(Why) Are Coarse hones faster than Fine hones?

HeavyHanded said:
Isn't this pretty much what I stated?

At low pressure they are fairly close though the coarse still has advantage. In order to drive the coarse abrasive further into the steel more force needs to be applied. Yes the fine abrasive fails to deliver even with more force and presumably a like increase in depth or even greater as a percentage of its total size (proportionately, it cannot dig deeper than it stands proud), but I never claimed otherwise. Added depth per pass = greater stock removal for a similar feed rate, it requires additional force for the coarse abrasive to distinguish itself.

The 80% figure - 80% of a 20 micron abrasive depth is 16 micron. 80% of a 100 micron potential depth is...80 microns. Again, these are random assignments - actual abrasive depth is a fraction of these numbers in most cases. In many cases with a coarse abrasive it is probably not possible to drive the abrasive to 80% depth with anything approaching normal operating pressures. Not needed in any event, 50% in this example is still 50 micron, far more than the 20 micron depth of the smaller abrasive.
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I just want to be sure that we are on the same page. :thumbup:

Using "% depth" as a measure of anything is not likely to be helpful. Consider the distance of the binder-surface from the work-piece as you attempt to reach this % depth, or how much work-piece material must be displaced to achieve it. Remember, the abrasive particles do not exist in isolation, they are surrounded by their compatriots all pursuing the same depth (well, not all, we know that no hone is engineered with perfect uniformity of grit size among the abrasive particles, but you get the idea), and they are also surrounded by the space between each particle. In the fine grit (your 20 micron example), there are MANY many more particles pushing in and, conversely, holding back the hone from reaching the desired level of penetration. THAT is why it takes so much more force to get the same level of wear-performance (measured by amount of material removed from the work-piece) with the fine-grit vs the coarse-grit.

Look at the chart presented:

It takes 2 kgf for the (presumably) 15 um abrasive to achieve the same rate of wear as the 30 um abrasive achieves with only 1 kgf. And at 4kgf on the 15 um abrasive you have not been able to meet the performance of the 30 um abrasive using only 2 kgf. It is possible that using even more force with the high-grit/low-micron hone will cease to present improvements in performance as it "bottoms out" while the low-grit/high-micron hone continues to perform until eventually it too "bottoms out".

Recognize that the reason that the hones have roughly equal performance at the low-force levels is that the low-grit/high-micron teeth are already penetrating deeper than the high-grit/low-micron teeth. If it were otherwise, there is no way low-grit could match high-grit due to the massive difference in the number of teeth making contact. The highest-grit hone always has the highest number of teeth making contact. If the high and low grits were penetrating to the same depth (not % depth) at a given force level, the high-grit would win out because of number of teeth alone. But that is not what is observed! Both the 1979 and 1999 papers show equal performance for low and high grits at low pressure when clearing is efficient. The low-grit should be at a disadvantage due to fewer teeth working, but the fewer teeth allow for deeper penetration at a given level of force = more material removed per tooth which compensates for the reduced arsenal and more than compensates as more pressure is applied.

In other words, it is possible that the force required to achieve "80% depth" or whatever fraction you choose is the same regardless of grit size.
 
chiral.grolim said:
I really have no explanation for ToddS' results since they disagree with well-established science on the matter. Let me see:



We don't "assume" they are faster, there are published measurements of the fact. That said, the 1979 paper above (there is probably a more recent one, but all refer back in agreement to this one) uses ToddS' force as their lowest level and only the Shapton Pro 320 & Chosera 1k would fit with their tests:

...
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In that experiment they use a 1/4 rod, so the pressure with 500g force will be 3 times the pressure I used. They are using emery paper and the pin (rod) follows a spiral so that it only sees "fresh" abrasive. I lapped the waterstones initially and again every 500 round trips of the workpiece.
 
