Mirrored edges, whats the point?

[crimsonfalcon07]

There are plenty of makers who swear by toothy edges over mirror finish ones. I can do both, and have used both. I'm leaning more and more towards toothy for most applications, because they are distinctly better for slicing, and it's a lot more mechanically common to slice than to push cut. I'll put a mirror convex on a chopper sometimes, but for most knives a toothy edge is better in my estimation.

Think of it this way, if you're like kurodrago and you think mirrored edges are always better. If that were true, serrated edges would never have been invented. Do you use a straight edge to cut wood? Funny how all saws have teeth, isn't it? If you were correct, shouldn't they all be mirror polished plain edges? There's a mechanical advantage inherent in a toothy edge. Might come from the increased edge area, might just come from the geometry. This one's really a no-brainer, and easy to verify. Try cutting some manila rope in a slicing fashion with a serrated edge, and try cutting it with a plain edge.

It's actually not that easy to get a really good toothy edge though. You have to get the grit to go 90 degrees away from the cutting edge, and then knock the burr off. Most people and sharpening devices run diagonally or parallel to the cutting edge, and that's not going to give you a mechanical advantage. I think this type of edge is called the ACA edge or microserrated edge by various people and companies. RyanW put one of these edges on his new SPK knife, for instance.

I can't deny that a mirrored edge is better for push cutting. But how often do you slice things, and how often do you push cut? And slicing is generally a more mechanically efficient way to perform the same task that push cutting does. So which is a superior edge? I'm not betting on the mirrored edge, as pretty as they look.

 

[Ankerson]

There are plenty of makers who swear by toothy edges over mirror finish ones. I can do both, and have used both. I'm leaning more and more towards toothy for most applications, because they are distinctly better for slicing, and it's a lot more mechanically common to slice than to push cut. I'll put a mirror convex on a chopper sometimes, but for most knives a toothy edge is better in my estimation.

Think of it this way, if you're like kurodrago and you think mirrored edges are always better. If that were true, serrated edges would never have been invented. Do you use a straight edge to cut wood? Funny how all saws have teeth, isn't it? If you were correct, shouldn't they all be mirror polished plain edges? There's a mechanical advantage inherent in a toothy edge. Might come from the increased edge area, might just come from the geometry. This one's really a no-brainer, and easy to verify. Try cutting some manila rope in a slicing fashion with a serrated edge, and try cutting it with a plain edge.

It's actually not that easy to get a really good toothy edge though. You have to get the grit to go 90 degrees away from the cutting edge, and then knock the burr off. Most people and sharpening devices run diagonally or parallel to the cutting edge, and that's not going to give you a mechanical advantage. I think this type of edge is called the ACA edge or microserrated edge by various people and companies. RyanW put one of these edges on his new SPK knife, for instance.

I can't deny that a mirrored edge is better for push cutting. But how often do you slice things, and how often do you push cut? And slicing is generally a more mechanically efficient way to perform the same task that push cutting does. So which is a superior edge? I'm not betting on the mirrored edge, as pretty as they look.

Depends on the media being cut, take a polished edge and start cutting Manila rope in a draw cut, yes it will work for awhile until it loses bite and it really won't take long compared to a more toothy edge.

I have had some mirrored edges just slide right across the rope unless the down force is really increased a lot so it would be more of a push cut than a draw.

In testing with the same knives cutting rope I have seen as much as a 7 LB difference in down force needed to slice through 5/8" Manila rope from the start, with the toothy edge taking much less pressure, that's 8 LBS to 15 LBS to make the same cut.

Manila rope is one of the more difficult things to cut, but it just shows the difference that can be seen.

 

[hardheart]

I always push cut. I carry folders, and folders are usually too short for slicing. Also, my cutting is usually in and around things, so I don't have room to slice without risking damage.

Teeth on serrations and saws are many many times larger than the ragged peaks and valleys of coarse edges. The mechanical strength is not on the same level between a quarter inch deep saw tooth 0.100" thick and a 5 micron deep tooth 0.001" thick. Serrated edges are also generally polished to some degree.

Velocity is a large component in slicing effectiveness. Plain edge meat slicers do pretty well, and there are some studies on the effect of speed on cutting ability. So it comes down to how much you move the edge, how fast you move it, how much down force you apply, and how long it cuts. These make up the differences in edge type, so how you cut and what you cut trumps any general statement on the best edge.

