Apex width

[jpm2]

I'm wondering how to get an idea of limit to apex width depending on the micron rating of a stone, if possible.

I'm sure "it depends" on a lot of variables like type of stone, pressure used, angle?, maybe type of steel? and stuff like that. But let's say we're using a non friable type stone like a fine diamond plate rated around 25 micron.

Does depth of cut make more difference than size of grit?
Would the apex width be limited to the 25 micron rating or anywhere close?
Any ideas what the minimum would be?

EDIT:
It appears I'm way off base on width of apex guestament according to this post
https://www.bladeforums.com/threads/sharpness-chart.1535016/
and this link
http://knifegrinders.com.au/12Resources.htm
if the data is correct.

I often get to this point

- shave forearm against the skin against the grain /BESS 100 /0.2 micron

straight off a fine diamond plate that's rated around 25 micron.

 

[wootzblade]

The abrasive grit size and the edge apex width you get with that abrasive are related by about an order of magnitude, i.e. grit #1000 (15 micron) gives you about 1 micron edge, and honing/stropping with a 0.5 micron abrasive refines your edge to 0.1 - 0.05 micron.
And you can get even better result with lighter strokes.

 

[jpm2]

This is confusing. According to the post above, I shouldn't be able to get anywhere close to 1 micron with a 25 micron plate, but the chart listing edge width vs sharpness descriptions suggest I'm getting at least 0.3 micron (scrape shaving).
Also, when my edge is easily shaving both directions, the edge clearly reflects light with 5x magnification, 30 lumen flashlight, and dark background.

 

[ToddS]

There is no correlation between "grit" rating and apex width. As an example, you can produce a 0.03 micron apex with that Fine DMT if you stay below the pressure threshold for grinding. As another example, the apex width produced by a 320 grit waterstone (with an angle jig) can be over 1 micron in the edge leading direction and well below 0.1 micron in the edge trailing direction.

Beyond this, edge width alone is generally not predictive of cutting efficacy.

The abrasive grit size and the edge apex width you get with that abrasive are related by about an order of magnitude, i.e. grit #1000 (15 micron) gives you about 1 micron edge, .....

No. Can you provide any source for this?

 

[HeavyHanded]

This is confusing. According to the post above, I shouldn't be able to get anywhere close to 1 micron with a 25 micron plate, but the chart listing edge width vs sharpness descriptions suggest I'm getting at least 0.3 micron (scrape shaving).
Also, when my edge is easily shaving both directions, the edge clearly reflects light with 5x magnification, 30 lumen flashlight, and dark background.

It is going to be very difficult to get a fast and dirty answer to the original question. Higher Rockwell steels will resist abrasive penetration at a given load, as will higher carbide content.

In general only about 10% or less of an abrasive stands proud of the surface on a vitreous stone, maybe a bit more on a diamond plate but I really don't know. So a 20 micron abrasive is only digging about 2 microns into the surface at most, and making scratch troughs about 2 micron across (though this is real tough to determine as the neighboring abrasives will tear the edges up, ruining any morphology that might be studied).

Abrasive size doesn't really limit apex width in detail but does influence how much across width and along edge variation you will have. Even off of a somewhat coarse edge you will have a lot of submicron apex areas but the line of the edge jukes back and forth and up and down by the depth of the abrasive - this might not be the full depth the abrasive is capable of digging.

When checking for light it is important to make sure the grind path is pointing directly into the light source or it will shine back along the grind troughs and not just the apex.

 

[Wowbagger]

320 grit waterstone (with an angle jig) can be over 1 micron in the edge leading direction and well below 0.1 micron in the edge trailing direction.

Exactly.
Burnish baby . . . burnish.

PS : baby bear burnish = not too little, not too much but juuuuuuuuus right.

 

[wootzblade]

...
No. Can you provide any source for this?

Todd, with all my respect, you yourself are the source. I assumed that from your saying at scienceofsharp that (a quote):
"There is a common misconception that finer grit correlates with sharper edges.
I think it is important to understand that grit size and scratch size differ by at least an order of magnitude (e.g. 0.5 micron abrasive does create 0.05 micron edge)."

Having read your comments in this thread I realize I did wrong generalization to the coarser grits, and apologize for that.

It's a pity though, that there is no at least an approximate rule of thumb to predict edge width for coarse grits. Or is?
Typically you start shaping bevel on razors, and we on knives on grit #1000.
We do an edge-leading grinding with enough pressure to grind off metal, alternating the blade sides, till come to the point where both sides of the edge meet at the apex, that is usually detected by a raised burr.
With the right technique, the burr will be tiny and hardly tangible, yet it is a reliable indicator the edge sides have met at the apex.
By your observations, what will be the edge apex width adjacent to the burr, i.e. right at the base of the burr?

The above is a part of our sharpening protocol, and we would really appreciate if you could tell at least roughly. I am pretty sure I saw your SEM images for grit #1000, but am not good at interpreting them myself.

