Blade Height and Knife Geometry Questions

[bowler1]

Hi,
I am curious to hear what you think about the effects of blade height (just to be clear I am talking about the distance between the cutting edge and the spine) and what the purpose would be of a knife with more blade height than another.

The reason I ask is because I recently got turned onto Bark River knives and bought both a Gunny and a Bravo 1LT. I figure I probably don't need them both so will probably sell one and I am trying to figure out which to keep since I like them both.

But when I started to compare them closely that although the Bravo 1LT looks much bigger (handle size aside which is purely a matter of personal preference) I see that the blade thickness is not that much different on the two (the Bravo 1LT is a slight bit thicker) and that the blades are pretty close to the same length (3.85 I believe vs. 4.25). The biggest difference is the blade height or width. The Bravo 1 is significantly higher / wider, but the cutting edges are not that much different in length or shape.

So why the super wide blade on the Bravo 1 and what would be the advantages and disadvantages, given that the cutting edge and thickness are fairly similar? Why do some knives have super wide / high blades like skinning knives do?

My guesses are the following: I assume that the Bravo 1LT has a wide blade since it was derived from the Bravo 1 which is quite thick at about .25 inches. I assume that the super wide blade allowed for a more gradual taper down to a fine edge to make it a better cutter. I also assume the wider blade meant more steel and therefore strength. My suspiscion is that this width/height is not really as necessary on the LT version.

My assumption that between the Gunny and the Bravo 1LT that the greater width of the Bravo would probably be a bit better splitter for battoning and a bit stronger/stiffer. On the other hand it would seem that the wider blade moves the cutting edge farther away from the centerline of the hand and therefore reduces some leverage for shear cuts.

What other advantages / disadvantages would you see between the higher / wider blade of the Bravo LT vs the Gunny?

I have used both them a little but not much so I have some limited observations, but am interested in the design theory in general.

thanks and sorry for the long and geeky post.

Matt

 

[Insipid Moniker]

Greater blade height allows for a higher primary grind which, all other things being equal, will result in better cutting geometry.

The easiest way to imagine it is to draw a triangle that's 1" on all three sides, then draw one with a 1" base, but the other two sides are 5" long. Which profile do you think will cut better?

 

[bowler1]

Thanks for the reply. That was kind of what I thought. What would be the tradeoffs though I wonder? There is always a tradeoff. Maybe more drag when cutting...???

Interestingly enough, from the limited testing I have done so far, it seems that the Gunny Hunter slices and shaves fine curls a little better than the Bravo 1LT. On the other hand though, the Bravo LT will bit much deeper into a piece of wood with a hard shear cut.

Matt

 

[herisson]

A wide blade is great for gathering the minced meat / fish / vegetables from the board and dump them in the pot. My preference goes to slicing capacity so I will go wide and thin blade... This one is amazing :

However, forget woodcrafting and batoning, definitely.

 

[Twindog]

Greater blade height allows for a higher primary grind which, all other things being equal, will result in better cutting geometry.

The easiest way to imagine it is to draw a triangle that's 1" on all three sides, then draw one with a 1" base, but the other two sides are 5" long. Which profile do you think will cut better?

This is right, at least to a point. As Insipid says, a higher blade height "allows" for a thinner edge. However, a tall blade can still have a thick edge and a large edge angle, wasting the potential of the blade's geometry.

The three things that most determine how well a blade can slice are sharpness of the edge apex (a 0.5 micron wide apex cuts better than a 2 micron apex width), narrowness of the edge (0.006 inches at the edge shoulders will cut better than 0.030 inches at the shoulders) and acuteness of the edge bevel (15 dps cuts better than 20 dps). Taller blades have more potential to realize the second two.

 

[miso2]

For small knives with flat grind, a wider blade provides a greater area for cut media to bind and therefore suffers from greater fiction, resulting in poorer slicing capability than a narrower blade.
My reground Lionsteel Otnat with a narrow and acute primary grind and thin edge (0.005") seems cut better than Manly Wasp, of which blade is much wider with a little thicker edge (0.009"), while the stock thicknesses are similar at 0.1".

 

[Houlahound]

For very thin stock a taller blade would have more strength I would think . This would be especially important if the steel was not great.

