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  • #61
    That makes it all the more unbelievable. The operator, in the interests of extreme accuracy, starts with a guess at the temperature difference between the caliper and the workpiece, and then, somehow, moves the vernier scale to compensate.

    So, in the case of say cast iron that is estimated 10*F warmer than the caliper, and 12" long, the scale would be moved 0.0008", but if it were aluminum, it would move 0.0015". This on a vernier scale that reads to 0.001". Of course, we can also assume the scale included the necessary information for coefficient of expansion of all common materials. There must have been some sort of vernier vernier to permit accurate movement of such small increments.

    No Evan, that does not fly.

    Of course it is important that a CMM is at a constant temperature. Some of them are huge, and minor temperature differences from one end to the other will have a definite effect on their reading. Regardless, the part measured must still be allowed to equilibrate before temperature measurements are taken.

    Again, a CMM is not a slide caliper, and is irrelevant to the discussion, which is whether a temperature compensated Starrett Master Precision Vernier caliper ever existed. Please stick to that topic, and offer something more than anecdotal evidence.
    Jim H.

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    • #62
      There must have been some sort of vernier vernier to permit accurate movement of such small increments.
      I thought it unusual which is why I recall it. I believe the mystery mechanism that permitted such fine movement was a thumbscrew. I know since you are well versed in old instruments you are disinclined to believe me if you haven't heard of it yourself. Keep in mind that Starrett will make anything you are willing to pay for and such a modification to a Master vernier caliper isn't out of the question if it wasn't a standard item or regular option.

      So, in the case of say cast iron that is estimated 10*F warmer than the caliper, and 12" long, the scale would be moved 0.0008", but if it were aluminum, it would move 0.0015".
      How many times do I have to say this? It has nothing to do with the temperature of what is being measured!

      The idea of temperature compensating the instrument is to insure that it produces a reading that accurately reflects what the instrument says it is. It is, in the case of a vernier caliper, to compensate for the change in length of the caliper with temperature. It's the same as a ruler. A meter stick that is warmer than standard is longer than a meter. That's why they used to make survey tapes from invar.
      Free software for calculating bolt circles and similar: Click Here

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      • #63
        You said;

        "First, tdmidget, there are calipers that provide temperature compensation. The Starrett line of Master Precision verniers in the larger sizes have or at least had a temperature compensation scale on the beam that was/is used to correct the reading."

        I have never seen one, and no one else seems able to verify the existance of one. There are more compelling reasons for one not to exist than for one to exist, and certainly no evidence that it was a production item, which your statement indicates.

        The Starrett Master Vernier caliper line came to be in the 60's. They are not antique, or even considered as old instruments. They are currently in production and readily available.

        I asked you to furnish proof. Show us a vernier caliper from any manufacturer with temperature compensation.
        Jim H.

        Comment


        • #64
          Originally posted by ckelloug
          The steel HF calipers appear to work quite well out of the box and I'd suspect the plastic ones do too to at least some extent. What I'd question is whether either continues to be accurate after hard use or use after a period of time. I'd also question whether they show warning signs and then start producing bad measurements or whether they just die a dusty death
          --Cameron
          My guess is that the shims will wear over time and cause jitter of the display. Experiments have been done to vary their thickness and jitter was reduced as we went from the original thickness down to a smaller amount. Further reduction in shim thickness caused the jitter to rise again. The stainless steel parts will also wear but I bet the shims wear faster.
          Rick Sparber

          [email protected]
          web site: rick.sparber.org

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          • #65
            [QUOTE=ckelloug]ligito,

            We only test prime grade steel measuring instruments on this thread. You kids with your plastic calipers: get off my lawn

            That was tongue in cheek. I bought it for measuring rod.
            I have an analog diak caliper but very little experience in how to use it and forget how to read it without retraining, everytime.

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            • #66
              ligito,

              My answer was tongue in cheek too. Did you not note the plagarism from Macbeth's monologue? I just couldn't set it up without answering the question. Not all humor is good humor and I'll file this one under humor that I made that was not found exceptionally funny by the audience.



