Bolt circle and True position

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  • Bolt circle and True position

    Hello everyone,
    I am new to PC-DMIS and operating our CMM. I am using 3.5 on a browne and sharpe. We make rotors for vehicles and I am concerned about the way our old CMM programmer set it up to check true position of the bolt hole circle. A rotor is pretty easy to imagine so I hope someone can help. First he would create the bolt holes around a large center hole about 3 -3.5". Then he would construct a circle using bolt hole 1, bolt hole2, bolt hole3, bolt hole4, bolt hole 5, and so on if there was more. I think he is only getting the true position of the bolt hole circle and not of each bolt hole. I don't think this is completely accurate for telling if the bolt holes themselves are off. We are having problems because the CMM is saying it is good but it won't fit on the hard gauge.

    I messed around with it for a while and I created the bolt holes just like him but then, instead of making the "Bolt circle", I "constructed a Set of features" and made the true position out of the set. Now the report says its bad when it won't fit on the gauge, which is what I wanted, but I also don't think it is figuring a "Bonus" for me.

    I am sure this is simple for all yall...Hope you can make me look good in front of the boss. lol

    Thanks for the help,
    Tom

  • #2
    Are each of the holes in the bolt circle dimesnioned with True Position?
    In other words, are there basic angles showing how they are to be positioned?
    Lately, it occurs to me
    What a long, strange trip it's been.

    2017 R1 (Offline programming)

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    • #3
      I agree with where I think John Riggins is going. I would expect one hole to aligned to an axis or implied to be on centerline at the very least. This one hole may even be made a datum from which the location of the other holes in the pattern are dimensioned. In any case I would expect a true position callout for each hole and one for the entire bolt circle. HTH (Hope This Helps)

      P.S. It is easy to imagine your rotor, but unfortunately it is also easy to imagine a half dozen different legitimate ways a drawing of a rotor might have GD&T applied to these holes and the bolt pattern.
      sigpic"Hated by Many, Loved by Few" _ A.B. - Stone brewery

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      • #4
        If you could post a section of the print I'm sure your problem will be solved.
        sigpic 1.61803399Δ
        ASSIMILATE INTERGRATE SYNTHESIZE

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        • #5
          Originally posted by TommyD View Post
          Hello everyone,
          I am new to PC-DMIS and operating our CMM. I am using 3.5 on a browne and sharpe. We make rotors for vehicles and I am concerned about the way our old CMM programmer set it up to check true position of the bolt hole circle. A rotor is pretty easy to imagine so I hope someone can help. First he would create the bolt holes around a large center hole about 3 -3.5". Then he would construct a circle using bolt hole 1, bolt hole2, bolt hole3, bolt hole4, bolt hole 5, and so on if there was more. I think he is only getting the true position of the bolt hole circle and not of each bolt hole. I don't think this is completely accurate for telling if the bolt holes themselves are off. We are having problems because the CMM is saying it is good but it won't fit on the hard gauge.

          I messed around with it for a while and I created the bolt holes just like him but then, instead of making the "Bolt circle", I "constructed a Set of features" and made the true position out of the set. Now the report says its bad when it won't fit on the gauge, which is what I wanted, but I also don't think it is figuring a "Bonus" for me.

          I am sure this is simple for all yall...Hope you can make me look good in front of the boss. lol

          Thanks for the help,
          Tom
          Depends on print as everyone has already stated.

          I have never inspected a rotor for a car but I would imagine the bolt circle is controlled in a couple ways. One, they probably have an individual positional tolerance for each hole relating to the others. Also, I would imagine the Bolt Circle would have to be centered on the rotor within a certain amount. So, there may well be a composite tolerance for the pattern to fit to the rotor itself and a second tolerance of the pattern to itself.

          You will have to post a section of the print or a sketch of how the print controls the holes.
          Bill Jarrells
          A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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          • #6
            Use a "Best Fit, Rotation Only" alignment. Position all 5 individually.
            sigpic GDTPS - 0584

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            • #7
              Hi guys,
              I don't have an angle tolerance or true position for each hole. There is just a tolerance for True position of the "bolt hole circle". I would leave it just the way it is but it won't tell me if one of the bolt holes has moved around the circle. Inspector 212's idea might work. Can you tell me what to do for that alignment. I will post a print if someone can tell me how. Everey time I try, it wants a URL.

              Thanks everyone,

              Tom

              Comment


              • #8
                Originally posted by TommyD View Post
                Hi guys,
                I don't have an angle tolerance or true position for each hole. There is just a tolerance for True position of the "bolt hole circle". I would leave it just the way it is but it won't tell me if one of the bolt holes has moved around the circle. Inspector 212's idea might work. Can you tell me what to do for that alignment. I will post a print if someone can tell me how. Everey time I try, it wants a URL.

                Thanks everyone,

                Tom
                If there is a True Position for the Bolt Circle then you must align to the Datums called out in the Bolt Circle FCF
                Bill Jarrells
                A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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                • #9
                  Attach a pic (Paper Clip Icon) rather than try to insert image (picture icon).
                  Bill Jarrells
                  A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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                  • #10
                    Here's a pic tell me what you think. I think it will post.

                    Thanks
                    Tom
                    Attached Files

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                    • #11
                      Originally posted by TommyD View Post
                      Here's a pic tell me what you think. I think it will post.

                      Thanks
                      Tom
                      All holes are to be true position 0.015(m) to Datum A.
                      You need to locate the Callout for Datum A on the Print.
                      Use a Basic Angle of 72°. Typically, you can align to one hole with this type of callout but you are actually allowed to best fit the pattern since the FCF invokes ONLY Datum A.

                      Now, if DATUM A is the Flat Face (surface) then the callout is pretty bogus. I think you will find Datum A is either the Outer Surface or the Inner Surface (Diameter Features).
                      Bill Jarrells
                      A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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                      • #12
                        It's perfectly clear. 5 hole bolt pattern. The GD&T is good. TP each hole individually with a tol of .015. Hard to read but it looks like MMC there too. Use two holes to align your axis though. That'll get you better pos.
                        Kami

                        sigpic

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                        • #13
                          In this case, I would assume that A is a bearing race or something of that nature. It can not be the brake surface or the callout is bogus, as Wingman stated. Align to your primary, this should already be done. Make sure your workplane is parallel to the axis of the pattern. Then, in the alignment window, click best fit, pick your features, click rotate only, OK, OK. Position the holes. HTH
                          sigpic GDTPS - 0584

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                          • #14
                            Originally posted by KamikazeKonrad View Post
                            It's perfectly clear. 5 hole bolt pattern. The GD&T is good. TP each hole individually with a tol of .015. Hard to read but it looks like MMC there too. Use two holes to align your axis though. That'll get you better pos.
                            What is Datum A?
                            sigpic GDTPS - 0584

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                            • #15
                              If datum-a- is a surface then all you need to report is perpendicularity for each hole cause thats all its asking for.
                              sigpic.....Its called golf because all the other 4 letter words were taken

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