FYI: For those who are interested: here is how profile tolerance works in V4.1

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • FYI: For those who are interested: here is how profile tolerance works in V4.1

    Just uncovered how exactly profile tolerances work in V4.1 (of course I never worked in a version lower than V4.0). Here are a few cases:

    Let's say you measure 3 point and you want to know what the profile of this "Set" is to a datum, here is how PC-DMIS calculates it:

    Case 1: all individual point-profiles are negative: PC-DMIS reports the lowest negative number (the MIN). This is correct.

    Case 2: all individual point-profiles are positive: PC-DMIS reports the highest positive number (the MAX). This is correct.

    Case 3: some individual point profiles are negative and some are positive. PC-DMIS will report THE RANGE!!!! It takes MAX and subtracts MIN. This gives the range. As you can imagine, the range can be almost twice the tolerance. So quickly PC-DMIS starts to report OUTTOL.


    It is my opinion that this is wrong, but who am I. This is the way it works and I can work around it. I am just glad that I finally understand. I will now start to report MIN and MAX instead of MEAS. From both MIN and MAX I can easily calculate the real profile tolerance.


    For those who wanted to know....

    Hope you enjoyed it, Jan.
    ***************************
    PC-DMIS/NC 2010MR3; 15 December 2010; running on 18 machine tools.
    Romer Infinite; PC-DMIS 2010 MR3; 15 December 2010.

  • #2
    Report the points as single points, not as sets, then you get correct data everytime.
    sigpic
    Originally posted by AndersI
    I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

    Comment


    • #3
      Originally posted by Matthew D. Hoedeman
      Report the points as single points, not as sets, then you get correct data everytime.
      Yes, another work around.


      Jan.
      ***************************
      PC-DMIS/NC 2010MR3; 15 December 2010; running on 18 machine tools.
      Romer Infinite; PC-DMIS 2010 MR3; 15 December 2010.

      Comment


      • #4
        ?Incorrect Profile?

        I'm not sure what you mean is it the profile of a line or surface or both? does PCDMIS not calculate the profile to ANSI/ISO standards?

        Help!!
        Job Function:
        Quality Engineer/Programmer
        Machine Type:
        Global
        Software Version:
        V2010 MR1
        CMM Experience:
        25+ yrs.

        Comment


        • #5
          Be careful here....I'm not quite sure how your tolerancing and measuring the profile on your part but remember one thing about profile....it's just a numerical measurement...not a relationship per say. I find people get confused with this. Say for example that you are locating a surface 1.000 basic from another (datum) with a profile callout of say, .005. Let's now say that you measure a set of 10 points to create your scan based on your alignment and get these results: 5 points at say .0012, .0012, .0014, .0012, .0010 and 5 points at -.0005, -.0005, -.0006, -.0008, .-0019. Now look at these points for as second. Your print could call out a 1.000 basic to establish the profile from another datum feature but due to your location and alignment on the part, you could have plus-minus points depending on which side the "line" your deviation happened to swing. How's PCDMIS gonna look at this based on a form & location callout? Simply put, it will display your bilateral tolerance of +/- .0025 from the 1.000 basic but as a numerical display of profile it will kick out a reading of .0033 based on the extreme of the positive .0014 to -.0019 points in the scan. It's just a numerical profile display and it's perfectly ok.....point to rememeber...profile itself is just a number... It's looks like it's wrong because you may be seeing that tolerance of +/- .0025 and wonder how can I have a profile of .0033 with that tolerance. Remember, it's also about location....and some of your points are perfectly ok floating around in your established .005 profile zone, but back and forth across the positve-negative zero line of your alignment. I'm hoping that's where you're getting the confusion but if not....we have lots of memory to write some more....B
          Physics dictates to man why his world acts the way it does....Chemistry tells him why it smells the way it does.

          Comment


          • #6
            That is the essence of a profile, the highest(if all high) or lowest(if all low), or the range if a variety of high and low is encountered. I don't know of another way it is to be reported can you explain your basis for thinking this is wrong?
            sigpic

            James Mannes

            Comment


            • #7
              Jan,
              Another thought. You aren't thinking of profile as the largest deviation and then doubling that reading are you? We use to have customers (many years back)that thought this was the correct way to report out profile. Just trying to get a handle on what your thoughts are.
              sigpic

              James Mannes

              Comment


              • #8
                I agree with James. PC-DMIS is reporting profile correctly and it's been doing it that way as long as I've used it (V. 2.0). However, I still come across quite a lot of customers and others who believe in the doubling of the worst deviation method. Some even insist that I report it out that way.

