6.A. INTRODUCTION

Let us recap where we are conceptually: Assemblies achieve their KCs when the parts are in the correct relative positions and orientations, within specified tolerances. Parts get to their desired positions and orientations by joining to each other at places called assembly features. In order that the final assembled state be correct, it is necessary that the features be in the correct positions and orientations with respect to each other on each of the parts, again within some specified tolerances. In Chapter 2, we saw that KC flowdown is the way to identify which parts have a role in delivering each KC. In Chapter 3, we learned that assembly features allow us to build a connective model of an assembly. Chapter 4 showed that each part can do its job locating adjacent parts if its assembly features provide kinematic constraint to the parts it joins. In Chapter 5, we learned that GD&T permits us to define features on parts and provide datums or frames that create kinematic mating of the parts to others. GD&T also focuses on ensuring that the parts will assemble interchangeably 100% of the time. Statistical tolerancing allows us to take advantage of cancellation between positive and negative errors in parts that are assembled, permitting looser tolerances on each part than worst-case tolerancing does. Now we need a way to find out if an assembly will deliver its KCs in the presence of variations...