How to override Rule 1 of GD&T (ASME Y14.5 – 2018)
👉 RULE-1 of GD&T (Perfect Form at MMC requirement) could be bypassed in certain cases.
👉 Straightness & Flatness are the only form controls as per ASME Y14.5-2018 which can override Rule 1 of GD&T.
👉 We can do so by following ways:
1. By adding the note “Perfect form at MMC not required”
2. By applying “Independency” modifier to regular FOS.
3. By associating Straightness or Flatness Feature Control Frames with Regular FOS dimensions.