Quick question: simple point to point measurement

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  • Quick question: simple point to point measurement

    Hi, I have been asked to just take some simple point to point measurments to get distance and thickness measurments.

    Am i right in saying the pcdmis software will only take into account the direction you ask it to measure, say in X. So if i measure two points in X it will ignore any discrepancies in allignment in Y and Z as the points will obviousley be hard to take exactley in the same place and direction. Or will it give me a true distance between two points, taking into account not only the distance between the two points in X but also Y and Z?

  • #2
    Originally posted by bigtallanddopey View Post
    Hi, I have been asked to just take some simple point to point measurments to get distance and thickness measurments.

    Am i right in saying the pcdmis software will only take into account the direction you ask it to measure, say in X.

    So if i measure two points in X it will ignore any discrepancies in allignment in Y and Z as the points will obviousley be hard to take exactley in the same place and direction.

    as long as you state X axis, 2D, when you dimension the distance ^

    Or will it give me a true distance between two points, taking into account not only the distance between the two points in X but also Y and Z?

    as long as you state 3D when you dimension the distance ^
    the key to making this work correctly is make sure you are in the correct workplane when you do this!

    HTH
    sigpic
    Originally posted by Ironhoe
    I got something under my sporran for you, take care of it and you got my vote.

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    • #3
      Originally posted by bigtallanddopey View Post
      Hi, I have been asked to just take some simple point to point measurments to get distance and thickness measurments.

      Am i right in saying the pcdmis software will only take into account the direction you ask it to measure, say in X. So if i measure two points in X it will ignore any discrepancies in allignment in Y and Z as the points will obviousley be hard to take exactley in the same place and direction. Or will it give me a true distance between two points, taking into account not only the distance between the two points in X but also Y and Z?
      Depends how you ask for it.

      You can ask for...

      3d - straight line between points
      2d - straight line in the current work plane (so ignoring and difference in z for example but straight line in xy)
      2d - parallel of perpendicular to a particular co-ord system axis or a feature - this is probably the one you want, tick parallel and then either x or y to get the distance in that direction.

      I'm not sure how you're getting on with alignments yet, but you'll need to be careful if not properly aligned, plus you may also be getting cosine error on your probe hits if your not properly aligned.


      The 2 Dimensional option calculates the two-dimensional distance between features. All features used to calculate the 2D distance are first projected into the current work plane before the distance is computed, except as noted below when you attempt to calculate the distance perpendicular to a third feature defined as a plane.

      PC-DMIS computes the maximum, minimum, and average distances between the two features. If the distance is between two lines or planes, the maximum, minimum and average are computed using the measurement point data. (Verify that the distance type is set to 2 Dimensional.)


      2D distances that are calculated using three features will be either parallel or perpendicular to a datum feature. The datum feature can be any previously measured or constructed feature.

      Important: If the third feature is a plane and the distance is being calculated perpendicular to the datum feature then the current work plane is ignored.

      To calculate the distance using three features:

      Select the two features that will be used to calculate the distance.

      Select the third (datum) feature. (Using a line for the third feature will provide the best results.)

      Verify that the correct orientation is marked.

      Select the To Feature check box.

      Click the Create button.

      PC-DMIS will calculate the distance between the first two features parallel or perpendicular to the third (datum) feature or axis.
      Automettech - Automated Metrology Technology

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      • #4
        Originally posted by bigtallanddopey View Post
        Hi, I have been asked to just take some simple point to point measurments to get distance and thickness measurments.

        Am i right in saying the pcdmis software will only take into account the direction you ask it to measure, say in X. So if i measure two points in X it will ignore any discrepancies in allignment in Y and Z as the points will obviousley be hard to take exactley in the same place and direction. Or will it give me a true distance between two points, taking into account not only the distance between the two points in X but also Y and Z?
        In addition of all it said above, you have to take care of the ball contact... If you measure along X a point on a surface which is along XY, the measured point is different than the contact point...
        A CMM is not a caliper, you shouldn't use it as a caliper...

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        • #5
          Originally posted by JEFMAN View Post
          In addition of all it said above, you have to take care of the ball contact... If you measure along X a point on a surface which is along XY, the measured point is different than the contact point...
          A CMM is not a caliper, you shouldn't use it as a caliper...
          so basically measure perpendicular to the surface?

          It all seems to be alligned properly, thankfully its a relatively square shape. Just need to "2d - parallel of perpendicular to a particular co-ord system axis or a feature" use this option and hopefully it will work.

          thanks for the help

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          • #6
            Originally posted by bigtallanddopey View Post
            so basically measure perpendicular to the surface?

