Guardbands - Using Gage Studies to define a guardband


Raul Suarez

I am familiar with the MSA method of using the average of multiple measurements to cut down the %R/R figure. But I recall, from a previous job, that the R/R number can be used to determine a GUARDBAND. Example, spec limit +/- 10 cm. R/R= 2 cm. Hence modify the limits to +/- 9 cm.

Is there a statistical justification for th is?

Don Winton

Is there a statistical justification for this?

Guardbands are a somewhat common practice.

I am not sure if this is statistical valid, but it is probably a good practice. By modifying your 'manufacturing' tolerance range versus your 'acceptable tolerance' range, you are probably assuring your customer receives a product that is suitable and acceptable.

Only one word of caution. Be certain that when a process capability is performed, it is clear against which tolerance the capability is calculated against. It may cause confusion if this is not done.


Just the ramblings of an Old Wizard Warrior.
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