Drawings or data?

There seems to be two approaches to managing production data – a simulation of traditional methods, with all parts fully documented on large engineering drawings, and an (almost) paperless digital approach based on CAD data (STEP, IGES, etc). The use of drawings in the second approach is focussed on communicating information on issues like fit, finish, tolerances and assembly that cannot be incorporated into the CAD data. The traditional approach is particularly favoured by Q&A staff, who want to have detailed drawings to examine when parts are delivered. This approach illustrates a fundamental misunderstanding about the use of digital data, which is that, once the data is checked, finalised and production machines programmed, all the parts made using it will be correct. There are of course exceptions to this, most notably (and ironically) parts from some rapid prototyping systems, which can be distorted by cooling and the proximity of other parts during the build process. For most parts, however, working directly from CAD data will produce identical components that do not require routine checking to see if they are accurate. The benefit of this is that drawings can now be used to communicate essential information: potential risks that need to checked; assembly issues; the correct use of colour and graphics; vital tolerances; and other data that is not inherent in the CAD files. Drawings are less cluttered by unnecessary dimensions (that are all 'built in' to the CAD data) and become far more useful production documents. They still need to be produced to BS8888 (the successor to BS308), but their role has changed. The other major benefit of this approach is that, if you are working with a correctly equipped supplier , they will be able to use your CAD data to programme production machines in a fraction of the time it would take to input all the dimensions manually. This can save a huge amount of time and money at the production stage.