Root Interface Condition Analysis
Locating features govern spatial repeatability and dictate exactly how parts nest before fasteners apply clamping load. When engineers confuse locating features with clamping fasteners, assemblies quickly suffer from positional drift, internal stress, and binding. A solid datum structure strictly isolates all six degrees of freedom without introducing redundant mechanical constraints.
Primary planar contact eliminates 3 degrees of freedom (Z-translation, X-rotation, Y-rotation), a precision round pin halts X and Y translations, and a secondary diamond pin arrests remaining Z-axis clocking rotation.
Using two round dowel pins with zero center-to-center pitch allowance locks distance tolerances, causing severe galling or total assembly refusal whenever ambient thermal shifts exceed 15 degrees Celsius.
Dimensional & Tolerance Interplay
Defining datums directly from functional faces rather than unmachined casting surfaces eliminates tolerance accumulation across mating parts. Precision locators should absorb minimal manufacturing variation, leaving clearance holes on fasteners to handle minor bolt misalignment without compromising the established mechanical datum structure.