Maybe private bar one gets to join (6)
I believe the answer is:
solder
'join' is the definition.
(soldering is a kind of joining)
'maybe private bar one' is the wordplay.
'maybe private' becomes 'soldier' (private is a type of soldier).
'bar' suggests deleting specific letters.
'one' becomes 'i' (Roman numeral).
'soldier' with 'i' taken out is 'SOLDER'.
'gets to' acts as a link.
(Other definitions for solder that I've seen before include "Melted alloy, used to join two metal surfaces" , "Soft alloy used to cement metal parts" , "Soft alloy used to cement metals" , "Metal bond" , "Join two metal surfaces, using an alloy" .)