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Check Your Zero

A recent OpenSCAD mailing list discussion started with an observation that the dimensions of printed parts were wildly different from the numeric values used in the OpenSCAD program that created the STL. Various folks suggested possible errors, examined the source and STL files to no avail, and were generally baffled.

Finally, a photo conclusively demonstrating the problem arrived:

Caliper - digital vs. analog scale

Caliper – digital vs. analog scale

Note the difference between the digital readout and the analog scale printed on the body.

Turns out it’s his first digital caliper: he simply didn’t realize you must close the jaws and press the ZERO button before making any measurements.

We’ve all been that guy. Right?

FWIW, our Larval Engineer can probably still hear me intoning “Check your zero” every time she picks up a caliper or turns on a multimeter. Perhaps she’ll think fondly of me, some day. [grin]

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  1. #1 by jim oslislo on 2017-03-18 - 10:24

    I bought a 12″ Harbor Freight caliper which would loose 1 inch! at one place in it’s travel. I quite enjoyed smashing it to smithereens. Learning my lesson, I bought a “new” 12″ Mitutoyo caliper from Ebay at a price too good to be true. It turns out they are incredibly good counterfeits complete with fake calibration paperwork. I can’t figure out why they go to such a degree to copy the Mitutoyo and then don’t go the extra step to make them work right. Well, you get what you pay for.

    • #2 by Ed on 2017-03-18 - 19:16

      The HF caliper was so cheap you couldn’t justify the gas to return it. I know that feeling and haven’t darkened the local HF store’s doorway for a year or so.

      Maybe a “works right” copy would provoke Mit to fire a lawyer up their collective tailpipe? Hard to imagine that would do any good, but …

      • #3 by RCPete on 2017-03-19 - 09:30

        I checked out the new HF store in town. I still have no reason to buy anything from them.

  2. #4 by Daniel B. Martin on 2017-03-18 - 10:50

    Larval Engineer?!?? She’s a REAL engineer with a college degree and on the first rung of a high-pay career ladder. Wow!!

    • #5 by Ed on 2017-03-18 - 19:25

      I think of it as clearing the gantry and starting the long burn to (her own) orbit, but, yeah, she’s on her way!

    • #6 by david on 2017-03-18 - 21:02

      Oh dear. How time flies.

      • #7 by Ed on 2017-03-19 - 09:18

        That’s easy for you to say! [grin]

        (It wasn’t more than a few months ago, as my memory tells it, when she helped knead the bread.)

  3. #8 by Jose I Romero on 2017-03-18 - 14:58

    Another reason why i totally love my vernier calipers, you wont be able to knock the zero out of alignment unless you drop it real hard :)

    • #9 by Ed on 2017-03-18 - 19:27

      Although I kept a few vernier calipers, they don’t see much use these days: switching from metric to inch so I can pick out the right drill is wonderful.

      • #10 by Jose I Romero on 2017-03-19 - 00:10

        I must admit that became a new problem for me since I moved to the ‘states. Oh how I miss simpler times back home where everything was metric.

        • #11 by Ed on 2017-03-19 - 09:28

          I measure nearly everything in metric, because millimeters are about the right size for objects around here. I’d need metric drills for anything critical, but the next-larger inch equivalent works just as well for my simple, low-strength needs.

          Don’t get me started on lumber or plumbing …

          • #12 by Jose I Romero on 2017-03-19 - 12:05

            Same here, also the fact that buying “standard” drills and fasteners is so much easier and cheaper than the metric equivalents.

            • #13 by Ed on 2017-03-19 - 16:02

              The number-size drills get a lot of use, because they cover the most useful sizes with good granularity, and I’ve actually bought some replacements.

              On the other paw, the contents of the letter and fraction sets don’t see the shop lights very often.

  4. #14 by RCPete on 2017-03-18 - 19:37

    My “favorite” goofup involves a measuring tape while woodworking.Last one was last week. I needed a window piece 35-3/4″ long, and started from the right. Saw the 35″ mark, measured 1/4″, and got a perfect 34-3/4″ stick. That upside down number kills me far too often. OTOH, I usually buy a little extra wood…
    Blessed are the pessimists, for they have backup plans.

    • #15 by Ed on 2017-03-19 - 09:29

      Always buy one more stick than you need: it’ll come in handy!

      • #16 by david on 2017-03-20 - 04:42

        Or as I say too often: measure three times, cut twice.

        • #17 by Vedran on 2017-03-20 - 12:48

          Or as I say too often: measure three times, cut twice.
          and it’s still to short :)

  5. #18 by celem on 2017-03-19 - 09:14

    I have two of these cheap Chinese digital calipers. While handy, they aren’t super accurate, run down the battery far too quickly and turn on when within a few feet of fluorescent lights. While I still use them some, I keep the batteries removed. I purchased a used, high quality mechanical micrometer and it is very accurate, reliable and uses no battery.

    • #19 by Ed on 2017-03-19 - 09:31

      Aaaaand your grandchildren can use it, long after battery corrosion ate the fancy digital versions!

  6. #20 by Vedran on 2017-03-20 - 12:58

    I have a 10$ Chinese made ones from local Lidl store chain. It’s plenty good for that money and actually works fine. Still on OEM battery after year or two and it sees daily use.

    On course, I had to take it apart and shorten one or two of the tiny screws that hold the sensor to the jaw to allow it to seat properly and stop wiggling but after that… :)
    It’s repeatable to about 1/20 mm but it’s so cheap I don’t mind throwing it around the shop and it’s still more precise then my “good” mechanical ones that read in 1/10 of mm

    • #21 by Ed on 2017-03-21 - 08:36

      Doing the last 5% of product design and manufacturing counts as “practice” around here. [sigh]