Can you see the difference between 7 & 8 foot rockers? :)

[Query]

http://mgrunes.com/boots/DrawArcs/Compare7_8foot.png
is a 1200 pixel/inch drawing of 7 & 8 foot rocker curves. If viewed with Firefox or Chrome, you can see the lines, which are only 1 pixel wide. Not sure about other browsers.

The curves are so close!

The scales have 16 tics/inch, 1 big tic/inch.

Yet we mean skaters dare claim 8' rocker blades are faster and more stable, and 7' blades turn and spin better.

Pity the poor maligned skate techs who only think they are doing a good job. Virtually invisible changes can make customers upset.

(P.S. It was an easy mod of a program I created to draw many scaled rockers at http://mgrunes.com/boots/DrawArcs, used to measure blade shapes.)

[AlbaNY]

It is pretty nuts to see the slight difference. 

I’ve tried two blades with 7’, but briefly, and they felt nice but not so different than the two 8’ I have spent a lot of time on.  I’m firmly in the camp of believing skaters can easily adapt to different blades if they want to, and a skilled skater can do great things on pretty much any blades.  *Bleep* rentals though.   

[tstop4me]

The more pertinent question is:  "Can a skater feel the difference between an 8' vs a 7' radius main rocker?"  Similar to previous discussions on:  "Can a skater feel the difference between a 3/8" vs a 7/16" vs a 1/2" radius of hollow?"  This is the criterion that I refer to as "the proof of the pudding".

[Query]

A lot of people claim it is harder to center spins, but easier to land jumps (for stability), on 8 foot rockers. Including some on this board.

I don't know how well controlled any experiments they ran are.

I.E., other blade shape factors differ too, blade to blade. As perhaps they should? All other things being equal, an 8' rocker would otherwise lift the toepick less off the ice.

I think you are implying there are psychological factors too.

My point though was that a skate tech would probably have to take a measurement to see the difference. Given the minimal training a lot of them have, and the pressure to sharpen as many blades/hour as they can, I wouldn't expect most of them to notice the difference.

[tstop4me]

I think you are implying there are psychological factors too.

My point though was that a skate tech would probably have to take a measurement to see the difference. Given the minimal training a lot of them have, and the pressure to sharpen as many blades/hour as they can, I wouldn't expect most of them to notice the difference.

Nope, I'm not implying any psychological factors.  My point is you determine functionally how small an increment is significant; and then you settle on the proper tools and procedures for measurement.  You seem to be approaching it the other way:  The visual difference between images is hardly perceptible, so how could it make a difference?

When I switched from a 7' to an 8' radius main rocker, the difference was immediately apparent to me.  With a 7' rocker, I always struggled to complete the circles on my Figure-8s; but when I switched to an 8' rocker, the glide was so much better that I had no problem running out of steam.  And part of my warm-up exercises involves skating backwards the entire length of the ice.  The first time out on an 8' rocker, I was zipping so unaccustomedly fast that I crashed into the boards behind the red line; something which I had never done with a 7' rocker.

[AlbaNY]

Tstop, that’s interesting.  I felt faster in that way on 7’ Coronation Aces in a test try vs my 8’ Pattern 99s. 

I stick by my belief that blades actually don’t make much of a difference.  (Except the bleeping rentals.)  People hate on Aspire XPs, but I found them adequate and accomplished a lot on those.  CA felt really nice, but at the end of the day I could do the same things on the P99s.  Same for Phantoms.  Granted I do single jumps, so perhaps I’m missing the stability feature or not, but most people seem to complain or talk about spins and blades and not jumps.  I really haven’t felt that much difference on any of the blades.  Like, it’s nice on the P99s or CA, but if I had to use Aspire XPs it would be fine (and that is with questionable sharpenings on a bench grinder for close to a year.)  Aspires maybe don’t glide as well, but spinning actually worked well.  Basically it seems nice to have better blades, but it really, really doesn’t matter much.  IMO

Except those rental blades.  No one with figure skating goals should use them ever.   

[Query]

tstop4me, I wasn't saying there is little or no difference. I do know very small changes make a huge difference. Differences I can barely see have made a huge difference in how i skate.

I'm just trying to figure out the basic geometry and intuitive physics of blades.

This was originally inspired by the idea of making my own blades for myself - though I'm realizing that's a lot more complicated and expensive than I thought, in terms of tools and even the raw materials.

But then I just got curious. Why aren't short blades just a miniaturized version of long blades? But if that were true, the toepicks woudn't be the same size (which as we were told in another forum, they do seem to be), and a 12 inch (mounting plate length) blade would have twice the rocker radii of a 6 inch blade (just an example; I know most blades don't cover that large a range) - which we know they don't.

