How can I compare grits?

Ive been using MDF with various polishing compounds this weekend. Just puttering with an old plane blade and my mark 2 jig to see if any of them took me beyond my shapton 6000. (I havent bought that 0.5 micron paste yet.) Bought some tripoli, red jewelers rouge and a yellow stick they said is for stainless steel. Only the yellow showed black streaks, so Im guessing it was the only one doing any cutting. Also bought valve grinding compound but didnt try it out. Like I said, I was bored and decided to putter a bit.

Got me to thinking though. Is there a way to compare the grit of sandpaper to that of my stones and also to the honing compounds? For example, is 2000 grit paper really coarser than my 6000 stone? Is that no-name stainless steel polish finer or coarser than that 6000 stone? Is there a credible way to compare these abrasives, or does each manufacturer use their own definition of grit?

Thanks folks!
Fred

Comparing grits? Well, stone ground grits are the best (white corn, please). Other than the edible type, I do recall seeing a comparison chart somewhere, but I can't put my finger on it. Be aware that different grit measurements yield vastly different results.

yellow stick is usually aluminum oxide, as far as I can tell - some of the branded ones are 3 microns or so, about the same as the aluminum oxide in autosol. Jeweler's rouge is probably iron oxide. I don't know what's in tripoli, but I'm sure google could tell you. Of those, the al-ox is the most aggressive.

Green stuff varies in terms of hardness and what's in it (aluminum oxide might be added to speed it up), but the green color is from chromium oxide pigment/abrasive. It isn't all 1/2 micron all the time, though, so you can't just assume that the green stuff is the same in all of the bars (it might be, but who knows).

If you want to make judgments for judgment's sake, then you more or less have to know the size of the particles involved in whatever you're doing, and then have a sense from experience what that means (for example, a 5 micron diamond won't leave an edge nearly as refined as a 5 micron grit of novaculite, or even of aluminum oxide).

For practical purposes, though, the particle size itself should be good enough to give you an idea of what's what.

[QUOTE=Frederick Skelly;2119202]Ive been using MDF with various polishing compounds this weekend. Just puttering with an old plane blade and my mark 2 jig to see if any of them took me beyond my shapton 6000. (I havent bought that 0.5 micron paste yet.) Bought some tripoli, red jewelers rouge and a yellow stick they said is for stainless steel. Only the yellow showed black streaks, so Im guessing it was the only one doing any cutting. Also bought valve grinding compound but didnt try it out. Like I said, I was bored and decided to putter a bit.

Got me to thinking though. Is there a way to compare the grit of sandpaper to that of my stones and also to the honing compounds? For example, is 2000 grit paper really coarser than my 6000 stone? Is that no-name stainless steel polish finer or coarser than that 6000 stone? Is there a credible way to compare these abrasives, or does each manufacturer use their own definition of grit?

Thanks folks!
Fred[/QUOTE

An ancient Geology Professor taught me to very lightly touch a stone or mineral to a tooth in one's head to compare grit. He said this is the way it has been done as long as humans have been using rocks. Works very well since you can feel the difference in your bones, but it is hard on tooth enamel.

Stan

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Originally Posted by Frederick Skelly

Is there a way to compare the grit of sandpaper to that of my stones and also to the honing compounds? For example, is 2000 grit paper really coarser than my 6000 stone? Is that no-name stainless steel polish finer or coarser than that 6000 stone? Is there a credible way to compare these abrasives, or does each manufacturer use their own definition of grit?

Thanks folks!
Fred

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As Dave said, you need to compare the micron sizes. The attached chart, which I got from Chris Schwarz's blog a couple years ago, will get you started. It's not that comprehensive, but you get the idea.

Couple of things from that chart, not trying to be picky, but don't want people to buy stones to find out they're something else:
* the norton 8000 is definitely closer to 3 microns
* the shapton 15000 is 0.98 microns (or at least that was the spec when I got mine)

If it looks like a free lunch on the chart, the number is probably wrong. At the same time, I'm not aware of any chart out there that's got perfect numbers on it for everything.

I don't have any clue what the lee valley waterstones are, but there is no 1 micron 8000 grit stone to my knowledge. Back then, all I remember lee valley having was a king combo stone and some norton stones (oilstones...I think they might've had norton's waterstones, too).

Still, it's useful to get an idea how fine some stones are vs. others....like the grit size of the medium and fine india, which can do a fairly nice job when they're settled in. And the coasre crystolon....

