Automatic tool changers (ATCs) are devices used in CNC machine tools to exchange the tool in the spindle with the tool in the magazine. In this paper, the design of the ATC of a CNC horizontal machining center which was realized for a CNC machine tool manufacturer is introduced. After examination of several alternatives, it was decided to implement the disc-type ATC. A magazine was designed with 24 tools with a maximum tool diameter of 150 mm and a maximum tool weight of 8 kgf. The designed ATC can change the closest tool within 4 s and the tool farthest away within 6 s. (C) 1997 Elsevier Science Ltd.