            It all seems to be alligned properly, thankfully its a relatively square shape. Just need to "2d - parallel of perpendicular to a particular co-ord system axis or a feature" use this option and hopefully it will work.

            thanks for the help
            In effect yes - but it's not that straight forward, if you're taking manual hits with the joystick they're always squared up to your current co-ord system. So if you had a face at 45° and you took great pains to drive the probe perp to the face, it would be for nought as the software would actually 'square' the hit up to the nearest axis.


            Edit to add - this is for individual points, if you're measuring lines or circs you may still get cosine error, but the issue described above wouldn't occur. If you're using '3d' features (cylinder, sphere, planes etc) cosine error won't be a problem.

            The thing with cosine error is it's not linear - 45° out witha 4mm tip would give approx 0.6mm error.

            With a smaller tip this would be less, as you approach more normal to the surface this would be less. The problems with CMM's is you can get an answer which for all intents and purposes looks as if it's right, but is actually incorrect.
            Last edited by NinjaBadger; 02-17-2015, 07:23 AM.
            Automettech - Automated Metrology Technology

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            • #7
              Originally posted by bigtallanddopey View Post
              so basically measure perpendicular to the surface?

              It all seems to be alligned properly, thankfully its a relatively square shape. Just need to "2d - parallel of perpendicular to a particular co-ord system axis or a feature" use this option and hopefully it will work.

              thanks for the help
              Not trying to beat the proverbial dead horse but you are making an alignment to this part correct? No matter how square you think you have set the part on the CMM it will be off and you will have error because of it.
              sigpic

              James Mannes

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              • #8
                Originally posted by JamesMannes View Post
                Not trying to beat the proverbial dead horse but you are making an alignment to this part correct? No matter how square you think you have set the part on the CMM it will be off and you will have error because of it.
                It is alligned to the best of my knowledge and ability, I cannot share the part because its still in development. There are two sides which are at 90 degrees to each other, the only plane that could be missaligned is the Z plane, that is beacause to get a cross section the extrusion is cut by hand. I wouldnt have though this would affect any mesurements taken in X and Y too much? or am i completely wrong there?

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                • #9
                  Originally posted by bigtallanddopey View Post
                  It is alligned to the best of my knowledge and ability, I cannot share the part because its still in development. There are two sides which are at 90 degrees to each other, the only plane that could be missaligned is the Z plane, that is beacause to get a cross section the extrusion is cut by hand. I wouldnt have though this would affect any mesurements taken in X and Y too much? or am i completely wrong there?
                  Impossible to say - I think we're just trying to get at whether it was 'eyed up' as being square to the CMM, instead of programatically aligned to. (I don't know if programatically is even a proper word but I like it and I'm keeping it!!)
                  Automettech - Automated Metrology Technology

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                  • #10
                    Originally posted by NinjaBadger View Post
                    Impossible to say - I think we're just trying to get at whether it was 'eyed up' as being square to the CMM, instead of programatically aligned to. (I don't know if programatically is even a proper word but I like it and I'm keeping it!!)
                    It was 'eyed up' and then alligned, then i wrote a very simple programme that seemed to take up pages and pages that you guys could have written in about ten lines.

                    and apparantly programmatically is a word.

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                    • #11
                      Now I read it back of course it is - if only my spelling was half as good as my programming


                      If you think you've understood it and the method should work, but you've no other means to verify that with, you could set up and 'experiment' to measure a slip gauge for example, and prove your technique works that way first.
                      Automettech - Automated Metrology Technology

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                      • #12
                        Does the part lend itself to being layed out via manual measurement? That would verify anything on the CMM.
                        sigpic

                        James Mannes

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                        • #13
                          Originally posted by NinjaBadger View Post
                          Impossible to say - I think we're just trying to get at whether it was 'eyed up' as being square to the CMM, instead of programatically aligned to. (I don't know if programatically is even a proper word but I like it and I'm keeping it!!)
                          My wife hates it when I make up words! (She's an English teacher) I like it too.

                          One of my favorites is jack-assery.


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                          Negative, Ghostrider...the pattern is full...

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                          • #14
                            Originally posted by Rookie View Post
                            My wife hates it when I make up words! (She's an English teacher) I like it too.

                            One of my favorites is jack-assery.


                            Sent from my iPhone using Tapatalk
                            As long as you hyphenate it, you're good to go.
                            Systems Integrator
                            Hexagon Manufacturing Intelligence

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                            • #15
                              Hahahahhahaa


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