How bad can temperature degrade CMM accuracy

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  • How bad can temperature degrade CMM accuracy

    When our new lab was constructed two very poor AC units were installed. The entire summer the lab has been at least 76-77 degrees but the past month or so it has remained closer to 80-82 degrees with around 3-5 degree variance throughout a 24hour period. Management and facilities want to drag their feet on addressing the issues and no one making decisions on the equipment have any knowledge or have ever worked in a lab. They seem to be more of the mindset " its fine just tip cal more to make up for the worsening accuracy". I don't know what more official documentation might be out there to provide. Looking at the temperature station at my desk now we are at 81.2 degrees.

  • #2
    Your profile states you have a hexagon CMM, is that accurate? Doesn't it have temperature compensation? if so, are you using it? it should mitigate a lot of the variataion.
    What is the material type?, size?, and dimensional tolerance ranges? of the product you are working with?
    Thermal coefficent of expansion can have a major influcene on product acceptance when you are 12degrees off, without compensating for the growth... but for smaller or less precise parts, it's noise.

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    • #3
      It really does depend on your tightest part tolerances and the material the parts are made from. Your customer's environment also matters if you're measuring at +12 degrees and they're at-12 degrees. You'll forever be chasing your tail while people try to accuse you of incompetence. Standard temperatures at least lets everyone start out of the gate evenly.

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      • #4
        I know it will go over like a lead balloon but when the reject comes just save those emails that you sent to them with your concerns and dont loose any sleep over it ?

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        • #5
          Your profile states you have a hexagon CMM, is that accurate? Doesn't it have temperature compensation?
          Even on a machine that has temperature compensation enabled, you can still run into problems. It is generally the rate of change that causes issues rather than the temperature itself. If the temperature is stable, the machine can compensate and function perfectly well, providing the temperature is within the range specified for that machine. If the temperature is fluctuating rapidly you will have problems. Because the CMM is made from lots of different materials (e.g. steel, granite, plastic, aluminium), which all have different coefficients of thermal expansion, it cannot react to rapid changes in temperature. As a general rule, most of the tech sheets for our machines will state a rate of change of no more than 1°C per hour over any 1 metre volumetric area. There may be slightly more variance allowed for shop floor machines but my general advice is - check the environmental specifications for your particular CMM. If you don't have access to the tech sheet, you may be able to download one from https://www.hexagonmi.com/en-GB/prod...uring-machines . Failing that, contact your local Hexagon office and they should be able to provide the information.
          Neil Challinor
          PC-DMIS Product Owner

          T: +44 870 446 2667 (Hexagon UK office)
          E: [email protected]

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