Using a Cylinder as the A datum in an alignment..How?

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  • Using a Cylinder as the A datum in an alignment..How?

    This is a problem I've stuggled with since the beginning. My head is stuck on plane, line, point, 3-2-1 and for the life of me I can't see how you can use a circular feature to create a plane.
    I just got handed the print I've attached to this post and if anyone has time to take a look I'd sure appreciate it. As you can see the A datum seems to be created by the two holes on the left side of the part, then creating a cylinder from them produces the A datum. one the two holes on the right side is the C datum, I get that I think....it's stopping rotation but where the heck is the origin or B datum on this print??? Where am I suppose to assume it's at??? inbetween the two circles that create the A datum??? How is a cylinder a plane???

    Arrrgggg.....help before my head implodes...

    Tc
    Attached Files
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    Heading for the Badlands...


    Mitutoyo Bright Apex 916 / Renishaw PH10M / TP20 Extended Force Probe / PC-DMIS 3.7MR2

  • #2
    A cly is a line, a line can be leveled

    A line can be rotated to

    A line can be the origin for two axis, a circle for the 3rd.
    I talk dirty to my cmm. Justn

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    • #3
      A cylinder has a vector.
      Ok.
      If you set a coffee cup on the CMM granite, the vector of the cylinder (coffee cup) is the same as the granite. You can level to that cylinder just the same as you can level to the granite.
      By the way, I did not see a datum -B- on that dwg either. It woyld make sense to have -B- as one flange or the other that -A- and -C- go through.
      Lately, it occurs to me
      What a long, strange trip it's been.

      2017 R1 (Offline programming)

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      • #4
        There is no B datum. It is not defined nor is it referenced.

        I'd level and origin to -A- and rotate -A-to-C- according to the print. I would agree that a -A- should be assigned to one of the faces and have -B- as the first hole, perp to -A-. Pi$$ Poor design.
        sigpic What's our Vector, Victor?

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        • #5
          Originally posted by John Riggins View Post
          A cylinder has a vector.
          Ok.
          If you set a coffee cup on the CMM granite, the vector of the cylinder (coffee cup) is the same as the granite. You can level to that cylinder just the same as you can level to the granite.
          So just to be 102% clear here.....in leveling the granite or coffee cup we're talking a + / - Z axis line correct? so when I level that line it's like the rim of the coffee cup is perfectly parallel to the surface of the granite???

          Tc
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          Heading for the Badlands...


          Mitutoyo Bright Apex 916 / Renishaw PH10M / TP20 Extended Force Probe / PC-DMIS 3.7MR2

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          • #6
            Originally posted by Otto Square View Post
            Pi$$ Poor design.
            Yeah, I seem to get alot of that around here...but at least it's keeping me working for now......

            Tc
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            Heading for the Badlands...


            Mitutoyo Bright Apex 916 / Renishaw PH10M / TP20 Extended Force Probe / PC-DMIS 3.7MR2

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            • #7
              Take -A- as 2 circles then construct the line. Rotate the line and level it, set as origin for cmm axis X and Y, z will be the table, but z is nothing. Then measure -C- get the dims for it then you rotate to -C- and get the rest of the part.
              I talk dirty to my cmm. Justn

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              • #8
                The axis of the coffee cup is perpendicular to the surface of the granite. The top of the rim of the coffee cup "might" be parallel to the surface of the granite.

                B&S CHAMELEON/PCDMIS CAD++ V2011

                There are no bugs, only "UNDOCUMENTED ENHANCEMENTS!"

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                • #9
                  Originally posted by TCeckels View Post
                  So just to be 102% clear here.....in leveling the granite or coffee cup we're talking a + / - Z axis line correct? so when I level that line it's like the rim of the coffee cup is perfectly parallel to the surface of the granite???

                  Tc
                  If the rim is perfectly perpendicular to the axis of the cylinder (the walls of the cup).

                  Let's go simple here. Grab a pen or pencil. Stand it on end in front of you. Now, that pencil can rotate three ways. It can rotate left to right (tip it left and right), it can rotate toward or away from you (tip it toward and away from you), and it can rotate about its axis (spin it). Now, if you level to that pencil, you can control two of those rotations. If you point your pencil to align with the Z axis (up and down), it can't tip left or right and it can't tip toward or away from you. It can still spin however.

