Gage R&R Studies - Part that has 10-20 critical dimensions

S

Shahzad67

#1
Question:

How do you conduct operator or equipment variation on a part that has 10-20 critical dimensions?

Do you select one dimension and have the operators measure one particular dimension?

Thanks
 
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bobdoering

Stop X-bar/R Madness!!
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#2
How do you conduct operator or equipment variation on a part that has 10-20 critical dimensions?

Do you select one dimension and have the operators measure one particular dimension?
I suggest looking (at a bare minimum) at two studies for each gage used: the tightest tolerance characteristic, and the most awkward characteristic to measure (the difficulty of measurement by the operator that hold the highest operator influence - either by how they hold the part or gage, or how the have to read the gage, etc.)

If it meets those, then you should be good for anything that provides a better situation.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#3
Are all of the characteristics being measured with the exact same hand held gage? then I might agree with Bob's suggestion.

However, since you don't mention what the product is, what the characteristics are or what gage(s) are beign used, my generic answer is that each characteristics/gage combination needs to be qualified individually. My organization produces medical diagnostic instruments and each critical characteristic is qualified separately and completely. While appliation of MSA to such a complex device might be obvious, I also have each critical dimension of pieces and parts seperately qualified. An example is of a plastic pipette tip with 6 critical dimensions. during the R&R phase for thsi tip we discovered that a critical dimension, measured with an optical comparitor - wasn't being measured correctly by the supplier. Unfortuantely their bias was in the direction of a critical failure mode.

Ther is a reason we do measurement systems analyses and it's not just to check the box for your customer report. It really is a matter of pay me now, or pay me (1000X) more later...
 
S

Shahzad67

#4
We produce PVC extrusion profiles for window fabricators. I have attached a drawing of a part. You will see there are a lot of critical dimension that are outlined in the drawings and the operators check these dimensions using calipers.

I just took over the role of quality recently. Upon my review i noticed that majority of the quality issues are due to dimensions (parts not fitting with each other, parts not fitting in customer fabrication saws or punches).

I appricate your help. Thank you
 

Attachments

bobdoering

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#5
Wow. That print hurts my brain just looking at it. :tg: It really does not give a good impression of how difficult each measurement is, just because it is a cross section. I don't know how long the sample is you have to hold to measure, but it could be a real challenge. I would do this: Sample a few inside dimensions (such as 700 +/- 10), outside dimensions (such as 2.509 +/- .015), some step measurements (such as .090 +/-.007) and see if they even come close to an acceptable gage R&R. If they do, you may want to continue to do some more to satisfy yourself the caliper is "good enough", but if they don't, you have a metrological knot to sort out.

Have you begun any gage R&R studies at all? If so, how did they work out?
 
S

Shahzad67

#6
Thank you for your feedback. No we have not done any GRR studies at all. This is my first attempt. I will take the three dimension that you have highlighted and work with them. However, I am a bit worried as I already know that the operator variation is going to be pretty large.

The operators usually cut a 4-5 inch piece to perform their inspections. So it's not very difficult.

Once again thank you for taking the time to reply to my posts.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#7
Remember, it is a gage system - not a gage - that fails. If you can minimize operator error by solidly fixturing the specimen rather than having them hold it in their hands, for example,you can make improvements on the system - sometimes sufficient to pass. Of course, you need to maintain those systems - going back to measuring them in your hand would defeat the purpose.

When reviewing the results, also remember that all gages are bad - but you might find one that is good enough! Gage R&R is how you judge it.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#8
to add to Bob's wise advice, remember that this is a process of discovery, understanding and improvement. It is not a game with a score that leads to winners and losers.

Start with a basic repeatability and reproducibility study, understand your soureces of variation and work to reduce teh largest so that you get a measurement system that provides valuable (actionable) data on your product variation.
 
S

Shahzad67

#9
Appreciate all the help. One more quick question. We use go-no-go gauges to check our profiles. Any thoughts on what your experiences have been with go-no-go gauges.

Thank you
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#10
if well built they can be very useful.

I also perform measurement systems analysis on go, no-go gages suign the techniques outlined in the referenced attachement...
 
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