So, why don't polished edges "bite"?

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KennyB

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So, I don't really want to debate the virtues or merit of coarse vs polished edge, but with all the discussion going on lately I do want to learn a little bit more about a certain thing people are observing about polished edges, and that's that they don't have any "bite".

I've observed this too and it really confuses me. How can you get an edge so polished that all the hair-testing tricks will indicate it's razor sharp, yet then it just skates over fabric or plastic when making certain kinds of cuts... For me I noticed whenever I was trying to make a plunge cut into a big sheet of plastic with the belly of the knife, it would just skate off the belly, requiring me to use the tip instead. However, for the most part, a blade like this will sail through the same material with a pushing cut.

Is this just the way polished edges are, or is this an indicator that you've been rolling the apex? If the latter, why do such edges still appear to be sharp when doing "hair tests", yet come up short when actually trying to use the edge?
 
I think the best way to visualize it is to think of a hand saw. Both edges are about the same thickness but one cuts when moved and one doesn't. Pushing either edge through something would be nearly the same. The other way of visualizing would be that on a microscopic level, the non polished edge is like a series of little points like the one you found, worked. A third way might be to think of a serrated vs plain edge and how they work.
 
KennyB said:
So, I don't really want to debate the virtues or merit of coarse vs polished edge, but with all the discussion going on lately I do want to learn a little bit more about a certain thing people are observing about polished edges, and that's that they don't have any "bite".

I've observed this too and it really confuses me. How can you get an edge so polished that all the hair-testing tricks will indicate it's razor sharp, yet then it just skates over fabric or plastic when making certain kinds of cuts... For me I noticed whenever I was trying to make a plunge cut into a big sheet of plastic with the belly of the knife, it would just skate off the belly, requiring me to use the tip instead. However, for the most part, a blade like this will sail through the same material with a pushing cut.

Is this just the way polished edges are, or is this an indicator that you've been rolling the apex? If the latter, why do such edges still appear to be sharp when doing "hair tests", yet come up short when actually trying to use the edge?
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That will depend on the steel.....

Some steels are very aggressive and even with a polished edge they bite like crazy while others don't seem to do as well.

Also the grain of the different steels can have a large effect on this, some steels that are very fine grained won't do as well as others with a coarser grain with a polished edge.

Take a very aggressive steels like S90V or 10V and polish the edge it will still bite like crazy due to the very high vanadium content.
 
Some say s30v isn't great polished, but I feel opposite. It bites plenty...

1213884182_kt3GG-XL.jpg
 
I think a lot of what it has to do with is people do not know how to use the edge they're using against the material they're cutting. I cut zip ties all the time, I cut food all the time. It's never a problem with a polished edge. I also don't push cut with a coarse edge, I don't try and saw with a refined polished edge.
 
I view it like this.

Using a PUSH CUT, A (well) polished edge will not "bite" your skin...but it may lay it wide open. The difference between the polished edge gliding/skating on the surface of the skin (as in shaving with out nicking you) vs. biting in and laying you open has everything to do with the angle of the edge relative to the surface you are shaving or cutting.

(in my understanding/opinion) A toothy edge by contrast is a somewhat random collection of edges where the facets (left from the grinding media) intersect. These edges may connect to form a continuous edge from tip to choil depending on how refined it is, but it does not make a predictable smooth line or arc as it trends from tip to choil. Rather, it traces a very erratic 3 dimensional trace as it trends from tip to choil (if viewed under strong magnification). Because this edge has a 3D trace with portions of the edge oriented in many directions it is impossible to predict or hold constant the angle between the edge and the surface the knife is on...so it will not skate, and the portions oriented nearly perpendicular to the surface will "bite".

If you push cut a tomato with a polished edge and put the edge perpendicular to the surface, it will push easily in and cut. Open up the angle as if you are going to shave the tomato and it will skate. Resist this transverse movement of the blade and it will cut...you just have to use the edge properly.

I really do not view this as one type of edge does everything better or worse than another....they are different and they do things differently. Select your tool accordingly for the job, and then use it to the best of its ability.
 
KennyB said:
So, I don't really want to debate the virtues or merit of coarse vs polished edge, but with all the discussion going on lately I do want to learn a little bit more about a certain thing people are observing about polished edges, and that's that they don't have any "bite".

I've observed this too and it really confuses me. How can you get an edge so polished that all the hair-testing tricks will indicate it's razor sharp, yet then it just skates over fabric or plastic when making certain kinds of cuts... For me I noticed whenever I was trying to make a plunge cut into a big sheet of plastic with the belly of the knife, it would just skate off the belly, requiring me to use the tip instead. However, for the most part, a blade like this will sail through the same material with a pushing cut.

