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  1. Bob Doering
    Post

    Apply control limits to a non-normal distribution

    For the sake of a capability study, you need to quantify all your points - even though the data may (or may not be) handy for ongoing control....
    Post by: Bob Doering, Dec 19, 2018 in forum: SPC - Statistical Process Control
  2. Bob Doering
    Post

    NDC (Number of Distinct Categories)

    You are correct - if you were the manufacturer - and not the purchaser - of a product, then you may have more of an interest in using PV instead...
    Post by: Bob Doering, Sep 14, 2016 in forum: Gage R&R and MSA - Measurement Systems Analysis
  3. Bob Doering
    Post

    NDC (Number of Distinct Categories)

    Try calculating the ndc using tolerance (TV= (USL-LSL)/6) instead of the PV from the samples. If that is >5 then you may be able to justify the...
    Post by: Bob Doering, Sep 14, 2016 in forum: Gage R&R and MSA - Measurement Systems Analysis
  4. Bob Doering
    Post

    NDC (Number of Distinct Categories)

    1. ndc is calculated based on the variation of the samples you used in the study. It does not use tolerance. That is the only thing that shows...
    Post by: Bob Doering, Sep 14, 2016 in forum: Gage R&R and MSA - Measurement Systems Analysis
  5. Bob Doering
    Post

    Capability for one sided specification

    See attached for some tips on calculating capability for unilateral tolerance. It only works if both sides are bounded, such as roundness....
    Post by: Bob Doering, Jun 1, 2016 in forum: Capability - Process, Machine, Gage …
  6. Bob Doering
    Post

    NDC (Number of Distinct Categories)

    Use Tolerance (USL-LSL) instead of PV.
    Post by: Bob Doering, May 4, 2016 in forum: Gage R&R and MSA - Measurement Systems Analysis
  7. Bob Doering
    Post

    NDC (Number of Distinct Categories)

    Although SPC control limits are related to process variation, I also prefer to see ndcSPC where you use UCL-LCL instead of PV, and you should have...
    Post by: Bob Doering, May 4, 2016 in forum: Gage R&R and MSA - Measurement Systems Analysis
  8. Bob Doering
    Post

    NDC (Number of Distinct Categories)

    Yes, you have more "statistical buckets" within your tolerance than within your process variation (or, more accurately, the amount of variation...
    Post by: Bob Doering, May 4, 2016 in forum: Gage R&R and MSA - Measurement Systems Analysis
  9. Bob Doering
    Post

    NDC (Number of Distinct Categories)

    That is why there really should be an ndc as a function of tolerance to give the "statistical discrimination" as a function of tolerance. There...
    Post by: Bob Doering, May 3, 2016 in forum: Gage R&R and MSA - Measurement Systems Analysis
  10. Bob Doering
    Post

    Capability Calculations for Unilateral Specifications

    Yes, I usually get a Weibull or beta distribution with form data. You CAN get a normal distribution if your data is so far away from the physical...
    Post by: Bob Doering, Apr 22, 2016 in forum: Capability - Process, Machine, Gage …
  11. Bob Doering
    Thread

    Capability Calculations for Unilateral Specifications

    Some people like to default to the "half Cpk" approach (report Cpu or Cpl) when forced to calculate capability for a unilateral specification....
    Thread by: Bob Doering, Apr 18, 2016, 3 replies, in forum: Capability - Process, Machine, Gage …
  12. Bob Doering
    Post

    Question about wall thickness in a tube

    I would measure and report the thinnest and thickest value for each section. You can then take all of that data and determine its distribution in...
    Post by: Bob Doering, Mar 14, 2016 in forum: Capability - Process, Machine, Gage …
  13. Bob Doering
    Post

    8.1.1 Identification of Statistical Tools

    Depends on the variable. I can convince people to use charting in machining because it can tell them when to make adjustments and when to change...
    Post by: Bob Doering, Mar 14, 2016 in forum: SPC - Statistical Process Control
  14. Bob Doering
    Post

    Cpk & Ppk Target

    Also, QS9000 is obsolete, but when utilizing these indices you MUST understand their statistical limitations. These limitations are nicely laid...
    Post by: Bob Doering, Mar 14, 2016 in forum: Capability - Process, Machine, Gage …
  15. Bob Doering
    Post

    8.1.1 Identification of Statistical Tools

    Good point, Tony! Even if all you have is attribute issues, there are attribute methodologies to determine if you are heading off track or not!
    Post by: Bob Doering, Mar 14, 2016 in forum: SPC - Statistical Process Control
  16. Bob Doering
    Post

    PC study example from AIAG

    Attached is the data set from Appendix F of AIAG SPC book
    Post by: Bob Doering, Jan 7, 2016 in forum: Capability - Process, Machine, Gage …
  17. Bob Doering
    Post

    SPC A-D TEST FAIL

    Yes, I would post the data for review. I am suspicious as to what you indicated that your gage has way too little resolution for SPC. If you did...
    Post by: Bob Doering, Jan 5, 2016 in forum: SPC - Statistical Process Control
  18. Bob Doering
    Post

    SPC, sample size, and ANSI Z1.9

    Beth is correct, acceptance sampling has nothing to do with SPC sampling. SPC sampling depends on the process and the nature of its variation....
    Post by: Bob Doering, Nov 30, 2015 in forum: SPC - Statistical Process Control
  19. Bob Doering
    Post

    Subgroup in SPC

    It is no so much of a question of what effect the subgroup size has on the study - that is simple: the correct subgroup will generate the most...
    Post by: Bob Doering, Nov 17, 2015 in forum: SPC - Statistical Process Control
  20. Bob Doering
    Post

    Dr Wheeler's Article on Probability and Control Charts

    I got the "control comes after capability" from: From his perspective, a major purpose for creating the chart was to provide help to get the...
    Post by: Bob Doering, Nov 13, 2015 in forum: SPC - Statistical Process Control
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