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                  • #10
                    Originally posted by TCeckels View Post
                    So just to be 102% clear here.....in leveling the granite or coffee cup we're talking a + / - Z axis line correct? so when I level that line it's like the rim of the coffee cup is perfectly parallel to the surface of the granite???

                    Tc
                    I think a coffee can is a better visual. But, yes. The vector of the can would be perpendicular to the granite, so you could level to either one and the result would be the same. Like if you had a stud sticking up from the table that your -A- dropped onto, that would originate and level. Another stud for -C- would set the rotation.
                    sigpic What's our Vector, Victor?

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                    • #11
                      Your primary alignment defines the first of 3 planes. Now grab Goodluck's pencil again, and a sheet of paper. Mark a dot in the center of the paper. Now shove the pencil through the paper at this point. The pencil, being the axis of the measured cylinder, has now created your zplus plane, the paper. The other two planes, defined by the secondary and tertiary datums, will be perpendicular to this plane, and to each other.
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                      • #12
                        I dun know what the [email protected] you guys are on about......

                        No reason to make it seem complex, a cly is a line, to figure out how you level and rotate it as such use the graphics window, to see how you can lock down 2 of the points watch the tetra.
                        I talk dirty to my cmm. Justn

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                        • #13
                          Originally posted by justncredible View Post
                          I dun know what the [email protected] you guys are on about......

                          No reason to make it seem complex, a cly is a line, to figure out how you level and rotate it as such use the graphics window, to see how you can lock down 2 of the points watch the tetra.
                          I must really be a droolin' idiot. the visual makes sense to me and I think I understand it but I can't see to make it work with the alignment. The trihedron doesn't stay put to represent the way the part sits on the table.

                          Using the Bottom Left pic on the print....the way it sits on my table the BW surface is my Y-. X+ would go from A hole to the C hole and Z- would go up. So with the pencil visual I should be leveling to Y- correct?? That would keep the part from rotating from top to bottom or left to right correct? So I level to Y- and then depending on which hole I choose first my rotate about is either gonna be X ( + or -) around Y- correct???
                          So, what to do with B or an origin??? or do I not need one because the cylinder takes care of two axii and the rotate takes care of the 3rd???


                          I know I'm making this harder than it probably is....somebody slap me!!

                          Tc

                          Maybe I'll just join the militia and start shooting stuff....be a lot less stress than doing this somedays.......

                          BTW.....thanks for the visuals guys...it does help. I'm a camera guy so pics are the best way to get thru my fat head.
                          Last edited by TCeckels; 02-17-2009, 04:56 PM.
                          sigpic
                          Heading for the Badlands...


                          Mitutoyo Bright Apex 916 / Renishaw PH10M / TP20 Extended Force Probe / PC-DMIS 3.7MR2

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                          • #14
                            Originally posted by TCeckels View Post
                            I must really be a droolin' idiot. the visual makes sense to me and I think I understand it but I can't see to make it work with the alignment. The trihedron doesn't stay put to represent the way the part sits on the table.

                            the way it sits on my table the BW surface is my Y-. X+ would go from A hole to the C hole and Z- would go up. So with the pencil visual I should be leveling to Y- correct?? That would keep the part from rotating from top to bottom or left to right correct? So I level to Y- and then depending on which hole I choose first my rotate about is either gonna be X ( + or -) around Y- correct???
                            So, what to do with B or an origin??? or do I not need one because the cylinder takes care of two axii and the rotate takes care of the 3rd???


                            I know I'm making this harder than it probably is....somebody slap me!!

                            Tc

                            Maybe I'll just join the militia and start shooting stuff....be a lot less stress than doing this somedays.......
                            BTW......thanks for the help guys, the visuals do help. I'm a camera guy so I need pics<g>
                            sigpic
                            Heading for the Badlands...


                            Mitutoyo Bright Apex 916 / Renishaw PH10M / TP20 Extended Force Probe / PC-DMIS 3.7MR2

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                            • #15
                              Level ZPLUS to Datum A
                              Rotate XPLUS to Datum A and Datum C (choose them in that order)
                              Set XY origin to Datum A
                              Set Z origin to Datum B, (which should be the plane datums A and C are in).
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                              Global Advantage 12-22-10
                              TESASTAR M SP25 4.3mr2

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