I think that's why they made ancient battle weapons for lopping off limbs so tall.

 

[Korean Hog]

If two blades were made from the exact same thickness of stock but one was wider in the way you're talking about,
I would think that the end result would be that the wider blade would be thinner behind the edge as a result.
The strength aspect mentioned makes sense as well, seems like a lot of the fixed blades I've seen with a full flat grind
do tend to be a little wider than blades with a Saber grind, but it could just be aesthetics.

I'm interested to here others' opinions on this as well.

 

[Houlahound]

the wider blade would be thinner behind the edge as a result.

Doesn't that depend on the grind. I would agree with your statement if the grind type and angle were the same. If not then I think no.

 

[Korean Hog]

Doesn't that depend on the grind. I would agree with your statement if the grind type and angle were the same. If not then I think no.

I was thinking it, but forgot to type it in my "all things being equal list"
Yeah it'd have to be same thickness, same bevel angle, same length and possibly shape of blade too.
The point was that all things being equal besides blade width, I would think the wider one would end up thinner behind the edge.
I'm thinking one of the many things that has to be considered when designing a good knife.
You wouldn't want to wind up too thin behind the edge.

 

[Houlahound]

I was thinking it, but forgot to type it in my "all things being equal list"
Yeah it'd have to be same thickness, same bevel angle, same length and possibly shape of blade too.
The point was that all things being equal besides blade width, I would think the wider one would end up thinner behind the edge.
I'm thinking one of the many things that has to be considered when designing a good knife.
You wouldn't want to wind up too thin behind the edge.

We are in the era of overbuilt knives where modern folks feel they need to chop firewood with their knives, use it as a pry bar and cut thru car doors etc.

So end use determines the design parameters.

 

[Korean Hog]

We are in the era of overbuilt knives where modern folks feel they need to chop firewood with their knives, use it as a pry bar and cut thru car doors etc.

So end use determines the design parameters.

Yep, wide knives that are also thin are probably best for the kitchen but this thing from ESEE looks cool

.12 spine, so not a thick blade at all since this is a machete.
The extra width keeps some weight on the blade for chopping power.
Not a very tall grind either

 

[Houlahound]

Yep, wide knives that are also thin are probably best for the kitchen but this thing from ESEE looks cool

.12 spine, so not a thick blade at all since this is a machete.
The extra width keeps some weight on the blade for chopping power.
Not a very tall grind either

Are you using "width" consistently, I'm getting confused.

 

[Korean Hog]

Are you using "width" consistently, I'm getting confused.

I'm calling thickness the thickness of stock the knife is ground from and width the measurement from the cutting edge to the spine.
Or you could think of it as the measurement from the spine to the cutting edge as I wouldn't want you to get confused

 

[Houlahound]

I wished we just used the word height for spine to edge distance.

 

[Korean Hog]

I wished we just used the word height for spine to edge distance.

10/10 people would confuse that with length because length would be the height if the knife was on it's point or butt end

 

[Houlahound]

10/10 people would confuse that with length because length would be the height if the knife was on it's point or butt end

The thread started with this from OP.

"I am curious to hear what you think about the effects of blade height (just to be clear I am talking about the distance between the cutting edge and the spine) "

I feel this is a more natural definition most people get.

Each to their own.

 

[Korean Hog]

The thread started with this from OP.

"I am curious to hear what you think about the effects of blade height (just to be clear I am talking about the distance between the cutting edge and the spine) "

I feel this is a more natural definition most people get.

Each to their own.

 

[Alberta Ed]

Check out Larrin's Knife Engineering: Steel, Heat Treating and Geometry -- the best book I've found on this fascinating subject.

 

[comis]

Just borrowing Miso's drawing earlier, I think if all things being "equal", the difference in height of the blade(from edge to spine) for a full flat grind may look something like this:

I think the 'advantage' of a 'taller' blade is more material behind the edge/potentially sturdier, whereas the disadvantage are more weight/less agile(imagine trying to carve with a really tall blade, the turning radius is larger)/more drag in some application.

But in reality, it is rare to find two knives only differ in height like this, so more must be taken into account(purpose/geometry/steel/HT/etc) when making the comparison.