still cant tackle the rotation concept

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  • still cant tackle the rotation concept

    hello guys

    im still rocky , and the way i approach my learning is by understanding the idea, not just by getting instructed on how to do it , with that bieng said , i still cant get the concepte behind rotation in aligenement , dont get me wrong i know all about the 6 DOF etc

    its just i wish i can understand it the way i understanded that the origin is the "zero" of the translation of an axe , (setting a plane to z origin means the plane is 0 on z ) but the setting rotation what does it does ?
    ​​​​
    Last edited by Mranaskw; 01-16-2020, 03:41 PM.

  • #2
    Watch the trihedron as you are building your alignment. It will rotate about all 3 axes and translate along all 3 axes initially (6 DOF reamaining). After the leveling to Z (leveling to Z locks down rotation about X and rotation about Y), it will only rotate about Z and slide along all 3 axes. Once you set Z zero (this locks down Z translation), it will only move in X and Y and rotate about Z. Then rotate to X or Y about Z (this constrains rotation about Z) and it will only translate along X and Y. Set your origin for X and Y and it will be fully constrained. The trihedron gives you a nice visual of how each step of the alignment works and what it does to constrain the part.

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    • Mranaskw
      Mranaskw commented
      Editing a comment
      thank you so much mike , one last thing , how to figure out the direction which it will rotate about?

  • #3
    Suppose that you have a flat rectangular part and you are going to do a 321 manual alignment. By 321 alignment I mean level and set Z origin to a 3 point plane, rotate and set y origin to a 2 point line and finally set X origin. This full alignment will make the CMM XYZ origin and the part XYZ origin the same. The leveling part of the alignment is two rotations combined into one operation. The two rotations are about the X axis and the Y axis. The final Z rotation is what you need to do the final orientation of the part.

    It's similar to how a part would be inspected using a surface plate and height gage. Part would be leveled against a angle plate. You would then measure at least two features and rotatethe part as needed so that the part datum is parallel to the surface plate.

    Hard to express in words what is done every day. Hope this helps.

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    • Mranaskw
      Mranaskw commented
      Editing a comment
      you explanatio made it almsot there i'm missing one thing from you and will be at it , how to know the direction where to set the rotation (about z but toward which axe ?)

  • #4
    Take a piece of notebook paper. When you level and translate 1 origin (Z), it's like laying the paper on the surface plate. Now put your finger on the middle of the paper and spin the paper round and round while moving your hand that's holding the paper back and forth and left and right. Now, take a ruler and STOP the paper from spinning (rotation). The paper is leveled on the surface plate and rotated to the ruler and let's say the ruler is also the X translation so it's stopped from moving right or left. The only thing left to stop, is the Y which will keep the paper from moving back and forth.

    HTH
    153010 Global Advantage w/ LSPX1H_T Analog Probe
    7107 Global Classic TP20
    2019R1 SP1 CAD++

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    • Mranaskw
      Mranaskw commented
      Editing a comment
      thanks dear , i really appreciate your simplicty , i would be gratfull if u can use it one more time to explain to me how to figure out the direction which i should set the rotation abojt

    • RIDER
      RIDER commented
      Editing a comment
      If you put the ruler on the left side of the paper running in the Y direction of the machine, then it would be rotate the Y+ about the Z+ and X origin on the ruler.

  • #5
    here is a very basic video on a plane line point alignment https://youtu.be/miIyjKB1LK4

    You understand the 6 dof? You are locking them down from moving creating a coordinate system.

    The plane locks down 1 translation and 2 rotational dof. Z translation and XY rotation. (3)

    The line locks down 1 translation and 1 rotational dof, Y translation and Z rotaion. (2)

    The point locks down the last dof which is X translation. (1)

    Feature that locks down 2 dof of rotational freedom is you level feature (usually) which is the plane whos vector is Z plus 0,0,1.

    The feature that locks down the last dof of rotational freedom is your rotate feature which is the line whos vector is X plus 1,0,0. (IMPORTANT:It must be probed in the X Plus direction. Left to right. If you probe it right to left you'll see you alignment has flipped 180 degrees)

    That takes care of your part rotating in XYZ, now to work on translating in XYZ.

    The point constrains X translation only so X orgin.
    The line constrains Y translation so Y orgin,
    The plane constrains Z translation so Z origin.

    What I would do is practice this alignment as outlined and then purposely change it to see how it affects the trihedron. Once you mastered this, try probing top plane, front plane, and the left plane for a plane plane plane alginment. you'll get the same result. Then probe the right side plane and redo your alignment with top plane, front plane and RIGHT plane to see how it changed.

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    • #6
      it uses the vector direction of the surface not the actual surface, in case you are wondering why stuff is out 90° from what you expected

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