Apparatus (2) for assembling a core (4) for receiving wound sheet material: which core (4) comprises a tube (6), a first end member (8) inserted in a first end (10) of the tube (6), and a second end member (12) inserted in a second end (14) of the tube (6); and the apparatus (2) comprising a base (16), first chuck means (18) mounted on the base (16) and for insertion in the first end member (8), second chuck means (20) mounted on the base (16) and for insertion in the second end member (12), a ram (22) mounted on the base (16) and for applying axial pressure on one of the first and the second end members (8, 12) such that the first end member (8) is forced into the first end (10) of the tube (6) and the second end member (12) is forced into the second end (14) of the tube (6) thereby to ensure that the first and the second end members (8, 12) are accurately fitted in the tube (6), first drill means (24) for drilling at least one fixing aperture in the first end (10) of the tube (6) and the first end member (8) thereby to enable the fixing of the first end member (8) in the first end (10) of the tube (6), second drill means (26) for drilling at least one fixing aperture in the second end (14) of the tube (6) and the second end member (12) thereby to enable the fixing of the second end member (12) in the second end (14) of the tube (6), and monitor means (28) for sensing ambient temperature and enabling the length of the core (4) to be measured at the time of the assembly of the core (4) in the ambient temperature and thereby to ensure that the length of the core (4) falls in temperature and length parameters set for subsequent winding of the sheet material on the core (4).