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Plane line point vs plane plane plane

Smallsvillanova
Hello everyone,

I am aligning and programming utilizing a J-corner fixture. In my experience i have been told that aligning to plane plane plane would be ideal for several reasons. My colleague believes that a plane line point is better. I do not have as much experience as he does but through all my training i have been told that whenever possible i should align to 3D features. Any insight, experience stories, or bits of wisdom are greatly appreciated.

Thank you!
  • Ok, I'll repeat it here - have a nice read :-)
    Assuming ZPLUS is 'up', XPLUS is 'right', YPLUS is 'forward', measuring on the ZPLUS, YMINUS and XMINUS surfaces (because that's how my example was written). If your reality is different, you have to change things (left as exercise to the reader).




    Primary is easy
    - measure a primary plane PLN_Z

    - construct a "Tangent plane", PLN_TZ, math type CONSTRAINED_L2, BFRE (CONSTRAINED_MINMAX if you are in ISO)

    - align level PLN_TZ, Z-origin PLN_TZ




    Secondary is a bit more work
    - measure a secondary plane PLN_Y

    - construct a "Tangent plane", PLN_TY, math type CONSTRAINED_L2, BFRE

    - align rotate YMINUS around ZPLUS to PLN_TY

    - locate the 'highest' measuring point on the YMINUS surface:

    - ASSIGN/TPY = PLN_TY.HIT[1..PLN_TY.NUMHITS].Y

    - ASSIGN/YZ = MININDEX(TPY)

    - align Y-origin to PLN_TY

    - in the Edit Window, change PLN_TY in the alignment command to PLN_TY.HIT[YZ..YZ]

    NOTE: This will not rest the secondary on two or more points, just the highest one, so not exactly according to the standards. See note (1) for a refinement.





    Tertiary is quite similar to secondary...
    As the alignment is now locked in all directions, all we have to do is locate the 'highest' point in the XMINUS direction:

    - measure a tertiary plane PLN_X

    - locate the 'highest' measuring point on the XMINUS surface:

    - ASSIGN/TPX = PLN_X.HIT[1..PLN_X.NUMHITS].X

    - ASSIGN/XZ = MININDEX(TPX)

    - align X-origin to PLN_X

    - in the Edit Window, change PLN_X in the alignment command to PLN_X.HIT[XZ..XZ]





    Full code 

    [LEFT][COLOR=#000000][FONT=Arial][SIZE=12px]PLN_TZ =FEAT/PLANE,CARTESIAN,OUTLINE,NO[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] THEO/<122.733,48.648,0>,<0,0,1>[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ACTL/<122.733,48.648,0>,<0,0,1>[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] CONSTR/PLANE,TANGENT,PLN_Z,,[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] MATH_TYPE/CONSTRAINED_MINMAX,BFRE[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px]A2 =ALIGNMENT/START,RECALL:A1,LIST=YES[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/LEVEL,ZPLUS,PLN_TZ[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/TRANS,ZAXIS,PLN_TZ[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/END[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px]PLN_TY =FEAT/PLANE,CARTESIAN,OUTLINE,NO[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] THEO/<35.126,0,-21.7>,<0,-1,0>[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ACTL/<35.126,0,-21.7>,<0,-1,0>[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] CONSTR/PLANE,TANGENT,PLN_Y,,[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] MATH_TYPE/CONSTRAINED_MINMAX,BFRE[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px]A3 =ALIGNMENT/START,RECALL:A2,LIST=YES[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/ROTATE,YMINUS,TO,PLN_TY,ABOUT,ZPLUS[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/END[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ASSIGN/TPY=PLN_TY.HIT[1..PLN_TY.NUMHITS].Y[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ASSIGN/YZ=MININDEX(TPY)[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px]A4 =ALIGNMENT/START,RECALL:A3,LIST=YES[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/TRANS,YAXIS,PLN_TY.HIT[YZ..YZ][/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/END[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ASSIGN/TPX=PLN_X.HIT[1..PLN_X.NUMHITS].Y[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ASSIGN/XZ=MININDEX(TPX)[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px]A5 =ALIGNMENT/START,RECALL:A4,LIST=YES[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/TRANS,XAXIS,PLN_X.HIT[XZ..XZ][/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/END[/SIZE][/FONT][/COLOR][/LEFT]


    ------------------------------------------------------------------------------------------

    Note (1) - a 'slightly better' rotation of the secondary

    Now it's getting hairier...

    First do the secondary tangent plane exactly as above. Then comes the 'trick' part - move the origin temporarily to the found highest point, calculate the angle from this to all the other points and find the angle with the smallest absolute value. The signed value is how much we can rotate the coordinate system, touch [at least] two points of the secondary surface and still have all points on the same side of the calculated 'plane' (we are still 'tangent'). 




