Gage R&R for Big Parts - Approving a Variable Gage using only 1 Part

M

Mexicanquality

#1
Hello,

I would like to know how could I approve a variable gage if I only have one part to carry out the study (because the parts are very big)?

In detail, how could I assure that the gage is capable if I am not able to have 10 parts only one part because the production rate is very low and the wiegth is very heavy.

Thanks

Yoel Mtz
 
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G

George Weiss

#2
The convential wisdom of choosing/approving a gage with a spec/test-uncertainty of 10 times better than measurement being performed is a guide to go by. This is the frequently commented gage 10:1 guide/rule. Another is the 4:1 TUR and TAR guide/rule. The 10:1 guide is a first application of inspection tool quality restriction. Small lot R&R would be a process improvement tool development to review this tool and other parts of the process as the numbers of parts develops.
Beginning the R&R data collection with the first part is also a possible plan.
:agree1:
I would suggest more information about the gage and the measurement to get a specialist response in that particular field.
for example: Are you measuring Large metal parts for a European customer/parent-firm product, a large gas tank, or other?
Is this item under a medical regulation or a military first article inspection special requirement?
 
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Miner

Forum Moderator
Staff member
Admin
#3
For what will the gauge be used (i.e., inspection or process control)?

If used for inspection only, you could get a crude estimate of R&R as a % Tolerance. I would use more than 3 operators.

Keep in mind that this is a very crude estimate. Because you have a single part, your repeat measurements will be highly suspect because the operator can easily remember the first measurement unless you allow a longer period of time in between measurements. You also will be unable to detect operator x part interactions.

This could allow you to provisionally accept the gauge until you have additional parts. However, if the gauge is used for process control you will be unable to even do this unless you have an independent measurement of process variation.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#4
you can perfrom the R&R 'dynamically'. when the part is available and you are going to be measuring it anyway, you can have multiple operators measure each characteristic multiple times. You will build enough history to validate the repeatability and reproducibility.

Thinking only about product acceptance: In the mean time you have useful data for each part at release to understand the measurement error vs the actual dimension of the part and its distance from the tolerance.

If every repeated measurement is within spec - the part is within spec. If all of the measuremetns are out of spec, the part is out of spec. If some of the measurements are within and some outside the spec, then you have a decision to make. but at least you have the data to tell you that the part is either marginal to the limits OR your measuremetn variation is so large you have no idea where your part really is. Either way - you have learned something valuable.
 
G

George Weiss

#5
The idea of doing a Gage R&R is not a bad one, but is it needed emediately?
Is this a customer or standard practice?
Developing the data with multiple inspectors is a beginning,
but is an attempt to develop poor/limited data into a R&R report a good idea?
Is there a method to simulate more parts?
Can another similar part be used?
Can other production information develop a lead-in for your R&R report?
Is there another process evaluation tool for single item batches?
The evaluation of a single item creation might fall into the idea of verifying each process point accuracy/uncertainty.
If the part has several machining efforts, then each one might be analyzed.
This would more likely have been done in an earlier engineering and design point.
You could develop a validation of this earlier study, by attempting to validate each, or some machining activities.
 
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bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#6
Since we do not have any idea what the part looks like, I am going to throw this out - and you will have to determine if it applies:

If you had a very large round part (or a part with a round feature)- you could pick various locations on that diameter and have them represent other parts, e.g. 5 locations, 5 parts. To make the best of the exercise, you should load and unload the part prior to each measurement - whether it be on a fixture or on a table. As far as memorization - randomize the points taken, and only collect the individual point data each time (don't let them see previous data).

If you do not have a round feature, several locations along a feature with a single length would do (such as sides of a square or along two sides of a rectangular feature).
 
G

George Weiss

#7
The original question was approval of a gage for a measurement.
The R&R analysis is a process evaluation. (the gage being part of it and being evaluated).
The question was about a gage.
Can an evaluation of this gage be performed without many parts?
The accuracy and repeatability, and other important specifications are part of the gages’ calibration. :agree1:
Asking for a calibration with data, and uncertainties is a method of validating the gage.
And this information then could be useful if you really wanted to know that much.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#8
The original question was approval of a gage for a measurement.
The R&R analysis is a process evaluation. (the gage being part of it and being evaluated).
The question was about a gage.
Can an evaluation of this gage be performed without many parts?
The accuracy and repeatability, and other important specifications are part of the gages’ calibration. :agree1:
Asking for a calibration with data, and uncertainties is a method of validating the gage.
And this information then could be useful if you really wanted to know that much.
Yes, you can verify that the gage reads accurately to a standard - or passes calibration. In fact, that is clearly the first step in the analysis. It's core focus is 'bias'. It is accuracy and (to a small degree) repeatability to the standard (but not the actual usage).

To determine if the gage is appropriate for use to measure a particular dimension of a particular part ("Is the gage system adequate?"), then that question is answered by the gage R&R. Reproducibility - not a function of calibration.
 
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