Originally Posted by
megan
I'm on the road at the moment so unable to give the exact difference between UK and US drawing standards, but the change was to bring the drawings into line with US engineering practice. Of course Packard also introduced their own mods, supercharger drive, mags and pressure carb that didn't cut out with -ve "g". One major issue facing Packard was having to manufacture dies, taps etc in order to keep the British threads on screws, nuts etc, which led to some delay in the program.
The main difference is the UK, and most of the rest of the world, uses first angle projection and the US uses third angle projection. I had to look that up - it's nearly 45 years since I had to make something from an engineering drawing so don't ask me to explain the difference now! I did know...
As I said, I've no idea if Packard based their drawings on Ford's or RR's but since there was already a set in existence with mass production tolerances it would seem a bit daft to start again. Time was short and according to Hooker it took Ford a year.
IIRC, Packard didn't want to make their own taps and dies but nobody else had the capacity so they were left with little choice.