Help me understand "toothy" vs "polished"

[ToddS]

I have been struggling for some time to understand what is meant by a "toothy" edge. I don't think there is a consensus on the meaning, and I think that is part of my issue. There is also the problem that optical microscopes can be very misleading when imaging the edge of a blade, combined with the assumption that scratches determine the geometry of the apex.

I suspect that some people use the term "toothy" to describe any edge that feels "sticky" or passes the 3-finger test. Others seem to distinguish only by honing grit, low grit are toothy, high grit are polished. The problem is that, in reality, polished edges can be sticky and low grit hones can produce polished edges.

It would be helpful if some of you could provide your own understanding of the terms, and examples of how you would prepare blades you would call toothy and how you would prepare blades you would call polished. Also, what sort of tasks each (using your own understanding of the terms) display different performance between the two.

 

[Obsessed with Edges]

At the most basic level, I tend to equate 'polished' with any edge that I don't actually feel when it cuts me, and 'toothy' with an edge that hurts like the devil when it cuts me. Both make me bleed just as much and cut just as effortlessly; but the PAIN is the difference.

The 'polished' & painless edge would be akin to something honed in a tight grit sequence up through a UF ceramic and further polished on a strop to mirror (by naked eye, not magnified). The painful 'toothy' edge could be far more variable in finish; anything from the ~150-grit belt-finished factory edges on some of my Case knives, all the way up through an EF DMT (1200 mesh/9µ), or maybe even an EEF DMT (8000/3µ), depending on the steel.

I also tend to equate 'toothy' edges with anything that'll immediately 'grab' the media being cut, even by incidental contact. Something that'll bite into and cut the face of a phonebook page, using the belly of the blade, for example. I wouldn't ordinarily expect a more 'polished' edge to do that, without making more of a deliberate effort.


David

 

[Jason B.]

In waterstones you could consider most 2k and under stones the creators of toothy edges. From about 4k but maybe closer to 6k you get into polished edges. Beyond 6k is silly unless you are honing a straight razor.

As David said,

When the edge grabs more and bites into what it's cutting. If you feel it with your fingers it grabs them, you feel the "teeth" of the edge as they want to cut your flesh. Yes, you can get a similar feeling with polished edges but I would describe a polished edge as more of a burning sensation where as toothy is more of a ripping pain.

FYI, I'm not exactly cutting myself but the fingerprints do become damaged

 

[Mikey's Deli]

Polished: sharpen to a point beyond noticeable micro serrations.

Toothy: sharpened to a lesser point, maintaining micro serrations.

Does that make sense, fellas?

 

[Jason B.]

Does that make sense, fellas?

None of this makes sense.

 

[Mikey's Deli]

None of this makes sense.

Ok. Where am I wrong? Isn't it toothy because of the micro serrations?
Not spoiling for a fight. Looking to better understand.

 

[Obsessed with Edges]

Polished: sharpen to a point beyond noticeable micro serrations.

Toothy: sharpened to a lesser point, maintaining micro serrations.

Does that make sense, fellas?

I think that's part of what Todd is asking to clarify (or 'quantify' might be more accurate). What exactly are 'micro serrations'? By what standard are they 'noticeable' or not? By what grit are they produced? How wide/deep are they? Even a polished edge will have them to some degree (can't hide under a SEM or other high-mag microscope view), and each individual's idea of what they are will likely vary. Many don't even refine an edge beyond ~320 or so, calling that finish 'micro-serrated', with anything higher being 'polished' in their view. Still others might not call it 'polished' until it's well beyond 2000 (or 8K, 15K, 100K, etc).


David

 

[Mikey's Deli]

I heard that. I should have said refined to a lesser extent.

 

[Jason B.]

Ok. Where am I wrong? Isn't it toothy because of the micro serrations?
Not spoiling for a fight. Looking to better understand.

I meant the thread in general.

 

[ToddS]

I think that's part of what Todd is asking to clarify (or 'quantify' might be more accurate). What exactly are 'micro serrations'? By what standard are they 'noticeable' or not? By what grit are they produced? How wide/deep are they? Even a polished edge will have them to some degree (can't hide under a SEM or other high-mag microscope view), and each individual's idea of what they are will likely vary. Many don't even refine an edge beyond ~320 or so, calling that finish 'micro-serrated', with anything higher being 'polished' in their view. Still others might not call it 'polished' until it's well beyond 2000 (or 8K, 15K, 100K, etc).


