Picture a coarse cheese grater. The large pieces of grated cheese will clear the grater much quicker than a fine grater, which is more likely to clog. The coarse grater will process the block of cheese much quicker, even though there are far more teeth in the fine.
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(Why) Are Coarse hones faster than Fine hones?
- Thread starter ToddS
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Picture a coarse cheese grater. The large pieces of grated cheese will clear the grater much quicker than a fine grater, which is more likely to clog. The coarse grater will process the block of cheese much quicker, even though there are far more teeth in the fine.
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Yes, that's my point, if clogging/loading is an issue it will affect the fine hone more than the coarse hone, which doesn't help explain why the fine hone is actually faster than the coarse hone.
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I guess we'd need a standardized test of some sort for a number of folk to perform. Relative to this discussion the mystery for me is why your (Todd) results are so similar across hones.
I hog off steel on my coarse hones at a pace none of my finer stones could match even if I sacrificed them to large amounts of force. This effect becomes downright extreme as the surface area of steel to be worked increases. If I could reset bevels at the same speed with a medium or fine hone I wouldn't bother with a coarse one.
Again, I guess we could speculate on X/Y and perhaps the coarse hone removes more at depth and the fine hone more at the surface, but once again that disregards the huge increase in abrasive volume as the grit size increases. Its removing every bit as much steel across the surface and to a deeper depth than the finer abrasive, as the point clears a larger chip, in both depth and width.
For myself, if I am setting the bevel on a dull knife and opt to try on a less coarse stone (say 240 or 320 instead of 120) it often takes longer than doing a proper progression. I'll get through the coarse stone in a matter of minutes for both sides, then it generally takes a bit longer on the next stone. After the medium/coarse I find I can move up through the next stone or two very rapidly.
The coarse stone is the doing the most work and finishes in the least time. The stone that is tasked with cleaning up that grind pattern and prepping for further refinement takes the longest, even though it is (seemingly) doing less stock removal.
At a guess I'd say I lean on both of the first two stones about the same - close to a pound. Once I'm done with them I drop to probably half the amount of force and get done quicker as they're doing less work, finishing with a quarter or less of what I started with.
Perhaps at 320 or so the effect begins to drop off, but the difference between 120 and 320 is notable. The difference between 120 and 220-240 is notable.
I hog off steel on my coarse hones at a pace none of my finer stones could match even if I sacrificed them to large amounts of force. This effect becomes downright extreme as the surface area of steel to be worked increases. If I could reset bevels at the same speed with a medium or fine hone I wouldn't bother with a coarse one.
Again, I guess we could speculate on X/Y and perhaps the coarse hone removes more at depth and the fine hone more at the surface, but once again that disregards the huge increase in abrasive volume as the grit size increases. Its removing every bit as much steel across the surface and to a deeper depth than the finer abrasive, as the point clears a larger chip, in both depth and width.
For myself, if I am setting the bevel on a dull knife and opt to try on a less coarse stone (say 240 or 320 instead of 120) it often takes longer than doing a proper progression. I'll get through the coarse stone in a matter of minutes for both sides, then it generally takes a bit longer on the next stone. After the medium/coarse I find I can move up through the next stone or two very rapidly.
The coarse stone is the doing the most work and finishes in the least time. The stone that is tasked with cleaning up that grind pattern and prepping for further refinement takes the longest, even though it is (seemingly) doing less stock removal.
At a guess I'd say I lean on both of the first two stones about the same - close to a pound. Once I'm done with them I drop to probably half the amount of force and get done quicker as they're doing less work, finishing with a quarter or less of what I started with.
Perhaps at 320 or so the effect begins to drop off, but the difference between 120 and 320 is notable. The difference between 120 and 220-240 is notable.
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David Martin
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This echos my experiences. ^ It doesn't really matter what steel (up to S30V) the same results in regard to speed of grinding occurs. A coarse stone removes more metal quicker.
But metal removal really slows down at around 300 grit. (SiC, diamond and alumina oxide) using approximately the same force. Some I'll use 2 lbs. on when cutting a bevel shoulder down on the coarse stone.
added: When I mention a coarse stone I'm meaning a stone in the neighborhood of 80-150 grit. (a stone I would use to reprofile) Not something 'labeled' a coarse stone. i.e. a coarse diamond stone, 325 grit. DM
But metal removal really slows down at around 300 grit. (SiC, diamond and alumina oxide) using approximately the same force. Some I'll use 2 lbs. on when cutting a bevel shoulder down on the coarse stone.
added: When I mention a coarse stone I'm meaning a stone in the neighborhood of 80-150 grit. (a stone I would use to reprofile) Not something 'labeled' a coarse stone. i.e. a coarse diamond stone, 325 grit. DM
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It's a very simple experiment if you have a +/- 1 milligram scale.
chiral.grolim
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I found what I was looking for in one of the references in that paper, (Gahlin, R. & Jacobson, S. (1999). The particle size effect in abrasion studied by controlled
abrasive surfaces. Wear, Vol. 224, No. 1, pp. 118-125).
