Steam locomotive manufacturing process (1930s)

[Lone Cat]

Here is a documentary video how a steam locomotive has been made. This one is british-made though so be prepared for different accent, different lingos, and different 'devices' you may not found in American ones.

http://www.youtube.com/watch?v=aHIEudnoRYU

The Creation of LMS 6207. This one is pacific-type with inside cylinders (Brits and Europeans were willing to fit ones to max out the locomotive speeds and powers, Americans don't because (they think) these things were unneccessary (and simple Walshaerts/Bakers with outside cylinders were sufficient), fitting ones added maintenance costs. Yet the Belpaire firebox also found its way to the New World! Many RR companies installed ones into their new engines.
During its heyday, Steam locomotives take some weeks to built, the manufacturing technique was considered 'modern' for that time (and interesting enough, British Industrialization doesn't completely 'remove' blacksmith crafts, it really 'displaced' blacksmiths from barn shops to huge, machine-powered foundries... yep that was before the first computers were invented), the process doesn't include 'testing' though.
But that was many decades ago. When CNC milling tools became available (thus made SMEs level machinery enterprises and specialized-built M1911A1 pistols available too!) Do sand mold steel castings and steam hammer neccessary to make a fleet of modern steam? (ones that can be manned by diesel-trained engineers with minimum switching costs). I don't know if DLM (Swiss manufacturer of modern steam locomotives) still uses old techniques to make the new engine? http://www.dlm-ag.ch/en/locomotives

Another fact is. locomotive driving wheels were cast with siderod joints.. but without counterweights. why? Does counterweight has to be inserted separately?

[Silverback]

As far as I know each wheel and set of wheels needs to be balanced separately by adding different amounts of lead to the balance weight boxes and this also needs to take into account the connecting rods and the coupling rods too - which may change in design. From what I've read its far more complicated than balancing a road vehicles wheels. Don't forget too that for a 2 cylinder steam loco the cranks are offset by 90 degrees and different amounts too for 3 and 4 cylinder locos (and sometimes its possible there can be a split drive where different cylinders drive different axles) so there may need to be some reciprocating forces to take into account too.