The invention relates to a core drill with an end portion (3) and a drill bit portion (1-2). The end portion and the drill bit portion are joinable in a watertight fashion with a sealing element (11). The sealing element (11) is provided in a space between the end portion and the drill bit portion, such that it is being compressed in a sealing fashion when the end portion and the drill bit portion are joined. The end portion and the drill bit portion are locked together with a joining element (8, 10) which achieves this locking effect when moves in the radial direction of the core drill. When the joining element moves in this direction, the end portion and the drill bit portion move towards each other. Thus the sealing element is being compressed while concurrently the end portion and the drill bit portion are joined together. This is further achieved without the joining element having to extend in the axial direction of the core drill. Typically, the joining element (8, 10) is constituted by a set screw.