David

Thank-you for this. Indeed, I am trying to understand the significance of irregular edge geometry.

I can accept the description of an edge that "bites" as being "toothy" but in reality I seldom observe features that I would describe as "teeth" or "serrations."

 

[grizzled gizzard]

I think the best practical definition could most easily be described with the standard three finger test.

If the edge feels slick and shaves well it's polished. If it feels slick and doesn't shave, it's dull.

If the edge grabs your fingerprints, it's "toothy".

If you feel any pain at all, you've cut through several thousandths of skin. I've never done that. I've never heard of this being a painful way to check your edge.

It's definitely an acquired sense. What you really learn is how much pressure and how little movement it takes to make the determination.

Within reason, grit size isn't as important as grit shape, but the substrate obviously has a large effect too. Stones and hones are different animals.

Boron carbide is a very hard abrasive, but it's not "sharp". Poly diamond is the "sharpest" abrasive I'm aware of.

Strop on 1um boron carbide and compare that to 1um poly diamond. Even at 16K, the difference is polished vs toothy.

You will hear razor guys talking about the difference all the way to .025um (640,000 grit) poly diamond.

 

[HeavyHanded]

Thank-you for this. Indeed, I am trying to understand the significance of irregular edge geometry.

I can accept the description of an edge that "bites" as being "toothy" but in reality I seldom observe features that I would describe as "teeth" or "serrations."

This is why I describe them as "irregularities" - they don't look like serrations, but they do function more or less the same. There are high points that wind up being submicron, with lower points between. The slopes between may or may not have edges going down into the low spots that are still below a micron or low enough in the single digits that they still cut well. Also, some materials do not need submicron or even low micron edge to part them as long as the irregularities catch and tear to initiate the cut, or to tear the material when it piles up against the edge and reaches a given pressure threshold - imagine shrinkwrap.

A microscopic or SEM view of the edge is out of context without a view of everyday materials to get a feel for how the edge will interact with any given target.

How the edges are formed will effect the ratio and depth of irregularities by the overall mean deviation of the cutting edge - how much it meanders back and forth from the ideal centerline. It is my experience that different means can whip up edges that manipulate this ratio, so not all toothy edges cut the same by any means.

There's a lot to this, the topic almost needs to be broken down more.

 

[Nisto]

I have blades that feel toothy and blades that feel smooth after going through the same sharpening process.

For example, my Gene Ingram #1 in D2 feels very toothy when sharpened on the Sharpmaker Ultrafine rods. A custom I had with similar blame geometry, FFG and 40 degree secondary bevel but made from 52000 never got that toothy edge despite different sharpening attempts including using the Sharpmaker. In the end I sold it on.

For me toothyness is a function of blade steel and heat treatment.

Nick

 

[Bob6794]

Toothy: Think of a coarser blade that isn't as refined/polished and it has what seems like micro serrations due to the groves that are still in there from the more coarse media that was used to sharpen it. These act like little saw blades and helps it in slicing applications.

Polished: More refined and those micro serrations are far less noticeable so it doesn't grip and want to dig in and act like a saw blade but prefers to be pushed through an object with ease like a very smooth wedge and there are very little serrations to hinder this in this use. So it works better with push cuts.

They can both be sharp, extremely sharp no less. It's a question of what application you are using the knife for which determines which finish would work better but by the nature of it neither is better than the other. Though a lot of us find a happy middle ground we like, with me I personally love the finish off of my norton economy stone the india version on the fine side and think that probably the best all around finish I can get from everything I own and tried thus far.

 

[ToddS]

I think the best practical definition could most easily be described with the standard three finger test.

If the edge feels slick and shaves well it's polished. If it feels slick and doesn't shave, it's dull.

If the edge grabs your fingerprints, it's "toothy".

That makes sense to me, with one exception. A very keen stropped/polished straight razor will sink in to the thumbpad with even the lightest touch.

