How can you ensure GD&T requirements are met with complex geometries?

Based on my experience, the datum points will divide good GD&T from bad ones! These points are defined together with the project design phase! Must be followed, otherwise the reference is lost! Good production specialists understand how important are these specifications and reference datum schemes!

DATUM references would likely be selected attending two critical characteristics: * Guaranteeing part's isostatism: that is, part position and orientation should be completely defined. * Simulating part's mating, in order to obtain measurements which reproduces as far as possible part behaviour in the assembly. It is also recommended, to avoid the impact of inevitable small imperfections over the whole measurements to select DATUM points as far as possible among themselves.

Tolerances definition are key to understand the sigma level! It is not possible to reach 6 sigma level in a machine for example if your tolerances are badly defined. A good design sets the tolerances to the quality level you want to reach! Of course the cost for straightening tolerances follow somehow with same proportion! For example, a very expensive watch need to be much more precise compared with an inexpensive one. It means that the customer expectation will be different! Lower expectations can open the tolerances but it will not be the case in the expensive one!

Tolerance Zones should match part's requirements to accomplish assembly, functionality, and sometimes (only sometimes), aesthetical features. At this point, when part's geometry is specilally compliated or part is too big, is important to avoid the use of standard tolerance zones which are not justified enough but to apply a tolerance zone. E.G. Do we really need such tight tolerance for a part whose assembly and functionality is guaranteed already and customer couldn't notice a larger deviation? Because the use of thight toleranes when there's no need to, will increase significantly the costs.

To check correctly that production part matches requirements is a must to have the adequate devices. A CMM machine with up to date calibration certificate, aided by a good software (e.g. Metrolog X4) will let us to ensure our parts are good enough to deliver to our customers in an easy way. It is important to report measurements to guarantee traceability and having them available to our customers at any point of production.