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These are the results of my "low pressure" test
removal-rate3.jpg
 
I don't see myself buying those anytime soon but you can get a 0.001g scale for about $20 if you want to try this yourself.
 
So it would seem that the distinction here is that the finer abrasives can only cut at comparable speeds with the coarser abrasives at lighter pressures and if the swarf is kept cleared away. At heavier pressures or if the finer abrasives don't get cleared so they can keep cutting efficiently it seems that the coarser stones will be faster.
 
I did a couple of measurements at about 5 times the pressure and the coarser stones did pull ahead. The Shapton Pro 320 was twice as fast as the Shapton glass 4k with about 5 lbs of force on the 1cm^2 workpiece. The pressure wasn't quite high enough to get the 320 to go muddy.
 
You're doing this just to irritate people aren't you ? :)

:) OK . . . I'll play . . . there is the chance I am totally deluded and I can do all of my sharpening with just 8000 grit. RRRRRRrrrrrriiiiiiight.

Which is faster coarse grit or fine.

While attempting to flattening A2 woodworking hand plane blade backs I learned some things.
I think.

I began with the Norton 220 water stone. You know that awful thing that crumbles and turns to rolly poly ball bearing like grit if you even have the audacity to get it wet and use it. After hours of rubbing the blade back and forth all around on those ball bearings I finally came to my senses and stopped. Using a Norton 220 water stone is like hitting yourself with a hammer . . . it feels so good when you stop. My opinion of it is that it would be good for a door stop if it were only a bit heavier . . . as it is . . . well . . .

I moved on

The first time I ever bought a diamond plate was solely for the purpose of flatten plane blade backs. DMT Extra, Extra, Coarse (220 or so). Sounds good doesn't it. "Diamond Grit" has a SOLID, exotic, INDUSTRIAL, quality to it. It was sooooo much better than rolly-polly-man but still was no where near up to this job in any shape or form.

The manufacture’s directions suggested to not press hard; to “let the stone do the work”.
Yah . . . after hours of gently persuading the blade backs to flatten I was desperate. I started experimenting with more pressure.

Finally out of desperation I even put the stone on the floor and really got my butt into it for long periods as you see Toshio Odate doing here.


Even some place for the swarf to go (down in the dimples) one would think this was the ideal way to flatten the backs of the plane blades.



You can see by the arc of the polished area that the areas closer to the corners of the edge were proud and the center is some what hollow. You would think that taking off such a small amount of metal would be fairly easy with an “‘Extra, Extra, Coarse” stone.
Nope the blades just laughed at me and kind of got scratched up a little bit but when polished were not flat . . . yet.



What finally did it :
Took an 80 grit zirconium alumina hand held belt sander belt (blue grit) great stuff ! ! !
Cut the belt and glued it down to a marble tile.
Flattened blades . . . just like one would want . . . in a timely manner.

In my mind end of story. Coarser grit removes hardened alloy steel faster than finer grit.
Other certainties (at least in my mind) :
  • Grit fixed to a flat surface cuts much better and FASTER than loose grit on some “magical” surface that one is asked to pay hundreds of dollars for.
  • Diamond at least the stones I have experienced are questionable abraders and at least for the less than hardest of the hardest steel alloys . . . diamond DOES NOT represent the best choice in an efficient abrader.
  • Some times manufacture’s recommendations are not always accurate or in the ball park
  • Extra, extra coarse is along the lines of 46 to 80 grit not 220 or maybe it just depends on ones perspective or use for it.

Oh and finally a so far unexplained phenomenon that I have observed is that having chocolate cake in the same room seems to accelerate the sharpening effect. I haven’t been able to pin down the physics at work here . . . kind of an “X” factor . . . I call it : CCE
Chocolate Cake Effect.

Life’s little mysteries. We can’t be expected to solve all of the secrets of the universe in one sitting though now can we ?


PS: raspberries have a marked catalytic effect
PPS: and the ice cream ? Do not under any circumstances introduce this substance into the mix unless you have first class facilities and training . . . there could be a run away melt down that could annihilate all life on earth as we know it. You have been warned !

