Mirror'd edge, why bother?

[Securis]

All this while, i've always been working hard to get the super steels/high carbide steels that i work with to as high a polish possible, whilst still retaining a respectable amount of bite. If i noticed i overdid the polish, i'd take it back a 2 steps to reintroduce that bite, and if that doesn't work, i'll re-do it.

I've been thinking, why bother, though. A coarse edge will definitely still have that bite, and it'd cut well. Other than aesthetics, whats the point?

Well, a couple months back, i saw Michael Christy's video on youtube.

TL;DW

He was testing on ZDP 189, 1 was polished, one wasn't. Both were sharpened to the point where it could whittle hair. Polished came out on top, almost 50% improved edge retention.

I was happy to hear these results, my work wasn't done in vain.

Then one day, i was having a chat with one of my customers who's really good at sharpening knives freehand. He says he only does coarse finish as all he ever needs is a working edge, but he was intrigued by the same video i posted up there. So i had a ZT 0566 in Elmax polished up, still with bite, to the level's i am used to.

His method was to count the cuts he would make with cardboard. He works in the factory, so the boxes are all manufactured from the same source, factor in how much dirt is in the boxes, and missing one or 2 counts for margin of error. The results were, in favor of polished by 30%.

I had a chat with another friend, who took a course in material science (not sure if he's on here). He said that yes, a polished edge would work on ZDP 189 (because it's high CR i think) but wouldn't work well on high V steels, as polishing high V steels would cause the V carbides to rip out. I haven't tested this theory yet, perhaps someone has, but i haven't seen it.

Just sharing what i found interesting. stay safe, stay sharp.

 

[FortyTwoBlades]

Coarse edges slice better and hold their edge longer in such cutting, but are more prone to rolling when making pushing cuts. Polished edges push-cut better and hold their edge longer in such cutting, but quickly lose their bite in slicing tasks. Striking the right balance between the two qualities based on the knife's intended range of use is important. The polish of the bevel itself doesn't mean much short of aesthetics.

 

[Securis]

What kind of cutting tests would truly put the knives through a good slicing test? I would be keen to try it out. Would slicing on the whole length of the blade through cardboard work?

 

[Mo2]

course vs mirror edge, it depends what your cutting. for some things you dont want a course edge at all. other things you may want it to be course. edge retention for course and mirror will differ depending on different factors and cutting different things will cause that to be different as well.

some testers like ankerson prefer a course edge for testing, while others like a mirror edge. which ones better? lol

 

[Bill DeShivs]

Coarse, not course. Please.

 

[Securis]

I mustn't have my head screwed on right. corrected, thanks.

 

[FortyTwoBlades]

What kind of cutting tests would truly put the knives through a good slicing test? I would be keen to try it out. Would slicing on the whole length of the blade through cardboard work?

Things like meat, twine, cardboard, etc. all work well.

 

[REK Knives]

Jim Ankerson here on bladeforums, who has done more testing than most people, says toothy edges last longer generally speaking. From my own experience I tend to agree, however I've not formally tested this yet. But when you factor in the time it takes to get the polished edge it's a no brainer for my own knives... I can sharpen 5-6 toothy edges in the time it takes to do one mirrored edge, plus I don't like how mirrored edges perform.

Also, I have serious issues with calling an edge stropped through .005 microns a toothy edge lol.

To each his own!

 

[TinyDog]

I have never understood the necessity of a polished edge other than it looks really nice I must admit. On a knife one does not intend to use it looks great but seems to be more of an obsession than anything else IMO. No disrespect for those who like it though as we are all a different pair of shoes. TD

 

[Wowbagger]

Yes I like polished edges. The WAY they feel cutting and HOW they cut what I cut.
That said I gravitate toward these steels : ZDP-189, M390 and M4 . . . but many other steels as well.

From a woodworker's back ground I like the surface left by polished edges but also found edge retention and accuracy of the cut (hand planes) to be superior with polished edges (off a jig also).

"but wouldn't work well on high V steels, as polishing high V steels would cause the V carbides to rip out."

Yes I haven't spent much time with these steels but the weeks I did spend with S110V that is exactly what I experienced . . . I call them micro saws. Not that polishing them caused the carbides to rip out but in use it was no time at all and the edge just petered out in a way that could be described just that way. From photos of highly magnified edges after use they do loose carbides and look toothy where as the other steels tend to wear more symmetrically. So . . . the V steels cut longer . . . (saw longer) . . .
I just hate the way the edge feels though : dullish very soon, inaccurate and uncontrollable for paring . . . nasty things (I'm holding up my index fingers to make a cross and am hissing and backing away slowly)
It's probably a flaw in my genes or something.
I plan to get one of the Spyderco UKPKs in S110V and give it another go. Maybe I can make the nasty stuff cut decent if I grind it thin enough . . .
Did I buy my first Spyderco Military in a V steel ? HELLLLLLL NO !

