Edge geometry or blade geometry?

Yvsa · Oct 29, 2000

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I hope I can state this in a way to make it understood the answer I am looking for.

I have seen the term "edge geometry" since I was a very young lad first interested in knives and I can't remember when I wasn't.

All of the edges will have a final edge bevel of 15* for comparison.

To get to the point, say you take a piece of steel that is 1 1/4" wide and 5/16" thick and put a flat grind on it. Then you take a piece that's the same width, but only 3/16" thick and put a flat grind on it.
Of course the thinner blade is going to cut better because there's not all that steel trying to get through the narrow cut the edge has made.

If you put a high hollow grind on the thicker blade there by thinning the edge that much more is it really going to have a better edge geometry than the flat ground blade? I realize that hollow grind is going to probably cut better at the beginning, but how will it perform when it gets the the thick spine?

Then the convex grind is going to be an entirely different application using the same dimensions or is it?

It's pretty much a given I think that a thinner blade with a comparable grind is going to cut better than a thicker blade.

So is it actually "edge geometry" or "blade geometry?"

And what really does a good "edge geometry" consist of and is it related to the overall "blade geometry?"

That's it for now. I have some more questions related to this, but don't want to make it any longer than I already have.
Thanks.

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>>>>---¥vsa---->®

"I would rather have a bottle in front of me than a frontal lobotomy."

........unknown, to me anyway........

Khukuri FAQ
Himalayan Imports Website

raker · Oct 30, 2000

Yvsa, I may be able to answer your question. As I understand it, the edge geometry relates to just the edge. This includes the length of the bevel, the included angel of the bevel and the transition area at the edge of the bevel. The blade geometry is the different shapes of the blade when viewed as a cross-section. There is flat grind with edge bevel, flat grind with no edge bevel, hollow grind,several shapes of convex grind, and the most feared of all, the wedge grind.

(a sharpened blank and you have to put the blade geometry on it you need). To me, what you are cutting will depend on the blade geometry and edge geometry. Hope I didn't muddy the water too much.

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Ray Kirk
http://www.tah-usa.net/raker

Yvsa · Oct 30, 2000

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Ray I have heard/read where a lot of the old ndn trade knives had no edge geometry,(dull), but had a flat grind blade geometry. This was so the elu could put the type of edge on it they wanted. Some of these old knives were sharpened to a high chisel grind for use on fleshing fresh skins.

And I can understand why one wouldnt want a very obtuse edge bevel on a straight razor, although you could make it "shaving sharp" it wouldn't do the job well.
And one wouldn't want a very acute edge geometry on a Bowie or an average utility knife although it would cut well the edge wouldn't last long.

So when someone sets down to design a knife the intended use determines the blade/edge geometry?

And would a flat ground blade say 3/16" thick and 1 1/4" wide with no edge bevels cut as well as a high hollow ground blade with the same dimensions?

Of course the flat ground blade would be stronger?

I guess maybe the answer I am looking for is what is the _absolute_ best blade/edge geometry
for all around use?

Or is there such a blade/edge geometry that would stay sharp longer than any other blade/edge geometry while being easily maintained in the home or afield?

And/or perhaps I am just splitting philosphical hairs?

------------------
>>>>---¥vsa---->®

"I would rather have a bottle in front of me than a frontal lobotomy."

........unknown, to me anyway........

Khukuri FAQ
Himalayan Imports Website

Ed Caffrey · Oct 30, 2000

I don't think there is a "perfect" geometry for every blade or every situation. What must be taken into consideration is the blade geometry must compliment the edge geometry, which must be matched to the type of steel being used, and so on. This is where I try to teach students to think in the "4th dimension", that, being an abstract term to include all the aspects of a blade coming together to create a high performance knife. Blade gometry would include not only spine to edge, but also ricasso to point, and from on side of the spine to the other. What I'm getting at is.........as humans we generally think in three dimensions, height, width, and depth. We generally seperate the three into there own areas. We as knifemakers must develop the ability to meld the three areas together to create the best mix we can for the combination of steel type and blade shape that we are producing. This will only come to each individual through much experientation and time. Everyone of us has our own opinion of which grind/edge/steel is best. What we must do is find the ones that work for us, prove it to ourselves, and then hold on to that. That is not to say do only that, but it will form a strong foundation to work from, learn, and take the next logical step.

