thereafter machining said end faces on said blank while orienting said machining operation by {TAIL ~ use} of {HEAD ~ the previously formed opening} of said rotor means; and 
thereafter machining said end faces on said blank while orienting said machining operation by { TAIL ~ use } of { HEAD ~ the previously formed opening } of said rotor means ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH