ISO GD&T Question concerning two adjacent planes on a primary datum non-cylinder.

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  • ISO GD&T Question concerning two adjacent planes on a primary datum non-cylinder.

    I am looking at a drawing I clearly don't understand. I have a part that does mount on two surfaces although the surfaces are perpendicular to one another. Datum A on my drawing is parallel to the to the X-Axis. Datum D is a plane perpendicular to the X-Axis. I then have 3 cylindrical holes and one slotted hole in line on the Z Axis running through the Datum A plane. One cylindrical hole is Datum B and the slot below it is Datum C. When I come to the feature control frames for the holes / slots it goes like this. True Position | Ø.2 | A – D | B | C |
    Planes A-D would make an line axis in the z direction? With datum B hole tie down the x direction rotation? With Datum C being the “Z” direction zero? I know that’s not right because all the drawing dimensions are coming the Datum B.

    I cannot wrap my head around the reason the engineer did not believe it would flush up against datum A and then rotate to datum D and align to datum B.

  • #2
    Can you post the print? Or at least a copy where you've blacked out all non-essential stuff to your question...so we can see your callout without having you violate confidentiality requirements?

    Comment


    • #3
      As I understand, I think A-D is a line constructed from a perfect angle between A and D (the defects should be equally distributed between both datums) and it defines Z axis.
      This line should also be the vector of a plane.
      The holes and the slot axes must be parallel to this plane (or perp to the line).
      B hole should define theX direction projected on the plane (it's a secondary datum) and the Y and Z origin.
      C define the a 0° angle from Z axis (you could have a non zero angle and have to check the alignment of holes)

      Hope it's clear, it's just a way of creating the tolerance zone without draw...

      Comment


      • #4
        GD&T.jpgLeft Side.jpgMain.jpg Here is what it looks like.
        Attached Files
        Last edited by T Schmidt; 03-01-2018, 09:31 AM.

        Comment


        • #5
          Can you insert a larger picture ?
          Like this, I think your text is clearer tan the picture !!!!!

          Comment


          • T Schmidt
            T Schmidt commented
            Editing a comment
            I believe this should help

        • #6
          Capture.JPG

          (In Memory of my Loving wife, "Ronda" who I lost March 7, 2016. I love you baby.)
          They say "Nobody's Perfect." I must be Nobody.

          Comment


          • #7
            We can't see the picture T Schmidt

            Remove the small pic and re-upload it doing it like this please

            Capture.PNG

            Comment


            • T Schmidt
              T Schmidt commented
              Editing a comment
              Sorry for the delay, I had to host a ISO transition audit.

          • #8
            ezgif.com-resize1.gif

            Wonder if he/she is ever gonna put a bigger print?
            Last edited by KIRBSTER269; 02-14-2018, 11:57 AM.
            (In Memory of my Loving wife, "Ronda" who I lost March 7, 2016. I love you baby.)
            They say "Nobody's Perfect." I must be Nobody.

            Comment


            • T Schmidt
              T Schmidt commented
              Editing a comment
              Sorry for the delay, I had to prepare / Host the ISO 9001:2015 transition audit.

            • KIRBSTER269
              KIRBSTER269 commented
              Editing a comment
              no problem T Schmidt was having fun posting goofy pictures

          • #9
            Originally posted by T Schmidt View Post
            GD&T.jpgLeft Side.jpgMain.jpg Here is what it looks like.
            Lets bump this so others can see

            (In Memory of my Loving wife, "Ronda" who I lost March 7, 2016. I love you baby.)
            They say "Nobody's Perfect." I must be Nobody.

            Comment


            • KIRBSTER269
              KIRBSTER269 commented
              Editing a comment
              T Schmidt did you say this is an ISO callout? or ASME?

            • KIRBSTER269
              KIRBSTER269 commented
              Editing a comment
              T Schmidt Whether or not this is legit or not, it will be sometime before I can actually check. I do see that, its like the engineer didn't have confidence in leveling on A and D is helping the balancing act of A. B and C is pretty much cut and dry. Problem with this, in the world of imperfection. Say you lay it on a plate and butt it up securely against A, and slide it down against D, you would just touch the highest point, or vice versa. If you can lay it down equally. It would touch the 2 highest points on each plane equally, leaving you with 2 lines parallel to each other. Maybe VinniUSMC will chime in on this, he usually can make light of this.
              Last edited by KIRBSTER269; 03-01-2018, 11:58 AM.

            • T Schmidt
              T Schmidt commented
              Editing a comment
              The Drawing reference "DIMENSIONS AND TOLERANCES IN ACCORDANCE WITH ISO 128-1 AND REFERENCES THIS DRAWING"

          • #10
            KIRBSTER269 I will chime in.

            I don't know whether ISO allows this or not. I wouldn't accept this as valid in ASME-land. The construction of A-D would make a vector perpendicular to both A and D, and as you mentioned, only A or D can physically control the level. And then poor C. C would be completely useless in this DRF. B would clock the part about the A-D "axis" and constrain the last degree of rotation.

