mystery steel, do much better with 15 dps angles. I find that 20 dps is approaching impracticality because of poor performance and bad edge retention.

 

[n7titan]

I'm hoping going with 25% was best, rather than 30%, for this kind of metal. What say you?

Check out this thread, it will tell you all about angles, thickness, and slicing ability.
http://www.bladeforums.com/forums/s...-Insane-performance-boost-in-cutting-ability!

Personally I like to roughly do 20 dps ( I freehand so this is a guestimate) and gradually bring the angle down if I see that edge retention is good enough to take a slight hit for cutting ability.

 

[yepimonfire]

Knowing you're asking Jason (and I respect and agree with his views on it), here's my take:

In most normal uses, the thinner geometry behind the apex is what makes it work better, even after the apex has dulled slightly. Buck Knives reduced their target edge spec to 13°-16° per side (26°-32° inclusive) for that very reason, after confirming better performance via CATRA sharpness testing. The apex still wears at the same rate, which is characteristic of the steel itself, not the geometry; but the thinner grind behind the apex will allow it to keep working longer. It can also be said that a thinner edge grind requires less force/pressure into the apex when cutting, which also helps to preserve the sharpness of the apex.

The ONLY thing working for a 40°+ inclusive edge is a perfectly-crisp apex. When that apex wears even slightly, either by dents/deformation or by abrasion, cutting performance drops off a cliff, because the backing geometry is so wide & blunt. A 30° inclusive edge and lower will still retain some cutting effectiveness in most normal uses, after a similar amount of wear at the apex, because the thinner grind behind the edge allows it. In essence, the cutting edge is just a 'wedge' after it dulls; the only thing left to make any difference in how it'll work is how wide or narrow that wedge is.

A wide-angled edge can definitely retain it's basic shape longer, being less susceptible to rolling or chipping. But by itself, the geometry (shape) of an edge that wide won't ever allow it to cut very well in the first place, and virtually not at all if the apex isn't always in perfect condition.

Manufacturers have long been very, very conservative with their edge grinds; I suspect it's due to their knowledge that a lot of people will essentially abuse it as a cutting tool (prying, 'screwdriver' use, etc). And assuming that sort of use, at least a very thick edge is less prone to severe damage (and subsequent warranty returns) caused by that abuse. Even if they put thicker edges on by design (and most do it accidentally), almost any modern steel or blade can do so much better, if actually used properly as a knife.


David

I have several knives that have 20° per side bevels and several with 15° and I really haven't noticed a difference in cutting ability, the biggest difference comes from the primary grinds bevel. For example my ka bar mule has a 30° inclusive and my cold steel voyager xl has about 40° inclusive, the voyager cuts better because it's got thinner edge geometry. They're both made of the same steel and they both dull at about the same rate. I've also got a kobun that's about 40 inclusive with a thin blade and super thin hollow ground blade and that thing cuts like a straight razor.

I'm not saying there is no difference, but I haven't seen one large enough to warrant the time and effort to reprofile. At 25dps or 30dps that's when I start noticing some bluntness.

 

[Obsessed with Edges]

I have several knives that have 20° per side bevels and several with 15° and I really haven't noticed a difference in cutting ability, the biggest difference comes from the primary grinds bevel. For example my ka bar mule has a 30° inclusive and my cold steel voyager xl has about 40° inclusive, the voyager cuts better because it's got thinner edge geometry. They're both made of the same steel and they both dull at about the same rate. I've also got a kobun that's about 40 inclusive with a thin blade and super thin hollow ground blade and that thing cuts like a straight razor.

I'm not saying there is no difference, but I haven't seen one large enough to warrant the time and effort to reprofile. At 25dps or 30dps that's when I start noticing some bluntness.

Primary grind does help, as with a thin hollow grind as compared to a thicker flat grind. If wanting to compare edge geometry directly, the other variables need to be equalized or eliminated first. Use two knives with same blade thickness & primary grind, OR start with one thicker-ground blade at 40° inclusive, and then take it down to that 25°-30° range you mention. That's when the difference in cutting ease will stand out. I didn't understand what 'sharp' really meant, until making just such an effort with some of my thicker-bladed knives.


David

 

[singularity35]

Check out this thread, it will tell you all about angles, thickness, and slicing ability.
http://www.bladeforums.com/forums/s...-Insane-performance-boost-in-cutting-ability!

Personally I like to roughly do 20 dps ( I freehand so this is a guestimate) and gradually bring the angle down if I see that edge retention is good enough to take a slight hit for cutting ability.

Most modern steels will only exhibit better edge retention going from 20 dps to 15 dps. No downsides except the time to rebevel.