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Ed Caffrey "The Montana Bladesmith"
ABS Mastersmith
www.caffreyknives.com

Cliff Stamp · Oct 30, 2000

Ycsa :

say you take a piece of steel that is 1 1/4" wide and 5/16" thick and put a flat grind on it. Then you take a piece that's the same width, but only 3/16" thick and put a flat grind on it. Of course the thinner blade is going to cut better because there's not all that steel trying to get through the narrow cut the edge has made.

These blades will cut nearly identical on most materials. The only exceptions will be on things that are will exert a lot of force on the blade far away from the edge, like a thick vegetable, a turnip for example.

If you put a high hollow grind on the thicker blade there by thinning the edge that much more is it really going to have a better edge geometry than the flat ground blade?

On some things yes, on other things no. On materials that tend to open up as you cut into them, rope and flesh for example, grinding a hollow into a flat ground blade will increase the performance as all the force is concentrated pretty much at the edge. However on binding materials like wood the hollow ground blade will wedge badly at the top of the grind, the extent of the binding of course is controlled by the steepness of the hollow curvature.

Then the convex grind is going to be an entirely different application using the same dimensions or is it?

It reduces the binding significantly. For example you can chop at a very smooth pace with one of your khukuris compared to the Trailmaster or any large flat ground bowie as it will bind readily. It also allows a thicker edge will a full spine to edge grind than a flat ground blade without having the need for an actuall secondary bevel which will raise a high pressure point.

So is it actually "edge geometry" or "blade geometry?"

Edge geometry is far more critical that blade geometry. Even 1/4" knives with good edge geometry cut exceptionally well, David Boye's hunters for example. There is little gained (again on most materials) with thinner stock, for example even going to the extreme of the 1/16" Deerhunter will not get you a better cutting knife as its edge geometry is not as good (just slightly worse).

And what really does a good "edge geometry" consist of and is it related to the overall "blade geometry?"

There are many factors which influence cutting performance, however the main one is simply the acuteness of the bevels. This has a much greater effect than other things such as the bevel width, the transition between the bevels, overall surface finish etc. . As well there are factors like handle effects. A good grip will greatly increase cutting performance, a poor one will destroy it.

Some of these things can be optomized independently of the type of work you are doing mainly as they increase durability, smoothing out the transition between primary and secondary bevels for example. However ofter factors like the acuteness of the bevels and going convex/hollow/flat cannot simply be chosen for the best performance without knowing the type of work that the blade will be doing. You could for example grind a much better cutting blade if the most stressful thing it was going to do was chop fresh pine as compared to seasoned oak.

-Cliff

Yvsa · Oct 30, 2000

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Many thanks to all you guys. This gives me quite a lot to think about and maybe has answered my questions and I don't know it yet.

I will hash it over in what little mind I have left and digest it all.
There were some things there I had not thought of.

Many thanks,
Yvsa.

Crayola · Oct 30, 2000

Yvsa, you also asked what is good for a great all round blade? While this is subjective, I find myself looking for certain traits in users.

Generally, I prefer a flat grind for it remains thin enough for most of its life to easily put an edge on and it is stronget than a hollow grind. On non-flat ground blades I look for the grind to go quite high though. For example, the grind on my Benchmade Sentinel folder is a spear point that actually is liek a dagger with only one edge sharpened. It is not as great a cutter as my Benchmade AFCK which has a higher grind on it. I don't really look at edges because I can thin an edge out quickly with my sharpening kit. Regardless of how thick the blade is, though, I sharpen according to the Joe Talmadge/John Juranich method of making sure the steel behind the edge (relief) is thin too.

For some reason I can no longer ponder elements of blade/edge geometry at the moment, so I'll leave you with that for now!

P.S., nice khukuris! I've been in a khukuri kick for the last week and comparing Cold Steel's Ghurka kukri with HI and GH khukris by reading everything I can get my hands on, especially on the web. Nice way to spend my free time!

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"Come What May..."

Yvsa · Oct 30, 2000

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Thanks Crayola.
I like the flat ground blade as well and I especially like them like my CS Trailmaster with a nice little appleseed edge on it.

And thanks for the comment on the khukuris. I have studied and read some reviews in some magz and am still convinced the HI Khukuri to be the best going!
Check out Cliff Stamp's reviews on them if you haven't already. They are awesome as always.