Coarse edge = Micro serrations yes or no

[Ankerson]

Very simple.

Do you believe a coarse finished edge is the same as a serrated edge (only on a smaller scale) or not.

There is a lot more to it than that...... It's really not that simple.

A lot depends on the steel and the HT and tempering.

Some steels cut very aggressively even with a polished edge while others not so much. S90V is dangerous because it's so aggressive, you might think it's dull but it will still cut like a razor blade due to the properties of the steel and the very high carbide content.

Take steels like M390, S90V, S110V, S10V with the High Alloy content that develops a lot of carbides they are extremely aggressive cutters. Once the carbides take over they will cut for it seems forever because they develop that toothy working edge.

Other Steels Like ZDP-189, CTS XHP that have a lot of chromium and develop chromium carbides tend to smooth out and dull faster, lose their bite after time. The only thing that really helps these steels is if they are run at high hardness, but once they start to dull they dull very fast as the edge smooths out.

 

[David Martin]

If one would do real world cutting tests on sisal rope using a coarsely sharpened edge @ 200g and a finely sharpened edge @ 600g . Then cut the rope counting the number of cuts until each were dull . You'd find the coarse edge delivers MUCH greater edge retention . Hence, the conclusion follows that as refinement in sharpening increases -- edge retention decreases . DM

 

[Ankerson]

If one would do real world cutting tests on sisal rope using a coarsely sharpened edge @ 200g and a finely sharpened edge @ 600g . Then cut the rope counting the number of cuts until each were dull . You'd find the coarse edge delivers MUCH greater edge retention . Hence, the conclusion follows that as refinement in sharpening increases -- edge retention decreases . DM

Actually no, that's not the case because the coarser the edge the faster it will break down because those tiny serrations are like little stress points that will fail long before a more finely tuned edge. That's just basic physics there, very simple really. That's given the same steel in the same blade sharpened to different finishes.

The very coarse edge will cut with less force than the finer edge at 1st, but as the sharpness curve develops the finer edge will match the coarser edge then cut longer because the edge is stronger so it will stay sharp longer.

I have done extensive testing on this with High Alloy steels and except for one steel (Low Alloy) I have found it to be true, now the High Alloy Steels do work better than the lower alloy steels in the tests.

 

[David Martin]

Actually no thats not the case as I've done extensive testing and found this to be true many times using the same steels sharpened to different grits . Testing it on cutting sisal rope, chicken and deer . Its just basic testing . DM

 

[Whelen Nut]

This is a link to a wood working site that shows several images of a "dull" edge and a sharpened one under an electron microscope. It seems to me that once you get to the really fine polish grits there aren't really any serrations left to speak of.

http://blog.woodworking-magazine.com/blog/Sharp+And+Dull+For+An+Electron+Microscope.aspx

 

[xtestifyx]

Actually no thats not the case as I've done extensive testing and found this to be true many times using the same steels sharpened to different grits . Testing it on cutting sisal rope, chicken and deer . Its just basic testing . DM

I'm sure I'm not the only one who wants to see more of your testing, that would be interesting

I'm not doubting you in any way nor am I questioning Ankerson's tests, it would just be nice to see more people chime in and let the determination go to the readers

 

[Ankerson]

I'm sure I'm not the only one who wants to see more of your testing, that would be interesting

I'm not doubting you in any way nor am I questioning Ankerson's tests, it would just be nice to see more people chime in and let the determination go to the readers

Yeah I would too....

Always like to see things that go against basic physics.....

I think they call that magic or something.....

 

[David Martin]

Guys, it been posted here numerous times ...how'd you miss it. Theres one on the index page in 'coarse stropping' and goes from some months back . What law of physics are you refering to that my tests go against . Micro serrations . A serrated blades points don't break off and become dull quicker . Instead it will last 3 times longer ( as Spyderco stated) than a standard blade . Jump and make fun as your nature dictates . I think well have to disagree on this one . I've been hammered before here and yet they didn't do the tests either. DM

 

[Ankerson]

Guys, it been posted here numerous times ...how'd you miss it. Theres one on the index page in 'coarse stropping' and goes from some months back . What law of physics are you refering to that my tests go against . Micro serrations . A serrated blades points don't break off and become dull quicker . Instead it will last 3 times longer ( as Spyderco stated) than a standard blade . Jump and make fun as your nature dictates . I think well have to disagree on this one . I've been hammered before here and yet they didn't do the tests either. DM

There is a huge difference between a Serrated blade and what we are talking about here.

Yes a serrated edge will last longer than a straight edge given the same steel, but that's not the subject here, not even close to being the same subject.

The topic here is course edges and finer edges and that doesn't follow that same pattern because it's not the same thing.

 

[unit]

never mind....

 

[Ankerson]

You are right the subject of this thread has NOTHING at all to do with what lasts longer.

