Steel,sharpening and angle

B

Bart student

Joined
Nov 17, 1999
Messages
676
Hello folks,
If you had to put percetages on it, what would make a knife a good,sharp knife. I mean, something like 50% steel contribution, 35% grinding angle and 15% sharpening angle.
The grinding angle is meant with hollow, flat,convex and to what degree. Afterall, a blade of 1/4' doens't cut as good as razor.
I know blade shape is important too, but let's leave that out of it.
So: 1: % Steel type or other alloy
2: % Grinding angle
3: % sharpening method.
I did not say just for edge retention.
Why I want to know? I plan on making a non-destructive knife test and we (me and my friend) need to put our knives in cathegories, and we could do that based on your answers. So help us out, 3 numbers will do.

thanks in advance, Bart.
 
Since you are talking only about sharpening, not about edge durability at all I would say:
15%
35%
50%
It should be noted that angle is determined by the task that the edge is intended for. It could be as little as 10 deg. on one, and 35 on another.
 
I think there might be some more variables in the equation. Over the past year I have been playing with rounding the corners a little on the primary sharpening bevel. This may only apply to hollow ground blades which are all I do, but I'm learning that hard angles seem to retard cutting ability. This is not to say that's all that matters, but it certainly seems to help.

The Moran edge which is entirely convex is supposed to give superior cutting, and there are theoretically no angles there. I'm sure the final sharpening bevel is angled, but the blade above it may round into that angle and reduce friction.

With that mud thrown into the water, I'll toss in some more. It depends on what you're cutting. There is little doubt that the finest possible sharpening angle will cut best, but it may not cut for very long. Straight razors are very sharp due to their fine edge, but they often are resharpened (stropped) in the middle of a single shave. I doubt one would make it through a hard object at all. I'm sure velocity is a contributing variable. And finally, "cutting" itself has a couple distinguishing elements, chopping and slicing. These last two may well be differently influenced by the polish on the final edge. And on and on...

all that ignored, I would roughly gauge your list as:

Steel: 30%
Grinding Angle: 30%
Sharpening Angle: 40%

Tough call though...

------------------
Jerry Hossom
www.hossom.com
 
Jerry :

[Moran edge]

I'm sure the final sharpening bevel is angled, but the blade above it may round into that angle and reduce friction.
Click to expand...

Not exactly friction, it has much less drag.

Bart, you can't split the performance up like that as the steel type forces the way the blade needs to be ground to have the necessary durability.

Sharpening can be seperated a little as you don't want to have the same finish for different types of cutting. Very high polishes are great for push cuts and impacts but they have little bite and don't slice well. Agressive edges with large teeth slices really well but respond poorly to impacts and generate lots of resistance to push cuts.

However even sharpening is influenced by the steel type. Very fine grained steel for example will take a much better polish than coarse large carbide steels. Very ductile, tough and strong steels will give much more durable microteeth.

So basically, assuming you have makers who know how to work with the steels and will grind and heat treat it so as to optomize the knife for what you need it to do, a better blade material should always give a better blade.

-Cliff


[This message has been edited by Cliff Stamp (edited 02-22-2000).]
 
It depends a LOT on what you're cutting. If you are shaving you're cutting through a somewhat hard material that is very thin. The only part of the blade that contributes to the cutting is the final bevel on the edge. So what counts the most there is the final bevel angle (which can't be any shallower than the overall blade taper) and the smoothest thinnest edge. So the primary grind on a straight razor is thin so that you can easily maintain a thin smooth final grind. They are made of a very fine-grained steel to get down to a wispy thin edge.

If you were cutting 1/4" diameter hair you want the thinnest blade you can get away with. This is because you need to bend the whole shaft away from your blade as you force it through the material. You are not just fighting material at the apex of your edge, you are also bending the remaining material ahead of your cut. For this work the best blade shape it the thin razor utility knife shape. Very thin with a sharp edge. Another good edge for this is a thin blade with a coursely ground edge. This works well if you can apply some cross cutting motion to your cut.

Blade thickness always increases cutting effort. When you cut small diameter material the only part of the thickness that comes directly into play is one material diameters worth. When you get into thicker material you will find that your primary grind wedges into the material and/or drags on the material. This is where you get into arguments about full grind verses hollow grind functionality. The hollow grind has a clear advantage on small diameter hard materials, but it may not work as well on thick hard materials. I generally prefer hollow grinding on thick soft materials like meat. It may or may not offer more drag, but it is a lot easier to produce a razor edge on a hollow ground blade.

So to rate the relative importance of blade characteristics you have to say for what type of material and in what thickness. I standardize on thick soft materials--meat typically. I would rate the factors:
60% blade profile (thin and accute are important), 25% final grind contour, 15% alloy/heat treatment. All this assumes doing the best possible with the materials. I want that 15% sharper edge that the material can provide. I really like A2 tool steel.

 
Jerry, drag is a more general term that describes the forces on an object passing through a fluid (which is a very general term, not restricted to liquids). Drag includes friction but also covers forces due to the shape of the object which induce pressure gradients about it.

Relative to this thread, when you have very abrupt changes in profile (like at the bevel to primary grind juncture) these creates very high drag because of the distortion the material gets. Smooth transitions can cut better even when the surfaces are rough because they distort the cutting medium less.

Jeff, have you used CPM-10V?

-Cliff
 
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