Gently drilling metal base for tall structure (7)
I believe the answer is:
steeple
'tall structure' is the definition.
'gently drilling metal base' is the wordplay.
'gently' becomes 'p' (musical abbreviation for 'piano', softly).
'drilling' means one lot of letters goes inside another (inserted letters drill through others).
'metal' becomes 'steel' (steel is a metal alloy).
'base' becomes 'e' (Euler's number - base of natural logarithms).
'p' going into 'steel' is 'steepl'.
'steepl'+'e'='STEEPLE'
'for' is the link.
(Other definitions for steeple that I've seen before include "Pointed church tower" , "Jack up this?" , "Tall tower with spire on top of church" , "Pet eels (anag)" , "point" .)