[jacquesm]

Yes, this is a very good point. Access to good tools is essential to do this kind of work safely, you can have all the knowledge in the world, if you can't measure accurately, test your welds non-destructively, machine things without adding stresses that the material is ill equipped to handle and assemble properly then it is very easy to mess things up in a critical way. Miss an inclusion in a weld (which could very easily happen), have some vibration due to imbalance, a hairline fracture from metal fatigue and with a helicopter as your project it can only end in one way.