            I say either A or D needs to be picked, and given that B and C appear to be through A, my vote would be A. D doesn't make sense with B and C.

            All of this is in my experience with mostly ASME. There could very well be some ISO stuff that I am unaware of that makes this legit, but from my point of view, it's no bueno.
            "This is my word... and as such is beyond contestation."

            Comment


            • KIRBSTER269
              KIRBSTER269 commented
              Editing a comment
              I've been thumbing through the ISO book (notice I said thumbing). I didn't see anything that would back this call out. I myself tried to logically lay this out, forget the CMM, just lay it out. I couldn't come up with any good conclusions with this. except what I already mention, which was pretty much worthless.

          • #11
            What if he produces an intersect line of A datum and D datum and levels/origins to it?! That would be projecting error out quite a bit for D, but it might be what the engineer intended.

            Comment


            • T Schmidt
              T Schmidt commented
              Editing a comment
              I'm glad I'm not the only one scratching my head on this... Thanks for looking at this for me.

            • VinniUSMC
              VinniUSMC commented
              Editing a comment
              Use the @ symbol. @mckenzie

              It doesn't always work for me though, for some reason. KIRBSTER269 Any idea why tagging doesn't work sometimes?

            • KIRBSTER269
              KIRBSTER269 commented
              Editing a comment
              mckenzie T Schmidt VinniUSMC JEFMAN works for me. Only if I had a space or misspell it didn't work.
              Last edited by KIRBSTER269; 03-02-2018, 08:29 AM.

          • #12
            I know this is a Bad drawing but bear with me. A is the bottom, and D is the side. Like I stated before. If you butt a against the perfect 90. D would only touch the highest point? If A and D laid down equally, then it would touch 2 highest points on each plane, leaving you 2 lines and you have to level to the relation of the 2 lines? They're asking for A and D on 2 different axis to work together. When in fact its more like conflicting with each other.

            Capture1.JPG

            Maybe in ISO your Trihedron can be crooked
            Last edited by KIRBSTER269; 03-01-2018, 04:48 PM.
            (In Memory of my Loving wife, "Ronda" who I lost March 7, 2016. I love you baby.)
            They say "Nobody's Perfect." I must be Nobody.

            Comment


            • KIRBSTER269
              KIRBSTER269 commented
              Editing a comment
              By the way, all I have is the ISO 1101 book. You might have to invest in the 128-1 book.

          • #13
            Hi Kirbster !
            It's A-D, not A|D.
            In ISO, those are totally different.
            As I stated in #3, the defects must be equally distribted between both datums.

            Comment


            • JEFMAN
              JEFMAN commented
              Editing a comment
              Good night !
              I wouldn't dimension the part like this, but I think I understand this dimensionning.
              Levelling on an intersection is "special", but the real explanation on it should come of the part functionnality...

            • KIRBSTER269
              KIRBSTER269 commented
              Editing a comment
              Well Jeffery, I thought you were gonna "WOW" me with some off the wall equation. I'm so disappointed.

            • KIRBSTER269
              KIRBSTER269 commented
              Editing a comment
              Oh and by the way Jeffery I know it was A-D. My point was combining the 2 so it creates one didn't really make since to me, from 2 axis. I was just trying to justify it laying it out still didn't make since to me. That's all. Hey you have a wonderful weekend bud. My point was negative on purpose.
              Last edited by KIRBSTER269; 03-02-2018, 04:46 PM.

          • #14
            My 2 cents... Since A & D are co-datums I would treat them as 1 feature equally weighted, leaving 1 translational degree left, which I would use B for. C get's kicked to the curb because there's nothing left for it to do. Poor C. :-(

            Comment


            • JEFMAN
              JEFMAN commented
              Editing a comment
              Very interesting point of view !!!!!

            • VinniUSMC
              VinniUSMC commented
              Editing a comment
              This would be similar to treating it as a complex surface in ASME. While I can see how that would work physically, I don't see how you can force PC-DMIS to use it in that manner. You'd be forced to bastardize the DRF to create the alignment. Maybe just a 3D BF of the A-D points?

            • Max Tasty
              Max Tasty commented
              Editing a comment
              Based on the drawing I would pick up A & D as planes and intersect them. I'd use that 3d line as my spatial/level and 2 translation. I'd bisect the angle between A & D and rotate to that to equally distribute the error and translate to B. Then you could rotate back to A or D the bisected amount to get the linear dims to report correctly..

              Having said that, I'm pretty sure it's safe to assume that the engineer isn't quite sure how to convey what they want because they've used C and there's nothing left for C to do in the A-D/B/C callouts. I'd be curious to see what they actually want. Also, the planes don't look very big and you could get some major projection error when intersecting them.

              I agree that doing a 3D best fit would bastardize the FCF but hey, the damage has already been done by the engineer. ;-) It would probably be the most accurate way to measure this part based on those callouts.
              Last edited by Max Tasty; 03-02-2018, 10:00 AM.
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