Oh unless you finish sharpening and put all the sharpening supplies away in containment . . . then . . . of course . . . you / we . . . are perfectly safe.
 
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So it would seem that the distinction here is that the finer abrasives can only cut at comparable speeds with the coarser abrasives at lighter pressures and if the swarf is kept cleared away.
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Ah Oh !

that seems to go along with what I have said (found from actual observation / use) that slurry is silly and counter productive, especially in fine stones, and that frequently rinsing the stone under the running water tap and keeping the pores of the stone clean and cleared of extra grit and metal swarf (as opposed to letting the stone "age" and get better with use (I forget the term for that) is the best way to get the best and fastest edge up to and even including getting rid of any wire edge.

YES !
 
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I can see I made a mistake in using the word "coarse." I'm really only interested in 1k and higher grit.
 
One other factor that hasn't been mentioned so far is the surface irregularity of the object being abraded. Assuming a perfectly perfectly flat surface being abraded and everything else the same between the two abrading surfaces except for grit, I can see that the rate of material removal to be the same or close to the same for both given the original post. The total surface contact between the surface being abraded and the two hones are the same so the rate of removal would be the same.

But as the irregularity of the surface being abraded gets rougher than the smoother abrading material and approaches the grit of the grittier abrading material, then the surface to surface contact with the smoother hone is limited by its grit while the surface to surface contact with the rougher hone increases as there are more hills and valleys to interact with each other between the two.

Given the original post, I would suggest that over time as the surface is abraded by both hones, the surface can only approach and equal the roughness of the hone being used. At some point, when the surfaces matches the smooth hone, the rate of removal will be constant (assuming everything else remains the same - no wear) but the surface with the rougher hone will get rougher than the surface with the smoother stone and the rate of removal at that point will be higher than that of the surface being honed with the smoother hone.

What's surprising to me is that this isn't even a theoretically based discussion. Our practical experience should have pointed this out and it's not a mirage / illusion. If our thought experiments reach to a conclusion that contradicts apparent real world results, then it means the thought experiment was set up incorrectly.
 
Don't know why this is a discussion. Bigger teeth take out bigger chunks. As you make the teeth smaller they take smaller bites. Eventually you'll take such small bites that you need a microscope to see the bite marks. The teeth can be of varying sharpness and the teeth need to be harder than what they're trying to bite or the teeth will break. Even if your teeth are harder than what you're trying to bite, if you bite too hard or too fast or at the wrong angle, you may chip your teeth which degrades the ability of the teeth to bite.

In the end, your teeth need to be sharp and harder than what you're trying to bite into. The finer your teeth, the smaller the mark. And if you're seeking a really refined apex, then you need really, really fine teeth that leave almost no mark and those teeth need to be harder than the hardest part of the steel, ie, the carbides. If there are no carbides and if the steel is softer than whatever stones are out there, then by all means, use whatever.
 
Rey HRH said:
One other factor that hasn't been mentioned so far is the surface irregularity of the object being abraded. Assuming a perfectly perfectly flat surface being abraded and everything else the same between the two abrading surfaces except for grit, I can see that the rate of material removal to be the same or close to the same for both given the original post. The total surface contact between the surface being abraded and the two hones are the same so the rate of removal would be the same.

But as the irregularity of the surface being abraded gets rougher than the smoother abrading material and approaches the grit of the grittier abrading material, then the surface to surface contact with the smoother hone is limited by its grit while the surface to surface contact with the rougher hone increases as there are more hills and valleys to interact with each other between the two.

Given the original post, I would suggest that over time as the surface is abraded by both hones, the surface can only approach and equal the roughness of the hone being used. At some point, when the surfaces matches the smooth hone, the rate of removal will be constant (assuming everything else remains the same - no wear) but the surface with the rougher hone will get rougher than the surface with the smoother stone and the rate of removal at that point will be higher than that of the surface being honed with the smoother hone.

