What is different about different blade sizes?

[Query]

Someone once told me that the front part of common brand (MK, JW, Ultima) blades was identical for different length blades within the same model. (That person worked as a sharpener for Riedell - but it was before Riedell made their own blades.)

I.E., that for a given model, the toepick (shape, size, position & angle relative to the front of the front mounting plate) and spin rocker length(s) & radii were all the same, and that the main rocker radii was the same, and that the height of the mounting plates above the ice was the same. In other words, you could turn a long length into a short length blade of the same model, simply by cutting off the rear part. (Except for the position of the rear mounting plate - if the change was too large, you couldn't attach it to your boot heel. Which would be bad. )

But that would mean that for little kids with little feet and adults with big feet, that blade model would interact completely differently with their bodies.

As an example, lift height would be completely different, the angle of roll between the toepick and the back of the blades would be different.

Were they correct? If not, what changes?

Also, does anyone know exactly what "lift angle" means? E.g., is it the angle of the mounting plate wrt horizontal when you are just barely touching your toepick along with part of the curved rocker section) of your blade? Or the number of degrees of roll between that point and the back of the blade? Or between the transition point between rocker lengths and the back of your blade? Something else? Or is it one of the figure skating terms (like rocker & sweet spot), with a variety of meanings according to different people?

 

[SK4T3]

I have a variety of JW CA sizes available. I'm able to make measurements if you like, to help you with research.

 

[Query]

I have a variety of JW CA sizes available. I'm able to make measurements if you like, to help you with research.

I would love that! Come to think of it the guy from Riedell was probably only talking about rocker profiles - I don't know if he was thinking about the height and placement of the mounting plate relative to the rest of the blade, or the shape and size of the toepick. And maybe it was only his impression - I don't know that he took any measurements. Other people have sometimes talked about rocker radii being the same, but I'm not sure about the lengths of the segments of the blade with different radii.

Profile would be somewhat easy to check. You could trace the profile of one blade (including toepick with a thin writing implement that can get very close to the blade - like a mechanical pencil held at an angle. And put the other blade next to it.

The height of the mounting plate would be more difficult. But I think you could do it with a ruler. And the position of the toepick with respect to the front of the mounting plate - I think you would need a square with a ruled scale, or a square + a ruler.

But an old blade, that has gone through a few sharpenings - or even one sharpening, since many skate techs - even some mail order companies - routinely re-profile blades (some brands, including JW, have a reputation for imperfect consistency - believe it or not, sometimes the left & right blade don't match), so wouldn't have the same shape as a blade straight from the factory. To make matters worse, some of their blades have evolved over time.

But I'd love it if you would do what you easily can, and tell me how much use the blades have seen.

 

[SK4T3]

Let's start with some Calipers:

Toepicks (Measurement from Top Pick to Drag Pick)

• JW CA 9,00 --> 28,0mm (1/3 model)
• JW CA 9,00 --> 28,5mm (1/4 model)
• JW CA 9,25 --> 28,5mm (1/4 model)
• JW CA 10,00 --> 28,5mm (1/4 model)
• JW CA 11,25 --> 28,5mm (1/4 model)

Stantion Hight (base on current Sharpenings):

• JW CA 9,00 --> 41mm (1/3 model)
• JW CA 9,00 --> 40,5mm (1/4 model)
• JW CA 9,25 --> Back 44mm Front 43mm (1/4 model)
• JW CA 10,00 --> Back 44mm Front 43mm (1/4 model)
• JW CA 11,25 --> 44mm (1/4 model)

 

[tstop4me]

What do you mean by 1/3 model vs 1/4 model? Do you mean 1/3" vs 1/4" increments in sizes?

 

[SK4T3]

What do you mean by 1/3 model vs 1/4 model? Do you mean 1/3" vs 1/4" increments in sizes?

