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.
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.
But can you put a square peg through a round hole? Will centroid of one plane to another plane give you the
real min or max distance between planes? And upon achieving said distance the following ways above, can you fit that distance between the
actual minimum parallel condition of both planes. If not, is there more information needed? In dealing with my engineers they have been far more interested to know the actual distances at multiple points vs. that of an average mating condition. Just saying. I guess it depends on what you are looking for and sometimes to much information can be a bad thing. They will pick the way that makes them happy. Remember, it will more than likely come down to a judgement call and get shipped anyway.
Correct! Man, I was beginning to wonder. Anyway, don't we all wish we had such open tolerance limits? In reality we can't have all that space between the sides or surfaces in his case. Well, at least most of us can't.
Will centroid of one plane to another plane give you the real min or max distance between planes?
No. It gives you distance between the average center of the planes, in the manner described in my previous post. If you want to know the max/min, simply use F10 and add that column to your report. It's important to know that's not the true max/min, it's the max/min for all the hits you took. Possibly there is some uninspected portion of the surface that contains the real world min/max that we weren't lucky enough to hit.
And upon achieving said distance the following ways above, can you fit that distance between the actual minimum parallel condition of both planes.
You're starting to lose me here, but I'll hazard a guess. I would say the minimum parallel condition would be given by the drawing/CAD. So using a Distance Dimension would pass/fail the part based on the centroids' relationship (again, subject to the manner described in my previous post), but the max/min would show us how the entire surface is performing relative to the required dimension, not just the centroid.
Cliff's Notes: That's happening already. Activate F10 and keep in mind that you haven't truly inspected the whole surface.
f not, is there more information needed? In dealing with my engineers they have been far more interested to know the actual distances at multiple points vs. that of an average mating condition. Just saying. I guess it depends on what you are looking for and sometimes to much information can be a bad thing. They will pick the way that makes them happy. Remember, it will more than likely come down to a judgement call and get shipped anyway.
Engineers are notorious for asking for information that doesn't necessarily relate to form/function, usually "just because they want to know". In my mind, that is typically indicating that they've realized a shortcoming on their drawing. Maybe they currently have a Distance Dimension and have realized that they actually need a Surface Profile, to ensure that every point on the surface is within a tolerance band. Note that we have excellent ways in PCDMIS of using graphical analysis to find the information that they are interested in knowing.
Cliff's Notes: Try scanning and Profiling that surface. Maybe that'll satisfy their max/min concerns.