I remember in the old days we used to sharpen knives with files when cutting a lot of rope because it would cut more aggressively. The trade off was the edge wouldn't last very long so repeated sharpening needed to happen.

This was back in the 70's....

With everything there is usually a trade off, we have to give up something to get another.

 

[richard j]

stevenkelby says a lot in this thread for a coarse edge vs a highly polished edge http://www.bladeforums.com/forums/showpost.php?p=9207988&postcount=710

 

[Ankerson]

stevenkelby says a lot in this thread for a coarse edge vs a highly polished edge http://www.bladeforums.com/forums/showpost.php?p=9207988&postcount=710

I read that, but what he is talking about is perceived sharpness, not edge retention because he never pushed that M4 edge long enough for it to develop that toothy working edge.

A lot depends on the steels in question in the end as there really isn't just one fits all answer 100% of the time.

 

[jimnolimit]

if i get a chance i'll try to do a cutting test. im thinking of taking pics @375x of both the 60 grit edge and maybe the 600 grit edge before and after cutting 50-100 feet of cardboard. i'll put a spot of magic-marker on the blade so i can mark the area that i took the pics of. what does everyone think?

 

[HeavyHanded]

Yeah I would too....

Always like to see things that go against basic physics.....

I think they call that magic or something.....

My own testing supports DMs conclusions. While the bulk of my testing to failure has occurred under workplace conditions and is therefore somewhat anecdotal, I've found pretty much a direct correlation between grit and retention. Almost the exact opposite of what you have found - the highly refined edge cuts better at first and quickly looses its ability to cut as the edge radius wears. While I'm sure the same wear is taking place on the coarse edge, the greater variation in cutting forces allows it to continue severing materials longer. The only exception to this rule that I have found is if the edge in question is only being used for one type of cutting (draw or push). In that case, the finer edge will push cut longer, and the coarse will draw longer. My camping hatchet, honed on a fine Arkansas stone will make repeated chops through fairly hard wood (birch, beech) and still shave arm hair. It also sports a 45 degree edge bevel and because of this cannot slice worth a darn.

In any event, this thread isn't about retention, efficiency, or any of those considerations, but IS about the cutting mechanism of the coarse edge relative to a serrated edge (not a fine edge). Here's my newly developed description based on a view of the ground edge (coarse or fine - it's all just a question of scale until one strops the grind pattern completely smooth) as a wave form. The edge begins it's cut and starts to bite in. There are two main mechanism at work - areas where the edge bevel is relatively straight it simply cuts using pressure much like a fine edge. These areas are relatively scarce on a coarse edge. As the edge is drawn through, the angle of the cut begins to shift as the "waveform" is pulled across the material. In some places the shifting angle causes the edge to"scrape" through the material somewhat like a saw. It becomes a process of scrape and slice, at the same time the edge has high and low points. The highest and lowest points are going to be primarily where the cutting edge is straight, and the transitions between are going to provide the scraping action. On softer materials, there isn't a scrape, the material simply shifts as the edge continues to cut through.

A serrated edge on the other hand relies much more on it's teeth to separate and divide materials (why on some really tough rope you have to use less pressure with a serrated edge or it'll choke). On softer materials you can still press cut with a serrated edge, but it will always lead with and start most of its cutting with the tip of it's teeth and the first little bit of the slope on either side of the teeth. As the material holds on it encounters the trough of the serration and gets cut like a fine edge - with pressure.

Just my opinion, I don't have an electron microscope.

HH

 

[unit]

This is what interests me the most (cutting mech). Unfortunately I fear that all any of us can do is speculate a bit with the aid of still images provided by others. I doubt we will find many SEM videos that capture what actually happens at the edge. I enjoy the intelligent discussion none-the-less.

 

[Ankerson]

My own testing supports DMs conclusions. While the bulk of my testing to failure has occurred under workplace conditions and is therefore somewhat anecdotal, I've found pretty much a direct correlation between grit and retention. Almost the exact opposite of what you have found - the highly refined edge cuts better at first and quickly looses its ability to cut as the edge radius wears. While I'm sure the same wear is taking place on the coarse edge, the greater variation in cutting forces allows it to continue severing materials longer. The only exception to this rule that I have found is if the edge in question is only being used for one type of cutting (draw or push). In that case, the finer edge will push cut longer, and the coarse will draw longer. My camping hatchet, honed on a fine Arkansas stone will make repeated chops through fairly hard wood (birch, beech) and still shave arm hair. It also sports a 45 degree edge bevel and because of this cannot slice worth a darn.

In HH

You are talking about perceived sharpness, not edge retention and that will vary depending on the steel and materials cut.

If I had a cut a lot of cardboard at work I would go with a High Vanadium steel like S90V and polish the edge, once the edge started to break down and the carbides took over it would still cut for a very, very long time.

