From one of the people here that does RetroFits for a living here are a few points:
If the machine does not have usable motors and drives then it is definately worth going to one of the large companies, personally I prefer Mitsubishi over Fanuc, not necessarily because of the product (although it is comparable), because Mitsubishi are easier to deal with and phone support is really fast.
I have done Fanuc, Mitsubishi, Camsoft, plus many in-house designed stand-alone systems based around Acroloop and Galil.
For anyone considering using a package they have not used before, or have not done a retofit before, believe me, there is no quick way, there is going to be a learning curve, Most of this will be doing the machine interface, PLC/PMC R,S,T,M codes and tool changers etc.
The upside of using a complete package is that the CNC G codes & Canned cycles, etc, are already written, the motors and drives match the system and integration is minimal. This equates to Less time taken for the retro.
There are good systems like Fagor, which I believe still have the option of using your own drives, they are also a good company.
Mainly like anything else with CNC, you get what you pay for.
My 2¢.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.