Is this GR&R (Gage R&R) acceptable on the surface

C

Creech

#1
Hello -
Attached are results from a gage R&R. I'm not sure if this is acceptable. My total tolerance is .002. My readings were from a micrometer measuring a shaft, 3 places, 120 degrees apart. I then took the average. The categories are 1. This comes up from time time and typically gives us a bad R&R. I'm not sure this is the case this time. Any thoughts on this would be appreciated. - Rich
 

Attachments

Elsmar Forum Sponsor
L

lee01

#2
Re: Is this GR&R acceptable on the surface

Welcome to the forums,

First of all I'm not sure you should be using a micrometer to measure your shaft :lmao: (sorry personal joke).

Assumptions: we are talking about inches, you conduct GRR regularly.

Reading your post it appears you are regularly conducting a GRR on your equipment, and you say you sometimes find an error. This leads me to ask if you have found an error in the process and not an abnormality in your readings?

How are you deciding you 120 degree apart? is it a case of there you go its roughly a 3rd way round the shaft? if so is your shaft not perfectly round and your building the ovallity into the calculation every now and then.

As for acceptable, only you and your customer can determine what acceptable GRR result your operating with. (And not the typical 10% rule that people think it is).
 
C

Creech

#3
Re: Is this GR&R acceptable on the surface

Leeo1

Thanks for the reply. Yes the assumptions are true. And yes my company does gage R&Rs from time to time. The reason the 3 times at 120 degrees is because the parts are not perfectly round, say .0005. I found that measuring the parts in one place I had to much part variation. I would measure part 1 at say .1820 then the same part .1815 then .1818 and so on. We found the parts oval. So I averaged the 3 readings and hence the data. I'm told that I have to have less than 30% GRR and less than 10% PT and 5 categories. But then I look at the chart and it shows the operators very close in their measurements. I'm just a little confused. Thanks
 
F

Frank T.

#4
Re: Is this GR&R acceptable on the surface

My first thoughts are:

Are both operators checking the part at the same 3 places, same 120 degree location?

Variation in the circularity of the shaft are factors if not measuring the same locations.

The operators touch/feel, when turning the spindle on the micrometer, plays a factor as well.

Just my :2cents:

Bye the way, welcome to the cove. :bigwave:
 
J

justncredible

#5
Re: Is this GR&R acceptable on the surface

Mark the parts where they need to measure them, measure them in one spot and use 3 operators, you need to be able to have a system that can identify 5 parts, that is the 1 NDC, yours will only identify 1 part out of 10 right now.

Why are you useing anova? Why does it show one operator, and then 2 on the reports?

Just crashed this cmm 2 times writing this......LOL
 
C

Creech

#6
Re: Is this GR&R acceptable on the surface

Thank you for the welcome.

The operators had used (just so happens) 3 , 120 degree features to visually turn the parts 120 degrees apart to measure the parts. They used 3 clicks on a digital 1 inch mic. We could probably improve the measurement. I'm thinking the distinct categories are effecting the GRR. Does that make any sense? Thanks
 
C

Creech

#7
Re: Is this GR&R acceptable on the surface

justncredible - Not really sure why I'm using ANOVA. It is just by default. As for the operators, I have no idea how the data is displayed. As you can tell I am very wet behind the ears to this subject, unfortunately I have no internal support. Thanks
 

Miner

Forum Moderator
Leader
Admin
#9
I'll try to adress several issues and misconceptions that I noted in the above posts.

1) Averaging the measurements as you are doing is an excellent method of reducing the impact of the within part variation (ovality). Variation is reduced by the square root of the sample size (SQRT of 3 = ~1.7), so you have reduced within part variation by almost half.

2) Your operators are very close in their measurements. The Operator portion of Reproducibility is 0. The issue is the interaction between part and operator that was caused by part number 2. Have both operators remeasure part number 2 and reanalyze the study with the remeasured part data.

3) justncredible, There were 2 operators. The 1 that you saw was the degrees of freedom for two operators (df = n - 1 = 2 - 1 = 1)

4) The number of distinct categories is correlated to the %GRR, but does not cause it. The two are different metrics measuring the same thing.

5) ANOVA is a better method than the Range method used in most spreadsheets. It provides the operator x part interaction, which the Range method does not provide. In addition, the Range method uses the range to estimate the variation versus the direct calculation of variation by ANOVA. Stick with Minitab over the spreadsheets.

6) Regarding the ndc and %GRR: These metrics are highly dependent on the variation of the 10 parts used in the study. They must accurately reflect the actual process variation. 6 standard deviations of the parts used in this study were 0.0003576. How does this compare to your process capability measured the same way (average of three)? If it is smaller, your ndc/%GRR will be worse than they actually are.
 
