Edge Geometry: Physics and Preferences

CapitalizedLiving

CapitalizedLiving

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I want to collect information about edge geometry for the purpose of design and furthering my general knowledge about blades. I'm no scientist but here is my take on the subject based on my experience:

I was just outside testing two knives, one had a full convex grind and the other had a full convex grind with a microbevel. The former cut with far less drag and held its edge with no problems. The latter felt a bit sticky and also held its edge with no problems. I have a general theory which was supported by this evening's tests, which is that (all other aspects considered equal) a grind with no microbevel has less material behind the edge than an edge with a microbevel, leading to less drag due to the reduction of friction from (a) less material and (b) the lack of a "shoulder" or angle that interrupts the transition of the cutting substrate from the edge to the body of the blade.

I see a lot of microbevels added to knives for the reason of added durability and the ease of sharpening using mechanical devices (ceramic rods positioned at exact angles, for instance). However, it is my opinion that the best possible compromise between minimized cutting friction and minimized edge deformation under stress of impact is a convex bevel with no microbevel. I've tried flat and hollow ground knives as well, both with and without microbevels, and feel that the convex grind with no microbevel presents the greatest number of advantages in edge holding, resistance to impact-induced deformation, and ease of maintenance when damage is incurred.

Now it's your turn - what edge geometry do you prefer, and what are the reasons behind your preference? The more technical your answer, the better for my purposes although you may bore other readers and possibly yourself as well. But it might just be worth it!
 
CapitalizedLiving said:
I want to collect information about edge geometry for the purpose of design and furthering my general knowledge about blades. I'm no scientist but here is my take on the subject based on my experience:

I was just outside testing two knives, one had a full convex grind and the other had a full convex grind with a microbevel. The former cut with far less drag and held its edge with no problems. The latter felt a bit sticky and also held its edge with no problems. I have a general theory which was supported by this evening's tests, which is that (all other aspects considered equal) a grind with no microbevel has less material behind the edge than an edge with a microbevel, leading to less drag due to the reduction of friction from (a) less material and (b) the lack of a "shoulder" or angle that interrupts the transition of the cutting substrate from the edge to the body of the blade.

I see a lot of microbevels added to knives for the reason of added durability and the ease of sharpening using mechanical devices (ceramic rods positioned at exact angles, for instance). However, it is my opinion that the best possible compromise between minimized cutting friction and minimized edge deformation under stress of impact is a convex bevel with no microbevel. I've tried flat and hollow ground knives as well, both with and without microbevels, and feel that the convex grind with no microbevel presents the greatest number of advantages in edge holding, resistance to impact-induced deformation, and ease of maintenance when damage is incurred.

Now it's your turn - what edge geometry do you prefer, and what are the reasons behind your preference? The more technical your answer, the better for my purposes although you may bore other readers and possibly yourself as well. But it might just be worth it!
Click to expand...

I agree, micro-bevels have no advantages over zero grinds, however, They do serve to reduce the amount of steel you lose with each sharpening. As for me, I like a Scandi grind. It has a big bevel that goes to a zero edge, and retains thickness for the majority of the blade while still leaving a nice taper that takes a crazy edge. (Plus it's really easy to sharpen. :thumbup: ) The closest knife I currently own to a Scandi is a Kabar, which has the Scandi style, but with a microbevel at the end. So yes, micro bevels are only good for knives that don't have a lot of vertical steel, that you have to resharpen a lot. Like the Buck 110.
 
I do like an edge that is thirty degrees inclusive, with a forty degree microbevel. I like this for the reason you stated, ease of sharpening. However a micro bevel also extends the life of your blade over time, as less metal is removed each time you sharpen, or touch the edge up. Lately if a knife comes with a good factory edge I just put a forty degree micro bevel on it. On my Elmax mule however I went thirty degrees inclusive. Just for testing ect. I am thinking about staying at thirty degrees inclusive for awhile. Just to try that out.
I got ninja'd by pootnanny :D.
 
I'm curious if both knives you tested had the same amount of material behind the cutting edge? And were the same in every other way except for what you have mentioned?

I'm in the testing phase myself, not totally sure what I like best, and obviously application is key. There must be a curve of some sort that represents when more mass is beneficial, and not a hindrance because of drag. So thin is good, but when is too thin? Obviously the medium being cut is of significance, after initial cut what does the material behave like.

I'm currently trying to see if I can discern a difference in convex vs. non convex...and...I'm marveling at the mystery (to me) of the scandi edge. Mainly in small wood cutting chores, vegetable slicing, and phonebook paper.
 
Thinner blades with lower angles cut better, that's about it. Friction coefficient goes with angle of forces, so reduce surface roughness and reduce your sharpening angle. A microbevel is an increased sharpening angle, it doesn't really matter if it is backed up by convex or straight grinds.
 
I prefer a thin blade with a thin grind with an acute edge with fairly steep microbevel.
What I like about this is that it cuts like a utility knife, it goes through cardboard like nothing, and if it ever chips or rolls, because it's so
thin behind the edge, it takes a very short amount of time to repair the damage.
 
hardheart said:
Thinner blades with lower angles cut better, that's about it. Friction coefficient goes with angle of forces, so reduce surface roughness and reduce your sharpening angle. A microbevel is an increased sharpening angle, it doesn't really matter if it is backed up by convex or straight grinds.
Click to expand...

