Monday, July 23, 2012

The Nest of the Lotus Flower (II)

This is a follow up to the previous post, specifically in regards to a question Ward Wilcox asked:
I have heard there are a two or more lines of Sigma Stones. The line sold by Lee Valley are different than the ones Chris purchased. Do you need to soak the Sigmas? The Sigma display on Lee Valley claims they are soft but cut very fast. DJY states the 1000 grit is too slow if I understand him correctly. How do Sigmas measure up to Shapton pros?

I asked Stuart Tierney of Tools from Japan to provide an answer, as he has a much better picture of the scene than I do, and here's what he wrote - detailed and long enough to merit a second post in this thread:

Hi Ward, Stu here.

There are indeed two 'full' lines of Sigma Power stones, plus a 'back catalog' of various others that nobody you know of (except me) has heard of.

The one LV have are 'Select II' from the updated original series. Let me explain...

Originally there were 2 'Select II' stones, the #1000 (grey) and the #10000 (yellow). About 2 years ago, give or take, Sigma Power expanded the 'Select II' line with a #240 (bright green), a #3000 (darker green) and a #6000 (orange/yellow).

These are singularly unique stones. All use Silicon Carbide as their abrasive and have NO binder. Every other manufactured stone has a binder of some kind to hold them together, these ones don't.

This is a double edged sword...

It's good because Silicon Carbide is very hard and will cut virtually any blade steel with ease, and because there's no binder the entire stone is 'good stuff'. So they'll cut anything and do it very quickly.

It's bad because a binder tends to allow the maker to adjust the 'friability' of the stone, in essence, how quickly the stone breaks down with use. With these 'no binder' stones, that 'adjustment' is lost to a large extent. It's very apparent in the 3 coarser stones (240, 1000, 3000), less so in the finer 2 (6000, 10000) because the finer stone's particles are smaller and in better contact with each other, they tend to 'hold together' a little better.

The funny thing is, this 'friability' is only a concern when the steel is relatively soft and easily abraded. These stones were specifically developed for High Speed Steel which is usually quite hard and very tough, both making it quite difficult to abrade with conventional sharpening stones. If you use hard HSS on these stones, they change significantly into stones that are actually quite 'flat', still fast and very effective. On 'normal' steel, they do tend to dish a little faster than I'm happy with, but they do work faster than almost any other stone so the dishing is less (because they work faster) than it might otherwise be. 

There are 3 additional stones with the 'Select II' label now, a #400, the #1200 Chris has here and the #13000 which is also shown here.

The #13000 has been around for many years, but Sigma Power have changed the label on it from 'ceramic' to 'Select II' as internationally, the Select II branding is more widely known and recognised. The stone is the same, the label has changed, nothing more.

The #400 originated late last year from a request for a stone that was coarse, but showed stronger dish resistance than the #240. 2 stones were produced, a silicon carbide stone similar to the existing #240 and a white alundum (WA) stone, with a binder in it. The SiC stone was an improvement over the #240, but still dished too quickly. The WA was not as fast as the SiC stone, but the dish resistance was excellent. As that was the desired property, the WA stone went into production. As it deals well with HSS, it was no concern to use the brand recognition of Select II on this stone, so that's what it got. A pink label no less...

(It was cheaper too. I still have both prototype stones and would like to see the SiC stone go into production as well. The knife sharpener folk will love it!)

The #1200 came into being from concerns about the Select II #1000 dishing too rapidly for many tool sharpeners when used with Western style tools. I asked for the same stone with some binder in it to 'firm it up' a little. The straw that broke the camels back was the FWW review where the ceramic #1000 did quite well, but the Select II #1000 did poorly.

The #1200 was the answer to that.

The Select II #1200 is again, a WA stone. The abrasive is finer (genuine #1200 grit), the ratio of binder to abrasive is changed toward more abrasive and the binder is a tougher, less likely to break down type.

As a result, the #1200 is very hard, has very strong dish resistance but still works quite quickly. Because of the high ratio of abrasive to binder, this stone still works well with HSS and also deals with 'normal' steel well.

Now here's where the line is blurred somewhat...

The #1200 has a Select II label on it, but it's closest relative is the older Sigma Power 'ceramic' line of stones, specifically the #1000 'hard' and not the Select II #1000.

The 'ceramic' line of Sigma Power stones have had sporadic availability outside of Japan for quite a few years. When I first started my little store, I made sure I was able to get these stones and make them available on a more consistent basis.

Not long after starting up the store, I contacted Sigma Power directly (previously through a dealer) and they decided to deal with me directly, which means I 'have their ear' when it comes to new products.

Their 'ceramic' line are more conventional stones with a binder in them, in this case it's a true 'ceramic' type binder and the name reflects this. In many other 'ceramic' type stones, the ceramic signifies the abrasive is a manufactured abrasive so is consistent and tougher than naturally occurring types. In the case of other 'ceramic' stones, the binder may be a ceramic material (fired at high temperature and fused together), a resin, a plastic or a baked binder. These binders allow the maker to fine tune the working characteristics of the 'stone' (is a plastic/WA concoction really a 'stone'?) to get what they want from it.