Is this just the way polished edges are, or is this an indicator that you've been rolling the apex? If the latter, why do such edges still appear to be sharp when doing "hair tests", yet come up short when actually trying to use the edge?
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The answer is quite simple... cutting technique.
 
You don't 'push cut' with a hacksaw. You saw (read: slice)
You don't 'slice' with a chisel. You push cut.

If your method of cutting tomatoes is to slice, a toothed edge with work better for you.
If you push cut your tomatoes, a polished edge will work better for you.

For the term "work better for you" you can substitute "feel sharper when you use it."

Most people use both cuts when using a knife, depending upon what is being cut. Usually, we don't think about it, we just do it. Not everybody cuts a tomato or a fish fillet the same way, so everybody has a different opinion about which works best. If it's working well, it must be sharp, right?
Or not.


Stitchawl
 
All right, so then that's pretty much the way it's supposed to be... Cool, basically what I wanted to know.

I think I do a little bit more slicing than push-cutting when working with food. Most of the stuff I've push-cut is just envelopes or push-cutting through the top of a plastic food package to open it up. I think that's because I mostly cut up meat.

Anyway, good to know, now I can just use my coarse edges when I need to slice things with the belly.
 
no he is a troll ... can't cut meat with a polished edge, it's worthless, butchers know more about knives than knifemakers ....
 
To the OP, they don't bite because there's no tooth left to deconstruct your target material. With a polished edge the cutting surface is more or less one continuous plane that cuts using a concentration of pressure. IMHO using a drawing motion with a highly polished edge might result in a slightly more predictable cut, but seldom increases the ability of the knife to cut a given material. One of the primary reasons I don't like the polished edge even when fresh off the strop is that it can cut unpredictably depending on the density of what I'm cutting. No such drawback to the coarse edge.

General question re polished edges on common knife steels. I'm not speaking about some of the PM or high carbide content metals, but ones like 440c, Aus8, 154cm. Is it anyone else's observation that repeatedly using a polished edge in a draw cut will result in more rapid wear of the edge compared to using it with a fairly strict push-cut? IME polished edges fail ahead of coarse ones in my work and general use environment. That said, I keep my axe and camping hatchet refined on a Hard Arkansas and stropped (somewhere in the 1500-2000 grit range estimated). These edges shave arm hair easily and survive multiple hard use sessions and unless really beaten on will continue to shave arm hair much longer than I would have believed possible. How to reconcile this with what I have come to find from my smaller pocket/belt knives where a similarly prepared edge cannot come close to this performance?
Not trying to stir the pot, just trying to further some understanding. We all hold our own opinions based on our personal experience (or I hope so). How to reconcile these differing experiences?

HH
 
samhain73 said:
Bark Rivers Mike Stewart has said that S30V does not even begin to show it's true ability as a steel unless it's polished.
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Polishing it extends the dullness curve by adding another stage and the carbides help it a lot.
 
HeavyHanded said:
General question re polished edges on common knife steels. I'm not speaking about some of the PM or high carbide content metals, but ones like 440c, Aus8, 154cm. Is it anyone else's observation that repeatedly using a polished edge in a draw cut will result in more rapid wear of the edge compared to using it with a fairly strict push-cut?

HH
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Anybody...?
 
HeavyHanded said:
Anybody...?
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I like a slightly less polished edge on non-PM "common" steels. Specifically, I'm taking them to a 2 micron finish vs a 1/2 micron finish. I don't know what others consider a "mirror polish" is but that's my method.

With a very fine polish on a PM steel, it settles into a working edge after the very thin bit is worn down without rolling over. With a lesser steel, it will roll over instead of getting toothy so I leave it less polished. Now I also use different angles for PM steels (20 degrees inc) and non-PM steels (30 degrees inc) so there is another variable in the mix. But this formula works well for me.

I love how aggressive 154CM gets with a 2 micron finish. Scary.
 
dsmegst said:
I like a slightly less polished edge on non-PM "common" steels. Specifically, I'm taking them to a 2 micron finish vs a 1/2 micron finish. I don't know what others consider a "mirror polish" is but that's my method.

With a very fine polish on a PM steel, it settles into a working edge after the very thin bit is worn down without rolling over. With a lesser steel, it will roll over instead of getting toothy so I leave it less polished. Now I also use different angles for PM steels (20 degrees inc) and non-PM steels (30 degrees inc) so there is another variable in the mix. But this formula works well for me.

