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I need help with measuring distance at an angle.

Malgorzata

Hello everyone,
I need advice...
The operator says that the parts are good, the angle is perfect (20 degrees), I get a different result on the CMM after measuring.
Am I making some mistake? I only have one year of experience...
I don't like CON1 (position on the x-axis). CON1 is made up of 8 points to see only the average of the angle and i location (print doesn't call out)).
I would like to add codes but i don't know how to do it...





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This is how i created:

WORKPLANE/ZPLUS
MOVE/POINT,NORMAL,<17.88762,5.57913,-0.19795>
TIP/T1A90B90, SHANKIJK=0.99979, -0.02011, -0.00449, ANGLE=-90.78014
PNT14 =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
THEO/<5.64,0,-0.225>,<0.3420223,0,-0.9396918>
ACTL/<5.63419,0.00011,-0.20894>,<0.3420223,0,-0.9396918>
TARG/<5.64,0,-0.225>,<0.3420223,0,-0.9396918>
SNAP=NO
SHOW FEATURE PARAMETERS=NO
SHOW CONTACT PARAMETERS=YES
AVOIDANCE MOVE=NO
SHOW HITS=YES
HIT/BASIC,<5.64,0,-0.225>,<0.3420223,0,-0.9396918>,<5.64,0,-0.225>
ENDMEAS/
PNT15 =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
THEO/<5.8,0,-0.18>,<0.3420223,0,-0.9396918>
ACTL/<5.78983,0.00012,-0.15185>,<0.3420223,0,-0.9396918>
TARG/<5.8,0,-0.18>,<0.3420223,0,-0.9396918>
SNAP=NO
SHOW FEATURE PARAMETERS=NO
SHOW CONTACT PARAMETERS=YES
AVOIDANCE MOVE=NO
SHOW HITS=YES
HIT/BASIC,<5.8,0,-0.18>,<0.3420223,0,-0.9396918>,<5.8,0,-0.18>
ENDMEAS/
LIN4 =FEAT/LINE,CARTESIAN,UNBOUNDED,NO
THEO/<5.80559,0,-0.1782>,<-0.9626509,0,-0.2707456>
ACTL/<5.78964,0.00012,-0.15191>,<-0.9388199,-0.000083,-0.3444084>
CONSTR/LINE,BFRE,3D,PNT15,PNT14,,
OUTLIER_REMOVAL/OFF,3
FILTER/OFF,WAVELENGTH=0
WORKPLANE/YMINUS
DIM ANGL3= 2D ANGLE TO LINE LIN4 FROM XAXIS ,$
GRAPH=OFF TEXT=OFF MULT=1.00 OUTPUT=BOTH
AX NOMINAL +TOL -TOL MEAS DEV OUTTOL
A 20.00000 0.00000 0.00000 20.14569 0.14569 0.14569 -------->​

