Damn, sorry to say E3D, but every time I see those hotends I can't help disliking that design and wanting to invent something better.
It just feels so much like the cheapest thing possible to manufacture on simple machines, usability and ease of doing repairs really comes second, sorry to say again.
My colleagues asked me so many times now if we can somehow fit the UM2 hotend on the Delta Tower that I am actually considering to do that..
Regarding the original E3D nozzles I believe they were made with that two step design only because that was the cheapest way to make them (two standard drills).
Carl actually started off more or less copying that design, but after some discussion we decided to make our own design (the jet nozzle).
It was kept compatible with the E3D outer dimensions but has that cone inside instead among other changes.
To be completely honest, the only research I did was to look up all other designs available, test as many as possible and combine that with my experience to get some reasonable dimensions
The 60 degree angle seems to be common among manufacturers and is a suitable choice if you want to get away reasonably cheaply regarding tooling.
E3D actually continued remarkably long with their two step design, considering all competitors had the cone shape from start, even though the two step design seems to work quite well too.
And the full metal hotends with PLA, well maybe it works with a really powerful direct feeder and 1.75 mm filament, but with bowden and 3 mm filament at least I am unable to get it to work reliably. A thin PTFE liner inside the E3D hotend made it work like a charm though
