Jason discusses form controls on a per unit basis using the example of controlling flatness on a large surface in this Question Line Video.
Surface finish and flatness both limit the amount of variation in a surface – one at the micro level and one at the macro level. Is it permissible to call out both on the same surface?
Check out this question brought up about Flatness in our GD&T Fundamentals Course. We get a lot of questions about when flatness can be applied and how datums can be used with this. There are...
GD&T Flatness is a common symbol that references how flat a surface is regardless of any other datum’s or features. It comes in useful if a feature is to be defined on a drawing that needs to be uniformly flat without tightening any other dimensions on the drawing. The flatness tolerance references two parallel planes (parallel to the surface that it is called out on) that define a zone where the entire reference surface must lie.