C

Creech

#10
I did a little experiment and modified the data by adding "made up size" to a few of the readings and I got an incredibly good gage R&R

%Contribution
Source VarComp (of VarComp)
Total Gage R&R 0.0000000 0.14
Repeatability 0.0000000 0.14
Reproducibility 0.0000000 0.00
Part-To-Part 0.0000008 99.86
Total Variation 0.0000008 100.00


Process tolerance = 0.002


Study Var %Study Var %Tolerance
Source StdDev (SD) (6 * SD) (%SV) (SV/Toler)
Total Gage R&R 0.0000335 0.0002011 3.72 10.06
Repeatability 0.0000335 0.0002009 3.71 10.05
Reproducibility 0.0000015 0.0000088 0.16 0.44
Part-To-Part 0.0009015 0.0054091 99.93 270.46
Total Variation 0.0009021 0.0054129 100.00 270.64

To me, it seems if I have more part variation I'll get a better GR&R. I understand that if I don't span the range of the tolerance then I can't call the gage good. But in this instance (using a mic) can't I assume my measurements will be linear? The machinery we use is very accurate and repeatable. Dare I say "intentionally make parts that span range".

Thank you for taking the time to respond.
 

Attachments

Thread starter Similar threads Forum Replies Date
B Gage R&R Acceptable (10-30%), deduct Total Variation from Tolerance Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 12
C Lowest Acceptable Grade for Master Gage Set Calibration and Metrology Software and Hardware 1
A Help with acceptable screw gage values per standard BS 919 for Go/ No Go gage General Measurement Device and Calibration Topics 4
G Ford - Type 1 Gage Study MSA (Measurement Systems Analysis) acceptable? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 7
D Acceptable % on a Gage R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
A Gage Block Repair - What type of stone is acceptable for removing burrs General Measurement Device and Calibration Topics 5
A Acceptable Criteria for Variable Gage R&R according to the MSA Manual 3rd Edition Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
S What are Acceptable Limits for Gage R&R Results Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
J Acceptable Gage R&R - What is acceptable %error for Gage R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
J Acceptable Gage R&R Output Results - EV, AV, R&R, PV, and TV Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
J What is an acceptable Gage R&R (Repeatability and Reproducability) system? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
Q Gage Pin Sets? Calibrate/Verify them all or just a sample size? General Measurement Device and Calibration Topics 9
S If 4 operate to measure, what is the value of k2?(MSA gage R&R) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
S Faro Arm, Gage R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
8 MSA--Should I Use Parts or Gage Pins? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
C Gage Block Grade 1 - Calibration Measurement Uncertainty (MU) 15
R Gage Measuring 15 Parts at a Time Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
Q Gage calibration in disarray ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 12
M Gage R&R automated test equipment Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
PQ Systems Recipe for Success! 10 Ingredients for a Healthy Gage Management System Using GAGEpack Software 0
D Gage Repeatability for Faro Arm Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
S Comparing measurement results for a part from two ring gage General Measurement Device and Calibration Topics 3
M Quick Gage R&R Question Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
PQ Systems Best Practices In Gage Management Using GAGEpack Software 0
PQ Systems Gage R&R - 3 Part Series Using GAGEpack Software 0
I Excel based Gage R&R VS Minitab calculation Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
R Repeatability Type 1 Gage and Gage R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
W Proper gage to use for receiving inspection General Measurement Device and Calibration Topics 9
A GAGE R&R Binomial with master list (for method validation) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 0
Q Gage calibration / tracking software General Measurement Device and Calibration Topics 5
A R chart from ANOVA gage R&R test Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 12
M Type 1 Gage r study Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
T Plug Gage Calibration Calibration and Metrology Software and Hardware 1
L Gage R&R TMV Acceptance Criteria Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
S MSA for attribute relation gage Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
E Zero part to part variation - Gage R&R project Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 15
M Gage R&R and right way to measure Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 16
L Gage RandR on automated equipment. IATF 16949 - Automotive Quality Systems Standard 7
B Gage calibration frequency, ISO and IATF - What are the requirements Calibration Frequency (Interval) 3
D Difference between Test Method Validation and Gage R&R Qualification and Validation (including 21 CFR Part 11) 19
R Determining Uncertainty from Gage R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
C Correct Calibration Method for Dial Depth Gage General Measurement Device and Calibration Topics 6
C Gage Block Wringing General Measurement Device and Calibration Topics 3
B Gage R&R with NDC=1 Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 19
S Type 1 Gage R&R or something else? Reliability Analysis - Predictions, Testing and Standards 6
G Should I perform Gage R&R only at the beginning of a new project? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
V Thread Plug Gage Pitch GO Diameter out of spec AQL - Acceptable Quality Level 8
G Gage R&R - Where am I going wrong? Part of a FAIR submission (Aerospace) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
R Gage R&R Excel templates Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
K Gage R&R with more than 3 appraisers Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2

Similar threads

Top Bottom