Rob Kirkham wrote:
"But it makes me wonder - would useful CAD drawings substantially reduce a
manufacturer's costs and make some projects more viable?"
Good question. I am not sure the jury is in on this point. Certainly, the discipline that building a good 3D model entails (one has to look at ALL dimensions and make them work as the model is being built in 3D) is much more usefull than a traditional 2D presentation drawing (similar to old MR or RMC drawings with sides, ends, top and bottom and maybe some cross section views).
However, the factories in China (or Japan) may still choose to redraw everything anyway, negating any cost savings. I've seen factory drawings that were obviously done by different engineers for items that should have shared common elements. (for example, A & B units of the same model diesel). I don't know if this results in totally separate tooling for what should be one part. People who have tooling done in house have enough problems much less those that have it done on the other side of the Pacific..... Some times it seems like the work is being done to maximize work so streamlining the process might not be factored in as cost savings by the factory.
3D CAD does make visualization and checking of the final product before committing to tooling easier. 3D CAD has to be completely dimensioned to enter the part..... so dimensional errors are limited to deviations from the prototype and not just mistakes in calculations. Looking at 3D models of the individual parts and assemblies it is much easier to detect things that look wrong than cross checking between many sheets of paper 2D drawings. Items can be viewed and compared to photos much easier. Mechanical interfaces (truck swings, coupler mounting heights, etc.) are much easier to check in 3D as well.
3D CAD has changed the approach to design of a model. It used to be that you'd start with overall drawings and work down to the details of the components (roof, body, trucks, details, etc..). Now it is pretty much the reverse..... you design details to assemble into a whole.
I almost brought the Kato factory manager to tears when I suggested that if the 2D drawings of a model were provided to us in advance of production we could work out the paint and lettering schemes.... which often uncover errors in placement of details (because a stripe or lettering doesn't line up right). The 2D drawings are generated from the very end of the 3D design process.... just before tooling is cut..... and it would have interupted the production process, even though it would have been a good final check.
Most of the importers are dealing with factories that use sophisticated 3D design. I know of a couple of companies that have 3D as part of their research packages before the factories get involved, but don't know what cost savings might be realized from such improved R&D packages other than any errors that are avoided.