What's surprising to me is that this isn't even a theoretically based discussion. Our practical experience should have pointed this out and it's not a mirage / illusion. If our thought experiments reach to a conclusion that contradicts apparent real world results, then it means the thought experiment was set up incorrectly.
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I'd thought about this earlier, but it seems Todd is using hundreds of passes and tracking the removal every 250 passes, at least that's what was put up on page 2 of this thread re Shapton Glass 16k.

The initial surface condition will make a big difference at first. If it's too far from the grit to be measured it could effect the results even after hundreds of passes, but he went out to 2000 back and forth. If the surface isn't converted at that point then the results likely aren't valid.

I agree, a standard starting finish is a prerequisite, preferably the finish of the hone being tested.
 
HeavyHanded said:
I'd thought about this earlier, but it seems Todd is using hundreds of passes and tracking the removal every 250 passes, at least that's what was put up on page 2 of this thread re Shapton Glass 16k.

The initial surface condition will make a big difference at first. If it's too far from the grit to be measured it could effect the results even after hundreds of passes, but he went out to 2000 back and forth. If the surface isn't converted at that point then the results likely aren't valid.

I agree, a standard starting finish is a prerequisite, preferably the finish of the hone being tested.
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There are two ways to approach this measurement, one is to produce a standard starting finish, say 20k grit, then go to the hone under test for some number of passes and then measure the loss of mass. This is the approach I would use if I wanted to show what the surface of the metal looked like after that particular hone, but it's not ideal for accurately measuring mass loss.

What I did instead was prepare the waterstones by lapping with the Atoma 400 on all but the Sigma 220 where I used an Atoma 140. The diamond plates were used as they are.

Then do some number of passes, between 100 and 250, weigh the workpiece, rinse the hone, do another set, weigh & rinse, etc. I re-lapped the waterstones every 500 laps. This approach removes many potential errors from variations in force applied, length and direction of the passes, etc. More importantly it allows me to observe consistency of repeated measurements.

Some of the hones were faster immediately after lapping, but this was short-lived (10-50 laps), compared to the 500 laps between lappings. So what I'm measuring is the equilibrium rate (where enough material has been removed to prevent any contribution from the initial surface finish).
 
ToddS said:
Because I actually measured the removal rate, and didn't observe the expected correlation between grit and removal rate.
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Do you believe there's a difference between polycrystalline abrasives and mono? Have you checked the difference? I'm really just curious.

If you had a single rock shaped like a square and you had a single rock shaped like a big gnarly chunk of concrete and you embedded them firmly into the ground and then rubbed a piece of glass repeatedly over both, once the single cutting point of the square rock was worn down, it doesn't seem like it'd cut that well leaving much smoother and shallower cuts. If you took 100 much smaller square rocks, put them all together, and stuck them in the ground it'd take longer for those points to wear down.

With the one, big gnarly chunk of concrete, it'd keep cutting the glass for quite awhile longer. If you took many much smaller pieces of gnarly concrete, the jagged pieces would break or wear off faster than the single big chunk leading to smoother and shallower cuts.

So thinking of it this way, is it possible that most diamond hones are monocrystalline and the larger grit sizes just wear down much faster than the smaller grits leading to the conclusion that lower grits leave sharper edges where in reality the smaller grit monocrystalline particles just cut more effectively for a longer time? And conversely, larger grit polycrystalline cut at a more efficient pace longer than the smaller polycrystalline particles?

To wrap up my thoughts, would starting with larger monocrystalline diamond particles and at about 600 grit swap to polycrystalline diamond or CBN where the particles break down leave a more consistent edge?

And are your tests on simple soft carbon steels like razors or do they include very hard, high carbide steels and do they act the same? And if they increased the density of lower grit size particles would it leave a more even finish?
 
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