A5 =ALIGNMENT/START,RECALL:STARTUP,LIST=YES
ALIGNMENT/LEVEL,ZPLUS,PLN2_Z
ALIGNMENT/ROTATE_CIRCLE,YMINUS,TO,CYL1_AA,AND,PNT2,ABOUT,ZPL US
ALIGNMENT/TRANS,ZAXIS,PLN2_Z
ALIGNMENT/TRANS,XAXIS,CYL1_AA
ALIGNMENT/TRANS,YAXIS,CYL1_AA
ALIGNMENT/ROTATE_OFFSET,-20,ABOUT,YPLUS
ALIGNMENT/END
WORKPLANE/XPLUS
PLN4 =FEAT/PLANE,CARTESIAN,OUTLINE,NO
THEO/<0,0,0>,<1,0,0>
ACTL/<0,0,0>,<1,0,0>
CONSTR/PLANE,ALIGN,WORKPLANE
PNT11 =FEAT/POINT,CARTESIAN,NO
THEO/<0,0,-1.74828>,<-0.9971964,0,0.0748284>
ACTL/<0,-0.00032,-2.13663>,<-0.9999968,-0.000083,-0.0025427>
CONSTR/POINT,PIERCE,PLN4,LIN4
DIM LOC4_LIN4= LOCATION OF POINT PNT11 UNITS=IN ,$
GRAPH=OFF TEXT=OFF MULT=1.00 OUTPUT=BOTH HALF ANGLE=NO
AX NOMINAL +TOL -TOL MEAS DEV OUTTOL
X 0.00000 0.01969 0.01969 0.00000 0.00000 0.00000 ----#----
Y 0.00000 0.01969 0.01969 -0.00032 -0.00032 0.00000 ----#----
Z -2.12000 0.00200 0.00200 -2.13663 -0.01663 0.01463 <--------
END OF DIMENSION LOC4_LIN4​
Attached Files
  • Rotate about the correct axis by the 20° basic then tolerance your distance. Make sure that you are in the correct workplane when doing this if you want reference distance. The print calls for profile and that is all you need to do is report profile, the software will do what is needed
  • in reply to dwade
    I thank you for the quick reply. I do it like that.
    The only thing I don't like is that the operator said that he has the perfect angle, because he checked it on the machine.
    The only thing that, my angle is not perfect 20 degrees, and I rotate the ALIGN to a perfect angle of 20 degrees. It can throw me away on 2.12 in. How can I create an alignment given the measured angle before? Is there any code that I can put in the alignment to rotate according to the measured angle?
    Example:
    Measured angle is 20.09 degree. i would like to rotate in this angle. The angle on each piece may be slightly different.
  • Basics are absolute, you would not rotate based on the 20.09º the part may actually be, the rotation in your alignment for evaluation would still be 20º. You could use the alignment to shift the 2.120 basic (after the 20º rotation) in the proper axial direction and then measure the surface and report its deviation from 0 leaving you with a +.005/-.005 tolerance boundary for the profile to J. As dwade said, your workplane is important if you chose to evaluate against the 2.120 basic.
  • in reply to dwade
    you can NOT check something on the machine you made it on to prove that it is right. If the machine is wrong then the check is wrong.
    AND, nothing is perfect. The CMM is the most accurate machine in your shop and it is NOT perfect.
  • in reply to dwade
    Matthew D. Hoedeman, I told him the same thing, i.e. the person who set the parts on the machine.
    I have 20 years of experience with various machines, only with CMM I have 1 year of experience. I like to make sure that whatever I do, I do it right.
    Did you see my question about the code in the alignment?
  • Here's my take. Your part is cylindrical in shape, yes? Then your profile of that surface in detail D is essentially measuring a CONE, as defined by the angle and basic offset (angle A and side b known).
    If it were me:
    I would datum to the center of the part, rotate so you have a securely controlled 6DOF alignment to the part in some way.

    Start copy/paste with pattern segment:
    Then align/rotate +20° about X axis (presuming Z is your cylindrical part axis). Make sure it tilts the correct way!
    Within that same alignment window offset Z the -2.120". Again confirm polarity here, you want tetrahedron to look parallel to the conical section in detail D, not 2" the other way lol.
    -Then measure a tiny line-section of that cone with as many hits as you can (or if you want to K.I.S.S. run an array of individual probe points along the line).
    --All hits should have normal Z vector and z coordinate nominal of zero.--
    Recall alignment back to original datums.
    End copy/paste with pattern segment:

    -Copy paste the above segment of code with pattern 3x (to make 4x 90° section cuts of the cone sampled), 5x (to make 6x 60° cuts) 11x (a dozen 30° cuts)... whatever you feel is necessary to affirm the profile is within spec.
    You will likely need to manually create define and adjust probe angles for some of the pasted pattern to access the surfaces (hence why i didn't suggest to loop it)... but you will end up with a series of section cuts of the cone.
    -Construct a measured cone from the lines. You might need to "explode" the lines into individual hit values before the measured cone is a successful representation of the part.
    ​-Dimension the measured cone.

    The measured value of the angle isn't necessary to quantify, nor is the measured value of the basic offset. you just need to quantify the MAX+MIN profile variation from the theoretical exact location.
  • Scan a line on the cone surface, make sure it is scanning parallel to the cone centerline.
    Make sure you are in the correct workplane.
    Distance, 2D, point (intersection diameter 10.8 and plane) perpendicular to the (scanned) line will get your [2.120].
    Angle, 2D between line and the end plane should give you the [20°].
  • I would create a first alignment level and origin Z on the plane, origin XY at the intersection of the cylinder and the plane.
    Then, I would create a point at Z=2.119*cos(deg2rad(20), x=0,y=0 and origin on it.
    Then I would measure some vector points at some different radii (for example R1=11.3, so X=11.3,Y=0,Z=11.3*tan(deg2rad(20), i=sin(deg2rad(20)),j=0,k=-cos(deg2rad(20))
    Copy paste with pattern around Z.
    Create a feature set, and dimension t_value for each point.
    Max-min=profile
  • Thank you for all your ideas, according to some ideas I created the program at the beginning.
    Every idea is a good lesson for me and I thank you for that.

    One thing I'm wondering, what does it really mean Z=2.119*cos(deg2rad(20)?
    JEFMAN, Can you write it with a mathematical formula? I would like to understand this idea more.
  • in reply to Malgorzata
    2.199 !!!!! (2.120-0.001)
    and 2.199/cos(20)...Disappointed
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