    [LEFT][COLOR=#000000][FONT=Arial][SIZE=12px]PLN_TY =FEAT/PLANE,CARTESIAN,TRIANGLE,NO[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] THEO/<108.5,0,-14.8333>,<0,-1,0>[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ACTL/<108.8335,0.1469,-14.8317>,<0.0017223,-0.9999006,0.0139948>[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] CONSTR/PLANE,TANGENT,PLN_Y,,[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] MATH_TYPE/CONSTRAINED_L2,BFRE[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px]A2 =ALIGNMENT/START,RECALL:A1,LIST=YES[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/ROTATE,YMINUS,TO,PLN_TY,ABOUT,ZPLUS[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/END[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ASSIGN/VI2=MININDICES(PLN_TY.HIT[1..PLN_TY.NUMHITS].Y)[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ASSIGN/VI1=VI2[1][/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px]A3 =ALIGNMENT/START,RECALL:A2,LIST=YES[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/TRANS,YAXIS,PLN_TY.HIT[VI1..VI1][/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/END[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] WORKPLANE/ZPLUS[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ASSIGN/ANG=RAD2DEG(ATAN(PLN_TY.HIT[1..PLN_TY.NUMHITS].Y/(PLN_TY.HIT[1..PLN_TY.NUMHITS].X - PLN_TY.HIT[VI1].X)))[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ASSIGN/AANG=ABS(ANG)[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ASSIGN/IANG=MININDEX(AANG)[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ASSIGN/ANGT=ANG[IANG][/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px]A4 =ALIGNMENT/START,RECALL:A3,LIST=YES[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/TRANS,XAXIS,PLN_TY.HIT[VI1..VI1][/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/ROTATE_OFFSET,ANGT,ABOUT,ZPLUS[/SIZE][/FONT][/COLOR][/LEFT]

[LEFT][COLOR=#000000][FONT=Arial][SIZE=12px] ALIGNMENT/END[/SIZE][/FONT][/COLOR][/LEFT]
    This alignment should be compatible with the older ASME standard of 'candidate datum set', but is not the same as the CONSTRAINED_L2 of current ASME, or the CONSTRAINED_MINMAX of current ISO. Probably close, but not the same.



    " Assuming ZPLUS is 'up', XPLUS is 'right', YPLUS is 'forward',....."

    er, should YPLUS be to the rear, not forward?
  • in reply to AndersI
    Aaaarrrgghhh! I hate the formatting changing combination of this forum and Microsoft Edge browser...
  • in reply to Matthew D. Hoedeman
    Probably - I'm offline, don't sit in a machine, so forward for me is away into the screen...
  • I like the idea of trying to mimic what the ASME standard explains using tangent planes and extracting the furthest points using variables and constructions. How often is this actually used in practice though? I've seen a lot of programs written by suppliers and customers that state ASME standard on their print and none of which used this method. Not saying it's proper, just that I haven't seen it in practice, only in theory. In order to "accurately" find the highest points, are each plane scanned with high point densities to ensure the the points closest to the highest points are found?
    if someone can give me opinions on this, it would be appreciated. It seems to me, if a plane is only probed using 4 to 10 points (idk the size of these parts or planes) and a tangent plane is constructed, one of those points may not actually be lying on the highest point of the plane which would cause error. Also, if correlations are required with you and a customer and both use tangent planes, I would think that the alignment could change to some degree depending on where the points are placed and correlations could fails when tight tolerances are involved.
    Thanks for the insight.
  • , your questions are interesting, and a lot of people should ask them to theirself... But I'm not sure that THE answer exists...
    You're right, the number of hits is important, but nobody can measure the entire surface.
    Just think to the necessary number of hits to dimension flatness, and it should be the right number. (of course, if you just want to have a good value, 3 hits gives a perfect flatness, and the BF plane should be the same that the tg... Wink)
    Scanning is a nice solution, but needs using outlier filters, and tangent planes don't have this option. So, you can create a filtered BF plane and then create the tg plane from its hits.

    Now it's coffee time, and it's friday !
    Happy week-end, all !
  • I like the idea of trying to mimic what the ASME standard explains using tangent planes and extracting the furthest points using variables and constructions. How often is this actually used in practice though?

    Too seldom :-)

    Jokes aside, if your parts are perfect, you don't need this. The worse your parts are (rough surface, form errors, out of square datums, etc.) the more important it gets. I'd guess machined parts are almost always 'good enough', welded parts could be trickier (but mostly have larger tolerances)...
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