I have several knives that have 20° per side bevels and several with 15° and I really haven't noticed a difference in cutting ability, the biggest difference comes from the primary grinds bevel. For example my ka bar mule has a 30° inclusive and my cold steel voyager xl has about 40° inclusive, the voyager cuts better because it's got thinner edge geometry. They're both made of the same steel and they both dull at about the same rate. I've also got a kobun that's about 40 inclusive with a thin blade and super thin hollow ground blade and that thing cuts like a straight razor.

I'm not saying there is no difference, but I haven't seen one large enough to warrant the time and effort to reprofile. At 25dps or 30dps that's when I start noticing some bluntness.

I even put rubber bands on my sharpmaker rods to reduce the angle from 20 dps to around 17-18 dps to do a microbevel with. With the same amount of work, the more acute angle just feels noticeably(I notice anyway) more grabby and just gets hair whittling that much faster. It's probably a YMMV thing though.

 

[n7titan]

Most modern steels will only exhibit better edge retention going from 20 dps to 15 dps. No downsides except the time to rebevel.

Good to know.
It's hard to say what angles I'm actually using though, plus all of them have a slight convex due to sharpening inconsistencies. The primary bevel may be between 15-20, but the cutting edge may be 25 dps, no one knows.
I have to judge everything with use and decide which direction I want to take it whether thinner, more obtuse, more acute, etc.

Really though a working edge is easy, and my mistakes in sharpening mostly result in a slight convex which isn't bad at all.

 

[rogerxd45]

thanks for the explanations, when you put it that way it makes perfect sense. now I need to reprofile my zt0770 in m390 down to 15dps which isnt going to be fun. my spyderco in s110v took FOREVER to put a 15dps edge on it. hopefully the m390 wont be as bad.

 

[singularity35]

thanks for the explanations, when you put it that way it makes perfect sense. now I need to reprofile my zt0770 in m390 down to 15dps which isnt going to be fun. my spyderco in s110v took FOREVER to put a 15dps edge on it. hopefully the m390 wont be as bad.

When I thin down a bevel, I usually take a lot of breaks for maybe coffee or a snack. Avoiding exhaustion will pay dividends in the quality of your edge.

 

[rutcrazed]

Knowing you're asking Jason (and I respect and agree with his views on it), here's my take:

In most normal uses, the thinner geometry behind the apex is what makes it work better, even after the apex has dulled slightly. Buck Knives reduced their target edge spec to 13°-16° per side (26°-32° inclusive) for that very reason, after confirming better performance via CATRA sharpness testing. The apex still wears at the same rate, which is characteristic of the steel itself, not the geometry; but the thinner grind behind the apex will allow it to keep working longer. It can also be said that a thinner edge grind requires less force/pressure into the apex when cutting, which also helps to preserve the sharpness of the apex.

The ONLY thing working for a 40°+ inclusive edge is a perfectly-crisp apex. When that apex wears even slightly, either by dents/deformation or by abrasion, cutting performance drops off a cliff, because the backing geometry is so wide & blunt. A 30° inclusive edge and lower will still retain some cutting effectiveness in most normal uses, after a similar amount of wear at the apex, because the thinner grind behind the edge allows it. In essence, the cutting edge is just a 'wedge' after it dulls; the only thing left to make any difference in how it'll work is how wide or narrow that wedge is.

A wide-angled edge can definitely retain it's basic shape longer, being less susceptible to rolling or chipping. But by itself, the geometry (shape) of an edge that wide won't ever allow it to cut very well in the first place, and virtually not at all if the apex isn't always in perfect condition.

Manufacturers have long been very, very conservative with their edge grinds; I suspect it's due to their knowledge that a lot of people will essentially abuse it as a cutting tool (prying, 'screwdriver' use, etc). And assuming that sort of use, at least a very thick edge is less prone to severe damage (and subsequent warranty returns) caused by that abuse. Even if they put thicker edges on by design (and most do it accidentally), almost any modern steel or blade can do so much better, if actually used properly as a knife.


David

Thanks for the great explanation. I learned something and had a good laugh. The last sentence is priceless

 

[rogerxd45]

this thread has also motivated me to send my knives off to RazorEdge (he is a forum sponsor) for some work... ive heard nothing but good things
im going to send my spyderco manix 2 in s110v in for a regrind. The thinner blade should make it much sharper, and i plan on also having him take the edge down to 15dps.
everybody ive talked to says having a blade reground to be thinner makes a huge difference. I know i will be losing some overall toughness but thats not an issue as i dont abuse my knives at all. i would definitely say i baby them. im a chef and i learned long ago to treat your knives with great care and respect and how important it is to use the correct tool for a job (if your a Nascar driver you wouldnt take your track car off roading. The same thing goes for knives) , i would never use my knife to pry something

i just want to say thanks again for the detailed responses to my questions, you guys made it very easy to understand. im just glad i got that all cleared up.