ABSTRACT
The collective effect of the geometric tolerance and the size together, considered as one entity, is much more telling for functionality. If we consider both, we end up considering the difference between the result of the aforementioned boundary generated by size and geometric control as an item worthy of consideration. This boundary, whether generated by the MMC concept or the LMC concept, is known as the virtual condition. The boundary opposite the virtual condition is the resultant condition. Virtual condition is a constant worst case boundary created by the collective effect of the size and geometric control, while the resultant condition is the worst case nonconstant boundary that is simultane-
ously generated by these controls of size and geometry. Perhaps a truer functional design mean should be considered the difference between these two boundaries rather than merely the difference between the MMC and the LMC. However, since we should be considering the mean difference between the worst and best cases, we should instead be considering the mean difference between one of these worst case boundaries and the size considered most friendly to the functional needs. For example, in an MMC concept situation, we specify a MMC symbol next to a geometric tolerance such as a positional tolerance. This generates a worst case mating boundary. The best case mating condition would be LMC size (using none of its geometric tolerance). So, the true design mean in such a circumstance would be the halfway size between the virtual condition (MMC concept) and the LMC size. Deviations from this mean would seem to be more functionally vital than just the deviations from the mean between MMC and LMC alone. Likewise, charting or graphing a deviation such as the actual produced worst case boundary and the design Virtual Condition boundary would be more telling and productive than what is currently done. I would then define an as-produced worst case mating boundary as the minimum cylinder that can be circumscribed about a shaft with the cylinder's center at perfect orientation and location.
