Strop questions, Part 2

[Frederick Skelly]

Hi guys.
As I read your answers to Prashun's thread, some additional questions came to mind from my own sharpening routine. I didnt want to hijack that thread so I'll ask them here if you dont mind......

1. Does anyone know what "grit" the smooth side of hard leather is roughly equal to? I finish with a 6000 grit Shapton. So Im trying to get a sense of just how much finer the leather is, without any compound.

2. Does anyone know what "grit" the Veritas green compound compares to?

3. How about a piece of smooth MDF?

As always, thank you.
Fred

[Jim Koepke]

Hi guys.
As I read your answers to Prashun's thread, some additional questions came to mind from my own sharpening routine. I didnt want to hijack that thread so I'll ask them here if you dont mind......

1. Does anyone know what "grit" the smooth side of hard leather is roughly equal to? I finish with a 6000 grit Shapton. So Im trying to get a sense of just how much finer the leather is, without any compound.

2. Does anyone know what "grit" the Veritas green compound compares to?

3. How about a piece of smooth MDF?

As always, thank you.
Fred

High Fred,

I have the search terms > particle size of various polishing compounds < but I do not have the time right now to find the ones with the best answers.

In my thought process leather or MDF do not really correspond to a "grit size." They are not particles abrading the steel. They are surfaces polishing the steel. Though even the softest material causes abrasion, it isn't caused by a grit as much as it is friction.

jtk

[Patrick Chase]

2. Does anyone know what "grit" the Veritas green compound compares to?

Let's see if we can do this noncontroversially...

Lee Valley says that "The average size of scratch pattern it leaves behind is 0.5 microns". For comparison the Sigma #13000 uses ~0.75 um abrasive, the Shapton #15000 uses ~1 um abrasive, and the Shapton #30000 uses 0.5 um abrasive. Taking LV's claim at face value would put therefore put the equivalent grit at #20000-#30000 depending on whose scale you use.

What we know about that compound is that it consists of a combination of 0.5 um chromium dioxide particles and "larger" calcinated alumina particles. To my knowledge the size of the latter hasn't been disclosed.

A lot depends on the substrate. I think (and a lot of people share this opinion) that the Alumina particles tend to recede into soft substrates like leather such that they don't leave objectionable scratches. I wouldn't recommend using it on, say, a metal plate or glass though.

The final thing I would say is that IMO it's "good enough for woodworking". I don't think that it really matters if it's the equivalent of #10000 (my own "best guess" for green compound on a soft backing, based on looking at the scratch patterns under a scope) or #30000, because either will leave an extremely good edge. If you're entering Japanese planing competitions or honing razors then it might become relevant, though.

[Steve Voigt]

Following on from Jim's post a little: the purpose of an untreated leather strop isn't to abrade away material; its to get rid of any remnants of the burr. Perhaps it polishes the the edge a bit, but the effect is pretty minimal imo. So talking about grit size isn't really relevant.

[Frederick Skelly]

Ok. I see. Thanks for the lesson guys!

Best,
Fred

[Curt Putnam]

Note that a brown paper grocery bag has abrasive qualities although I have no idea of grit equivalent. It will lose a fine wire edge though.

[Hilton Ralphs]

Let's see if we can do this noncontroversially...


^^ This made me laugh!

For the record, I strop my EDC knives on my hand after use. This seems to keep an edge fairly keen.

[paul cottingham]

I've used the cardboard from a cereal box with and with the LV rouge as a strop. Worked pretty well. But leather and maple work better.

[Malcolm Schweizer]

Since leather is not granular, it would be hard to associate a grit to it, but certainly it would be finer than any granular abrasives.

I would put put the Veritas green chromium oxide at or around 30,000 grit based on my experience and viewing scratch patterns under a 10x and 20x loupe. There was a big controversy about the grit rating and, whether based on that controversy or not, the description changed to reflect the scratch pattern and not the grit of the particulate. Pure green chromium oxide breaks down to around 0.5 microns. I have used pure chromium oxide powder and can't find any real difference versus the Veritas green "crayon." In the other thread about stropping, I did mention that I make a couple of passes with a piece of metal (a spare blade) before passing with the knife or tool because that ensures the particles are broken down and no stray particles exist. This is complete and total overkill, and I mainly do this when sharpening chef knives- especially when a chef gives me their prized $500 knife to sharpen. It is worth mentioning, however, because we are discussing fractional microns and the finest possible edge. The particulate must break down before you get the 0.5 micron minimum size. I doubt it comes off the crayon at the 0.5 size, though I have not analyzed it under a microscope.

Again, I want to give my disclaimer that all this is really overkill for most woodworking applications, and I am a severe sharpaholic who enjoys sharpening way more than he should. It is fun seeing just how fine of an edge you can get on an iron or a chisel. The green crayon works very well and does leave a very fine mirror polish. It is a quick and simple step that takes little time to do.

[Frederick Skelly]

Thanks again guys!

[Andrew Pitonyak]

Let's see if we can do this noncontroversially...

Pretty sure I can make anything controversial..... <see what I did there?>



Lee Valley says that "The average size of scratch pattern it leaves behind is 0.5 microns". For comparison the Sigma #13000 uses ~0.75 um abrasive, the Shapton #15000 uses ~1 um abrasive, and the Shapton #30000 uses 0.5 um abrasive. Taking LV's claim at face value would put therefore put the equivalent grit at #20000-#30000 depending on whose scale you use.


I have a spread sheet where I list all sorts of things and the "stated abrasive size". When I first started this sheet, I was annoyed because even for sandpaper with a stated grit size, they might list different abrasive size.

Somewhere in there I realized that if I say 1 um, I don't really mean 1. I really mean that there is some kind of distribution of sizes. So some are smaller and some are larger. I do believe that some of this is specified in some of the standards used, and even those may have changed over time.

Oh, and sometimes, there is some rounding going on. I mean, if the size is 59.5 um, you can probably list it as 60 um and for most applications it just won't matter.

Although it offends the neat and tidy part of my brain, I grudgingly accept that what Patrick says. I suspect that Patrick has known this for a very long time (as in longer than I), and if we were just hanging out, I would likely learn much.

[Patrick Chase]

Somewhere in there I realized that if I say 1 um, I don't really mean 1. I really mean that there is some kind of distribution of sizes. So some are smaller and some are larger. I do believe that some of this is specified in some of the standards used, and even those may have changed over time.

Many waterstones follow JIS R6001-87, which does indeed constrain the maximum and distribution of particle sizes (http://www.gnpceramics.com/techdata/Spec%20-%20JIS%20STD.pdf). There are however some well-known scofflaws who march to their own drummer, invariably with higher-than-specified sizes. The latter point might be vaguely related to Warren's observation (in another thread) that Shaptons leave pretty coarse scratches relative to their stated grit :-).

Micron-graded diamond abrasives generally follow ANSI PS 62-74 (http://gsi.nist.gov/global/docs/vps/psfiles/PS_62-74.pdf) (it actually starts on p. 6 of the PDF) or the newer ANSI B74.20-81 (good luck finding that one online. IIRC the ranges are basically the same).

I agree with your point that the micron number itself isn't very useful without the distribution constraint. I think that once you have that nailed down it becomes VERY meaningful though.

EDIT: In case it isn't clear, the JIS spec constrains the maximum particle size, the 97th percentile particle size, the median (50th percentile) particle size, and the 6th percentile particle size.