              --Cameron

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              • #67
                I asked you to furnish proof. Show us a vernier caliper from any manufacturer with temperature compensation.
                Sorry, but I cannot. The item in question is no longer on sale on e-bay. I am not however a habitual liar. As I said, it may have been a special. All the instrument manufacturers will make specials if a customer so wishes. As I recall the mechanism was very simple. The scale on the jaw was movable via a thumb screw. It was adjusted to match the temperature on a scale below the vernier markings. This isn't much of a change as the vernier scales are adjustable for calibration anyway.
                Free software for calculating bolt circles and similar: Click Here

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                • #68
                  Dim memory of an unreliable source aside, I think it is quite safe to assume that Starrett never manufactured a temperature compensated vernier caliper.

                  Even if one were to exist as described, it is not a temperature compensated caliper, but one which the operator, for some reason, could fudge manually to bias the reading, which would only be correct at only one single dimension, and a guess at that at best.
                  Jim H.

                  Comment


                  • #69
                    All I can add is that the memory isn't at all dim. I still have some degree of the edetic ("photographic") memory I had when young. I can review the images in my head.
                    Free software for calculating bolt circles and similar: Click Here

                    Comment


                    • #70
                      I just got off the phone with Evans bear dog, and he confirmed that he saw it also. For only knowing 50 words or so, we communicated surprisingly easy.

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                      • #71
                        Originally posted by mochinist
                        I just got off the phone with Evans bear dog, and he confirmed that he saw it also. For only knowing 50 words or so, we communicated surprisingly easy.
                        Give yourself some credit...you know a whole lot more than 50 words...I've read some of your posts and they had a whole lot more than 50 words in them, mind you some words were used more than once.
                        Home, down in the valley behind the Red Angus
                        Bad Decisions Make Good Stories​

                        Location: British Columbia

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                        • #72
                          Evan, is that a typo or another red-herring?
                          edetic/eidetic

                          I hope it is the former, or your argument is moot.
                          Just got my head together
                          now my body's falling apart

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                          • #73
                            Evan your contention that the instrument is compensated for itself and not for the difference between the instrument and the part makes no sense at all. The whole point of accurate measurement is to allow parts to fit regardless of who made them or where. For instance parts for the Boeing 787 are made all over the world, dispersed as far as Italy and Japan. If not all measured to the same standard temperature, how will they fit in Seattle? No one cares what the part size is at nonstandard temperature. Why would anyone want such an instrument? If one was curious about the size change then take your hot or cold part to inspection and check with an instrument that IS at standard temp. Of course then that instrument will be out of service until it returns to the standard temp.

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                            • #74
                              I just got off the phone with Evans bear dog, and he confirmed that he saw it also.
                              First of all, she is a she. And, she knows a lot more than 50 words. Furthermore, she isn't allowed to answer the phone.

                              Evan, is that a typo or another red-herring?
                              edetic/eidetic
                              No, it's an acid. I make a lot of typos and didn't notice it as I was on the way out to do some work. Note the note on the lower right of this post.

                              Evan your contention that the instrument is compensated for itself and not for the difference between the instrument and the part makes no sense at all.
                              You must be joking. That is the entire rational of temperature compensating a measuring instrument. The point is for it to perform in the same fashion regardless of temperature, usually limited to some range of temperature.

                              No one cares what the part size is at nonstandard temperature.
                              Oh really? I do. My double arm tracking drive wouldn't work if I hadn't taken changes with temperature into account. Also, one does not always have the luxury of being able to measure something at STP. In order to make an accurate measurement you MUST have an instrument that produces a reading that is either temperature compensated for changes in the instrument cause by changes in temperature or those changes must be well characterized so a compensation can be applied to the data if necessary.
                              Free software for calculating bolt circles and similar: Click Here

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                              • #75
                                If the need for temperature compensated measuring instruments were a MUST, they would be readily available. I have yet to turn up one in any form.

                                I do see a few CMMs that claim temperature compensation, but further reading reveals most are apparently temperature adjusting ala the Albion gage. They compare temperatures at various points, and use a computer program to bias the output. This is not true compensation as being discussed here.

                                Of all the catalogs I have, and instrumentation I have had or seen, I have never seen any common measuring instrument, or for that matter, lab or other high precision instrument that has temperature compensation. Many are marked with a temperature, 68*F on older, non ISO gages, to indicate the temperature at which they are calibrated. This information is all that is necessary for the user to make any adjustments needed.

                                And, no one needs to be concerned what the part size is at non standard temperature. The end use has nothing to do with the dimensioning for machining. Those dimensions are given at standard temperature.
                                Jim H.

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