CMM measurement and usage in the Automotive Industry



Hi :bigwave:

I was hoping someone has some experience of using CMM's in the automotive industry.

The problem !
As I'm sure you already know, a Car or Truck ect. has a Y-plane down the center, the left side of the vehicle is negative Y and the right side is positive Y.
As most parts of the vehicle are mirrored down the Y-plane, we show results for either side of the Y-plane with positive deviations as outwards from the Y-Plane and a negative deviation towards the center(normal deviations as opposed to mathematical). This is especially useful if there is a skewed tolerance in the Y-direction on the drawing which is valid for mirrored parts on both sides of the Y-plane.
Every year or two we run into the same discussion both internally and with our customers about how we present our measuring results in the Y-direction, some say that we should report mathematically with all positive deviations towards the positive side and opposite for the negative, others say report correctly today .
The problem is no one can present a customer standard, I saw a General Motors standard many years ago but cannot find it today.

Does anyone else has similar experiences and how do you report your measurements, even better can anyone point to an industry standard.

Thanks in advance !



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A Quick Bump!

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Danny Hoover

Involved In Discussions
I have attached an example of the SAE coordinate system which I have used for Tier 1 submissions to GM, Ford, Chrysler, etc.
In my experience we did not modify the original CAD file, but would align the CMM to the CAD file and offset to the original coordinates.
We used gages many times, but they were built to the CAD coordinates, or rotated (with sign-off) 90? or 180?.
Prints were inspected as drawn.
Best advice, ask the customer before you inspect what they require.


  • Car Coordinate system.docx
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