Alignment troubles!!!!!

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  • Alignment troubles!!!!!

    I am almost embarassed to ask this. I have a part that must be checked in the free state and stay in car position. THis is a simple part but the datum scheme is giving me fits. I have tried several alignments and cannot get the C datum to zero out. running 4.2mr1 any suggestions would be great. See attached for datum scheme
    Attached Files

  • #2
    What have you tried that is not working? Looking at the datum scheme I would think that the secondary and tertiary datums are reversed. In practice I would see the C datum being your anti-rotation and the B datum being your origin.
    Saving the world, one bad part at a time.

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    • #3
      Good call out Eric I think you are right.

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      • #4
        I have tried to level to the a datum rotate using c and b then origin on b. Have used itterative and best fit and have even tried rotating out of car but that can't happen. The problem is that my alignment is showing my c datum with a .06mm error after the alignment is complete and the part does not look nearly as good on the cmm as it does on the fixture. I would use the fixture but there is to much in the way to check it.

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        • #5
          Originally posted by bsacmm View Post
          I have tried to level to the a datum rotate using c and b then origin on b. Have used itterative and best fit and have even tried rotating out of car but that can't happen. The problem is that my alignment is showing my c datum with a .06mm error after the alignment is complete and the part does not look nearly as good on the cmm as it does on the fixture. I would use the fixture but there is to much in the way to check it.
          Are you measuring that "C" as a line of some kind? ONCE you "origin" on "B", is will be "X0Y0" and any error between the line that is "C" and the hole that is "B" will show up on the "C" since you've origined on "B".
          sigpic
          Originally posted by AndersI
          I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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          • #6
            C is not a line it is a simple antirotation pnt. When i try an itterative alignment i get b to show zero but c will show up to a .5mm error but thru other measurements and seeong it on the gage this isn't possible. I know this is got to be something simple but I have been looking at this to long and needed other eyes to see it.

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            • #7
              It is entirely possible that -C- checks out.

              I'll have to admit that using a small and short feature like -C- is stupid, but remember that it can only control rotation. What if the -C- wall is farther away from -B- than it's suppposed to be ?

              The thing that bugs me about this dorky datum scheme is how short -C- is for rotation.
              sigpic

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              • #8
                Originally posted by bsacmm View Post
                C is not a line it is a simple antirotation pnt.
                What on the print indicates that ?
                sigpic

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                • #9
                  Yes! I agree but the customer refuses to change it. And the tol. at the far end of the part has some of the trim tol. at +/-.30mm. I am almost tempted to add thickness to c datum just to get it to check the way it looks on the gage but I know that isn't the correct answer either.

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                  • #10
                    Originally posted by Robert Masters View Post
                    What on the print indicates that ?
                    I agree ..... seems to me that - c - should be a line
                    sigpic

                    It goes "dink" so it must be workin'

                    Bollocks

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                    • #11
                      I would have to say that nothing on the print says that. I am using the print and the gage (which only has a single pt for rotation) as a guide for setup>

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                      • #12
                        Originally posted by bsacmm View Post
                        Yes! I agree but the customer refuses to change it..
                        Then your customer needs to be drawn and quartered
                        sigpic

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                        • #13
                          Maybe I can try using two pts on the c datum as a line and see if that helps. I have not tried that yet.

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                          • #14
                            Originally posted by bsacmm View Post
                            C is not a line it is a simple antirotation pnt. When i try an itterative alignment i get b to show zero but c will show up to a .5mm error but thru other measurements and seeong it on the gage this isn't possible. I know this is got to be something simple but I have been looking at this to long and needed other eyes to see it.

                            Where are you measuring C then? As it is on an angle it will make a big difference. On something like this you would need to have a very small position and fixture tolerance for your iterative alignment because if you don't take the point at exactly the right distance from B you WILL induce error into your alignment.
                            Saving the world, one bad part at a time.

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                            • #15
                              Originally posted by bsacmm View Post
                              Maybe I can try using two pts on the c datum as a line and see if that helps. I have not tried that yet.
                              Truth to tell, it looks WAY TOO CLOSE to the B datum for you to get any kind of good readings from it. That point shown on the edge is almost at the point where a perp-line from the c-datum edge through the b-datum would be, that's gonna make it DAMN HARD to get it aligned.
                              sigpic
                              Originally posted by AndersI
                              I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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