 

[FortyTwoBlades]

Yes I like polished edges. The WAY they feel cutting and HOW they cut what I cut.

[...]

From a woodworker's back ground I like the surface left by polished edges but also found edge retention and accuracy of the cut (hand planes) to be superior with polished edges (off a jig also).

In woodworking, you're push-cutting so a polished edge is more desirable than a coarse one in most circumstances.

 

[Lapedog]

I thought polished edges last longer as they have less things for the medium being cut to grab on to. Coarse edges seem to tend to go faster because they have all that jagged material which catches on what it cuts deforming the edge microscopically. Also wouldn't polished edges last longer becaise as they break down they become coarse edges which are theb worn to dull edges.

Even mirror polished blades resist scratches better as they abrade less easily.

 

[Wowbagger]

I watched the video. Thanks for that.
PS: the lock on mine is perfection . . . just the way I like it . . . press the release and the blade easily drops without much effort. No play no rock no complaints !

 

[Securis]

This is the explanation i had in my mind, but would like to confirm if it is fact or not. I am open to other theories that people have and would like to see whatever data has been accumulated during testing.

 

[FortyTwoBlades]

The infamous Cliff Stamp has done quite a bit of testing verifying this relationship between scratch pattern and edge retention in different sorts of cutting tasks. The direction of the scratch pattern impacts the amount of slicing aggression in which direction the cut is made, too. It's very noticeable with scythes, and all the old-timers would say to make sure your scratch ran from heel to toe or your blade wouldn't bite correctly.

 

[REK Knives]

Cliff has studied this topic here and found that when cutting soft material a toothy edge will have longer retention, and Jim Ankerson admits the same here. However, when chopping (i.e. push cutting) a polished edge seems to have longer edge retention, see here. You should also read this testing as well when you get time... note that he tests how much force is required to push cut through rope and to slice through rope - it's interesting =)

The problem is that you have a lot going on here to draw conclusions, especially from one test in one video with one knife of each. What technically needs to be done is have multiple samples of the same steel with the same geometry done in a blind or double blind test over multiple runs, maybe 5-10 runs. After this was done you would be able to look at all the data and draw reliable conclusions.

So for a few examples, pics pulled from Science of Sharp blog.

Here you have a straight razor edge finished straight off of a Shapton Glass 8k stone, no burr pressent. Keep in mind these are much lower angles than knives but I'm just showing these pics to give you some idea of the variation that can occur in edges.

However, after only 10 passes on a hanging latigo leather strop loaded with 0.25 micron mono-diamond spray, you get this, a severe burr that is extremely weak.

And here is a knife edge at 20 dps after being sharpened on a 1500 grit ceramic stone, then stropped with a .25 micron poly diamond compound.

And the same edge after after cutting approximately 20 linear feet of heavy (double) cardboard. Notice in this case (carbon steel) how it is blunted... the polished edge didn't wear down into a coarse edge.

Here is an edge finished on a 16k shapton then stropped on a hanging denim loaded strop w/ mothers mag polish, then a 1200 grit DMT (EF) stone applied the micro-bevel at the apex. While not what I would describe as fully 'toothy' it gives a good idea of toothy vs. the following picture.

Here is what I would describe as a mirrored/polished edge with no toothiness whatsoever... Here is the progression "A carbon steel straight razor blade was honed edge-leading on a Shapton GS 8k, followed by a stropping progression of 100 laps on a chromium oxide loaded hanging horsehide strop, followed by 100 laps on 250nm cubic boron nitride (CBN) on Nanocloth, and finishing with 30 laps on 100nm CBN on Nanocloth. " It should be noted that 100nm (nanometers) is equal to .1 microns, which is actually coarser than the video above that was described as 'toothy'.

You can do more research on your own, but basically I am showing all the above pics to help you see what's really going on at the edge itself can be influenced in so many ways it's impossible to draw a conclusion off of one or two tests.

 

[HeavyHanded]

If you compare a highly polished machete or hatchet to a coarse edged one, the polished will penetrate deeper and hold the edge longer.

If you compare a coarse edge to a polished one when cutting Manila, the coarse one will cut with less force and hold the edge longer.

