Prompted by
SAS's last post I got to thinking about what gearboxes internals involve. Hats off to the engineers/designers/manufacturers. Shakespeare in "As You Like It" wrote "And thereby hangs a tale", in the case of gearboxes, thereby hangs a tail - yours and mine.
https://www.geartechnology.com/issue...x/Involute.pdf
https://ntrs.nasa.gov/archive/nasa/c...9860005142.pdf
http://www.dtic.mil/dtic/tr/fulltext/u2/a257727.pdf
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADP000703