First of all, I think you have done a great job of prolonging the life of your blades. About how many hours have they had on the ice?
If you aren't careful, sharpening tends to blur the "sweet spot" - the place where the rocker curvature abruptly changes from the main (back) rocker radius to a shorter (front) spin rocker radius. That's true whether you use a hand tool like Pro-Filer, or the bench power tools like pro shops use. Especially if you use long continuous strokes of uniform pressure from front to back and/or vice-versa - usually a great technique, but occasionally, you may want to re-emphasize the sweet spot. You may even want to move the sweet spot to the position on your foot you want to spin over.
My personal feeling is that it is easier to spin - though I am awful at it - if you can "feel" the place where that rocker changes, and spin there. Otherwise it is too easy to rock forward and back, because you can't feel where you are on the blade. Of course many good spinners don't need this - they can feel exactly what their body is doing, and don't need this type of help. I've seen some people, especially kids, spin incredibly well on incredibly badly sharpened blades. I don't know how they do it.
Depending on the blade design, the main rocker is approximately 7' - 8' radius, and the spin rocker, probably just ahead of the balls of your feet, has a .75' to 2' radius. If I remember correctly, many Ultima blades have about a .75' spin rocker, and many MK blades have about a 1.5' - 2' spin rocker. Some Wilson blades have two sweet spots up front - separating 3 different zones of rocker radius. I don't know whether the original Coronation Ace does.
The method I think you once posted of measuring the rocker radius using a straight edge may not accurately measure the short spin rocker zones, because it requires too long a length of uniform rocker radius. That's why I instead try to place the blade against curved lines like
http://mgrunes.com/boots/rocker.pngPrint it. You may have to cut away the area around the desired curve so you can lay it right alongside the edge of your blade. Unfortunately, if your printer is in poor condition, it may not print with uniform curvature.
For calibration purposes, you could check your printer scaling - the horizontal grid lines will be .25" apart, and the curves will be .35" apart on the x-axis. It may help to use a magnifying glass to see the very small blade deviations from the printed curve.
However, I'm not sure the exact rocker radii matters all that much, for most purposes. They can even be a bit non-uniform, though I personally try to avoid that. I believe it is the sharp transition between two zones, creating the feel-able sweet spot, that matters most. (A sharp transition at the sweet spot may also help you initiate turns. Though, at least for me, initiating turns is easy - checking turns is the hard part. Alas, I don't know if any blade characteristic makes checking turns easier.)
I see no reason why the back of your blade should matter that much, because most of us don't spin there. I wouldn't grind down the back. All that would really do is give you a smaller main rocker radius, which would make it slightly harder to distinguish from the front spin rocker area - in other words, the opposite of what you want. It might also make the blade slightly slower. And doing it with a Pro-Filer would wear out that expensive tool a lot.
I occasionally re-emphasize my sweet spot in two ways - I reduce the spin rocker radius, especially near the sweet spot, and I add a very slight convex direction change, that makes it even easier to feel. AFAIK, that direction change is
not incorporated into any factory blade shapes - AFAIK, it is my innovation. Think of it like the cusp at the bottom of the top - it provides a point to spin upon. Or like spinning barefoot on the ball of your foot, with the front of the foot bent upwards, just like it probably is inside your boot.
The very small amount of direction change I seek isn't really visible, and I can only feel it when I skate on it, not with my fingers, or only the ghost of a sensation.) You MIGHT be able to see it in the reflection of the blade, at just the right angle, but don't count of it. Too big a direction change might make it harder to stay on that point, so is counterproductive.
I do both things by placing the Pro-Filer with the back of the cylindrical stone at the spin rocker, and the front of the tool closer to the toe pick. I push forwards towards the toe pick (I tape the toe pick, so I don't mess it up!), increasing the force as I go. Sometimes I tilt the Pro-Filer slightly forward, to get a stronger direction change. If there isn't enough space to place the entire Pro-Filer stone ahead of the sweet spot, you may have to use more tilt, so the back of the tool doesn't round off the sweet spot again.
Then I turn the Pro-Filer around 180 degrees, and do it again, because the Pro-Filer is an imperfect tool, and stroking it in the opposite direction evens out the length of the inside and outside edge.
Then I rotate the skate 180 degrees, and place the Pro-Filer so the back of the cylinder is at the sweet spot again, but the front is towards the back of the blade. And I do the same thing, stroking towards the back of the blade, increasing pressure as I go, and again with a tilt away from the sweet spot. And do the 180 degree exchange again.
As always, use a flat stone or equivalent to straighten and perhaps polish the edges, so they point vertically, rather than to one side.
Good luck. I bet these things PARTLY solve your problem. But, if your body is less sensitive to blade shape changes than it used to be, or your inner ear doesn't detect balance as well as it used to, or you have lost some of your fine motor control, or you have lost your muscle tone so your body flops around like a wet noodle, nothing can fix those things that I know of.
Many good professional sharpeners occasionally re-emphasize sweet spots, to make the curvature change sharp again. Some change the location of the sweet spot to better match the anatomy and preferred point of spin of the skater too. But I don't know if any of them also create a slight direction change there like I do.
As tstop4me says, you may eventually feel a need to shorten your toe pick. So it doesn't interfere too much. Say, in another 10 years?
By the way, if you brush your finger very lightly ACROSS the width of the blade rather than ALONG the length, you probably won't cut yourself, and can feel the edge much better. But I hesitate to tell that to kids, because they can be careless with their fingers. Even some adults don't understand what "very lightly" means. It works with knife edges too, even ceramic knife edges, and if you are super-super-careful, with razor blades. You can feel sharpness, and you can feel if the edge has been bent over.
Topic: Wear on 11-1/2 year old blades (Read 3366 times)