I have no issue with coarse edges. It may seem ironic, but I do believe I was the first one to try to hammer it into Vassili's head about how a coarser edge slices with less force, and prompted his rolled-up tp slicing video.

 

[Dorito Monk]

I have no issue with coarse edges. It may seem ironic, but I do believe I was the first one to try to hammer it into Vassili's head about how a coarser edge slices with less force, and prompted his rolled-up tp slicing video.

That's pretty interesting... Every time the topic of mirrored edges vs. alternative options comes up, that's the one video that always leaps to mind. :thumbup:

 

[hardheart]

I also have a couple videos up. One, I sharpen a knife on a cinder block and shave the hair from my arm. Another was me slicing newspaper. I asked people to guess what I sharpened the edge with. Some guesses were medium spyderco ceramic and 1000 grit waterstone. It was a double cut bastard file. Before I got into sharpening, I would use a single stone, 280 grit, and I would sharpen til it shaved my arm. Then I got into polishing edges. When it became apparent that lots of people were doing the same, and we started playing around with hair whittling, I started trying to regress edges. I got to whittle hair with spyderco medium, then a 120 stone. I made sure I could shave with 60 grit aluminum oxide and 36 grit silicon carbide.

Coarse edges work well if what you need is a coarse edge.

 

[The_Guide]

Coarse edges work well if what you need is a coarse edge.

How profound :thumbup:

 

[Ankerson]

I also have a couple videos up. One, I sharpen a knife on a cinder block and shave the hair from my arm. Another was me slicing newspaper. I asked people to guess what I sharpened the edge with. Some guesses were medium spyderco ceramic and 1000 grit waterstone. It was a double cut bastard file. Before I got into sharpening, I would use a single stone, 280 grit, and I would sharpen til it shaved my arm. Then I got into polishing edges. When it became apparent that lots of people were doing the same, and we started playing around with hair whittling, I started trying to regress edges. I got to whittle hair with spyderco medium, then a 120 stone. I made sure I could shave with 60 grit aluminum oxide and 36 grit silicon carbide.

Coarse edges work well if what you need is a coarse edge.

I used to use a file to sharpen knives with very long time ago, my old carbon steel slip joints, yeah they cut really well too.

 

[Sr Tyler]

well it can be said that there is less resistance when cutting because the edge is smoother. Cut phone book paper with a toothy edge, then a polished edge. It will glide through much more easy and even sound different

 

[Ankerson]

well it can be said that there is less resistance when cutting because the edge is smoother. Cut phone book paper with a toothy edge, then a polished edge. It will glide through much more easy and even sound different

Depends on how sharp the edge is more than how toothy it is, I have made cuts through phone book paper with almost no sound with non polished edges.

 

[richstag]

Depends on the media being cut, take a polished edge and start cutting Manila rope in a draw cut, yes it will work for awhile until it loses bite and it really won't take long compared to a more toothy edge.

I have had some mirrored edges just slide right across the rope unless the down force is really increased a lot so it would be more of a push cut than a draw.

In testing with the same knives cutting rope I have seen as much as a 7 LB difference in down force needed to slice through 5/8" Manila rope from the start, with the toothy edge taking much less pressure, that's 8 LBS to 15 LBS to make the same cut.

Manila rope is one of the more difficult things to cut, but it just shows the difference that can be seen.

Jim,

This is my main reason for honing my small EDC knives with well finished micro-serrations.

Also, when I was nutty about sharpening I got those silent newspaper edges, but man, by the time I cut up the entire newspaper into shreds (because it was such an awesome experience) it was making noise again :yawn:

Kevin

 

[Steel130]

Well because if this thread I have been goofing around with lower grit edge finish. So far I like it. Ankerson just a few questions from the previous page about the congress SiC stones. Do you just use water to lubricate them? Thats what I used on the Ruby stones I purchased from them. And do you know if the stones need to be flattened over time? Or have you had to yet? I think messing around with different edge finishes is a fun aspect of sharpening.

 

[kurodrago]

Depends on the media being cut, take a polished edge and start cutting Manila rope in a draw cut, yes it will work for awhile until it loses bite and it really won't take long compared to a more toothy edge.

I have had some mirrored edges just slide right across the rope unless the down force is really increased a lot so it would be more of a push cut than a draw.

In testing with the same knives cutting rope I have seen as much as a 7 LB difference in down force needed to slice through 5/8" Manila rope from the start, with the toothy edge taking much less pressure, that's 8 LBS to 15 LBS to make the same cut.

