JUST OUT OF CURIOUSITY

[Robert Ptacek]

In the debate between polished and toothy what is considered the demarcation line in grit between polished/toothy.

 

[Old Biker]

What grit standard do you prefer, FEPA-f, JIS, or one of the others? There is a big difference between some of the grit standards. Between there being multiple different grit standards, and everyone having a different opinion on what is polished, and everyone used to using the standard used by their favorite stone manufacturer. It's going to be difficult to know exactly what the answers are.

That being said. In my opinion, the line would fall about 13 to 14 microns. Courser would be toothy. Finer starts getting polished.

O.B.

 

[Obsessed with Edges]

I delineate 'polished' vs 'toothy' based on how the edge cuts, or at least how I perceive it cuts. For me, there's a certain 'bite' or zipper-like aggressiveness to an edge I'd call 'toothy'. Can feel it directly on the fingertips or even in the feedback felt and the sound heard (sort of a buzzing effect) when cutting into paper.

And for the 'polished' edge, that's the threshold where I don't perceive that same bite or any of the vibration feedback felt in cutting paper. Can still be wickedly sharp and will sail through paper nearly silently or slice a finger nearly painlessly or imperceptably. The nature of the edge's slicing aggressiveness is completely different from that produced by an edge with a more 'toothy' bite.

And both of the above can vary in terms of at what grit value it happens. That depends on other variables like the steel's makeup (carbides, i.e., wear resistance) and hardness. So, a 'toothy' bite produced on a less wear-resistant or less-hard steel, by a particular stone of a particular grit, might be more 'polished' when used on a harder and more wear-resistant steel, because the particular grit won't cut as deeply in the high-wear steel under the same pressure, as compared to how deeply it'll cut into a softer & less wear-resistant steel. I see this regularly in comparing the response of steels like 420HC vs. D2, using the same type of stone. The D2 will tend to approach 'polished' more readily, while the 420HC will take much deeper scratches from the stone's grit and will have that obvious, biting 'tooth' in how it cuts. I even notice it repeatedly in sharpening a single steel type at varying hardness, like 420HC. One blade at HRC 55-57, and another in the same steel at HRC 57-59. With a natural stone or an AlOx ceramic, I consistently see the edge a little more 'polished' on the slightly harder version of the steel, as compared to the micro-toothy effect perceived in the slightly less-hard blade in the same steel. This is why I don't associate 'polished' or 'toothy' with a fixed range of grit values. It depends on other variables in combination with the grit of the stone itself and how stone & steel interact with one another.

 

[FortyTwoBlades]

Grit is only one of many factors that result in the kind of finish produced on a given knife by a given stone, and toothy vs. polished is a sliding scale. As such it's not so much that it goes suddenly from being toothy to being polished, but rather that for every knife you should be considering where on the scale you want it to land, and then finding the abrasives that get you the edge qualities you desire. This will vary from knife to knife and stone to stone.

 

[Obsessed with Edges]

Throwing something else in, for perspective on grit ratings and how misleadingly 'coarse' they might be, or not.

I'd noticed this a long time ago, with relatively inexpensive stones in aluminum oxide in particular. You could buy some stones at a hardware store that were marketed toward use as smoothing stones to be used on the edges of ceramic tiles for the floor or countertop. The stones were often rated at something like 60 or 80 grit, which on the surface might seem much too coarse for use in sharpening edged tools like knives. But those same stones, even when they'd still grind or cut a knife steel relatively decently, would perform at a much finer level than the rated grit would imply. I compared their finishing characteristic more closely to other stones rated in the 400-600 range, in terms of the edge finish left by the stone. I think a lot of the stone's performance was likely due to grit shape (more blocky & rounded, less sharp or jagged) and perhaps its wear resistance as well. The stones' grit tended to wear or 'glaze' very fast in use, even on relatively simple steels. So, if the stone might've felt very coarse under the blade in the first pass or two of sharpening, its aggression would quickly taper off and from then on, it would function more like a mid/high-grit range stone. I have one of these stones today, and it performs less aggressively than some of my other AlOx oilstones in the 400+ range (like a broken-in Fine India, for example).

This is part of the reason why I don't put a lot of stock in a stone's rated grit by itself, until I've tried it out against some of the knife steels I'm familiar with.

 

[FortyTwoBlades]

That dynamic is likely due to the influence of grit protrusion, and is one of the reasons why I formulated my Manticore series in such an unconventional manner. Very coarse stones often have their surface grit aligned with the mold surface which makes them slick on first use, and the ratio by volume of grit vs. binder means that generating sufficient pressure to get grains to release can be tricky. As a result many ultra-coarse stones end up working like a planer blade set to a shallow depth of cut despite their grains being enormous. The difference in friability between the black and green silicon carbide helps maintain a higher degree of grit protrusion in use.

 

[000Robert]

I use Wicked Edge diamond stones. For toothy edges I normally take them to 800 grit and sometimes 1000 grit.

 

[Robert Ptacek]

A lot to think about.It does make sense that the same steel done at different hardness can have a different edge feel to them.Thank You.