                Comment


                • #9
                  Of course this all depends on the direction of the print. It is based on unilateral or bilateral tollerancing.

                  A.Gore
                  sigpicA.Gore

                  Comment


                  • #10
                    Originally posted by ag162
                    Of course this all depends on the direction of the print. It is based on unilateral or bilateral tollerancing.

                    A.Gore
                    Yes, That would be true. But, then the tolerance would reflect that e.g. +.6/-0.0 or vise versa. And at that point PC-DMIS should work with that.
                    sigpic

                    James Mannes

                    Comment


                    • #11
                      Hi Jan,

                      As far as I know profile of a surface is all about relationship. A profile tolerance feature control indicates a tolerance zone having the same form as the surface, with a uniform width equal to the specified tolerance within which the entire surface must lie. It is used to control form, and orientation. Unless otherwise specified the tolerance zone is distributed equally on both sides of the surface. Where orientation is required Datums are usually needed to create a spatial relationship, but are not required. Isn't this what PCDMIS is reporting?

                      James I know exactly what your'e talking about (doubling the reading) Pratt & Whitney was notorious for this, they actually put it in their Specs defining that method as the correct way to interpret profile (at least for them I guess).

                      Anyway I hope PCDMIS is correct let me know what you think.


                      Mike
                      Job Function:
                      Quality Engineer/Programmer
                      Machine Type:
                      Global
                      Software Version:
                      V2010 MR1
                      CMM Experience:
                      25+ yrs.

                      Comment


                      • #12
                        On a bilateral profile tolerance you would double the worst deviation from basic surface.
                        For example if you had a profile tolerance of 1.00
                        Although understood to mean +/- .5 the tolerance says 1.00
                        How would you express the deviation of a point that was +.6 to be out of spec?
                        The reason for the doubling is to properly express the deviation in terms of the callout.

                        I wish they would change the callout to say +/- .5 if that is what they mean, but this is where we are today.
                        Links to my utilities for PCDMIS

                        Comment


                        • #13
                          If you are measuring points to report the profile of a a basic surface then you would report it as +.5mm/-.5mm. If this is a feature set or scan and you are reporting a profile, then it would be +.5mm/-.5mm(the same as your point dimensioning). Think about it, if you use +1.0mm as your tolerance, and you report your measured point as 1.2mm, you are really screwing yourself by saying "my part is not .1mm OOT but .2 OOT. Why would you want to do that?
                          I'm pretty sure that I have some citations at work. But I am a geek and am answering from home. I will re-visit this tomorrow. cmmguy, do you have a resource that states your case? I would be interested to read it.
                          sigpic

                          James Mannes

                          Comment


                          • #14
                            I agree with you, but why is the callout 1.0(in my example) and not +/-.5?

                            How would you report the callout per the print?
                            If there is a general consensus is that it is "viewed" as +/-.5 then why hasnt the standard been changed to reflect that. If, however, the tolerance is defined as a single value of 1.0, how do you report it to the print tolerance without doubling the value of the worst deviation to come up with a value that will exceed the tolerance?
                            Links to my utilities for PCDMIS

                            Comment


                            • #15
                              Originally posted by cmmguy

                              ...How would you report the callout per the print?...
                              Originally posted by JamesMannes
                              If you are measuring points to report the profile of a a basic surface then you would report it as +.5mm/-.5mm. If this is a feature set or scan and you are reporting a profile, then it would be +.5mm/-.5mm(the same as your point dimensioning). Think about it, if you use +1.0mm as your tolerance, and you report your measured point as 1.2mm, you are really screwing yourself by saying "my part is not .1mm OOT but .2 OOT. Why would you want to do that?

                              I'm pretty sure that I have some citations at work. But I am a geek and am answering from home. I will re-visit this tomorrow. cmmguy, do you have a resource that states your case? I would be interested to read it.
                              I already answered that?

                              Originally posted by cmmguy
                              I agree with you, but why is the callout 1.0(in my example) and not +/-.5?


                              ...If there is a general consensus is that it is "viewed" as +/-.5 then why hasnt the standard been changed to reflect that...
                              That part I don't have an answer for, but that is the intent of a bilateral 1.0mm profile tolerance.
                              Last edited by JamesMannes; 08-29-2006, 11:47 PM.
                              sigpic

                              James Mannes

                              Comment

                              Related Topics

                              Collapse

                              Working...
                              X