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Profile Surface Legacy vs. Geotol

Looking to pick some brains here. I have a pretty standard callout (see attached) for surface profile. I have gotten away with almost exclusively using legacy reporting up until now. I have decided to dip my toes into GeoTol for this project. Typically I would take a series of vector points along the surface and report out their XYZT deviations. I am getting wildly different results when comparing the individual XYZT deviations of legacy to what we get when setting the part up in GeoTol.

The part is a car door.

Legacy datum is an iterative alignment using 4 separate planes to level to (A).
A circle (B) and round slot (C) to rotate around.
And that same circle (B) to origin to.

Using that alignment our largest deviation for this section (C to D) of vector points is ~3.4mm

When using GeoTol the result is 7.4mm

For geotol I:

Created a primary datum plane and called it A
Defined that new plane as A
Defined B as the circle B
Defined C as the round slot C

I created a data set of the 42 points that make up section C to D and set up the FCF just like the callout on GD&T.

A =FEAT/PLANE,CARTESIAN,OUTLINE,NO
THEO/<3138.512,807.3,1054.12>,<0,-1,0.0000001>
ACTL/<3138.534,808.522,1054.166>,<-0.0001932,-0.9999999,0.0003738>
CONSTR/PLANE,PRIMARY_DATUM,A1,A2,A3,A4,,
MATH_TYPE/CONSTRAINED_L2,BFRE
DATDEF/A,FEATURES=A,,
DATDEF/B,FEATURES=B,,
DATDEF/C,FEATURES=C,,
GAP_C_D =FEAT/SET,CARTESIAN
THEO/<2597.195,931.591,1059.523>,<0,0,1>
ACTL/<2594.191,931.69,1059.54>,<0,0,1>
CONSTR/SET,BASIC,GAP_01,GAP_02,GAP_03,GAP_04,GAP_05,GAP_0 6,GAP_07,GAP_08,GAP_09,GAP_10,GAP_11,GAP_12,GAP_13 ,GAP_14,GAP_15,GAP_16,GAP_17,GAP_18,GAP_19,GAP_20, GAP_21,GAP_22,GAP_23,GAP_24,GAP_25,GAP_26,GAP_27,G AP_28,GAP_29,GAP_30,GAP_31,$
GAP_32,GAP_33,GAP_34,GAP_35,GAP_36,GAP_37,GAP_38,G AP_39,GAP_40,GAP_41,GAP_42,,
MOVE/POINT,NORMAL,<-1169.71,1657.333,1951.929>
GAP_CD =GEOMETRIC_TOLERANCE/STANDARD=ASME Y14.5,SHOWEXPANDED=YES,
DATUM_MATH=DEFAULT,DISPLAY_COORDS=DRF,
UNITS=MM,OUTPUT=NONE,ARROWDENSITY=100,ITERATEANDRE PIERCECAD=YES,
SEGMENT_1,PROFILE_SURFACE,1.4,__,A,B,MMB,<size>,__ ,C,MMB,<size>,__,
TEXT=ON,CADGRAPH=OFF,REPORTGRAPH=OFF,MULT=10,
MEASURED:
GAP_C_D:7.442,
SEGMENT_2,PROFILE_SURFACE,COMPOSITE,0.8,__,<dat>,< dat>,<dat>,TOL_ZONE_MATH=DEFAULT,
TEXT=ON,CADGRAPH=OFF,REPORTGRAPH=OFF,MULT=10,
MEASURED:
GAP_C_D:0.439,
ADD
DATUMS/REPORTDATUMSIZE=OFF,
B(B):NOM=19,+Tol=0.1,-Tol=0.1,
C(C):NOM=19,+Tol=0.1,-Tol=0.1,
FEATURES/GAP_C_D,,​​

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  • I never use PLANE features in an iterative alignment. If you are taking 3 or more hits per net surface, simply take them as vector points, not as planes. You could bee seeing an issue with how the planes are calculated between the 2 methods. The iterative will use the centroid of the plane. And when you report the deviation of the plane (or the iterative calculation there of) it is reporting the centroid. This doesn't tell you the condition of that net surface, be it the actual part of a net pad on a fixture. single points will tell you the condition and then ALL the points get used for the alignment, not the centroid of the plane.

    individual points will tell you the deviation of that point, PROFILE will 'double' that value (think POSITION of a hole). This will take that 3.4 and double it to 6.8. Now, that is not equal to the geotol, but then you are using a different A for the geotol.
  • Ah. That was it. Thank you for the tip on the planes.
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