Gage R&R for two step measurement process

S

smeegus

#1
I was wondering if anyone has any tips on understanding the results of a gage R&R for a two-step measurement process. In order to meet the requirements of our customer we must have the % R&R less than 30 and the only way to achieve this is to break the steps out and study each step individually. What worries me is that we use the combination of the two measurements to monitor and control the process. Are there any good tips for developing confidence intervals for two-step measurement processes?

(The specific measurement involves measuring from a mounting flange to the center of a round feature. We first find the radius of the feature with an air type bore gage and then find the height of the bottom of the feature from the flange. The two measurements are then added to acquire the final dimension.)
:biglaugh:
 
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B

Bill Ryan - 2007

#2
smeegus said:
I was wondering if anyone has any tips on understanding the results of a gage R&R for a two-step measurement process. In order to meet the requirements of our customer we must have the % R&R less than 30 and the only way to achieve this is to break the steps out and study each step individually. What worries me is that we use the combination of the two measurements to monitor and control the process. Are there any good tips for developing confidence intervals for two-step measurement processes?

(The specific measurement involves measuring from a mounting flange to the center of a round feature. We first find the radius of the feature with an air type bore gage and then find the height of the bottom of the feature from the flange. The two measurements are then added to acquire the final dimension.)
:biglaugh:
As I see it you've got two gages to "R&R". One is the air gage and the other is the instrument used to "find" the height (transducer??). It doesn't make any sense to me to do an "R&R" on your addition of the two figures (you may need/wish to verify the program logic if it is done in a data acquisition type program).

BTW - Welcome to the Cove :bigwave:
 
Last edited by a moderator:
S

smeegus

#3
Thanx for the welcome, this site is a great resource!! :)

So what you are saying is that not only should the gages be studied individually but also the features should be statistically controlled separately?

My problem with that is the critical dimension on the print is the distance from the flange to the center of the hole, not the radius or the height or both.

I realized early on that they were two separate gages and should be studied independent of each other. I was not sure how the two distributions of measurement error would interact and affect the analysis of process capability. I guess I could have the drawing changed to reflect our measurement method and have two separate features.
 
B

Bill Ryan - 2007

#4
Without seeing the part, all the GD&T frames, and how the gaging system is set up, I don't know that I can adequately give you a response (but that hasn't ever stopped me from trying :rolleyes: )

How does your operator react if the height goes out of control/spec.? If you have two gaging inputs for a feature, it seems to me that you would want to "control" those two gaging features. I realize the "critical" feature is the height but does that, necessarily, mean you must control that, specific, dimension? We use many gages to measure a linear distance to a centerline of some feature but, in many cases, only track an X, Y, and/or Z coordinate. We've not had any problems with customers as long as we can show why we're doing what we're doing.

Although I don't think I would recommend it, have you studied the combined gaging in a "one step" gage R&R (just recording the height values)?

BTW - I'd be concerned with a 30% (Tol?) Gage R&R unless you are "guardbanding" you're tolerance some how.

Kind of surprised no one else has hopped in here. There are quite a few fellow Covers much more knowledgeable in MSA than I.
 
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