I don't understand why they aren't completely scaled like that. The angles of roll would be the same. The places where weight is borne on the foot would be the same. Etc.

One skate tech, who sharpened blades for a major skate boot brand, told me he thought the shapes of the front half of blades of a given model were identical, regardless of scale. But for reasons I mentioned, that makes no sense - why would a little foot bear the weight of jumping in the middle of the foot, while a long foot would bear it in the toes?

There are blade pictures online. E.g., MK, JW and Paramount have pictures of all their blade models, in almost a flat projection - close enough that I could perhaps calculate radii and transition points, if I knew the scale. I downloaded them all to play with. The image formats contain a scale, but they are presumably photographs not scans (because you can also see the mounting plates), so the scales might not reflect reality, as much as the photographers original intended display size. (I thought of using the published main rocker radii to scale the sizes, though I'm not sure the image resolution is fine enough to accurately calculate a main rocker length). Ultima's pictures are in a weird perspective, but other pictures of Ultima blades are available online. But - for the most part, none of these label the size of the blade, and they only display one size.

[marc]

Requête,
Tu pourrais m'envoyer un lien pour les photos des lames JW s'il te plaît.
Car j'ai acheté une lame d'occasion et je voudrais comparer avec la courbe du neuf.
JW parabolic ( je pense que c'est vieux mais ma fille voulait essayer).
Je suis toujours avec attention toute vos discussions et entreprendre de construire sa propre lame est un vrai challenge et je te souhaite d'y arriver....
Merci et au plaisir de lire tout vos message ici qui sont super instructif.

[Query]

Marc

This is primarily an English language board. I used Google translate.

Thanks! The JW pictures I looked at are on the JW website:

https://www.johnwilsonskates.com/products

I am not an expert! Not at skating, and not at shop work. I have given up for now on making my own blades.

I have found a lot of contradictory information and am trying to make sense of it.

Some of the best (English language) videos are at

Scarlet Skater:
  https://scarletskater.wordpress.com/2017/06/01/choosing-figure-skating-blades
  https://scarletskater.wordpress.com/2017/06/02/blade-profiles

Aimée Ricca's Youtube site, such as
  https://www.youtube.com/watch?v=SCTmQDZMyN0&list=PLhIvo-BmGcaU_Oz4eM2T7YCAZWDKkch4I
  https://www.youtube.com/watch?v=Y6CdHJyHdQg&list=PLhIvo-BmGcaU_Oz4eM2T7YCAZWDKkch4I&index=3
  https://www.youtube.com/watch?v=_Xx9Z-7NM4Y&list=PLhIvo-BmGcaU_Oz4eM2T7YCAZWDKkch4I&index=3&pp=iAQB

I also like at Everglides:
  https://everglides.co.uk/
  https://www.youtube.com/@everglidesskatingspecialis495
  https://www.youtube.com/watch?app=desktop&v=PjRFziQKKrA

And Coach Julia:
  https://www.youtube.com/watch?v=h516z1Tneuk
  https://www.youtube.com/watch?v=pEAnb4kRrFU

And
  https://www.danielyeow.com/2011/inline-to-ice-1
makes it clear that my information on speed skating rockers is wrong or out of date.

SP Teri's website says their boots are designed to balance in the center, not the ball of the foot.

Aimée Ricca's videos claim blades should be 1/2 inch to 1/8 shorter than the boot - mine may be too long.

A skate tech (not sure how expert, or if he is correct) recently told me that long figure skate blade sizes use the same rocker radii as short ones, but the lengths of the segments using each radius changes. He didn't know exactly how.

[Kaitsu]

When I switched from a 7' to an 8' radius main rocker, the difference was immediately apparent to me.

Which blades you had when your noted this difference?
Was the supplier specification and skating feeling the only ways you used verify rocker radiuses or did you use some measurement method to ensure which were the actual radiuses in your blades?

[Query]

I switched from JW Coronation Ace to MK Dance when I was almost a beginner, stayed with them for a long while, then to Jackson Ultima Matrix (1 - not the current Matrix models). The Ultima blades included many runners of Ultima Dance, and one pair of runners for Ultima Supreme and Ultima Synchro.

I did not record the Coronation Ace profile. I didn't record the MK Dance profile until until they were fairly old. A good skate tech told me I had modified the MK Dance profile without intending to. I didn't understand sharpening well enough when I started sharpening the MK Dance to record the profile.

I did look at the rocker profiles of the Ultima Matrix 1 runners when they were new. All seemed to my eye to have the same profile (all 3 models!), except for the toepick. I don't know if that is true of modern Ultima blades. But a lot of figure skaters greatly prefer the MK or JW blades, as you must know.

So I can't be very helpful to you there. I'm not sure I could convince a shop owner to let me walk in and trace many blades. Especially if they knew I had considered making my own, and did sharpen my own! Sorry!