For rope I would use a serrated blade if I had to cut it a lot.

 

[HeavyHanded]

You are talking about perceived sharpness, not edge retention and that will vary depending on the steel and materials cut.

I guess I'm not sure what you mean by "perceived sharpness". Strictly speaking, edge retention is going to be governed entirely (all other things being equal) by the characteristics of the steel in question. If by "perceived sharpness" you mean the ability to continue cutting within the confines of a number of fixed variables, than that to me is "edge retention", especially if one of those fixed variables happens to be blade steel. Not all of us have the means to purchase the best steel for a given application and instead have to select our edge preparation with some extra thought. Since you've already stated that there is no one size fits all solution for cutting chores (and I agree entirely), I'm not sure what else there is to say that isn't pure opinion based on personal experience. Sounds to me like you're implying the steel composition might bear more heavily on things like cutting efficiency and edge retention than other considerations, like mechanism of cutting, edge angle etc. I have to admit, I haven't been testing for this phenomena (with all other variables controlled).

Back to the OP - another thing that occurs to me, as grit size increases, so would the total length of the cutting edge. There would also be greater shifting in the angle and pressure of attack along the edge, and due to these factors (longer cutting length and greater variety of cutting forces), push cutting would become even more inefficient as the edge would be trying to separate the given material in a number of planes. In some cases the material would be compressed toward itself and in others it would be divided more aggressively. Hmmm
Just kicking some thoughts around.

HH

 

[unit]

Back to the OP - another thing that occurs to me, as grit size increases, so would the total length of the cutting edge. There would also be greater shifting in the angle and pressure of attack along the edge, and due to these factors (longer cutting length and greater variety of cutting forces), push cutting would become even more inefficient as the edge would be trying to separate the given material in a number of planes. In some cases the material would be compressed toward itself and in others it would be divided more aggressively. Hmmm
Just kicking some thoughts around.

HH

First bolded phrase...do you mean as grit size DECREASES the cutting length would increase? I think you do. The polished edge (HIGH GRIT) would better represent the shortest (straight line) distance, where a coarse (lower grit) would lead to a more irregular edge....right?

Second bolded phrase...I JUST got done conducting some experiments along these lines...my results would tend to agree and demonstrate this.

 

[unit]

Back to the OP - another thing that occurs to me, as grit size increases, so would the total length of the cutting edge. There would also be greater shifting in the angle and pressure of attack along the edge, and due to these factors (longer cutting length and greater variety of cutting forces), push cutting would become even more inefficient as the edge would be trying to separate the given material in a number of planes. In some cases the material would be compressed toward itself and in others it would be divided more aggressively. Hmmm
Just kicking some thoughts around.

HH

More on this...what an interesting point, you make!

Here is some more conjecture (I am not stating this as fact, but my observations seem to support it)

Push cutting may be a whole other set of variables to consider. Are you push cutting something like a 3 mm thick bit of rope, a 1 mm thick piece of tissue, or something really small like a hair (or even a smaller fiber)? When the thing you are push cutting has thickness approaching the scale of the irregularities of the blade edge it will behave like a finely polished edge so long as the thing you are cutting aligns with a facet edge aligned nearly perpendicular to it. This is perhaps similar to the way a highly polished serrated blade will tend to pass many of the sharpness tests (tree topping, hair whittling, etc.) but will tend to do so (perhaps entirely) in the troughs of the serrations. Again the serrated blade may not be the best analog in which to envision this...because the coarse edge would seem to be a 3D edge trace, where the Serrated edge is generally 2D.

Sort of like finishing up on a 60 micron/220 grit stone and then "testing" the edge by shaving/tree topping arm hair. A well honed edge on this grit can shave and tree top hair, but the irregular edge would not feel pleasant on the skin as some of those irregularities seemingly attempt to bite in to the flesh (shaving nicks). You might conclude that both a coarse edge (as I define it here) and a finer edge both will push up a nice pile of hair on your arm (so both are shaving sharp), both will tree top hair (but the coarser edge will only grab and cut the hairs aligned with the properly aligned facet edges for this task)...so both edges would seem capable of "tree topping", but the coarser edge does not have 100% of its edge aligned for this task. Both good, just different....and our paradigm for judging superiority perhaps is based on what we choose to cut in our tests...i.e. our "perceived sharpness"

Basically what I am envisioning and probably poorly describing is that a coarse edge would appear under magnification as a series of scalloped out 'facets" whose edges intersect creating a very irregular, but contiguous edge. If you encounter a tiny portion of this edge that is aligned perpendicular to the fiber you are cutting, it will push cut it in much the same way a polished edge would...the polished edge just tends to make all these facets MUCH smaller and their intersection more closely approximates a straight line.