When to Use DMP Flatness

[@chrmeiss67]

1) I‘m afraid, there is no reale feature function according to „flatness 0.005 M“ at datum A. 2) If this plate is srewed or stacked, a complete differend specification is required (please see: The plate can be screwed from two different sides). 2) If someone wants to use „flatness 0.005 M“ for whatever reason, then it is easier to write 1.000 -0.02 +0.025 without additional flatness. Kepp it simple! If a fit is required, it‘s a very good idea to keep in mind the gauge, which explanes the simulation of the missing contact partner. If you work with 3D-CAD it’s very helpful to work with assembly constrains to explane contacts. If you create a nominal design where all features with fit function are at MMS, all parts in your assembly are representing the go gauge against each other! A specification is only necessary to control maximum of fit clearance. Unfortunately with the modell of GD&T (or IS0 GPS) a specification uncertainty against nature function appears. Should we start to speak about this issue?

[@brettkrienke2109]

At 8:52 you say when using DMP flatness that those surfaces don’t have any form control. Certainly they are not uncontrolled. Although DMP Flatness breaks Rule #1, the limits of size are still controlling the form on the individual surfaces. There’s just no MMC boundary. Instead there is a virtual condition boundary that the surfaces cannot violate. So there’s still form control. Maybe you just meant it’s not as tight of a control as the “.005” flatness.