Anyway, the Sigma Power ceramic stones all have a binder in them and are available in #120, #1000 (hard and soft), #2000, #6000, #8000 and #10000 as well as the #13000. The #120 has SiC abrasive in it, the rest use WA (except the #2000 which has pink alundum. Long story but it's slightly different) and are fired in a kiln similar to a coffee cup.

They come from the same company, the labels are different but the ceramic were the 'original' stones, the Select II are newer and borrow from the 'ceramic' line when appropriate.

And the #6000 above?

It's from an even older line of stones, before there were 'lines' of stones. It got the 'ceramic' name when Sigma Power stuck a base on it.

So it's technically a 'ceramic' stone, just as the Select II #13000 is technically a 'ceramic' stone and the #1200 is in Sigma Power speak more a 'ceramic' than a 'Select II'.

I hope that's not too confusing, but with these two lines of stones borrowing from one another it never going to be an easy task to completely separate them.

Stu.

4 comments:

  1. If Stu is reading Chris's blog, I'd be interested in his comments as to whether he finds that the #1200 cuts faster than the Sigma Power #1000 hard? All in all, I find that using a cheap #800 King stone, or perhaps the King #1000 (not sure which I have), and then going to the the Sigma #1000, is a faster way to sharpen. I would want to purchase a Sigma stone that cuts along the lines of the King in terms of quickness, and then where next going to the Sigma #6000 would be a good transition.

    I also notice that putting the stones away wet, that they tend to get a skum like coating on them, where they change color and it makes them slick on the surface. At least the #1000, and possibly the #6000 as well, A Nagara stone rubbed over will clean it off. It could also be the residue from the steel that causes that if the stones aren't washed off after use. It hasn't been my habit to wash off stones after use. Yesterday I wiped the stones off after use, forgetting to later check the results, so today at the shop I can see if the color change persists, and also if simply washing off after use alleviates it.

    Informative thread.

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    Replies
    1. Chris...Thanks for the clarification via Stu. Chris mentions a KitaYama 2000. I have not seen this stone. I have a Kitayama 8000. Getting used to it and find it to be of very good quaility. Sounds like it is designed to remove scratches from coarser mediums or for light duty honning. Where can I find one? Second question for Chris, I wonder if you find
      man made high grit polish stones over 10000 grit to have any advantage to good natural stones...or.Toishi. Why pay money for artificial polishers when Natural stones are so great?

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  2. Dennis,

    thanks for your comment. Not sure how you put your stones away, but my habit has been to flatten and rinse them as a final step, and then I stand them up on edge atop my plastic water trough. I've never had any scum like coating form.

    And the King stones I gave up on long ago as they dish far too quickly. They do cut well. Hopefully Stu might chime in again in answer to your questions. I'm liking the 1200 so far - seems just about right as a starting stone, though I would also find a 800~1000 would work as well.

    Ward,

    good to hear back from you. The KitaYama 2000...I can't find anyone selling it online either, so I'll double check that it exactly what I have.

    As for fine man made stones vs natural, the main reason I use the man made is that they are considerably cheaper than the good quality Japanese natural stones. I'm hesitant to drop $500~$2500 (or more) on a natural stone. The one thing you do get with the synthetic stones is great uniformity of particle size, though natural stones apparently do have their advantages.

    ~C

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  3. Thanks for the reply, Chris.

    Yesterday taking a closer look, i found that it is only the #1000 stone that has the discoloration and slicking over on the surface when put away wet. Wiping it off before putting away seems to help, but the absorbed moisture still appears to have that effect to some degree. It isn't a big deal, only a minot inconvenience. The #6000, that I believe that we are both using, doesn't do it, nor the #13000. The #13000 is also an excellent stone, I find.

    It has always been my habit to put away the stones as is after use, and with the synthetics that I have been using for a long time, it has never been a problem. Draining them off seems like a good idea with these new stones. Flattening I do on a less regular basis than yourself, it would appear. It's true about the King stones wearing quickly, at least the red courser ones, and requiring pretty frequent attention to stay flat. I seldom touch the back of a blade to a coarser king stone, so a degree out of flat is not a concern.

    I have a few natural stones, mostly in the courser to mid range, none that I much consider a finishing stone. I have friends that have some rather expensive ones, speak highly of them, and there is the theory that a natural stone can give a better wearing tool edge, true or not? If you have two natural stones of the same degree of sharpening quality, and one is a more attractive stone, it will generally fetch a higher price. That can definitely be a factor in the higher cost range of natural stones. i always poo pooed that logic, thinking that the cosmetics of a stone is a minimally important element, then I obtained a stone that has some very pretty purple stripes running through a more neutral gray background. It quickly occurred to me that looking at it while sharpening is an enjoyable thing, and my opinion immediately changed to where if one has the budget, why not go for the cosmetics as well! Life is short....

    ReplyDelete

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