Inspection Accuracy VS. Dimensional Accuracy 3

[toriche]

Does anybody know what are the industry-accepted practices when it comes to dimensional inspection? Is there an industry standard for this?

I have seen dimensional inspections where inspection accuracy exceeds that of the engineering drawing. In other words, a 2-decimal place dimension in a drawing is inspected to 3 decimal places on the actual manufactured part.

To avoid unnecessary non-conformance reports, I would think that inspection measurements should be taken and reported with the accuracy specified in the engineering drawing.

Thank you for the help.
Toriche

 

[BillPSU]

The industry norm for inspecting a dimension is the gage have 10 times the accuracy of the dimension being measured. Lets say you have a part with a tolerance of 1.000 +/-.001 is the part acceptable at 1.0011 or .9989? So if a part comes in 1.0011 do you want it reported as 1.001 and out of tolerance?

 

[ajack1]

I agree with BillPSU, the reason for this is you always round up or down past the number of digits you measure. So to use Bills example even 1.0014 would round down to 1.001.

This becomes even more important if you use SPC.

 

[kagan]

The nominal dimension is not important. The tolerance band width is the key. For example if you have a band of 0,002 so you must use a device with an accuracy of 0,0002 at least. Also you can group your dimensions according to their importance. If you will use SPC, 1/10 is a good choice. But if it is not a critical dimension for assembly or safety or legal procedures, you can also choose 1/5 for accuracy of inspection device.