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Identify Variation

acgarcia
Good Morning,

I don't have a lot of experience is statistics. Can someone guide me on how to identify variation in my measured data? I need to know how much variation is present so engineering can adjust tolerances accordingly and also to make sure the CMM is trustworthy.

I placed a part in a fixture and ran my measurement routine. I did a do/unitl which gave me 6 reports and 6 rows in excel for each part serial number. Data was written directly into excel. Part remained in the fixture for the duration of the inspection.

Here is 1 part with its 6 runs.
































































Serial Run # ID OD TP X Axis Z axis
1 0 3.0768 2.679 0.005 -0.0024 0.0006
1 1 3.0769 2.679 0.0051 -0.0025 0.0005
1 2 3.0768 2.6789 0.0051 -0.0025 0.0006
1 3 3.0769 2.6789 0.005 -0.0024 0.0006
1 4 3.0768 2.6789 0.005 -0.0024 0.0006
1 5 3.0771 2.6789 0.0051 -0.0025 0.0007

  • Dear esteemed colleagues and degenerate operators,

    Got into a fist fight this weekend performing and MSA with a 5mm X 100mm X 100mm probe scanning a 3.5 ring gage with a 90 deg wrist. Basically I was not capable until I used temp. comp and the Gage Scanning algorithm. Our tolerance was +/-.001 and final Cpk was 1.34.

    Thanks.

    What was your Gage R&R % results?


  • What was your Gage R&R % results?



    with temp comped and using gage scan filter with a 5mm x100 x100 probe at A90B0.

    thx!
  • The Excel Cpk and Ppk formulae and the Minitab formulae are slightly different and yield different results. Minitab is the standard....just an fyi


  • {"alt":"Click image for larger version Name:\tType 1 Gage Study for C3.png Views:\t6 Size:\t7.0 KB ID:\t527494","data-align":"none","data-attachmentid":"527494","data-size":"full","title":"Type 1 Gage Study for C3.png"}

    with temp comped and using gage scan filter with a 5mm x100 x100 probe at A90B0.

    thx!

    That is a Type 1 Gage Study. Your Cgk is at 1.06 and P-Value is under 0.05. Not good. That would be a failed study. Plus your reference is above the mean of the part. Technically, from my understanding, your reference should be somewhere in the middle of your measurements. This is telling me your CMM does not measure near the reference standard. Therefore, this probe and/or measurement method should not be used to measure this feature.

    From Minitab:

    A reference value is the known and correct measurement for each part. The reference value is used for comparison during measurement system analysis. For example, you have a reference part with known weight of 0.025 g that you use to calibrate your scales.

    Reference values can be determined in many ways, depending on industry standards and company and customer expectations. The following are some of the characteristics of reference values:
    Reference values are an average of repeated measurements from more accurate measuring equipment.
    Reference values are endorsed by a professional group.
    Reference values are agreed on by the affected parties.
    Reference values are defined by law.​​
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