And yes folks it is that simple no matter what you have heard to the contrary. :thumbup:

It's been proven time after time over the years so it's not new.
 
hardheart said:
Thinner blades with lower angles cut better, that's about it. Friction coefficient goes with angle of forces, so reduce surface roughness and reduce your sharpening angle. A microbevel is an increased sharpening angle, it doesn't really matter if it is backed up by convex or straight grinds.
Click to expand...

Thank you very much! And with that said, what are your preferences in edge geometry and why?
 
somewhere around 12-13 per side on my folders, because I am not a hard user, but still clumsy enough to damage the edge. Preference to full flat or high hollow grinds. I freehand sharpen, so edges mildly convex without trying. I can get up to 20 per side when I feel lazy/frustrated and don't want to work the entire bevel to remove some small damage.
 
hardheart said:
Thinner blades with lower angles cut better, that's about it. Friction coefficient goes with angle of forces, so reduce surface roughness and reduce your sharpening angle. A microbevel is an increased sharpening angle, it doesn't really matter if it is backed up by convex or straight grinds.
Click to expand...

Ankerson said:
And yes folks it is that simple no matter what you have heard to the contrary. :thumbup:

It's been proven time after time over the years so it's not new.
Click to expand...

Exactly this. :thumbup:

I generally like my knives as thin as is appropriate for my tasks, with about a 30 degree included angle to the edge. Full flat grinds are also my preference. I do convex the shoulders of my edges but from the standpoint of thinning the transitional zone of the edge more than for its specific geometry. The smooth transition does make it easier to gauge appropriate force application during the cut vs. a straight geometry due to the lack of a hard shoulder, in my experience, but that's a feature that improves MY cutting performance rather than that of the knife.
 
I like the way that high hollow grinds cut. I like to micro bevel my knives for ease of sharpening and longer life of the blades. I do not like convex blades because I can not get them as sharp as a V edge.
 
Aside from the geometries feeling different in use as they maneuver through cuts, they also feel different depending on the material being cut. Cutting cheese, carving wood, peeling an apple, et cetera. Personal preferences and techniques are what make the difference for our individual choices (aside from cutting techniques, maintenance techniques also play a role in our decisions).

Niether is absolutely better than the other. I have an assortment of different types of geometries, and I am still discovering what I like more for certain applications...

Its like Rock Paper Scissors, in my mind. (flat, hollow, convex)
 
Orion's Belt said:
I like the way that high hollow grinds cut. I like to micro bevel my knives for ease of sharpening and longer life of the blades. I do not like convex blades because I can not get them as sharp as a V edge.
Click to expand...

That just means you need more practice! :p I just sharpen my convexed knives like I normally would a V edge. The main benefit is the overall reduction of the shoulder. ;)

The Government said:
Aside from the geometries feeling different in use as they maneuver through cuts, they also feel different depending on the material being cut. Cutting cheese, carving wood, peeling an apple, et cetera. Personal preferences and techniques are what make the difference for our individual choices (aside from cutting techniques, maintenance techniques also play a role in our decisions).

Niether is absolutely better than the other. I have an assortment of different types of geometries, and I am still discovering what I like more for certain applications...

Its like Rock Paper Scissors, in my mind. (flat, hollow, convex)
Click to expand...

Yup! total agreement.
 
Some good info posted thus far. The only thing I would add is that really thin really sharp blades not only cut with less effort, they allow more control and I am able to preserve a delicate edge longer by making controlled cuts.

Its like they say a sharp knife is a safe knife...well, a thin delicate knife seems to hold up well if you use it appropriately, but I am not sure I would recommend it for everyone;)

As pointed out by others...there is no "right answer" but with some practice and experience, you will be able to determine what works best for you in *most* circumstances.
 
I prefer convex edges at around 10-17° per side, depending on the application and I especially like zero-grind convex blades. I don't use a micro bevel because I strop my knives all the time and feel it's easier to just keep on letting it stay convex. I don't use my knives for work anymore though, so I have the time to sharpen them when needed.
 
Edge geometry = cutting + bevel. Ignoring the theoretical 'apex' line.

So far, many good points on edge bevel.

What are your thoughts on cutting-edge geometry and failure mode?
Geometry such as: width, serrated level, tooth (shape+bevel+cutting edge), smoothness, etc..
Failure mode be: deformation, roll/fold, break/chip, work harden, etc..

To keep it simple, maybe we can skip other factors such as: steels/ht/tasks/..
 
I vary according to the knife and it's intended purposes. Thinner is always better, and I will often use a microbevel to prevent damage. I'm sure it comes at a sacrifice of cutting efficiency, but not that much for me. I'm not a big fan of zero edge scandis, their bevel is way too thick for my liking. Yes, you read that correctly. I like FFG or high flat, or high hollow for the primary grind. And very thin. Think Krein level of thin. That's where cutting starts getting fun. :D
 
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