Yeah,
Older models had the 1/3 of increments. Because the one I have is 9" you cannot understand it's from the 9 1/3 and 10 2/3 "family" unless I mention it.

I actually have seen MK Plantom and MK Dance blades with CM sizes stamped on the footplate.

 

[tstop4me]

Yeah,
Older models had the 1/3 of increments. Because the one I have is 9" you cannot understand it's from the 9 1/3 and 10 2/3 "family" unless I mention it.

I actually have seen MK Plantom and MK Dance blades with CM sizes stamped on the footplate.

Wow, that's interesting. I know that MK used to use 1/3" increments; they didn't switch over to 1/4" increments until sometime after their merger with Wilson in 1997. Occasionally new old stock MK blades in 1/3" increments still pop up on eBay or online clearance sales (skate shops sometimes uncover vintage stuff when they clean out storage closets).

I bought my first pair of Wilson Coronation Ace in the mid-1970s. They were in 1/4" increments then. Do you have any idea how old your 1/3" increments Coronation Ace are?

 

[Query]

Fascinating!

Were these all your blades, or do you work in a well stocked store?

I've wondered about n/3 sizes too. I don't get why both systems are used.

 

[Query]

American shoe and boot sizes are in 1/3 inch units (in length, though the origin depends on the shoemaker, and whether you are talking men's, women's or tot - young child - sizes). Maybe there is a connection... Anyway, what's important is that you are saying the blade shape shapes have evolved over time, which skate techs had also told me. E.g., a guy who manages a Canadian skate store told me MK Dance have evolved fairly recently, to deal with the jumps that are now part of ice dance.

Since you say "current sharpening", roughly how much use have these blades seen?

I've been thinking a little bit more of how one can accurately measure blade shapes. I still think the best way is from photographs, or scans. And to guess the scaling of the images (for photographs - optical scans usually incorporate a scale into the image format) from the nominal main rocker radius. Except... 7 & 8 foot radius rocker curves are only a few pixels apart at 1200 dots/inch. And published images are usually lower resolution. So doing it the easy way, from 3 control points, might not yield a very accurate scaling estimate. I suppose I could do a least squares fit, to the detected edge boundary, to try to obtain a more accurate level estimate of rocker radius. Ugh. This is getting complicated. It was meant to be a very simple question. But maybe not one that can be easily answered without the specialized and expensive tools that measure rocker radius more accurately...

Too bad I don't have unlimited access to a skate shop that stocks a lot of new figure skating blades, and to their rocker measurement tool.

I was once told, by a speed skater who used to hold some U.S. speed records, that the fastest speed skate rocker radius for short or long track doesn't depend on the length of the foot or blade. But I think figure skates should be different. E.g., when you are at the point where both the toepick is and the rockered part of the blade is in contact, the weight projects approximately radially back into the foot. Perhaps that should be near the ball of the foot, and appropriate lengths should change with foot size... One not-so-expert tech told me that hockey rockers do depend on length, though I haven't tried to confirm that.

 

[SK4T3]

Wow, that's interesting. I know that MK used to use 1/3" increments; they didn't switch over to 1/4" increments until sometime after their merger with Wilson in 1997. Occasionally new old stock MK blades in 1/3" increments still pop up on eBay or online clearance sales (skate shops sometimes uncover vintage stuff when they clean out storage closets).

I bought my first pair of Wilson Coronation Ace in the mid-1970s. They were in 1/4" increments then. Do you have any idea how old your 1/3" increments Coronation Ace are?

Edit: CM/MM stamping is not easy; because you can have for example 295 boots with 275 blades

I think I could be wrong and mistaken JW with MK.
The 9" I (probably mistaken) mentioned as 1/3 'family" is approximately 40yo and possible Old Stock then.

Fascinating!

Were these all your blades, or do you work in a well stocked store?

I've wondered about n/3 sizes too. I don't get why both systems are used.

Figure Skating / Ice Dance Family.