The wear rate is the same for fine/medium/coarse densities of sharp tips.
That chart is only true with efficient debris removal...
This is the chart for inefficient debris removal:
In the chart you showed, they improved debris removal (think constantly flushing the hone with water to remove swarf) to eliminate the effect of clogging, which normalized the performance. Then they used THAT model with blunt-tips to again show an effect, which is ostensibly due to the increased force experienced at each point against the work-piece as a result of the points being more spread-out in the "coarse" tool, not so?
In their model, since they are only simulating grit size by instead using particle density, they eliminate the very real impact of grit-size itself and the achievable depth of cut even after blunting, which they do present in an earlier figure:
Where is the next paper wherein they use different grit "sizes" vs distributions to examine wear and blunting?
EDIT to add: here is a paper (not same authors) running the analysis: Effect of abrasive particle size on wear resistance in steels http://www.sciencedirect.com/science/article/pii/S026130690400278X
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That chart is only true with efficient debris removal...
This is the chart for inefficient debris removal:
...
Basically this is consistent with HH comment that open coat sandpaper is less likely to clog.
I'm going to grab a Sigma Power 240 from Lee Valley. They talk about making abrasion rate measurements for various hones, I'd certainly like to see their data. http://www.leevalley.com/en/wood/page.aspx?p=67089&cat=1,43072,67175
David Martin
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So, this last chart shows, as particle size becomes larger (think larger grit size) then wear coefficient plummets. DM
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Todd,
Either the Sigma Power Select II 240 or 1000 will also show what influence the friability of the abrasive has. The lower grit SPS-II stones produce a slurry readily under relatively low force and therefore expose fresh abrasive much more rapidly than waterstones with a stronger bond. Also note that the abrasive density on the SPS-II stones will be a lot higher than the other waterstones you have used because the SPS-II stones have almost zero binder in them.
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I've been meaning to pick one up for a while. The Shapton Pro 320 was a huge disappointment.
Yeah I was disappointed with it for razor work also. For knives it's not awful - though not really better than something like a Crystolon.
All told I'd say it's pretty hard to get this subject sussed out well since there are definitely so many variables. The coarseness of the hone surface during testing (i.e. lapped with a 140 grit diamond plate or on something higher - not to mention whether it's a new plate or an old plate - or even lapped on silicon carbide or other loose grit); friability of the hone; abrasive density, etc.
With a belt sander it seems like finer abrasives cut nearly as fast as coarse ones at first (grit within reason - obviously not comparing a 60 grit belt with a 6,000) but the gap opens up once the belts are used for a while. And I do believe the swarf surely plays a role in limiting the cutting speed of the finer abrasives quite a bit in certain circumstances at least. Working in a machine shop when polishing steel it is pretty obvious how much the cutting speed of the abrasives are slowed down once there's a little swarf buildup. Then give the paper a few good whacks or blow it out and it will start cutting quicker again.
All told I'd say it's pretty hard to get this subject sussed out well since there are definitely so many variables. The coarseness of the hone surface during testing (i.e. lapped with a 140 grit diamond plate or on something higher - not to mention whether it's a new plate or an old plate - or even lapped on silicon carbide or other loose grit); friability of the hone; abrasive density, etc.
With a belt sander it seems like finer abrasives cut nearly as fast as coarse ones at first (grit within reason - obviously not comparing a 60 grit belt with a 6,000) but the gap opens up once the belts are used for a while. And I do believe the swarf surely plays a role in limiting the cutting speed of the finer abrasives quite a bit in certain circumstances at least. Working in a machine shop when polishing steel it is pretty obvious how much the cutting speed of the abrasives are slowed down once there's a little swarf buildup. Then give the paper a few good whacks or blow it out and it will start cutting quicker again.
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Hi,
I think its two part , amount of mud/swarf buildup, and how hard you can push before you get mud.
The bigger the grit/tooth, the more force required to push it into metal,
but if the force you're pushing with exceeds the bond strength,
then you're getting mud/swarf buildup,
which slows down abrasion.
With norton economy stone (this is 120-320 grit),
on the coarse side and fine,
while the stone is pretty clean,
the scratch pattern is very harsh/deep/linear
"all" the force i'm using is going into abrasion/cutting
but once I push too hard and I build up a layer of mud cutting slows down
scratch pattern gets softer/random/shot peened ..
the force goes into pushing the mud out of the way
the cutting slows down
with higher grits/smaller particles/shallower rakes
less force is needed to achieve "full depth" of cutting
so after the force needed to move the mud out of the way is subtracted
there is still enough force left to get full speed cutting
that paper i linked calls it three-body abrasion , I remembered I found it in this review
David Martin
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Your 3rd & 4th paragraphs is what I experience as well when grinding. Even on a coarser stone the same occurs. It cuts well until the surface loads. Then it skates. DM
chiral.grolim
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The bolded above is not true.
