Measuring the profile and rocker of ice skating blades

Note: This information first appeared as a series of posts in the Skatingforums.com website. These were in responses to a thread started by member "Agnes Nitt" (forum name) in the Pro Shop section back in December 2015.

The work presented here was an attempt to carefully measure the rocker, and the entire blade profile, of a figure skating blade. I tested a new-in-the-box 10-1/2" Jackson Ultima Synchro blade that I never mounted.

The photo below provides a quick overview of the measurement fixture.

The machined miter slot in my table guides a sliding miter bar (an Incra Miter Slider) mounted on the underside of the jig to limit motion to one dimension. The miter bar fit in the slot is adjustable to minimize measurement errors.

I took rocker depth measurements each 1/2" of blade length, and compiled them into a graphic/regression program (Advanced Grapher v. 2.2). After the points were plotted and the vertical scale changed to visually exaggerate the rocker depth, I ran a curve-fitting routine on it. The resulting curve is a very good fit with an R^2 value of 1.0013. The resulting formula in case someone wants to duplicate this on a CNC machine is...

Y(x)= -(1.1252445*10^(-6))*x^7+(4.2795519*10^(-5))*x^6-(6.249962*10^(-4))*x^5+0.0044961*x^4-0.0169112*x^3+0.0380313*x^2-0.0996406*x+0.23539

You can visually assess the close fit between the two curves overlaid in the graph below. Blue represents actual blade measurements, and pink is the plot of the regression formula above.

Standard deviation is only 0.001" - better than most manufacturing tolerances can be held.

Then I plugged the Cartesian coordinate numbers shown in the table into an online calculator to find the rocker between the 1" from tail to the 5.5" from tail section of the blade. The web calculator is found at

http://mlmsolutions.biz/threepointcircle.php

The rocker measured 7.5' on the Jackson Ultima Synchro blade.

The advertised rocker is 8'.

These rockers are the primary skating rocker that is mentioned in the specifications for figure skating blades.

Rockers at various points along the blade

The useable blade ends at the root of the toe picks at the 10.9" mark, so this starts almost an inch back from the picks. I just picked the location based upon my own spinning technique. It arcs upward fairly quickly to the toe picks beyond that, and we never spin there.

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Here's what I found using a 2" "sliding window" along the blade. Rockers were measured starting from the tail of the blade...

2"-    7.58' rocker near the tail of the blade

3"-    7.59'

4"-    7.58'

5"-    7.25'

6"-    9.25' (the blade flattens out a little here)

7"-    9.81' (still a little flat here too)

8"-   3.08'  (rocker shortening toward toe pick as expected)

9"-   1.48'  (17.67  inches) rocker approaching the toe picks

I didn't have the data an hand for the rest of it up to the picks, but by now we are well into the spin rocker and closing in on the toe picks where blades see little use.

Recognize that with a smaller window comes less measurement precision. However I believe the flatness evident around 6-7 inches could be real. If that's the case, it appears that the transition between glide rocker and spin rocker is not a perfect tangent between the two arcs. It was probably put there when the blade was factory sharpened. Of course the next sharpening will change everything again anyway, so I wouldn't read too much into it.

We page created by
Bill Schneider
January 31, 2018