while looking for maxwells in belfast, i saw your post. i needed a diversion as i'm at dead end, so used the national censuses advanced search option for blacksmith and maxwell.
there were a few, but the one below is the only one listed in belfast (ormeau, down). the ages are not appropriate, but it may be a link to what you are looking for:http://www.census.nationalarchives.ie/pages/1911/Down/Ormeau...
the others found in 1901/1911 searches using parameters down/antrim for maxwell and blacksmith show a family in the ballymena area and another outside of banbridge. both have a robt connection as well, if i remember correctly.
ages again not appropriate but also found an eliza/robt maxwell connection:
Name: Robert Maxwell
Birth Date: 26 May 1866
Birth Place: Belfast No 3, Ant, Ireland
Baptism Place: Belfast No 3, Ant, Ireland
Father's Name: George Maxwell
Mother's Name: Eliza Morrison
FHL Film Number: 101125
some belfast 3 streets include:
Clifton Park Avenue
Foyle Street (1891)
Joseph Street (1940)
Liffey Street (1895)
Upper Malvern Street (1902)
Upper Meenan Street
Oldpark Road (Lower)
Shannon Street (1929)
hope you find your connection!