【转帖】how to gage rr flatness

yang686526

how to gage r&r flatness?
hi all,
one of our customers asks me to do the gage r&r on a sheet metal part. one of the critical requirements is flatness. we know that flatness (.008 inch) may be inspected by cmm(program and non-program) or manually with indicator. i thought that this may not a good idea to do the gage r&r because different people will hit different points/routes.
is someone can tell me the right way/method to perform this assignment?
determine which method of evaluation you are going to use for measuring the part (usually the least expensive to you that has a good chance of meeting the requirements) and do the gage r&r with that method.  the purpose of the r&r is to check gage capability which is why your customer probably requested it.  if this is a key dimension for them, knowing you are capable of measuring it can save a whole lot of headaches down the road.
regards,
do not do an r & r study on flatness since the method of measuring is not repeatable. you are absolutely correct that each person does touch on different areas even if one had the 10 parts and 3 trials. what a mess!!!!
an r & r study is to test the gauge for appropriate application and in the automotive industry, the r & r value should be under 30% of the process depending upon how critical the feature or characteristic is.
on the flatness, we would have a larger portion of the results with the method of contact rather than the gauge. if you proceed with this study, expect something like about 75% r & r value with the gauge only contributing about 15% and the differing methods the balance or 60%.
as a matter of fact, do not perform an r & r study on most geometrical symbols but on linear dimensions.
tell you customer, r & r are taken on linear dimensions where the gauge family is used.
hope this helps.
dave d.