Basically there are only 3 sizes in an inch for 1/3 and 4 sizes in and inch for 1/4; so it's more precise.

American shoe and boot sizes are in 1/3 inch units (in length, though the origin depends on the shoemaker, and whether you are talking men's, women's or tot - young child - sizes). Maybe there is a connection... Anyway, what's important is that you are saying the blade shape shapes have evolved over time, which skate techs had also told me. E.g., a guy who manages a Canadian skate store told me MK Dance have evolved fairly recently, to deal with the jumps that are now part of ice dance.

Since you say "current sharpening", roughly how much use have these blades seen?

Jumps now part in ice dance?

Oldest blade has 6 sharpenings.

 

[tstop4me]

I think I could be wrong and mistaken JW with MK.
The 9" I (probably mistaken) mentioned as 1/3 'family" is approximately 40yo and possible Old Stock then.

Thanks for the correction. That makes sense now. As I mentioned, I've seen (and worn) MK blades with 1/3" increments sizing, but never JW blades.

Basically there are only 3 sizes in an inch for 1/3 and 4 sizes in and inch for 1/4; so it's more precise.

Yes. On the flip side, 1/3" increments mean fewer sizes to manufacture and stock: lower costs for the manufacturer. There are current el-cheapo beginner blades that come in 1/3" increments.

 

[Query]

Hmm. It turns out there are freebee image processing programs like ImageJ that might be able to do the job of estimating positions, shapes and sizes in an image, possibly including finding radii... Maybe it would be easier to use one than to write my own purpose built software.

BTW, I have seen advertised a used 9 2/3 inch MK Dance blade.

An amusing question might be why inches are used by a UK company. I was taught in school an apparently oversimplified idea that UK & European law required measurements to be in the metric system. It must be that only applies to some things, and goverments left out figure skating blades.

 

[Query]

I was thinking about the best way to pass the info about blade shape.

Measuring curvature is hard, without the expensive specialized tool.

A relatively easy measurement would be the length of the "non-skating zone". I.E., you place a straight ruler on two points of the blade, the only place you can:
1. The tip of the furthest back pick
2. The other point along the curved part of the blade that the ruler can touch.

Then the distance between the two points would be that length.

That's imperfect, because every time you sharpen a blade, without trimming the pick in a way that keeps this length the same, that length increases (even if the sharpener is very careful to remove a uniform amount of metal from all places along the blade, which is actually somewhat hard to do with a powered sharpening machine, and even a bit hard to do with hand tools). But it's the most obvious way to get an easy measurement, unless you happen to have those rocker measurement tools.

And it's just one measurement, which doesn't actually give a single curvature. It depends on the exact height and angle of the toepick (which might or might not have remained the same). Since you didn't have more than 5 sharpenings on any of the blades, I'm guessing your sharpener(s) didn't bother to trim the toepick, but instead told you the blade wasn't usable anymore - or maybe you a very fast growth spurt. It also depends on both spin rocker sections (Coronation Ace has a total of 3 rocker sections. The main one in the back, and two up front, though, AFAICT, the furthest one forwards doesn't affect spins, because it is entirely in the non-skating zone.


I think my images of rocker curves (the ones that are 1 inch apart in radius) are good enough to roughly measure the radius of curvature of the spin rocker sections, but am not sure you would find that easy to do.


The other obvious way would be to take scanned images of as much of the front of the blade (or of tracings) as will fit the scanner. (Most printers now include scanners). If you use the blade itself, you would of course be careful not to scratch the glass, by not tilting it, and not dragging it. And the whole blade won't fit - just the flat part near the bottom. (I assume none of your Coronation Aces are parabolic, tapered, etc., so the sides of the bottom are parallel?) Ideally the highest resolution the scanner accepts,


Then I could send you a personal message with my email address, and you could send me an email with the images attached, and say which is which.


Or you could drop the images somewhere free, and send a personal message that says where it is, since we aren't supposed to use public postings to mention such services.

