Saturday, November 2, 2013

Sharp - Thoughts on sharpening stones

I was a belt sander and sandpaper guy. I mean, if it was good enough for Chris Becksvoort, it was good enough for me. This was back in the 80's. Kind of a moot point anyways because I had no money for fancy new sharpening stones and for some reason old oilstones just weren't on my radar. I read all of the magazines back then, and I don't really remember any serious talk about oilstones. I have no idea why, probably too old fashioned. I think that people were just getting exposed to the whole waterstone thing. Man-made ones, of course. The natural ones were for crazy folk (still true, I suppose).

So fast foreword a few decades and we sell our sailboat and we probably will not get another. Finally! An end to sanding! Time to tune up the old hand planes, an old Stanley 60 1/2 block plane and an even older Ott horned German smooth plane.


trocken holz unser stolz, Friedrich Ott & Co.
I also bought some great Port Orford Cedar to use in fixing up an old rowing skiff. Turns out that this wood can be, shall we say, difficult to plane. But if your tools are sharp, WOW! Really nice. Smells good too. Then I thought, "what tools can get REALLY sharp? Oh yeah, laminated steel......". Well, you get the picture.

So Japanese tools can get really sharp, sure. Of course, then you have to sharpen the dang things. Sandpaper on glass worked fine for the thin and relatively soft western style plane irons but wasn't cutting it for the Japanese tools. The problem was that even though they have these big honkin' bevels, I kept getting a rocker that made sharpening right to the edge difficult.  I eventually decided that this was due to the thickness of the paper used for the backing on the sandpaper. It is just too thick for precision work, creating in effect a very slight wave deformation in front of the leading edge of the blade. Likely a high quality lapping film and a very light touch would work well, but there is still the issue of adhesive film thickness. It seemed insane to me, but when you are talking about REALLY sharp things, you end up using numbers akin to a vanishing horizon. Smaller and smaller, an infinity of divisions.

I felt that I was hitting a wall in the sharp tool department, particularly in the coarser grit (Ha! I used to think that 100 was coarse, now it's 1000 that is coarse) and I was using a lot of sandpaper @ $1/ sheet. Then I bought an old mystery stone from a seller in Japan.

150-75-22 mm and ready for action, start from 600 grit diamond. Notice the uniformly shiny bevel.
He said that it was a natural stone, but wouldn't say for sure because he was selling it as received and it had not been cleaned up (WAY too common with Ebay sellers everywhere! WTF! It's like a contest to see just how cleverly they can mislead without getting called on it! What is wrong with people?!). It was an artificial as I suspected, my first waterstone and it was FAST, and it defined a cool line between the hard steel cutting edge and the softer iron backing.

Soft, muddy and fast, this took about 20 seconds. Cool lamination weld/line!

This effect is due to the physics of how the various metals abrade and interact with the small particulates that are an inherent byproduct of sharpening. Most abrasives are designed for maximum hardness and longevity. Sand paper, oilstones and man-made waterstones are all intended to perform the same function (abrade metal), bu they each behave in a very different fashion. Sharp abrasive particles are essentially stuck to a carrier. Sand glued to a board. The particles wear in use, the sharp edges get rounded, until they lose nearly all of their cutting ability. Time for a new piece of sandpaper.

Oilstones and waterstones are pretty close to being the same thing, they just differ in the carrier matrix that binds the abrasive particles together. Broad strokes here. Both have sharp abrasive qualities, but the waterstone's abrasives are more loosely held. They break free in use, exposing new sharp particles so they tend to cut very fast. The particles also roll around on the surface and that is what gives the differential appearance to the steel and iron laminations.

Oilstones are slightly different, in that the abrasive particles are tightly held and slowly released. That's why there are so many old stones around. They just don't wear out. Lots of people are still using sharpening stones that have been handed down for generations. Talk about  a good return on investment! The down side is speed, or lack thereof.

Good definition (Jnuts note...NOT a Japanese waterstone!)
Check out the differences in reflectivity. This is a good, very old chisel from my bottomless box of old tools. It's previous owner thought that it was worth sharpening, probable over 1000 times. That is more than you can say for a lot of the new ( and old!) tools that you find for sale (I strongly suspect that the crappy tools get chucked out the window in a fit of anger. 20 years later they get found and sold on Ebay as patinated....what a creative euphemism!) After sharpening it myself, I can see why. It is HARD! Let me rephrase that. The steel is hard, the iron is soft. That's one of the best things about these tools. Even though the cutting edge is SUPER hard ( like Rc=64!) it is still easy to sharpen.

Finally, we come to the interesting part (hahaha) for me at least. This is laughably simplistic, but bear with me. To a certain extent, resources guide technological development. Japanese edged tools have evolved hand in hand with natural waterstones. This is a real "chicken or the egg" conundrum.

Japan's geologic history of volcanic seismic activity has resulted in mineral reserves of sedimentary rock with a high silica content and a finely graded particle distribution. They happen to make very good sharpening stones! What they didn't have was lots of high quality iron ore reserves, so they made the most of what they DID have and a laminated blade construction is the result. That, at least, is the conventional thinking. I think that people like the laminated construction because it is looks cool AND it works amazingly well on many different levels. Subtle and yet very sophisticated  at the same time.

From a practical standpoint, having good sharpening stones mean that you CAN have harder and sharper tools. The hardest/toughest steel means nothing if you can't sharpen it! Use a different type of stone, like an Arkansas oilstone, and you'll find that the stone will tend to clog up and form a glaze from the very soft iron, which then leaves unsightly streaky skid marks on the tool. The tool feels grabby and sticky or gummy. This is what is known as "poor feedback". AND it takes a while to sharpen because the steel is so hard. For me, it WORKS better to use waterstones to sharpen Japanese edge tools.

"Good feedback" is when you can feel the abrasive qualities of the sharpening stone interact with surface that is being abraded. You can feel when the cutting edge is too acute, and you are digging in and altering the cutting angle of the tool. You can even feel the difference between the hard steel and soft iron. Ideally, I am focusing maybe 80% of the force on the hard steel edge. I do this by getting the bevel as flat as I can (or have patience for) and "willing" it to be so. Yeah, you read that right.....I "wish" my tools sharper. I concentrate, I INTEND my hands to guide the tool so that I can get the perfect vanishing angle. I need "good feedback" to do it though. And I am still trying to get the "perfect" edge.

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Like all of us, I am figuring this out as I go, so when you see something that is incorrect or flat out wrong (and you will!), let me know. This is a learning process. Real people and names, please. Constructive comments and questions are very welcome, but hate speak/politics are not! Life (get one!) is too short.

Thanks, Jason