Form Only - No Fit Vs. Form and Location

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  • Form Only - No Fit Vs. Form and Location

    Legacy Dimensions:
    What is the difference between a Form Only - No Fit profile dimension and a Form and Location profile dimension? Since the former has "No Fit" it should just report deviation relative to the current alignment, correct? Wouldn't this be exactly the same as Form and Location?
    2013MR1 SP6
    Global Frames, Tesastar-M Heads, LSP-X1M/H Probes

  • #2
    FORM ONLY reports deviation relative to three degrees of rotation only.
    FORM AND LOCATION reports deviation relative to three degrees of rotation and three degrees of location.

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    • #3
      FORM ONLY reports deviation relative to three degrees of rotation only.
      FORM AND LOCATION reports deviation relative to three degrees of rotation and three degrees of location.
      ???

      Aren't they just looking at the "T" deviation of each point in the profile, identifying the max and min "T" values, and then reporting the measured value using the appropriate calculation for ASME or ISO based on the Min and Max values? I'm not talking about the difference between profile of surface vs. profile of line here. I'm talking profile of surface form and location vs. profile of surface form only with the "NO FIT" option selected.
      2013MR1 SP6
      Global Frames, Tesastar-M Heads, LSP-X1M/H Probes

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      • #4
        I was speaking of both line and surface. ‘No Fit’ is new to me, I’m stuck with v2009mr1; maybe I shouldn’t chime in.
        “T” value is Form and Location, it does not apply to Form Only.
        How many profile of a surface option in v2012? ‘Form Only’, ‘Form Only no Fit’ and ‘Form and location’? or just ‘Form Only no Fit’ and ‘Form and location’?
        I would like to see Hexagon include Profile of multiple surfaces to profile window, no alignment involve…

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        • #5
          Originally posted by DaSalo View Post
          Legacy Dimensions:
          What is the difference between a Form Only - No Fit profile dimension and a Form and Location profile dimension? Since the former has "No Fit" it should just report deviation relative to the current alignment, correct? Wouldn't this be exactly the same as Form and Location?
          I never really thought about the "NO FIT" option. What you say makes perfect sense. I just added a formonly no fit profile tolerance and the results were identical to the formandlocation. So it would appear that you are correct. I turned on the graphical display and it looks like it takes the +tol and distributes it equally about nominal. So, I guess the only difference is that it allows you to enter a profile of .020 as .020 instead of ±.010 (?)

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          • #6
            So, I guess the only difference is that it allows you to enter a profile of .020 as .020 instead of ±.010 (?)
            And if you are using ISO calculations you can already do that in a form and location profile (it will automatically split the tolerance zone to make it equal bilateral with ISO calculations). We'll see if anyone else replies but I really think there is no difference at all.
            2013MR1 SP6
            Global Frames, Tesastar-M Heads, LSP-X1M/H Probes

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            • #7
              I am running into the same problem. I have a print with a cone shape. It asks for a surface profile of 3 mm with A and B datum in the GDT. I use the form and Location to dimension that part +/-1.5mm range. The same GD&T box also has a 1mm tolerance attached below, but it does not have the A and B datum attached. So I read that as just "Form", But when I use "Form Only" and just put a +1mm, it says my part is way out of tolerance. I know it isn't because I put it on an optical comparator and it is virtually spot on. Anyone know how I should dimension this.

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              • #8
                You are correct that the lower frame is form only if there are no datums associated. When you select form only you have an option for the type of best fit to use. Many companies will have standards that dictate the type of fit that should be used. If you aren't sure then the most likely candidate is least squares. What you definitely don't want to do is to choose "No Fit". This will cause it to be treated just like a form and location dimension.

                If your results aren't what you expect try turning on the textual analysis in the dimension. This will list every point along with its deviation in the report. You can use this to see which points are driving the value that is being reported. Also try creating an analysis view for the dimension so you can see what is happening graphically.

                If you still cant make sense of it try posting your code here so we can take a look at the alignments that you are using and how you have the dimension set up.
                2013MR1 SP6
                Global Frames, Tesastar-M Heads, LSP-X1M/H Probes

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                • #9
                  Picture 001.jpgPicture.jpgThank you for the info, I have tried using Form Only with Least Squares. My results end up being over a mm out of tolerance. I know this can't be correct because of the way it looks on our optical comparator. The Form and Location is in tolerance. How can the Form only be out of Tolerance?
                  I am leveling in Y minus with datum A as well as Stopping Translation in (origin) X and Z using Datum A. I have measured Datum B as a Radial Plane and used that to stop translation in Y. I have done this on many other similar parts and have had luck with the Form Only Least Squares, now I am just getting way out of tolerance readings and I can't see how.
                  Last edited by TUBECHECKER; 03-06-2014, 08:42 AM.

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                  • #10
                    So have you done what I suggested and dug into your results using the textual and graphical analysis to see exactly what is happening?
                    2013MR1 SP6
                    Global Frames, Tesastar-M Heads, LSP-X1M/H Probes

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                    • #11
                      I was tought (I could be wrong), that if you have datums like in this case you have to use Form + location.

                      If I am not mistaken, FORM only would have been OK if your callout would have been Profile 3 (no datum's).

                      Its been a long time since I did any kind of profile so, I could be wrong.
                      B&S One
                      PC-DMIS CAD v2014

                      Romer Infinity

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                      • #12
                        Yes DaSalo, I have thank you for your suggestion. I have my problem solved. I am new to the forum and look forward to helping as well as learning from everyone.

                        Wolfman, The top GDT that indicate Surface Profile 3mm to Datum A and B are asking for Form and Location. The bottom one that is calling out the 1 mm is just asking for the Form Only.
                        Last edited by TUBECHECKER; 03-07-2014, 07:42 AM.

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