Boron carbide is a very hard abrasive, but it's not "sharp". Poly diamond is the "sharpest" abrasive I'm aware of.

Strop on 1um boron carbide and compare that to 1um poly diamond. Even at 16K, the difference is polished vs toothy.

You will hear razor guys talking about the difference all the way to .025um (640,000 grit) poly diamond.

I have not tried 1 micron boron carbide, but none of the dozens of stropping compounds I have experimented with leave any sort of microscopic serrations on carbon steel. What sort of steel have you experienced this with? I could imaging a differential removal of iron vs carbide leaving a "toothy" edge...

 

[ToddS]

This is why I describe them as "irregularities" - they don't look like serrations, but they do function more or less the same. There are high points that wind up being submicron, with lower points between. The slopes between may or may not have edges going down into the low spots that are still below a micron or low enough in the single digits that they still cut well. Also, some materials do not need submicron or even low micron edge to part them as long as the irregularities catch and tear to initiate the cut, or to tear the material when it piles up against the edge and reaches a given pressure threshold - imagine shrinkwrap.

A microscopic or SEM view of the edge is out of context without a view of everyday materials to get a feel for how the edge will interact with any given target.

How the edges are formed will effect the ratio and depth of irregularities by the overall mean deviation of the cutting edge - how much it meanders back and forth from the ideal centerline. It is my experience that different means can whip up edges that manipulate this ratio, so not all toothy edges cut the same by any means.

There's a lot to this, the topic almost needs to be broken down more.

Essentially, sharpness is about pressure - force/area. We can increase pressure by increasing force or decreasing contact area (sharpening). There are two ways we can decrease the contact area; making the edge narrower (uniformly along the apex) or by producing high points (irregularities). We can also imagine that those high points will wear first, protecting the keen edges in the low points. As an example, a sewing needle easily penetrates skin, but a blade sharpened to the same geometry (in 2D) is too dull.

I reject the idea that this is not a microscopic effect - the difference between the two types of edges were are discussing occurs at the micron level. For example, a toothy edge will be made polished by simply removing the last 1 or 2 microns of the edge with a pasted strop.

 

[bgentry]

With a lot of stuff like this, at first I can only distinguish between VERY obvious differences. ...and as much as I *think* I'm a sharpening nut, I'm still rather unsophisticated compared to many people here. So given all that, I need a REALLY toothy edge to be able to experience the difference easily.

In my case an edge sharpened on a 100 micron belt and *just* touched up on a much finer (5 micron) belt until it is deburred is my standard for "toothy". An edge like that obviously slices differently and when cutting highly abrasive material LASTS a lot longer than even a moderately polished edge, like something that comes from a Spyderco medium (~600 - 900 grit).

Brian.

 

[HeavyHanded]

Essentially, sharpness is about pressure - force/area. We can increase pressure by increasing force or decreasing contact area (sharpening). There are two ways we can decrease the contact area; making the edge narrower (uniformly along the apex) or by producing high points (irregularities). We can also imagine that those high points will wear first, protecting the keen edges in the low points. As an example, a sewing needle easily penetrates skin, but a blade sharpened to the same geometry (in 2D) is too dull.

I reject the idea that this is not a microscopic effect - the difference between the two types of edges were are discussing occurs at the micron level. For example, a toothy edge will be made polished by simply removing the last 1 or 2 microns of the edge with a pasted strop.

I didn't say the mechanism wasn't microscopic, rather that images of various edge preparations are seldom if ever accompanied by images of the materials they cut well. Some toothy edges though, are readily discernible with the naked eye. And then sharpness cannot be readily separated from a description of what is being cut - some materials part with far less applied force when a toothy edge is drawn across them compared to a polished edge being pulled or pressed. Some materials part more readily when a highly uniform edge is pushed straight into them and will not part at all when pressed upon with a toothy edge, or resist parting when the edge is drawn across, toothy or refined.

Using the sewing needle analogy though it doesn't apply 100% to this conversation, most of them are not as sharp as they could be, and for a reason - the sharper needle will stick in individual strands, but we would prefer it slip through the weave. Edges are the same way, they work best if tailored to some extent for the material they will be cutting - they don't exist in a vacuum.