Or SK4T3 could trace one blade on tracing paper, and another on anything, and see how well they overlay. You can use normal paper, and place them on top of each other near a bright light source, but I've found that hard to do.

Or SK4T3 could trace one of the blades, and see how well the other blades fit against it.

Or maybe you can think of another way to make the comparison? tstop4me, your background might include ways to good ways compare 2D shapes that are supposed to be the same? How would you do this in a way that forum rules allow? Another forum we have used that allows public image posting isn't working very well right now. This one allows attaching images, but none that are large enough to do the job - I tried a 75 kilobyte image, which is pretty small, and it said it was too big

 

[Query]

I found a ridiculously simple way to approximately find the back point along the blade at which the radius of curvature first changes without using any expensive tools.

I traced the blade on a piece of paper. I slid the blade forward along the tracing, in such a way that the back of the blade continues to hug the tracing. Where the radius changes, the tracing starts to disappear under the blade.

Of course you could do the same with my computer image of rocker curves instead of the tracing. But I love the simplicity of using nothing but pen and paper.

I was trying to estimate radius of curvature from seeing how much longer a measurement along the curve was than a straight line measurement between two points. But, aside from the minor annoyance that there is no closed form solution for the radius from the "arc length" and the "chord length" (the practical solutions are iterative), the sufficiently flexible material I had on hand was also too stretchy to make an accurate measurement. I also tried pushing a straight edge along the curve (which of course tries to find the tangent direction at the point of contact), and trying to judge where the space between the blade and a point a couple inches away deviates more, but that seemed like a pretty hard to do thing to do accurately too.

BTW I have no problem measuring the spin rocker curvature of an (old style Matrix I) Ultima Dance runner using my (printed) imaged rocker curves to consistently place the radius of curvature to be 9 or 10 inches (probably in between), using the 1 inch radius spacing set, by looking at a blade length a bit over an inch. Same for my (old style Matrix I) Ultima Supremes, which are currently mounted on my skates. And it is even easier easy to see that the main rocker is much closer to 96 inches than to 93 or 99, on the 3 inch radius spacing set, by looking at a 4 or 5 inch long length. I don't have any blades convenient that I can test with the more complicated 3 rocker set of Coronation Ace. But I need a magnifying glass to read the little rocker lengths I've printed beside the curves with my old eyes. Oh well. Something to fix.

Anyway, the claim people have made that you can't accurately measure rocker curvature by eye, against a printed curve, simply isn't true. Smaller scale variation would be hard to see - that's where the expensive tools would be handy.

 

[Query]

OMG. It is so hard to trace toepicks. None of my pens or pencils are thin enough to do a good job. I tried a mechanical pencil at an angle - but the other picks get in the way. What would you use?

The only idea I've got - which sounds clumsy and inaccurate, is to put tracing paper over the blade, and use the side of a pencil or felt tip marker against the edge I am tracing over, through the tracing paper.

In the past, I've photocopied my blades, so I could retain the rocker (though I sometimes deliberately changed it a bit - e.g., the spin rocker on Ultima blades seems too short to me - nowhere near the ball of my foot - and it's such a short roll from the start of that to where the toepick starts to touch. Now that I think of it, the 9 or 10 inch Ultima spin rockers I measured might be on blades I modified.) on the flatbed scanner included in printers. But I can't walk into a pro shop with a big printer and do that. It might already be too hard to convince them to let me take measurements.

EDIT: A technical pen (with a thin metal sleeve around the writing tip) could get a little closer, and be consistent if I could hold it straight up and down. With work I could even scan the result, and write software to compensate for the width of the sleeve and tip. But no one works that hard at tracing shapes, do they?
Or a charcoal pencil and tracing paper, like the "rubbings" they had us do in elementary school. That wouldn't leave a mark on the blade.
All this to answer a simple question about blade shapes. I'm working too hard at this.