[tstop4me]

Which blades you had when your noted this difference?
Was the supplier specification and skating feeling the only ways you used verify rocker radiuses or did you use some measurement method to ensure which were the actual radiuses in your blades?

For many years I skated on Wilson Coronation Ace (plain carbon steel).  Then I switched to Eclipse Aurora (440C stainless).  It was supposed to be the same profile as the Coronation Ace, but not quite.  I didn't notice any difference in glide on the main rocker, but the spin rocker was flatter.  I skated on them for less than a year.

I then switched to the Paramount version of the Gold Seal, what they refer to as the 12" spin rocker model (440C stainless).  They claim it has the same spin rocker and main rocker profile as the Gold Seal. The Paramount runner has parallel sides; no concave side honing, no tapered blade thickness as in the Gold Seal.

I only went by the manufacturers' specifications for the main rocker radius (7' for Coronation Ace and Aurora vs 8' for Paramount).  I have no tools for measuring rocker radius.

[Query]

I only went by the manufacturers' specifications for the main rocker radius (7' for Coronation Ace and Aurora vs 8' for Paramount).  I have no tools for measuring rocker radius.

I have some rocker curves at http://mgrunes.com/boots/DrawArcs.

If you print them (e.g., using Microsoft Paint), and manage to convince your print driver to print them at a scale that the inch scales on the borders are correctly scaled (most print drivers and software do rescale by default, even if you tell them not to - which I hate), then you can easily place them behind your blades (fold the paper to get it out of the way of your boots and mounting plate and see). E.g., I have no problem telling by eye that my main rockers are closer to 8' than to 7' 9" or 8' 3". I couldn't be certain by eye whether my spin rockers were 9 inches or 10 inches, but think 9".

BTW, shortly after buying my Matrix (I) runners, I called Jackson Ultima and asked them whether the Matrix runners had the same shape as their non-Matrix blades with the same model names (Ultima Matrix Supreme, Dance, Synchro). They couldn't or wouldn't answer the question. When the MK/JW Revolution blades came out I asked HD Sports a similar question, and didn't get an answer for that either. Such basic questions...

At least in my case, Ultima spin rockers are NOT flatter than most MK or JW spin rockers (about 9" for me). But the spin rocker segment is short. So the distance between the back part of the spin rocker, and the touch point (in high school geometry we called it a tangent point), which many skaters like to spend most of their time between, is also short. True whether you measure it horizontally, vertically, or along the curve.

[tstop4me]

E.g., I have no problem telling by eye that my main rockers are closer to 8' than to 7' 9" or 8' 3".

You started off this thread by demonstrating how difficult it is to visually perceive the difference between a 7' vs 8' radius rocker.  But now you claim you can readily visually perceive the difference between an 8' vs 7'9" vs 8'3" rocker.  Huh?

[Kaitsu]

Here is that latest status of my profile tracing. https://youtu.be/T-6u9-aFaXg

Maybe Query can tell us by eye what are the radiuses, is there two or three radiuses, where they start and where they end. Even I have high-tech measuring tools in use, I have not managed to get closer than this, but I am still working. I claim that one root cause for this is that blade profiles are not what we expect or what it was in designer table. I can tell the radiuses I have used as soon as we have heard Query´s eye measurement results.

I am open to get advices which one of the radiuses I should change and/or which radius start / end point I should move and which direction. I can tell that I have already tested almost 10 different combinations. I am 100% sure that main rocker is flatter than manufacturer specification. That is quite common. Blade is unused blade.

[Query]

You started off this thread by demonstrating how difficult it is to visually perceive the difference between a 7' vs 8' radius rocker...

By placing the curves next to the blades - a form of measurement. And my plots, if you blow it up a bit, you can easily see differences near the top and bottom of the plots. At 1/1200 inch, well within human perception limits.

BUT given the pressure on skate techs in many shops to sharpen as many blades / hour as possible, they don't stop to take measurements.

I needed most of the length of each rocker segment to get precise measurements. The fancy expensive tools don't need that. (I also tried looking at curved vs straight line lengths - but measurements from my tape measures depend on the tension on the tape. I also tried to a straight edge and square, but it was too clumsy, or I'm too clumsy.)

The curvature difference between the main rocker, and the spin rocker(s), is large. If you place the blade along the curve, you can easily see where it departs from it. Or trace the blade, and move the blade along your tracing. You see the departure point immediately.

I have not tried the art supply store worker's suggestion - using graphite paper to impress the shape, and measuring that.

Also, one could scan the blade or tracing using an optical scanner, which I have done in the past, in a crude way. I have a 1200 dot/inch optical scanner. I have not yet attempted to verify that the scanned image positions, are accurate enough to work. Maybe not - it was cheap. I should also more fully check the positional accuracy of my laser printer.