And not all toothy edges are capable of being converted to a polished edge with a pasted strop, at least not without rounding them over. Is a sliding scale, an edge backhoned on a 6k waterstone might still qualify as "toothy". This why I say the conversation really needs some closer boundaries if specifics are going to be discussed. Otherwise, toothy draws better, polished presses better.

 

[ToddS]

I didn't say the mechanism wasn't microscopic, rather that images of various edge preparations are seldom if ever accompanied by images of the materials they cut well. Some toothy edges though, are readily discernible with the naked eye. And then sharpness cannot be readily separated from a description of what is being cut - some materials part with far less applied force when a toothy edge is drawn across them compared to a polished edge being pulled or pressed. Some materials part more readily when a highly uniform edge is pushed straight into them and will not part at all when pressed upon with a toothy edge, or resist parting when the edge is drawn across, toothy or refined.

Which cuts better is a topic for another thread. We would certainly have to distinguish between cutting, tearing, cleaving, shearing, etc. I think my confusion has been due to the use of the word "toothy" to describe a blades that bites, rather than one that is actually microscopically toothy or serrated.

Using the sewing needle analogy though it doesn't apply 100% to this conversation, most of them are not as sharp as they could be, and for a reason - the sharper needle will stick in individual strands, but we would prefer it slip through the weave. Edges are the same way, they work best if tailored to some extent for the material they will be cutting - they don't exist in a vacuum.

Sorry, I was specifically referring to the thumbpad feel, or cutting of skin. A needle is not typically very sharp but can penetrate skin because the small contact area results in high pressure.

And not all toothy edges are capable of being converted to a polished edge with a pasted strop, at least not without rounding them over. Is a sliding scale, an edge backhoned on a 6k waterstone might still qualify as "toothy". This why I say the conversation really needs some closer boundaries if specifics are going to be discussed. Otherwise, toothy draws better, polished presses better.

I assume you mean that backhoning on a 6k waterstone produces a foil-burr and after that is ripped off (by drawing through wood, etc) the edge has a "bite" to it and therefore you call it toothy.
"Rounded-off" is an interesting term - it sounds negative, but in fact this is the mechanism by which a burr is prevented/removed by stropping.

 

[HeavyHanded]

I assume you mean that backhoning on a 6k waterstone produces a foil-burr and after that is ripped off (by drawing through wood, etc) the edge has a "bite" to it and therefore you call it toothy.

Not exactly. If the waterstone has a somewhat soft binder, or loose abrasive on the surface, it can grind a very clean edge with inconsequentially small or no burr formation - provided the amount of pressure and approach angle are well controlled. Keeping in mind, abrasive mobility or lack thereof is one of the major determinants in the amount of burr formation.

It is my belief that this mechanism produces fine irregularity along the edge but with a relatively narrow cross section. On a similar sized abrasive with a leading pass, the edge will be more uniform. On an edge with the same amount of irregularity done with a leading pass on a fixed abrasive, the cross section will be a bit wider across the edge.

Also keeping in mind the above is speculation based mostly on performance and somewhat on what information I can glean from an optical microscope...

"Rounded-off" is an interesting term - it sounds negative, but in fact this is the mechanism by which a burr is prevented/removed by stropping.

Up to a point. Ideally the amount of upward force is only what is needed to work on the burr and we stop short of rounding the cutting edge to any appreciable degree. The issue with a very toothy edge is that the tips will erode rapidly, having relatively little mass compared to the lower spots on the edge. The toothy edge is also wider across - greater deviation across the theoretical center line of the edge. As the tops erode, the edge becomes more broad much more rapidly under the same treatment than an edge that started out more uniform.

A harder strop backing helps a great deal with this effect, but then it all depends on just how toothy, just how hard the strop is, how loose the abrasive is on the strop etc. When one strops on a hardwood lapping board or similar, there is very little rounding of the apex, on up to a waterstone where there is essentially none. But then the margin of error, the point at which burr formation or edge complications from loosing the target angle will become smaller as well.

I'm not sure that this is still applicable to the original conversation anymore, the exact definition of "toothy" has always been a bit slippery to pin down, kind of like describing what is "spicy". Past a certain point is obvious, but prior to that not everyone will agree.