Device for making a drilled hole with an undercut

In a device for producing a drilled hole with an undercut, comprising a drilling tool having a shank and a drilling head faced with a plurality of diamond chips, said drilling tool having an axial continuous bore therethrough, a drilling tool-holder structured to hold the drilling tool and a rotatable sleeve arranged on the drilling tool-holder and provided with a connecting opening for a cooling and flushing liquid, said continuous bore communicating with said sleeve so that portions of said cooling and flushing liquid introduced into said sleeve through said connecting opening can flow down toward said drilling head through said continuous bore, the improvement wherein the shank (2') of the drilling tool (2) is provided with a stop collar (12) for arresting motion of the drilling tool and also a cross-sectionally enlarged portion (17) located between the drilling head (11) and the stop collar (12), the shank of the drilling tool (2) tapering toward the drilling head (11) from the enlarged portion (17) and also tapering toward the stop collar (12) from the enlarged portion (17), and wherein the shank is provided with a plurality of longitudinally extending grooves (21) at least in the vicinity of the enlarged portion (17), the enlarged portion having a diameter approximately equal to a diameter of the drilling head.