I love how aggressive 154CM gets with a 2 micron finish. Scary.
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Alright, so 2 micron equates to (roughly) 1500-2000 grit CAMI. Something to add into the equation. In my experience this is the upper limit of where I'll go with the common steels and still expect reasonable edge retention, maybe a skosh higher. Thanks for your feedback.
HH
 
I my testing where the sharpening grits and cutting method is spelled out very clearly the more coarse edge cuts much longer and I think its because of the teeth points and their subsequent scallops between the points . As these are wore the steel looses its ability to cut abrasive material easily . Since, on the finely sharpened edge these are polished away hence the edge does not have the ability to slice cut rope, limbs, ect. yet will push cut . Still, for this method it requires a hard backing . Many have wrote about their polished edge skating off the material when attempting to cut rope . When they sharpened the same knife more coarse it would cut this easily . DM
 
Heavy,
I think, like you know, it depends on the steel and what your cutting. If you use the wrong technique for cutting something then it will not perform properly and adverse effect will occure. Like cutting a rope off a steel pipe, do you go edge first into the pipe and push cut the rope or put the spine on the pipe and push the tip through the rope. One leaves you with a flat and rolled edge and the other is only affected by the rope.

IMO the argument over coarse vs fine is a bit under thought. To me the steel can only wear at one rate and only be deformed as much as the specific thickness and stability of the steel allows. To me saying a coarse edge or fine edge is better is a bit misleading because its not improving hardness or wear resistance in the steel. When you change how the edge is sharpened your changing cutting dynamics not steel properties. Don't know if I should really say this but I'd be willing to bet that if edge finish was the only variable longevity of the edge would be a much smaller difference than style of cut needed to make the edge type work correctly. This line of thought comes from observations of my brother and father in their knife usage. I have adapted cutting style to edge type and in similar uses can make a edge last many times longer than either of them. My dad really doesn't care but my brother likes a coarser edge on his pocket knives. His cutting style is a sawing type that relies less on downward pressure and more on edge type and direction to accomplish the cut. By comparison if I made the same cut it would start with more pressure and have a even draw slice to compensate for edge type vs material cut.

I guess a better example would be manila rope, if you have a coarse edge it wil slice/saw through with ease. If you try this with a fine edge the rope will resist the fine and flat apex, the abrasive factors of the rope will then act like sandpaper simply dulling the edge. If you used the same polished edge and push cut or pushed and sliced (single direction slice) the rope would be cleanly cut and minimal damage to the edge would occure.

When I did my testing of the passaround RAT-1 blades they were both sharpened to 20 degrees inclusive and subjected to 100 cuts in 3/4 manila rope. Both were finished to a 8k diamond and push cutting was used on a bamboo cutting board. I could have used slice cuts because the edges still had enough "bite" but because of the material being cut and level of edge refinement I knew it would cause unpredictable results. In this case knowing how a edge type and cutting style would be used on a specific material was key in getting correct data.

I'm trying to get some pictures together now of 120 mesh through 8k mesh at 400x. My first run turned out a little unclear so I have to do it over :( I think you'll find them interesting though ;)
 
knifenut1013 said:
I guess a better example would be manila rope, if you have a coarse edge it wil slice/saw through with ease. If you try this with a fine edge the rope will resist the fine and flat apex, the abrasive factors of the rope will then act like sandpaper simply dulling the edge. If you used the same polished edge and push cut or pushed and sliced (single direction slice) the rope would be cleanly cut and minimal damage to the edge would occure.
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From a theoretical viewpoint, it sounds as though you think it might be a factor. I asked myself this question the other day at work as I was cutting through 15 pt paper with a utility knife. Even with a fresh blade and considering the thinness off the steel, it had a tough time push cutting across 20" of stock. This stuff is nothing like cardboard - far more dense. I had to induce some draw to the cut and it occurred to me this action could be causing wear to the edge that mightn't occur if a push cut only was being used. Of course, some chores just don't give the user the luxury of choosing how they're going to use their edge, and here's where planning ahead can really pay off. A great deal of my personal preference for coarse edges has been formed in this environment - cutting a wide variety of clay-coated and uncoated papers from newprint up to posterboard. I've already mentioned how well some of my chopping tools perform with a fine edge, and this got me to thinking. I never use these edges with a draw cut. Likewise I seldom use my coarse edges for a strict pushcut unless the material is fairly insubstantial or has too much grab for an effective draw cut (braided PVC tubing comes to mind, though once the cut is initiated I can fold the tube over and it parts easily with a draw cut). While it wouldn't be news to anybody that different edge types perform better with different cutting technique, I believe it might come as a surprise to some that cross-use of a specific edge could cause it to dull faster (and not just from striking unintended objects). This could also explain the gulf in opinion re varying edge preparations with plenty of real-world testing backing up both arguments and everything in between.
HH
 
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