Unless the geometry of the grit of smaller particles is also thinner (never seen evidence of that), then the force required for penetration of each tooth/grit is precisely the same. The difference is that big teeth/grit still have more body behind them that can penetrate even further into the work piece and dig a deeper hole then the fine grit/tooth can ever achieve. Add to this that the larger tooth/grit has more space around it (not packed as tightly) and not only does it have more room to push swarf out of the way BUT ALSO there are fewer peaks (teeth/grit) in the near vicinity to distribute the force of penetration across, so each large grit/tooth is applying more pressure for the same amount of force against a target.
The paper cited a couple times now above shows a bed of nails. When the nails (grit/teeth/peaks) are loosely packed (coarse grit), a given amount of force will allow each nail to penetrate a certain depth. If the same nails are densely packed (fine grit), it will require MORE force to achieve the same depth of penetration, not so? And, as you state, using more force results in more break-down and swarf build-up which slows down abrasion for the fine grit more so than the coarse grit.
Again, the bolded above is not necessarily true. It requires more force to achieve the same depth as with the coarse hone, and there is less room for moving swarf out of the way, so more force goes into swarf removal. The coarse hone can also cut to that shallow depth and indeed cut deeper than that with the same amount of force and still have room to spare for easy swarf removal, doing more cutting than ploughing. Not so?
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Yes and no.
The coarse grit has more volume per grit. So if the coarse and fine are both penetrating to the same depth, it will take less force to drive the more open pack to that depth and I agree with the above. As the coarse grit penetrates deeper, the volume of displaced metal increases rapidly in both breadth and depth.
I cannot be sure, but if you were to drive both configurations to 80% (random value) of their available depth it would likely require a lot more force on the coarse arrangement.
The coarse grit has more volume per grit. So if the coarse and fine are both penetrating to the same depth, it will take less force to drive the more open pack to that depth and I agree with the above. As the coarse grit penetrates deeper, the volume of displaced metal increases rapidly in both breadth and depth.
I cannot be sure, but if you were to drive both configurations to 80% (random value) of their available depth it would likely require a lot more force on the coarse arrangement.
chiral.grolim
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"80% of available depth" is pretty meaningless, since 80% of the fine-grit may be only 10% of the coarse grit, and the coarse grit will reach that depth with less force than is required for the fine grit.
Here is the 1979 paper on this stuff: http://www.sciencedirect.com/science/article/pii/0043164879901881
Here is the important chart, using 1095 steel in the bottom graph, and for our purposes the first sets of marks from the left sit within the grit-sizes normally discussed, i.e. <100 um, I'll guess 15um and then 30um for the first 2 marks.
Each of the 4 lines represents an amount of applied force: 0.5 kgf, 1.0 kgf, 2.0 kgf, 4.0 kgf. At the lowest force, the finest grit abrasive still exhibits worse cutting speed than the next coarser grit, but it is close. As the applied force doubles, the fine-grit abrasive barely increases, requiring 8X the force to achieve only 2X the wear-rate. In contrast, the next grit-size up almost doubles with each step up in force, and more to the point, doubling your grit-size effectively doubles your wear-rate at each force-level observed.
In other words, the fine-grit can only cut so deep and limits-out quickly with force-applied, but the coarse-grit (within certain bounds) requires less force to achieve the same depth-of-cut and does not limit-out so easily.
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Well, that makes a lot of sense ... I was keeping the blocky/dull particles in mind when thinking about it... but then what explains the difference in speed that ToddS is seeing?
The fine stone mud is being scooped off the stone where as the coarse hone mud remains?
chiral.grolim
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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:
Shapton Pro 320 = ~46 um
Chosera 1k = ~11.5 um
Shapton Glass 2k = ~7.5 um
Shapton Glass 4k = ~3.5 um
The chart in the 1979 paper doesn't present much precise distinction with their measurements at 0.5 kgf for the various grits, so it's hard to tell if they observed a significant difference in grinding-performance between the finer grits at that low level of force. ToddS says he couldn't see a difference. If ToddS were to increase the pressure to 4 kgf, would he notice a difference? More importantly, is such a level of force reasonable for our purposes?
It seems to be that at 0.5 kgf with efficient clearing of swarf, there isn't going to be a noticeable difference between coarse and fine grits or even "super fine" grits in terms of wear-rate on the work-piece. However, in efficient clearing or increased pressure will elucidate the differences in favor of the coarser grits. And this is because the coarse grits require less force to achieve the same depth of cut + less impeded by swarf build-up.
Soooo... how much force do you really tend to apply when grinding on the different grits? When polishing, a very light touch tends to be preferred vs "leaning in" when hogging off metal to reprofile a blade on really coarse grit.
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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.
Edit to add: this is probably reflected in the flatlining at higher levels of force even on coarse abrasives - its still not enough to drive the larger abrasive to all of the available depth.
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