 

[wootzblade]

Todd, I've found answer to my question on your webpage https://scienceofsharp.wordpress.com/2014/04/13/the-bevel-set/
With edge leading grinding on grit #1000, you found that:
"The Chosera 1k produces an edge width in the range of 0.5 μm, while the DMT 1200 produces a much keener edge, in the range of 0.1 μm"

You elaborate further:
"...the smaller edge width of the DMT 1200 edge is due to the greater convexity of the bevel near the apex.
Using our definitions of “keen” and “sharp,” the DMT 1200 edge is keener due to the narrower apex width; however, the Chosera 1k edge is sharper due to the smaller angle and narrower edge."

That's great, and thank you.
For some steels we use Japanese wheels JIS #800, comparable to Chosera, and for others CBN #1000 wheels, comparable to the DMT, so thanks to you we've got SEM data for both lines of our sharpening process.

Your findings will change the way we hone on paper wheels with diamond paste in the next step of our sharpening protocol: after the CBN wheel (your DMT analogue) we should be honing at the exact edge angle to narrow the edge on the sides; while after the Japanese wheel we should be honing at a +0.4 degree to sharpen the apex further (e.g. the edge that we set at 15 degree on the Japanese wheel will be honed at 15.4 degree).

You are a living legend, mate.

I am off to my workshop to do test runs with the BESS edge sharpness tester to confirm this new approach.
Thanks again

 

[wootzblade]

By gosh, we did it!
I take this opportunity to wholeheartedly thank Todd S. for the giant job he did on SEM studies and sharing it at scienceofsharp.wordpress.com

Having improved our sharpening protocols based on the SEM data studies, we now steadily get the same or better knife edge sharpness as the DE safety razors:
for quality mainstream steel, from Global and up, 20-35 BESS or near 0.05 micron edge apex width;
For premium high-end steel 15-20 BESS or under 0.05 micron edge apex width.
Note that the Gillette DE razor has 0.1 micron edge and scores 50 BESS.

This level of sharpness is extraordinary for knives, and is more readily achieved by dedicated straight razor sharpeners.

An edge that sharp easily passes the top hanging hair tests, and the Tally-Ho cigarette rolling paper held horizontally push-cut test that for us is an alternative to the hanging hair test.

That has become possible only thanks to the BESS edge sharpness testers and our computer software.

We can't tell you all details of our new sharpening protocol, but we've published the general description here:
http://knifegrinders.com.au/Manuals/SEM.pdf

For CBN (or diamond) wheels, the crucial discovery was to hone on paper wheels at 0.1 degree less. E.g. an edge set on a CBN wheel grit #1000 at 15 degrees per side, is honed at 14.9 degrees.
To set a paper wheel with such precision would not be possible without our software.
This refines the edge not touching the very apex that is already 0.1 micron after the grit #1000 as shown by SEM.
Thanks to that, the edge toothiness is preserved.

The remnants of the microburr are then removed by honing at the exact edge angle (15 degrees in our example) on a paper wheel with the finest diamonds 0.25/0.5 micron, and USB microscope shows the toothiness is all there, which is to advantage for knives.

At this step edges of all knives I've done by this method score about 50 BESS, telling me that we cleanly exposed that 0.1 micron edge that already was there, even before the paper wheels.
This is a true razor sharpness, as we know.

The final step takes them to the sharper than razors level, but I'll keep it secret for the sake of my business.

 

[EdgePal]

An obsidian chopped cutting edge is around 3 nanometer thick. (3 biljon parts of 1 meter).

1 nanometer = 0,000 000 001 part of 1 meter. (1 biljon part of 1 meter)
1 micrometer = 0,000 001 part of 1 meter. (1 miljon part of 1 meter) = 1 mikron.

Thomas

 

[jpm2]

I appreciate all the replies and feel I somewhat understand now.
In a nutshell, and to simplify it for myself, the size of abrasive grit has little to do with what apex width can be achieved, and more to do with width and depth of mini/micro/nano serrations/teeth?

 

[BluntCut MetalWorks]

Grit spacing/density is implicit to size, where psi is inverse to [sharpening contact area ^ 2], so it is matter a huge lot. It is much easier to get proper scratch depth with appropriate psi via grit spacing than by 'light/feature/kiss/etc..' pressure of coarser grit relies on our macro moody arms & hands.

Abrade vector/direction has direct affect on apex dip depth, where max dip depth at abs(90)* (perpendicular), min at zero* (parallel to apex line). Multi overlapped strokes will reduce these depth, however direction has more pronounce deterministic control over dip depth. Of course, zero* only when geometry allows.

Common sense would concurs... shallow cutting = shallow scratches & holes. Abrading vector (has many components, includes flat; curve surfaces) and velocity are can be more or less affects the outcome as static psi of grit density against steel.

I appreciate all the replies and feel I somewhat understand now.
In a nutshell, and to simplify it for myself, the size of abrasive grit has little to do with what apex width can be achieved, and more to do with width and depth of mini/micro/nano serrations/teeth?

