Using the Dimensioning Symmetry feature

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  • Using the Dimensioning Symmetry feature

    ok folks,

    I'm dealing with another print that as near as I can tell was written sometime during the days of the Roman empire and on this sheet there are 2 symmetry call-outs, #56 and #74. Having never had a need to use this feature before I read thru all the documentation I could find and then tried to apply that newly aquired knowledge to these print call-outs but so far I've gotten nothing but what I would call "wacky" numbers. It's possible I simply don't know how to read the results so I could use some help if y'all have the time.

    Print is attached and what I've done so far is create a line on either side of the datum feature as required and then the 3rd feature needs to be either a line or a plane. Well I can figure out, I think, how to create a line from the slot (#74) but I'm not so sure how to do that using just the B datum hole related to #56. irregardless on either feature my results are numbers like 35.83476, which makes no sense to me if I have a 0.1 tolerance.....

    Couldn't I simply measure the distance from one line on one side to the center of the datum feature and do the same on the other side and compare the two??? As long as the difference between the two is less than 0.1 things should be wonderful right? wrong? arrrrrggggggg help before my head explodes.

    Tc
    Last edited by TCeckels; 03-26-2009, 10:39 AM.
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    Mitutoyo Bright Apex 916 / Renishaw PH10M / TP20 Extended Force Probe / PC-DMIS 3.7MR2

  • #2
    I think I've posted on this subject before. The thing about PCDMIS and symmetry is the order of points and how they are taken.....I believe the help file shows an inside feature and how to take the hits on that.

    Because of the way the symmetry is defined, PC-DMIS limits the features that can be used for the symmetry dimension. Since the points must be equally arranged about the datum in order to find midpoints between them, you must either select a feature set with alternating points or two opposing lines with the same number of points


    Good luck
    ________________________
    DEA SCIROCCO-15-10-09
    TUTOR P -4.2 MR1-XP

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    • #3
      Just for the record Canada1 I did a search before I wrote my post and turned up very little info. The biggest discussion was on Concentricity.

      I'm already past where your post ends...I have my lines and datum feature. I am looking for suggestions on how to connect the dots so to speak.

      Thanks for the feedback

      Tc
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      Heading for the Badlands...


      Mitutoyo Bright Apex 916 / Renishaw PH10M / TP20 Extended Force Probe / PC-DMIS 3.7MR2

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      • #4
        The funny thing is concentricity and symmetry tolerance controls are similar concepts, yet PCDMIS define symmetry correctly but still does not calc. correctly, and concentricity is just wrong.
        I would create a series of vector points on one side then copy paste mirror flip X, and construct mid point of 2 opposing points. Report constructed midpoints using feature location instead of symmetry and for tol. I would split the .1 to .000 ±.05.
        May be someone on here has a better idea.

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        • #5
          Originally posted by lambo View Post
          The funny thing is concentricity and symmetry tolerance controls are similar concepts, yet PCDMIS define symmetry correctly but still does not calc. correctly, and concentricity is just wrong.
          I would create a series of vector points on one side then copy paste mirror flip X, and construct mid point of 2 opposing points. Report constructed midpoints using feature location instead of symmetry and for tol. I would split the .1 to .000 ±.05.
          May be someone on here has a better idea.
          This is better advice. I should have actually looked at your drawing.

          Constructed feartures dimensioned correctly do the same thing the Symmetry dimension feature does. I've had real trouble a few times over a few versions getting this feature to work correctly...Sadly that's not the only thing I have trouble with just like mirror and paste with pattern.....so clean and sweet on vectoral approaches and spacing and such it's good to learn this approach.

          It's critical all points are calculated correctly and the loc callout does just fine......so to answer your question completely.... yes as long as you have constructed your features correctly.

          Cheers
          Last edited by canada1_eh; 11-05-2008, 10:21 PM.
          ________________________
          DEA SCIROCCO-15-10-09
          TUTOR P -4.2 MR1-XP

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          • #6
            http://i307.photobucket.com/albums/n...giesen/sym.jpg
            TC, Here is Canada1 eh's post from 10/8/2008. I thought it was (and still is) good advice, so I logged in my secret place.
            Steven69
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            • #7
              Snippet from a PC-DMIS News folder, a write-up by Mr Ruggieri - a forum resident:

              * Measure required Line feature or features
              * Select Symmetry from the dimension section
              * Select Datum definition option and define required datums
              * Select feature
              * Select datum if not in main datum set
              * Insert required tolerance
              * Select datum
              * Change label (optional)
              * Create

              In the example, the tolerance is applied to the median plane created by the two inside surfaces of the slot to datum 'A' created from the median plane of the two outside surfaces.
              I think though there is a typo in the example as it in the explanation says datum A, but the 'walk-through' says datum B.
              PC-DMIS CAD++ 2o19 R1 SP10

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              • #8
                [QUOTE=vpt.se;198379]Snippet from a PC-DMIS News folder, a write-up by Mr Ruggieri - a forum resident:



                Yes, if your software uses this technique and the numbers come up right.. If not and you manual checks tell you different try and use the above technique.

                Not exactly sure if it's the software or my probing causing problems with this specific callout issue...... but that's life on a friday...

                cheers
                ________________________
                DEA SCIROCCO-15-10-09
                TUTOR P -4.2 MR1-XP

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                • #9
                  Originally posted by canada1_eh View Post
                  This is better advice. I should have actually looked at your drawing.

                  Cheers
                  Ya think?

                  <sigh>
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                  Mitutoyo Bright Apex 916 / Renishaw PH10M / TP20 Extended Force Probe / PC-DMIS 3.7MR2

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                  • #10
                    Originally posted by Steven69 View Post
                    http://i307.photobucket.com/albums/n...giesen/sym.jpg
                    TC, Here is Canada1 eh's post from 10/8/2008. I thought it was (and still is) good advice, so I logged in my secret place.
                    no need to keep it in a secret place that I can see....it's simply a cut and paste from the help file. I needed info past what that supplied but was unable to make my point.

                    Tc
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                    Heading for the Badlands...


                    Mitutoyo Bright Apex 916 / Renishaw PH10M / TP20 Extended Force Probe / PC-DMIS 3.7MR2

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