I wanted to decrease the rocker from 8' to 7' on my Jackson Ultima Matrix Dance runners, to make them more like the rather expensive MK Dance blades I had liked, without throwing away the 3 pair of MK Dance runners I now have. (I also have a pair of Supreme freestyle runners and a pair of Synchro runners. When they discontinued the interchangeable blade Matrix line, I bought all the runners I might ever want.) But that would ground away a LOT of metal, dropping lifetime, and force me to grind down the first toe pick a little too.

Then it occurred to me: What if I deliberately sharpened them to accent the sweet spot? That would less metal, maybe a couple hundredths of an inch - which meant I could easily put it back if I didn't like it, without losing much metal.

So I did.

It worked! As long as I spin, turn or twizzle right there, it is a lot easier. Feels like a completely different blade. Much easier to spin, turn or twizzle.

Maybe it makes sense to create a second sweet spot near the back, to make back three's easier... I don't test or compete, so I don't have to worry whether the skating organizations would consider a second sweet spot cheating. (Would they?)

Technical Stuff

A sweet spot along the blade is where there is a slightly convex angle between two different lengthwise (rocker direction) arcs, designed to make it easier to rotate there. AFAIK, all figure blades have one sweet spot, near where they think you will spin, turn and/or twizzle. Hockey blades have two, near the two ends, for much the same purpose.

Figure blade sweet spots are typically lost after a few sharpenings, unless the sharpener really knows what they are doing, and deliberately puts them back, because they are so subtle. Some skaters move their blade sweet spots to where they prefer to rotate. Hockey blade sweet spots are extreme, to allow fast turns, and probably never go away.

I'm not a pro, and am a klutz besides, so I use the Profiler hand sharpening kit, which contains one course and one fine cylindrical diamond dust sharpening stone, in holders that grasp the blade. I happen to like it very sharp, and have yet to find a shop with a machine sharpener that can get it as sharp. Besides, you waste maybe 5-10 times less metal at hand sharpening speeds. (At higher machine sharpening speeds, sharpening wheels grind away the blade to make an edge, rather than partly re-shaping it.)

I'm not sure the holders are needed - mostly they get in the way, so I have to remove the runners from the mounting bracket to fit them. I hate that, because the Matrix mount bolt metal is so soft, and the hex key that fits the heads so small, the key tends to strip the bolt, and I will eventually have to replace the bolts, or hammer in a slightly larger key or other screwdriver.

It comes with thin masking tape to make the fit tighter - which I used for this. The main purpose of the cyclindrical stones is to distort the metal in such a way as to create edges, though you still grind away some metal too.

It also has a flat fine sharpening stone, which you brush vertically from the direction of the mount towards and past the edge, at successive positions along the length of the blade, on both sides, to straighten the edges.

(Maybe there are cheaper brands of cyclindrical sharpening stone, in the right radii to match the hollow. I'd love to know of them.)

It normally takes 2 or 3 passes of the course grain cylinder, followed by a few passes of the fine grain cylinder, and a couple brushes at each point with the flat stone, to make blades really sharp, if the blade isn't too worn down.

So I used about 5 passes of the course cylinder, starting at the sweet spot, and increasing pressure as I moved towards the ends. I also taped the toe pick, so it wouldn't grind it off, and did the usual stuff with the fine cyclinder and the flat stone.

I use water as a sharpening lubricant on the stones, because it makes less of a mess in my bag than the included oil, and theoretically produces a cleaner edge.

(Using water is a traditional Japanese blade and tool sharpening model, which has recently become popular outside Japan.)

It was Easy. I think anyone familiar with hand sharpening methods could do it to their blades.

I would think if you created a second sweet spot near the back of the blade, it could make your jump landings really rocky. For jumps, you definitely want that flat for stability once your foot comes down.

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"You don't have to put an age limit on your dreams." - Dara Torres, 41, after her 2nd medal at the 2008 Olympics

Can you post pictures? Not that I'd ever sharpen my own blades like that - far too wussy here - but I'm curious to see the sharpened and unsharpened blades compared.

As for another sweet spot on the back of the blade - wouldn't that promote bad habits on the backspin? lots of people like to spin on the back of their blades on that one.

it would be great if you had some pictures! that sounds like it would work pretty well,so please put up some pic's! all hail you!

Confession: my artistic skills are somewhat more primitive than an infant, the very first time it grabs a pencil.

Since only a couple hundredths of an inch or so are removed, you wouldn't see a thing. (You can barely see the new or modified blade sweet spot - it doesn't take much of a curvature discontinuity to make it easy to rotate.)

But here is an image of a new blade, with a pencilled in modified blade profile. The modification has been grossly exagerated, to make it obvious. Of course, the new edge needs to be continued back to the back of the blade, and forward to near the toe pick.

The space between the new and old edges is the metal that needs to be removed.

http://picasaweb.google.com/grunes/M...88459194748610

I can definitely see why this would work. You should patent it or something

You cannot publish an idea in the open domain (e.g., this forum), then patent it.

