New Materials!

On Friday morning the shipment of new stones and assorted grinder materials finally cleared customs, and I sent Noah off to pick up a really cool John Deere crate (!?!?!). I did feel some remorse over sending an Aspen kid into the wilds of the industrial environs near Logan airport in Boston. But he made it out. Eventually.

So, finally, the long awaited grinder supplies have arrived. It seemed like a good opportunity to take a few pictures and post a quick update. Grinding is a well established industrial process, and while ski grinding has evolved to a high level of refinement, it remains grinding at heart. And the heart of any grinding operation is the stone. Grindstone is a consumable material. You dress the stone by cutting it with a diamond tool. That’s how we build different structures. It also eats up the stone. In the picture to the right you can see the stone that we’ve just finished up, compared with some new ones. On a Tazzari machine the new stone has a diameter of 350mm, and the discard diameter is usually around 280mm. That means you can cut about 45mm away from the radius of the stone. Each cutting operation consumes about 0.06mm (on average). So, we can put about 750 patterns onto one stone. Sometimes we get a cut that doesn’t come out right because the diamond is worn into the wrong shape. So let’s call it closer to 500 patterns. A lot of our structures utilize more than one pattern, and so functionally we can probably make around 400 final structures. An average batch will comprise 10 structures. So – 40 batches. About a year’s worth of work. Maybe 1500 to 2000 pairs of skis if we’re intelligent with the way we batch the work.

One of the exciting things about this shipment is that it included a new stone. New as in a new compound. Stone is like 3 dimensional sandpaper. And like sandpaper, you can get different kinds. Not just different grits (particle sizes), but different materials. Sand paper can commonly be found with abrasive materials like emery, garnet, aluminum oxide, silicone carbide, and others. I really don’t know what materials are used in ski grinding stones, but like sandpaper, grind stones can be made with different materials, and different particle sizes. They can also be made with different bonding agents (which hold the material together) which has a big effect on the hardness of the stone, and the way it works. Another consideration is porosity. The stones have voids in them, which helps them keep cool, and carry the cooling water. I heard someplace that some manufacturers mix walnut shells in with the stone, which then burn out when the stone is heated in a kiln. But I don’t know.

With all of these factors in play, the variation in stones can be huge. There seems to be a broad understanding in the marketplace that nordic skis require a “nordic specific” stone. I don’t have much experience with the stones or equipment used to crank out mass-produced alpine shop-service grinds. My guess is that these “nordic specific” stones are capable of taking more precise patterns, and are probably more delicate. Harders? Softer? Coarser? Finer? I don’t really know.

That’s a lot of stuff I don’t know. What I do know is that, for the past several years, Lars Svensson and Tazzari have been working on a new stone formulation with much finer particle size. I worked with one prototype version at the Olympics when Lars came over and stayed with me. That was far from a finished product, but it was clearly interesting and could hold an astonishing amount of information. Last night I put on the new “blue stone” (early versions were colored blue) and started playing with it. It’s astonishing. I could polish mirrors with this thing! The intent has been to have a specific stone for cold structures. I won’t start making any production grinds with the new stone until I’ve had a chance to do some on-snow testing. I may be looking for some volunteers to try some “blue stone” structures this winter. Maybe we should put a “BS” abbreviation on those grinds. Hmm. On second thought, maybe not.

I also got a new drive wheel. The drive-wheel is what pushes the ski through the grinder. There was nothing wrong with the old drive-wheel, but I had used a machine with the new wheel when I was working on skis in Oslo last March. It’s got a slightly different rubber compound, and thicker rubber, so it’s a little bit smoother. It’s not quite like the pneumatic tired used by Mantec that you can run right over the bridge. I’ve never run a machine with a tire like that. I’ve heard good things about them, but I’ve also seen them replaced with hard rubber wheels in some ski factory racing department machines. So what do I know? I know that Jake McDermott and I had to use a sledghammer and some real creativity to get the old driveshaft out, and were working on drivewheel replacement until 11 PM. I also know that I like the feel of the new wheel. It’s a little smoother when you lower it onto the ski, and at the back of the NIS plate on new skis – two areas where the old wheel could be a little jumpy.

The short version of this update is that I was up late beating on the grinder with a sledgehammer, but I’m back at work now, and happier than ever.

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