Downloaded from https://www.everyspec.com APPENDIX C MIL-STD-31000A C.6.1.3. 3D annotations. Annotations applied to 3D models shall conform to ANSI standards Y14.5M-2009 and Y14.41- 2003. All 3D models, both native and equivalent, shall be checked for conformance to these standards. Conformance errors may consist of the following:
Incorrect application of geometric characteristics to model features Incorrect use of base dimensions Inaccurate dimensions or dimensions not to scale Datum feature symbols missing or incorrectly applied Missing or incorrect use of symbols in tolerance blocks and dimensions Placement of annotations on incorrect planes or views Improper use of line types and arrowheads in leaders and dimensions Poor placement of dimensions (for example, dimensioning to the round edge of a hole) Dimension tolerances larger than dimension values Missing or partially missing annotations In addition, models that have been translated from their native formats to another format must be checked to verify that:
No annotations have been dropped, altered, or misplaced Links between the model annotations and geometry have not been broken View capture information remains consistent with the native model Annotations stored as graphics entities remain consistent with non-graphic attribute fields Examples of annotation errors are shown in Exhibit F. C.6.1.4. Model structure. Good practices for 3D model structures can be divided into two broad classes: the relationship among features in an individual part model and the relationship among part models in an assembly. Individual part models may behave more predictably if there are fewer dependent relationships among part features.
For example, good modeling practices would apply fillets or rounds last so that no other features are dependent upon them. Other model features should be defined on independent planes located at the root of the model tree instead of on surfaces of existing features. 75