Gage R&R Total Tolerance question - Use the full process tolerance?

0

02SCvette

#1
I'm working with another facility and came across what I believe is an error with the way they are completing GR&R's.
For example:
The part length is 1.00 +/- .005".
For the formula to calculate the repeatability:
%TOL = (EV / TOL) * 100 = xxx
They are using .005 for the TOL rather than .010.

I've always used the full process tolerance.

Who's correct?

Thanks for the help!
 
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D

David DeLong

#2
Re: GR&R total tolerance question

I'm working with another facility and came across what I believe is an error with the way they are completing GR&R's.
For example:
The part length is 1.00 +/- .005".
For the formula to calculate the repeatability:
%TOL = (EV / TOL) * 100 = xxx
They are using .005 for the TOL rather than .010.

I've always used the full process tolerance.

Who's correct?

Thanks for the help!
It was the tolerance range which in your situation is .010.
 
S

slho001

#3
hi:
just remind one more thing, if use MSA rev.3, tol shall be divided by 6 before putting into the formula
SL
 
J

Jaroslaw.Malkowski

#5
in my opinion it should be proces variation based on sigma - if not we should calculate TV.
But if we take into consideration the USL and LSL (specification limits) we always get low R&R (e.g. tolerance defined by dwg +/- 2)
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#6
In my opinion, if the gage is used for SPC, it should be based on the control limits - not the tolerance. In fact, there should be an ndc (calculated using the control limits) of about 10 to be of any value. That may not be the issue of the original gage R&R question, but should be kept in mind. :cool:
 
J

John Nabors - 2009

#7
There is a practice I have used that is probably cheating and will probably be cheerfully criticised by by fellow Covers, but I have gotten away with it so far. Say I have a particular customer (just to pick on someone I'll say Northrup Grumman) and I use a particular gage to check the product I provide to them. I'll find the tightest tolerance on any Northrup part I have that is inspected with that gage, R&R that one, and then use that R&R for any product that is inspected with that gage. IMHO, I can't use the same R&R for say, Lockheed Martin, I have to do a new one for them.. maybe I'm making too much work for myself in that instance but hey, it keeps me from going outside to smoke.. :rolleyes:
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#8
Say I have a particular customer (just to pick on someone I'll say Northrup Grumman) and I use a particular gage to check the product I provide to them. I'll find the tightest tolerance on any Northrup part I have that is inspected with that gage, R&R that one, and then use that R&R for any product that is inspected with that gage.
This approach is supported if the dimensions and parts that the gages are being used for are fairly similar. If all of the dimensions are round and ballpark same size, for example, you may find that approach handy. Where you can get into trouble is if you use the gage R&R - lets say a micrometer - for a part that weighs and ounce and is 1" long for a tight dimension used by measuring in the inspector's hand, and try to justify the same gage R&R for a part 36" long, 1 lb, measuring a diameter on one end (rude cantilevered load problem). This is why there is an interest in doing gage R&R on the actual part - just in case you might capture such a problem. :notme:

Overall, it is good to do what makes sense - after all, most of us need our resources to manufacture product, not gage R&Rs. Gage R&R's are like an "insurance payment" - and we do not have to have insurance for every possible calamity. :cool:
 
J

John Nabors - 2009

#9
This approach is supported if the dimensions and parts that the gages are being used for are fairly similar. If all of the dimensions are round and ballpark same size, for example, you may find that approach handy. Where you can get into trouble is if you use the gage R&R - lets say a micrometer - for a part that weighs and ounce and is 1" long for a tight dimension used by measuring in the inspector's hand, and try to justify the same gage R&R for a part 36" long, 1 lb, measuring a diameter on one end (rude cantilevered load problem). This is why there is an interest in doing gage R&R on the actual part - just in case you might capture such a problem. :notme:

Overall, it is good to do what makes sense - after all, most of us need our resources to manufacture product, not gage R&Rs. Gage R&R's are like an "insurance payment" - and we do not have to have insurance for every possible calamity. :cool:
Correct as usual, buddy!:cool:

To extend your insurance analogy, I live in Florida. I don't need earthquake insurance, but I'm darn sure covered against hurricanes and tornadoes.

:topic:
Do you remember the tornadoes that came through Central Florida in February 2007? The one that killed more than 20 people in Lake Mack missed me by about 400 yards. I was awakened by the hail, heard the tornado coming, and just about the time I thought I was a goner for certain, the sound began to recede. The next day I began planning to get rid of what I will charitably call a manufactured home and move to an actual house.

I lost a very dear friend in that storm.

Regards -John
 
J

Jaroslaw.Malkowski

#10
MSA also says:
R&R <= 10 - OK
and ndc =>5
What in situation if R&R = 7,5% and ndc = 3,2???
Is it OK
 
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