Functional Datum Features - Ep3

The GD&T Guy forges ahead with episode 3, chipping away at the "reigning idea" that there always must be datum features adding up to 6 DOF, even if it that means assigning datum references to features that do not play a role in locating a part in assembly. What this episode shows is that there are significant downsides to choosing non-locational datum features - some of which you may have experienced yourself, and which antagonize GD&T users every day. This video contains a multitude of examples and illustrations of the false requirements, inconsistencies, and conflicts that arise from this practice. It makes for a long video, but as the GD&T Guy says, it is important to "run to ground" all of these tools provided in the standard. In the end, we are pushed closer to the conclusion that if a functional datum feature cannot be found, it may be better to simply leave it out. 06:55 Segment Eight: Tertiary Datum Reference on One End 14:35 Segment Nine: Tertiary on One End - Multi-Segment Position Tolerance 23:56 Segment Ten: Centerplane Tertiary Datum Feature at MMB 28:37 Segment Eleven: Centerplane Tertiary Datum Feature at RMB 33:55 Segment Twelve: Centerplane Tertiary at RMB - Multi-Segment Position 40:57 Segment Thirteen: Centerplane Tertiary Datum Feature at LMB 47:36 Conclusions for this Episode Free, downloadable pdfs of drawings discussed in these videos can be found at: https://www.mountaintopdevice.com/gdt-guy-spring-2025