 

[microtech85]

In my view, as far as achieving a sharp edge, All of this techical info is overkill, unless you just want to acquire knowledge. I can whittle hair with 20cv by sharpening with the medium stone on spyderco double stuff followed by 2 to 3 passes on loaded strop. It really is not rocket science. My best advice is just experiment to find what you like best. You can get reliably sharp arm hair shaving edges with stones as cheap as store brand sic stones for $6. For me There is not too much benefit to try to get sharper than easy arm hair shaving sharp. When i bring a knife to hair whittling edge, it is lost after only about a dozen cuts through paper towel. I think for edc purposes, one may have a greater appreciation for a semi agressive cutting edge/ utility edge, than a razor smooth edge. It is for this reason i do not like to strop my knife too much; it results in a cutting edge that is not as effective for edc use.

 

[wootzblade]

Now and then I hear calls not to over-science sharpening.
I love one of my friend's likening of the science of sharp we pursue with auto-racing industry, he said: "Numerous automotive innovations which began in auto racing would have seemed like overkill for driving the family sedan at fifty miles per hour. Today many of those innovations have become part of everyday family auto technology... I can see these advancements gradually filter into everyday sharpening. "

 

[HeavyHanded]

In my view, as far as achieving a sharp edge, All of this techical info is overkill, unless you just want to acquire knowledge. I can whittle hair with 20cv by sharpening with the medium stone on spyderco double stuff followed by 2 to 3 passes on loaded strop. It really is not rocket science. My best advice is just experiment to find what you like best. You can get reliably sharp arm hair shaving edges with stones as cheap as store brand sic stones for $6. For me There is not too much benefit to try to get sharper than easy arm hair shaving sharp. When i bring a knife to hair whittling edge, it is lost after only about a dozen cuts through paper towel. I think for edc purposes, one may have a greater appreciation for a semi agressive cutting edge/ utility edge, than a razor smooth edge. It is for this reason i do not like to strop my knife too much; it results in a cutting edge that is not as effective for edc use.

End of day one has to remember - unlike many other endeavors, a knife edge is consumable. So, always a trade off of characteristics vs time in vs application. In some cases a highly refined edge is not even optimal, even in industrial applications.

 

[wootzblade]

Yep, but sales the sharpening service very well, believe me.
We now get sharper than razor edge preserving its toothiness, that is important for knives to cut through tomatoes etc, in kitchen and butcher knives volume sharpening, and the wow effect gets us more customers.

High-end blades owners send us their folders overstate, all across the country, to get the 0.025 micron edge, twice sharper than a safety razor, just because they want to have a safe queen in their collection that does all those sharp tricks, like whittling hair etc. Ours is the only sharpening service in Australia that can do it for M390, CPM-20CV Latrobe's version of Bohler's M390, S290, Vancron-40, ZDP-189 and alike hard alloys - thanks to "overkilling and oversciencing" the sharpening.

 

[microtech85]

End of day one has to remember - unlike many other endeavors, a knife edge is consumable. So, always a trade off of characteristics vs time in vs application. In some cases a highly refined edge is not even optimal, even in industrial applications.

yea, i can spend 5 minutes sharpening and get an edge that will very easily shave arm hair. Or, i can spend another 25 minutes and get it a little better but it won't stay that way for more than a few cuts. On the other hand, with my edc use my 20cv will hold an arm hair shaving edge for about 3-4 weeks without touch-up.
But really, as many know, achieving a sharp edge will be far more dependent on a person's skills rather than the tool used. If one is unable to get a sharp edge, the fault most likely lies with the technique and not the stone. There really is no shortcut. it just takes practice.

 

[wootzblade]

...
But really, as many know, achieving a sharp edge will be far more dependent on a person's skills rather than the tool used. If one is unable to get a sharp edge, the fault most likely lies with the technique and not the stone. There really is no shortcut. it just takes practice.

Anyone can get a sharper than a safety razor edge on his knife within 5-10 min simply following our sharpening protocol, we detailed on the BESS forum:
http://www.bessex.com/forum/showthread.php?tid=209&pid=1613#pid1613

You will need certain equipment to eliminate guesswork.

 

[jpm2]

In my view, as far as achieving a sharp edge, All of this techical info is overkill, unless you just want to acquire knowledge.

I find it hard to ignore when someone states their edge will perform certain sharpness tests, and it was finished on a certain high grit stone, and I sometimes find mine will do the same (or close) from a fine/25m/600 grit diamond plate, although admittedly a well worn one, plus ~3 swipes each side on plain denim. Then you hear talk of, and see pictures of apex measurements, how they were sharpened, and what sharpness tests they pass.

Some of the information is confusing, conflicts, and doesn't align with my own personal experiences.
I have no plans of changing my setup of so many decades, being very well satisfied with my edges.
My question was an attempt to roughly connect the dots of sharpening media micron rating, apex width, and sharpness tests.
I thank wootzblade and everyone else for their efforts, and understand it's only ballpark comparisons for us at best, but better than nothing and a good start.