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?

As noted in another thread
 
  https://skatingforums.com/index.php?topic=8931.0

if your printer distorts x and/or y scaling, printing my rocker curves will be useless to you.

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?

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.

I hope the issues aren't a manufactured problem by the site provider to try to force you to upgrade what you pay for the server.

BTW, I know many people who hire professional website creators have problems. I hope you make sure it is done in a way you can easily maintain it, without their help. KISS. And that you, not the commercial firm, owns all copyrights, licenses, and site registrations.

This particular paranoia is justified. I've known business owners and organization managers who ran into these kinds of issues. Website creation and management is poorly regulated at this time.

Addition info from a person associated with the rink: the blue stuff on the ice was probably paint, not refrigerant, that blurred when the ice melted, due to the failure. No pipes burst. I guessed wrong.

People have mentioned that some delays occur because original parts are no longer available. The rink was built in 1971. (That means it has lasted slightly longer than the 50 year lifetime estimated for the proposed new rink.)

Is it common for ice rinks to buy a sufficient supply of replacement parts to last the projected facility lifetime? I wonder if that would make sense.

Quote from: tstop4me on October 29, 2024, 05:24:32 PM
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.

The upgrade is more complex than I thought it would be.  I have hired a commercial firm to handle it.  I appreciate your patience as we move to a shiny new site together   

Jim

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.

4 days ago this was posted on https://www.facebook.com/bowieicearena

QuoteThe City of Bowie, Maryland requests proposals from qualified and experienced firms to provide Construction Management Services for all aspects of construction of a new single sheet ice arena located at 7800 Laurel Bowie Road, Bowie, Maryland, 20715.

The new rink design info is at https://www.cityofbowie.org/841/New-Proposed-Bowie-Ice-Arena-2024.

I have no additional pertinent information. But given the recent maintenance issues at the current site, it is important that something newer be built soon.

There does not appear to be a safe, practical way for pedestrians or bicycles to get across route 197 from the south or east of the site - not even for kids at the elementary school, directly across 197 from the proposed site, or for that matter from the senior center just south of it. I would love it if routes were be provided, along with a light with a pushable button for pedestrians or bicycles crossing 197, and/or a pedestrian bridge across 197.