Joined up and served? Not I (8)
I believe the answer is:
soldered
'joined up' is the definition.
(solder means to join together)
'served? not i' is the wordplay.
'served?' becomes 'soldiered' (served in the army).
'not' indicates named letters should be taken away.
'soldiered' with 'i' taken away is 'SOLDERED'.
'and' acts as a link.
(Other definitions for soldered that I've seen before include "Joined with metal alloy" , "stuck together" , "Joined metals by melting alloys" , "Joined metals using soft alloy" .)