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Gage RR – Resolution

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  • #50652

    Valdek
    Member

    Hello there, let me ask someone of you about the help in matter of finding proper resolution of measurement device. If the tolerance is 0.3 mm expected resolution should be 0.03 (10%) or 0.006 (2%)? Need to know it because performed gage r&r shows number of distinct categories = 1, what should I do to change? V

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    #174453

    Michael Mead
    Participant

    You have already noted the answer. It is a little confusing to me why some people require a 10% level of precision and a 10% GR&R.
    Anyway, I would guess that you do not have enough variation in your sample. You also do not have enough resolution in your gage to have different messurements for the same piece. So, either your gage and operators are too good or your process is too capable. In either case, to get a good GR&R you need to have some variation in the observed data. 

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    #174458

    BB
    Participant

    Hi
    What is the logic of the 1.41 factor in arriving at the no.of distinct categories ?
    BB
     

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    #174459

    Michael Mead
    Participant

    Well, you got me there. I don’t know anything about the number of distinct categories.  My guess is that 1.41 is the square root of 2.
    OK, who really knows?

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    #174460

    howe
    Participant

    According to the AIAG, you need at least five distinct categories to have an adequate measuring system.

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    #174465

    Remi
    Participant

    Hai Valdek.
    If the resolution of the gage is not at least 10* smaller than your area of interest (Product Range or Customer Tolerance) it will be very difficult to achieve a gage r&R% result of 10% or lower.
    So you have to think about:-do I want to distinguish my products very well among each other (=> Product Range) OR do I want to measure my products well within the area that my customer finds agreeable (Customer Tolerance)- How good does my gage r&R % result have to be (your choice)?  * 10% because that’s the rule for excellent  * 30% because that’s the rule for acceptable  * 50% because that’s practical  *100% because I can then at least measure roughly  * …?
    The combination of this gives you an indication how good the Resolution should be. And remember: to determine the Resolution you don’t need any measurements: it’s in the specs of your gage.#Distinct Categories is another parameter that measures the quality of your gage; there is a formula between gage r&R % and #DC (look it up in Minitab help if you want to no the function)
    Michael: 1.4 = SQRT(1.96) and 1.96 is in the formula of CI of Mu (see Minitab Help)
    Hope this helps

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    #174468

    Ken Feldman
    Participant

    The number of distinct categories is a critical element in determining whether the measurement system has sufficient discrimination.
    http://www.minitab.com/support/docs/Answers/Root2.pdf

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    #174469

    Valdek
    Member

    Thanks, but still the answer is not given for me, I perform the question in numbers – Range of results: 0,006 to 0,014, tolerance 0-0,3, number of samples 10, 2 operators, 3 trials each, cp and cpk for process data = more than 2, it looks like the resolution of device is to big, distinct number = 1, what to do to make satisfied customer? pls, do give me the answer, regards, V

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    #174470

    Mikel
    Member

    It is the square root of 2 (not 1.96 as someone suggested).Read Wheeler’s work on measurement systems and go through his
    derivation of Discrimination Ratio and you’ll understand where the 2
    comes from.

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    #174473

    Remi
    Participant

    Hai Valdek:
    Sorry, I can not decide for you. But I can explain how you could decide based on the info you already have. In my (maybe wrong) conclusion you don’t know exactly what all info is the tool gives you.
    Assuming 0.006-0.014 is the range of the measurents during the Gage r&R while the customer specs are 0-0.3 I conclude:
    -you use the default calculation of Minitab for gage r&R % -you use the default product range and not the Tolerance option-your products show small variation compared to customer wish (cp=2).So the result of the gage r&R tells you (with #DC as your decision parameter) that this gage system is not good enough to distinguish between the products! That does not necessarily mean that your customer will be unhappy.
    If you use the Tolerance option you get the result of %Tol as extra column which tells you how good the system is to determine the product value within the specs. Using the Tolerance option gives an extra column in the Session Window (no recalculations!). This means also that the number of distinct categories does not change!! The #DC is always related to the range of the products used in the analysis and not to the Tolerance value (or Historic Sigma) that you filled in under options.
    To estimate the gage r&R% from the tolerance option (=%Tol):the default gage r&R% * Range products/Tolerance. So I predict that you get a factor 8/300 smaller result (and the # DC will improve but I don’t know the exact formula and your #DC=1 could be a rounded up because Minitab has 1 as absolute minimum)
    hint: the top value of the column with 6*SD (or 5.15*SD) represents the CI of 1 measurement (ie if I have 1 measurement I have a high confidence (99.7% or 99%) that the real product value is within an interval of that width around my measurement).
    Hope this helps
     

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    #174476

    Remi
    Participant

    Hai,
    I stand corrected (again).
    “Being right is more difficult than being wrong because there is only 1 right and so many wrongs’
    Thanks

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    #174605

    Chris Whittaker
    Participant

    Gage R and R is used to ensure that your measurements are correct or acceptable to measure the process , they are not a measurement of the process.
    To correctly measure for Gage R and R you have 2 options …short term and long term measurement
     Short term is 2 operators measuring 5 of the same products in exactly the same way twice each.
    Long term is 3 operators measuring 10 of the same items in exactly the same way 10 times each
    the key here is to use the SAME , measuring tools, people and set of IDENTICAL items for each measurement
    This will ensure the discrimination, Linearity and stability of your measurement system is standardised.
    If your process variability is under 10% the measurement is acceptable, 10 to 30 % the measurement may be acceptable over 30% and your measurements are no good.

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    #174607

    Remi
    Participant

    Hai Chris,
    I don’t understand your definition/distinction of long and short term gage r&R. The only difference I see is the amount of data used and consequently the Confidence Level of your conclusions.
    I use the term Long Term Gage r&R for a gage r&R that is repeated every 3 months to check if the r&R values of the Gage System have changed  (and Bias is checked via a control chart on Golden Products on day2day or week2week basis).
    Also I don’t stress “The Same” like you do. I find it more important that the measurement is done in a representative way (like in real production life). Then you investigate an extra aspect of measurement influence on the data that will be used to Analyse. This aspect is seldom covered in the theory books.
    Remi
     

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    #174608

    Mikel
    Member

    Chris does not know what he is talking about with his short term /
    long term distinctions.Any study which represents the true measurement capability has to
    include ALL who perform the measure and should be repeated
    periodically including when the system is calibrated or repaired,
    when there is a new operator or fixture, when an operator has not
    performed the measure for some period of time.GR&R needs to be a requirement of the Quality System, not a Six
    Sigma tool. A SS project should only verify that the calibration and
    MSA studies are in place and adequate.By the way, the 10 to 30 % rule is crap. Is 30% adequate or not? I
    know the answer, do you?

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    #174610

    Chris Whittaker
    Participant

    It is not my definition or distinction , it is the AIAG definition /distinction of what constitutes a Gage R and R .
    You are looking for reproducability and repeatability  ( that is what the Rand R stands for) in order to do that you need to analyse in exactly the same way.
    As the AIAG wrote the theory books on Gage R and R and you want to comply to that standard then it is likely that you want to follow their methodology.
    You can do a MSA (measurement systems analysis) as often as you like but if you ignore the methodology as laid out by the AIAG then I would not call it a Gage R and rR…but if it works for you so be it.

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    #174615

    Mikel
    Member

    Go read the books Chris, you don’t know what you are talking about.They use the terms Short and Long. Not short and long term. They also did not write the books on the theory – that came out of
    GM in 1962.

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    #174617

    luke skywalker
    Participant

    Hey Darth,
    Was in Indy yesterday and had a chance to see the “beautiful” Lilly building on the way back to the airport. Could have sworn I saw a big flag that showed “Lilly, a Vader Subsidiary”. You must have really done some significant work up that way.
     

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    #174637

    andrewmc
    Participant
    #174642

    Chris Whittaker
    Participant

    Thanks for the feedback Stan.
    I will put it straight into  my “lets pretend I GAF about what you think file”

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    #174656

    Taylor
    Participant

    Chris with that type of closed mind attitude, you will never learn. Your answer was wrong. If your going to site books or guidelines, at least get it correct, or don’t post.

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    #174661

    BC
    Participant
    #174662

    Chris Whittaker
    Participant

    Outstanding Chad considering your first post was intercepted and deleted because it breached community guidelines.
    I am interested to know what it was that you originally posted that was deemed sufficent to be removed from the site?
    As a person who deems themselves worthy of being proficient to post to this site can you please enlighten all others as to what your original posting stated?
    HHHHHMMM did not think so …all mouth and no trousers.

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    #174664

    Chris Whittaker
    Participant

    I hope that the  LSS professionals like Stan and Chad that subscribe to this forum have been able to assist and  clarify your question and give you the solutions to your question without letting their little ego’s get in the way so that can move on.
    Good Luck!!

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    #174668

    Taylor
    Participant

    Chris
    Your interpretation is wrong, Completely wrong. My original message simply said you fail, and I will post again.
    I’ll state again, if your going to post answers, give correct ones.
    A Gage R&R is conducted to determine whether excessive variability within the process exist in the measurement system. The guidelines in the AIAG manual, are simply that, guidelines, they are not hard rules.  Samples to be measured should represent the process normal distribution. The original poster is having problem with the ability to determine one part from another. There is a couple reasons this happens, one is the sample of parts are not representitive of the process and/or the gage is not capable of measuring the difference in the samples. Which had already been answered, no input from you needed.
    To further Stan’s point, you don’t have a clue when it comes to Short and Long term. I have never heard anyone say that. And you are also wrong about where the AIGA manual came from. It was adopted procedure developed by GM; John Deere also has a very similar manual.  Again Stan is correct about how a Gage R&R should be used, so pull your head out of the sand hole its in and you might learn something
    Now if you want to continue to pick fights there is other sites with individuals who will debate with you all day long, I suggest you go there.
     
    Regards
    Ps: Duct Tape is like the Force, it has a light side and dark side, and holds the universe together

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    #174678

    Michael Mead
    Participant

    Chris,
    Some folks on here know all the answers, or the answers are not worth knowing. But, on the other hand, when Chad criticized you for saying “Short-term” and “Long-term” hmmm.  You would do better calling them the short method and long method. 
    Keep up the good work, but you must watch your p’s and q’s here.

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    #174686

    Taylor
    Participant

    Michael
    Attention to detail makes a big difference…………Agree?

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    #174717

    Michael Mead
    Participant

    Yes it can sometimes. If I never made a miskate, I would agree completely. :)

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    #174728

    Mikel
    Member

    Chris honey, it’s your ego that is fragile.
    Your advice is wrong and your understanding of this tool is shallow. The AIAG manual is called Measurement System Analysis, not GR&R. What is your System? 2 operators, 3 operators, or ALL who perform the measurments? MSA properly applied pertains to all who make the measurements.

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    #174777

    Chris Whittaker
    Participant

    Thanks stan for your input once again!

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