People say some imaging and CAD/CAM software, possibly including free software, can fit lines and arcs to image boundaries. I have not tried that. But they say that is a good measurement method for small parts - like toe pick angles??

I have only tried what I tried on Ultima blades (and not on modern Ultima blades). I don't know if other blades are consistent enough to measure.

[Query]

I updated that page slightly, to plot all the rocker radii (AFAIK) you are likely to find on a single page.
Here is the image.

It has 78 - 99 inch radii at 3 inch intervals and 6 - 30 inch radii at 1 inch intervals.

To test my claims, print the image twice, at least once on transparent media (tracing paper?), on a printer with at least 600 dpi resolution - preferably 1200 dpi. Laser printers might be best.

Put a bright light behind the two pages. They overlay exactly, unless your printer is junk.

Now shift over by one curve. You can't overlay the 96" (8 foot) and 84" (7 foot) curves, no matter what you do.

It is easier to see differences between two pieces of flat media than if one of them is a blade on a boot, because the latter is awkward but you get the idea. Now put one of the sheets behind your blades, and I bet you can measure the radius fairly precisely.

While you are at it, check that your printer uses the same horizontal and vertical scaling. Mine is slightly off... Ugh.

[Query]

My printer scales x & y differently by about 1 part in 60. Which means it is drawing ellipsoidal arcs, instead of circular arcs, and the printed scales are wrong along one axis.

I guessed it might be because one sheet was tracing paper, and was too thin to feed right - but that made no difference. I printed a 1/4" grid, to check whether this distortion is uniform (it is) and whether the axis are orthogonal (they are). I could fix the distortion, by changing the x,y scaling line in the postscript file:

  72 72 scale

but just for me. But if other people's printers have distortions  - and they might not have a linear distortion field - that wouldn't fix their problem. And many people here couldn't measure & compensate for a printer distortion field.

While my Samsung Xpres M2020W laser printer was not a top of the line printer, it was well rated online within its class, and retailed for about $400 or $500 when it wasn't on sale (it was). So I assume many other people have distorting printers too.

If I scanned a blade or tracing, the scan might introduce even larger distortions. My scanner is part of a Canon TS3122 inkjet printer, which sold for $9 new on a Black Friday (presumably discounted to encourage OEM ink cartridge purchases).

Such potential distortions ruin a lot of my ideas here, as far as usability of the drawn arcs as a measurement tool by other people here.

Sorry if I got your hopes up.

How do these distortions compare to typical consumer market printers?

[Query]

I took careful measurements, and realized neither scale is right. 

I need to increase x-axis size by approximately a factor of 9/8, and y-axis size by 12/11. That's accurate to within less than 1/64 inch over a 4 - 5 inch interval. I used a metal ruler I bought at Harbor Freight - obviously not what a machinist would use, but it should be fairly close to accurate.

It completely invalidates all my measurements that I did using my drawn arcs.

That seems like a strange coincidence, that it comes out to fairly exact fractions.

Is it possible that printers (or maybe specifically laser printers??) are required by U.S. law to modify x & y scaling by 8/9 and 11/12?

I remember a long time ago (decades) reading that photocopiers in the U.S. were required to shrink copies a bit so document copies were easier to detect, though I don't know how to confirm that.

Could one of you try to print on your printer

  http://mgrunes.com/boots/DrawArcs/DrawGrid.png

and see if the grid comes out in 1/4" increments, or if it is shrunk by those factors?

My method of printing: I used Microsoft Paint (which, BTW, is due to be removed from Microsoft Store) under Windows 10, went into Page setup, told it to print it in Portrait mode (Paint default is landscape), told it to use 100% scaling (Paint default is "Size to fit"), and then printed it, selecting 1/2" margins. (For reasons I have not figured out, Paint wants to print more than one page, so I only insert one sheet, and turn the printer off after it is printed, forcing cancellation of the print job.)

Or is this something that the knowledgeable community knows about, and routinely compensates for?

[Query]

I looked online, and a remarkable number of people complain about printer scaling problems. The incorrect scaling factors are said to vary printer to printer.

But one of the claims is that at some point, updating Microsoft Windows may lose the ability to do 100% scaling correctly. Too late for me to undo that.

Also some suggestions were to update the printer driver. But Samsung printer support has been taken over by HP. And various reports online claim that if you let HP update your printer drivers, you will need OEM Print cartridges. I wonder if HP already noticed my generic toner cartridges, and messed up the scaling to punish me.

So the best possibility, if I want to use my printed arcs as a measurement tools, is to measure the inch scales as well as I can, and compensate for scaling problems myself. I should warn people such problems occur, and add a correction option. Which I have now done in the updated web page.