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Originally Posted by David Weaver

If you want to make judgments for judgment's sake, then you more or less have to know the size of the particles involved in whatever you're doing, and then have a sense from experience what that means (for example, a 5 micron diamond won't leave an edge nearly as refined as a 5 micron grit of novaculite, or even of aluminum oxide).

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David,

Why is that? The "guesser" in me wonders if it's related to the breakdown of the novaculite or AlOx vs the hardness of the diamond keeping its ragged edge, but that's a classic ASSUME! :-)

Jim

When I read the title of this thread, I was sure it was about comparing southern grits (the kind you eat).:)

But then, I'm a southern boy who grew up on grits.

Mike

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Originally Posted by Jim Neeley

David,

Why is that? The "guesser" in me wonders if it's related to the breakdown of the novaculite or AlOx vs the hardness of the diamond keeping its ragged edge, but that's a classic ASSUME! :-)

Jim

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Novaculite, as far as I can tell, dulls. And more importantly, it doesn't shed grit, so it dulls and dulls. It's actually pretty sharp when it's fresh, one needs only to look at a picture under a microscope to see that it's not starting as big dull round pieces. It might not be quite as jagged as al-ox (which also dulls instead of fracturing, I guess it does both, but it will dull more than something like silicon carbide which readily breaks into smaller sharp pieces). Diamond doesn't break that fast, some doesn't much at all, and it's hard enough that it doesn't lose its sharpness quickly, either....well, for all I know, since they're manufacturing diamonds, maybe they can make diamonds any shape they want, but whatever the case, it definitely holds its keenness a lot longer than al-ox.

A side note, it's vital for any natural stone that is to cut very finely (compared to a synthetic finisher) to be hard enough to not shed grit while in use, or at least not very much of it.

http://www.tzknives.com/razorbevels.html

You can see that a coticule without "slurry" (loose grit rolling around) cuts much finer than even a norton. The garnets in coticules are huge by polishing stone standards. But they are almost round and they do not cut deep grooves unless they are loose and fresh.

Same with the chinese 12k. There's definitely nothing 12k about the grit in any of the guangxi stones, the particles are larger than anything in the norton stone by a lot, but they also are not very durable and when they break down and no more are shed, you can see the resulting polish on the left side. It takes a lot of patience to get to that, though. You can't tell the whole story by the scratches on the bevel, but they do for the most part correspond with how refined the edge is.

From experience, I may have said on here that the shapton stones cut deep. You can see on the 15k shapton bevel vs. the norton stones that the cuts look very deep, despite the shapton abrasive being no more than 1/3rd as large as what's in the norton hone.

It's just hard to know what an abrasive does without having some experience with it. I can say for sure that I don't like shaving straight off of any synthetic stone, and definitely not diamonds. A shave off of a non-slurried coticule is very comfortable and no razorburn. Same as the escher, comfortable and no razorburn despite what looks like fairly ragged pictures...some care has to be used with eschers to makes sure touch is light enough with a razor to avoid loose particles, the potential is a little higher than that picture shows, but some people do like to use them with slurry (and the edge on the slurry picture looks pretty good).

I think nobody ever gets that nutty about any of this stuff until they start to shave and you can feel the difference, sometimes painfully so. Plus, shaving straight off of anything shown here is somewhat dull (thus the linen on barber strops, which is also loaded with a very soft abrasive), even if it's not painful. But they would all be good woodworking edges.

Thanks guys!

David,

The link refers to "No slurry" and "with slurry". Is the "No slurry" due to using the stone dry vs wet, or ???

Jim

No slurry typically refers to using the stone with just clear water. All loose particles and slurry are cleaned off the stone so essentially the only abrasive doing the cutting is what's actually attached to the stone. When you raise a slurry you are doing 2 things...1) you are exposing fresh abrasive on the surface of the stone and until this abrasive dulls you are getting a more aggressive cut. 2) you have fresh abrasive (the slurry) actually sitting on the stone, which is rolling around and exposed on all sides and thus also adding to aggressiveness/coarseness of the cut.

With no slurry and just clear water the goal is to expose no new abrasive and to allow the abrasive on the surface to dull, leading to a finer smoother edge. I think it's pretty much the same concept as roughing up an arkansas stone with a diamond plate to get it to cut fast and/or cut less simple steels (e.g. A2), vs allowing something like a translucent or surgical black to really wear in to the point where it cut barely at all and really only polishes.

I'm with Mike. Stone ground grits ROCK.
Bill