i was measuring an oring groove that by calipers measured 0.645 the arm measured a plane to plane measurment of 0.234 i measured a plane at the top of the groove and a plane at the bottom of the groove and measured the distance between the two in 3d and that is number i got however all other dimensions i took using the same set up and alignment came out correct .
You can’t measure the distance between 2 planes and get an accurate reading because planes are infinite (they go on forever) and no 2 planes are exactly parallel to each other. The most you will get is a best fit as the CMM tries to find the closer or larger distance between.
Better to level and origin to one surface and then from there measure profile of points taken on the other surface. Recall the points and tolerance them accordingly.
This is incorrect.
It might be more correct to say, "If you attempt to measure a 2D Distance between two planes, PCDMIS will return the centroid - to - centroid distance between the planes in the workplane currently active. This is not desirable, as your changing hit pattern with every run will make the centroids (and therefore results) jump around. Not to mention, the software will return the XY distance between centroids when we are interested in a Z distance."
We could do any of the following:
From any workplane,
3D distance between the planes: PCDMIS returns the distance from the centroid of plane 1, perpendicular to plane 2.
From the XMINUS, XPLUS, YMINUS, or YPLUS workplanes;
a 2D Distance, Perpendicular to Feature. PCDMIS returns the distance from the centroid of plane 1, perpendicular to plane 2, but flat to the active workplane.
From the XMINUS, XPLUS, YMINUS, or YPLUS workplanes;
a 1D Distance, Parallel to Z. PCDMIS returns the distance in Z from the centroid of plane 1 to the centroid of plane 2.
Colin Simithraaratchy
Applications Engineering
Hexagon Metrology - Irving TX.
You can’t measure the distance between 2 planes and get an accurate reading because planes are infinite (they go on forever) and no 2 planes are exactly parallel to each other. The most you will get is a best fit as the CMM tries to find the closer or larger distance between.
Better to level and origin to one surface and then from there measure profile of points taken on the other surface. Recall the points and tolerance them accordingly.
This is incorrect.
It might be more correct to say, "If you attempt to measure a 2D Distance between two planes, PCDMIS will return the centroid - to - centroid distance between the planes in the workplane currently active. This is not desirable, as your changing hit pattern with every run will make the centroids (and therefore results) jump around. Not to mention, the software will return the XY distance between centroids when we are interested in a Z distance."
We could do any of the following:
From any workplane,
3D distance between the planes: PCDMIS returns the distance from the centroid of plane 1, perpendicular to plane 2.
From the XMINUS, XPLUS, YMINUS, or YPLUS workplanes;
a 2D Distance, Perpendicular to Feature. PCDMIS returns the distance from the centroid of plane 1, perpendicular to plane 2, but flat to the active workplane.
From the XMINUS, XPLUS, YMINUS, or YPLUS workplanes;
a 1D Distance, Parallel to Z. PCDMIS returns the distance in Z from the centroid of plane 1 to the centroid of plane 2.
Colin Simithraaratchy
Applications Engineering
Hexagon Metrology - Irving TX.