Manila rope is one of the more difficult things to cut, but it just shows the difference that can be seen.

I think that finished edges evolution it's interpreted backwards in here.

Did measured the push cut force applied also in the manila rope or you're going just in one direction?

 

[smokey0118]

I've heard the term "toothiness" used to describe one steel in relation to another. How does carbide size/distribution/type effect the "polish vs. microserrations" debate? If you put an equal polish on two blades of similar geometry, which carbide types would enhance slicing ability? I'm guessing bigger carbides and more of them ='s better slicing at a given polish level? Would the level of polish have any effect on the type of edge degredation within a given steel/heat treat? I'd wonder if a higher level of polish would limit microchipping along an edge of a more brittle steel or not...or at least a less-pure steel with more inclusions. There's a lot of data-driven conclusions and knowledge on here and I'm interested in trying to soak some of it up.

 

[Ankerson]

I've heard the term "toothiness" used to describe one steel in relation to another. How does carbide size/distribution/type effect the "polish vs. microserrations" debate? If you put an equal polish on two blades of similar geometry, which carbide types would enhance slicing ability? I'm guessing bigger carbides and more of them ='s better slicing at a given polish level? Would the level of polish have any effect on the type of edge degredation within a given steel/heat treat? I'd wonder if a higher level of polish would limit microchipping along an edge of a more brittle steel or not...or at least a less-pure steel with more inclusions. There's a lot of data-driven conclusions and knowledge on here and I'm interested in trying to soak some of it up.

It's not as complicated as you are making it out to be.....

 

[sodak]

Thanks for that info. I was coming back to this thread to ask that very thing. Do you just use water? Thats what I used on the Ruby stones I purchased from them. And do you know if the stones need to be flattened over time? Or have you had to yet?

Yes, I'm using water, and it works very well. I haven't had to flatten mine yet, but I think they will need it, they abrade off farily quickly.

 

[singularity35]

Yes, I'm using water, and it works very well. I haven't had to flatten mine yet, but I think they will need it, they abrade off farily quickly.

I find that using glass cleaner on the moldmaster keeps 'em clean better than water. I don't flatten them so much because they dish but to freshen a glazed surface. The 600 grit moldmaster I use dry.

 

[smokey0118]

polish= better push cut rougher=better slicing. Simple concept I get. I just dig the science part of it and am just learning is all. If you'd like to contribute to that, I'd appreciate it. Unless you're just saying while there may be slight differences in the performance in the questions asked above, they'd be negligible and only valuable in a theoretical discussion...but not real world differences.

 

[Ankerson]

Well because if this thread I have been goofing around with lower grit edge finish. So far I like it. Ankerson just a few questions from the previous page about the congress SiC stones. Do you just use water to lubricate them? Thats what I used on the Ruby stones I purchased from them. And do you know if the stones need to be flattened over time? Or have you had to yet? I think messing around with different edge finishes is a fun aspect of sharpening.

I use water most of the time or Windex.

Haven't had to flatten mine as of yet.

 

[Ankerson]

polish= better push cut rougher=better slicing. Simple concept I get. I just dig the science part of it and am just learning is all. If you'd like to contribute to that, I'd appreciate it. Unless you're just saying while there may be slight differences in the performance in the questions asked above, they'd be negligible and only valuable in a theoretical discussion...but not real world differences.

It's not really complicated...

The higher the Carbide content of the steel the more aggressive it will be given the same edge refinement as other steels with lower carbide content.

Steels with a higher compression strength will take thinner grinds and the edge will stay together better than steels with lower compression strength.

Extremely coarse edges will tend to chip out faster than edges that are more refined, there is such a thing as too aggressive to the point of losing efficiency or the cutting pressure will start to increase.

That's why I believe that something in the middle refinement wise or around 14-16 microns tends to be best for overall cutting efficiency and edge retention on more abrasive materials such as rope and cardboard, that's based on my own testing on a variety of steels, edge finishes, edge geometry etc.

That's also based on the belief of the less pressure needed to make the cut and or cuts the better because as the pressure increases it causes more edge damage or faster edge wear.

 

[hardheart]

Larger carbides mean a weaker position in the edge, and easier tearout. Sandvik posted a micrograph of carbide tearout in 440C,

and Roman Landes has done studies on it and focused on it in his books. It is part of the basis for his described property of edge stability. But you need to read German to get the info.

Here's something he made that may help. http://www.hypefreeblades.com/files/schneiden.pdf