Tangent Point - actually Cosine Error from incorrect IJK vector

I've a question about how the CMM calculates hits on tangent points. In the attachment I have a picture showing the issue.
I have 2 lines. Y is vectored with straight on hits. X is also vectored with straight on hits.
Since X- is not a 0/45/90 degree angle, but at a 20 degree angle form a straight on hit, will the ball calculate slightly off as it thinks it makes contact at 0 degrees, but actually hits earlier at 20 deg. thus creating the line 0.096mm sooner than it should have?

It obviously figures this out with circles/cones/cyliders, but it doesn't seem to do this with lines and points.
Should this be planned for and the measurement offset in calculation, or can it be corrected with some really specific (and tedious) vectoring so the probe knows where it should be hitting?

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Ken8282 over 7 years ago

How would I create Datum B and C in the attached picture? How do I get the points on the radii to establish Datum B? Datum C is even worse as it only shows 1 end of the line the other is off in space. I have a true position of a diameter to B and C.

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Ken8282 over 7 years ago

How would I create Datum B and C in the attached picture? How do I get the points on the radii to establish Datum B? Datum C is even worse as it only shows 1 end of the line the other is off in space. I have a true position of a diameter to B and C.

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RandomJerk over 7 years ago in reply to Ken8282

Create an offset line.

Measure the two radii, then construct on offset line between the two. When you create it, you'll make the offsets equal to the theoretical radius value, but then change the offsets in the code to the actual measured values:

CIR1       =FEAT/CONTACT/CIRCLE/DEFAULT,CARTESIAN,IN,LEAST_SQR
            THEO/<0,0,0>,<0,0,1>,0.7
            ACTL/<0,0,0>,<0,0,1>,0.689
            TARG/<0,0,0>,<0,0,1>
            START ANG=0,END ANG=360
            ANGLE VEC=<-1,0,0>
            DIRECTION=CCW
            SHOW FEATURE PARAMETERS=NO
            SHOW CONTACT PARAMETERS=YES
              NUMHITS=9,DEPTH=0,PITCH=0
              SAMPLE METHOD=SAMPLE_HITS
              SAMPLE HITS=0,SPACER=0.1181
              AVOIDANCE MOVE=NO,DISTANCE=1
              FIND HOLE=DISABLED,ONERROR=NO,READ POS=NO
            SHOW HITS=NO
CIR2       =FEAT/CONTACT/CIRCLE/DEFAULT,CARTESIAN,IN,LEAST_SQR
            THEO/<60,0,0>,<0,0,1>,0.7
            ACTL/<59.97,0.009,0>,<0,0,1>,0.689
            TARG/<60,0,0>,<0,0,1>
            START ANG=0,END ANG=360
            ANGLE VEC=<1,0,0>
            DIRECTION=CCW
            SHOW FEATURE PARAMETERS=NO
            SHOW CONTACT PARAMETERS=YES
              NUMHITS=9,DEPTH=0,PITCH=0
              SAMPLE METHOD=SAMPLE_HITS
              SAMPLE HITS=0,SPACER=0.1181
              AVOIDANCE MOVE=NO,DISTANCE=1
              FIND HOLE=DISABLED,ONERROR=NO,READ POS=NO
            SHOW HITS=NO
LIN1       =FEAT/LINE,CARTESIAN,UNBOUNDED,NO
            THEO/<0,0.3445,0>,<1,0,0>
            ACTL/<-0.0001,0.3445,0>,<1,0.0001501,0>
            CONSTR/LINE,OFFSET
            SURFACE NORMAL = <0,0,1>,MULTI POINT
            ID = CIR1,CIR2,,
            OFFSET = CIR1.R,CIR2.R