On my test rig I can run both pressure and draw cuts on Manila rope. As long as the edges are prepared cleanly, there is an almost cleanly inverse relationship between force needed to draw or pressure cut. Since most utility work requires a combination, a somewhat medium grit is ideal in my opinion.

I once did a test on the same knife - hair whittling polished compared to coarse just able shave some arm hair. The polished edge chopped through green ash thicker than my thumb with an easy swipe, the coarse edge barely penetrated 1/4". The coarse edge caught on free hanging canvas and slit it open like it was a zipper, the polished edge didn't even make it through. Other examples abound.

One thing needed to understand though, a polished edge as it dulls is dull - it does not turn into a coarse edge.

 

[Natlek]

Cliff has studied this topic here and found that when cutting soft material a toothy edge will have longer retention, and Jim Ankerson admits the same here. However, when chopping (i.e. push cutting) a polished edge seems to have longer edge retention, see here. You should also read this testing as well when you get time... note that he tests how much force is required to push cut through rope and to slice through rope - it's interesting =)

The problem is that you have a lot going on here to draw conclusions, especially from one test in one video with one knife of each. What technically needs to be done is have multiple samples of the same steel with the same geometry done in a blind or double blind test over multiple runs, maybe 5-10 runs. After this was done you would be able to look at all the data and draw reliable conclusions.

So for a few examples, pics pulled from Science of Sharp blog.

Here you have a straight razor edge finished straight off of a Shapton Glass 8k stone, no burr pressent. Keep in mind these are much lower angles than knives but I'm just showing these pics to give you some idea of the variation that can occur in edges.

However, after only 10 passes on a hanging latigo leather strop loaded with 0.25 micron mono-diamond spray, you get this, a severe burr that is extremely weak.

And here is a knife edge at 20 dps after being sharpened on a 1500 grit ceramic stone, then stropped with a .25 micron poly diamond compound.

And the same edge after after cutting approximately 20 linear feet of heavy (double) cardboard. Notice in this case (carbon steel) how it is blunted... the polished edge didn't wear down into a coarse edge.

Here is an edge finished on a 16k shapton then stropped on a hanging denim loaded strop w/ mothers mag polish, then a 1200 grit DMT (EF) stone applied the micro-bevel at the apex. While not what I would describe as fully 'toothy' it gives a good idea of toothy vs. the following picture.

Here is what I would describe as a mirrored/polished edge with no toothiness whatsoever... Here is the progression "A carbon steel straight razor blade was honed edge-leading on a Shapton GS 8k, followed by a stropping progression of 100 laps on a chromium oxide loaded hanging horsehide strop, followed by 100 laps on 250nm cubic boron nitride (CBN) on Nanocloth, and finishing with 30 laps on 100nm CBN on Nanocloth. " It should be noted that 100nm (nanometers) is equal to .1 microns, which is actually coarser than the video above that was described as 'toothy'.

You can do more research on your own, but basically I am showing all the above pics to help you see what's really going on at the edge itself can be influenced in so many ways it's impossible to draw a conclusion off of one or two tests.

400 grit stone work best for me ...........Probably looks like a handsaw for wood under SEM

 

[FortyTwoBlades]

ANSI 400 is about my favorite as well.

 

[HeavyHanded]

Cliff has studied this topic here and found that when cutting soft material a toothy edge will have longer retention, and Jim Ankerson admits the same here. However, when chopping (i.e. push cutting) a polished edge seems to have longer edge retention, see here. You should also read this testing as well when you get time... note that he tests how much force is required to push cut through rope and to slice through rope - it's interesting =)

The problem is that you have a lot going on here to draw conclusions, especially from one test in one video with one knife of each. What technically needs to be done is have multiple samples of the same steel with the same geometry done in a blind or double blind test over multiple runs, maybe 5-10 runs. After this was done you would be able to look at all the data and draw reliable conclusions.

...

This is why I made a rig that took me right out of the equation - I don't hold it, and all the loads are static. The only variable is how rapidly I set the load on the edge and how fast or slow I do the draw cuts. My tolerances tended to be equal to or less than 10% on the number of cuts, and under a full pound of force on the pressure cuts. Even then I noticed changes based on abrasive selection for a given steel, and the subjective factor of how different abrasives made different finishes at the same grit rating.

A really interesting thing about it, the testing generally ends before the knife is dull, so it takes a little less time than other testing protocol, and it detects performance changes that would be extremely tough to figure out by hand.

I should do more work with it, but am too lazy/distracted/not creative enough to come up series that I want to invest the time in.