Besides, the idea of a sweet spot is not new. I only emphasized mine a little more.

Let me explain a little better what I mean by a sweet spot. It may or may not be exactly what commercial figure blade manufacturers do. Does anyone know a place I could find a technical discussion of blade shapes, including sweet spots?

If you tried to spin (or do a one foot turn) on a flat blade, it would scrape more, and friction would slow down the spin or turn. A sweet spot is shaped to be more convex than most of the blade. This produces a more compact area of contact.

I am talking here about curvature in the lengthwise ("rocker") direction. Perhaps parabolic blades (thinner near center or sweet spot than at the ends?) try to do this in the width-wise direction as well, but I have never tried parabolic blades, and won't discuss them furher here.

Physics explanation: the further an area of contact between the blade and the ice is from the axis of spin, the faster it scrapes across the ice while you spin, and the more friction that scraping generates to slow down the spin. Hence, you want a compact area of contact (but not so compact it drills down into the ice until you end up with a less compact area of contact). I'm not sure how to work out the detailed physics, because there is disagreement about exactly what happens between the skate and the ice, even for normal skating, let alone for spins. E.g., it may involves fluid dynamics, and other more complicated boundary layer physics, instead of simple friction.

Aside: reducing the length of the contact zone also makes sense for spinning on snow. It is easier to do whirligigs (spin) as you slide downhill, if you use short trick skis. Likewise, whitewater and open water surf kayaks have more lengthwise (rocker) curvature than those designed for speed.

The price of a sweet spot is that it is hard to balance there. Oh well - that is the price of fast spins.

BTW, more or less the same discussion and principles apply to one foot turns as to spins.

It is possible most commercial figure blade designers create a sweet spot simply by changing the rocker radius (i.e., the lengthwise radius of curvature) there, so the radius is smaller forwards of the sweet spot. Some blades are shaped to vary the rocker curvature continuously, so it curves more and more towards the end (both ends, for hockey skates). One could also just use a smaller rocker radius at the sweet spot itself.

Anyway, the sweet spot shape I tried to produce was based on joining two arcs, of the same rocker radius, at an angle.

I don't know if that is the optimal thing to do. All I know is that it seemed to work for me.

P.S. The "sweet spot" I am talking about relates to the blade shape. People also refer to a "sweet spot" along the blade where they personally spin best. I think it makes sense to put them in the same spot. That might get complicated, because many people do different types of spins in different spots on the blade. One solution is to make everywhere a sweet spot - i.e., use a much smaller rocker radius. I'm not sure why figure skaters don't do that, but I guess it slows things down. As I said, I was just trying to compensate for the 8' radius in my current blades, which I find too large.

No, my coach already thought of it long since, and re-built the rocker of my blades, which he says are dying but will do the year out, he thinks.

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Mrs Redboots
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I love my computer because my friends live in it!
Ice dancers have lovely big curves!

If one is on the back of the blade in a backspin, it is not a backspin because then one is spinning on the FI edge instead of the BO edge. Not sure if that's what you meant by bad habits. No one I know who makes that mistake "likes" to spin that way.

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patatty is a patent attorney!!

In that case, a forward spin would not be a forward spin because you're spinning on a back inside edge!
But seriously, I don't think the terms "forward" and "back" spin have any real relevance anymore, particularly now that both spins are executed on both inside and outside edges to get difficulty levels under the new judging system. A "backspin" is just any spin that is on the right foot spinning CCW or on the left foot spinning CW.

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"You don't have to put an age limit on your dreams." - Dara Torres, 41, after her 2nd medal at the 2008 Olympics

Not quite. No credit is given for a backspin executed on the FI edge unless it has first been done on the BO edge and then changed to the FI after a min number of revs (4, I think). That said, I've seen adult tests pass without ever hitting that BO edge.

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Perhaps you high level skaters, with refined senses of balance, can spin perfectly at any point on any blade.

I'm trying to make it possible for a complete klutz (me) to spin at all without rocking and traveling all over the place.

Though making the blade more convex should make it harder to balance for spins, the effect has so far been the opposite: I can't always feel when I rock over different parts of the blade. Having one part of the blade different means I can feel when I am on that part, so I have a point to aim for.

Toy tops are made to spin on pointy (very convex) areas of contact too. Maybe something about that makes them center themselves a bit in spins?? I read about tops a long time ago - they were (then) considered one of the unsolved problems of mathematical physics, in that no one understood why they behaved the way they did.

Can I say that's sadly comforting? I don't spin on the FI (yay! and thank goodness because from watching the kids, it's hard to correct) but I do tend to spin more on the flat than the BO. When I do hit a really true BO I tend to loose my core and wobby the spin and kick out of it (now that I can finally do that). Just this week a group instructor told me "the goal isn't to get to the BO edge and then stop spinning. It's to stay there for the duration!)

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-Jessi
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What's the deal with Michael Weiss' "Freedom" blades? I know the tails are rounded and brought back up so he can do those cool heel-spreadeagles, but does he have a "second rocker" at the heel as well?

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