Core Drilling Machine Having An Interchangeable Drill Bit

A drill bit for usage with a core drilling machine comprising:

• a housing;
• an hollow drill shaft extending substantially along an axial direction, which is supported in a rotational manner in the housing of the core drilling machine and which can be rotated by means of a drive unit;
• a coaxial tool holder for receiving a drill bit, which is supported in an axially displaceable manner, wherein the tool holder comprises a locking mechanism adapted for securing the drill bit, if the drill bit is inserted into the tool holder, in a radial direction against axially falling out, wherein the locking mechanism connects the drill bit in a rotationally fixed manner to the hollow drill shaft and allows a limited axial movement of the drill bit relative to the hollow drill shaft;
• a first spring element;
• wherein the hollow drill shaft is suitable for receiving a shaft of an interchangeable centre drill in the front of an interior, wherein the centre drill can be coupled to the hollow drill shaft in a rotationally fixed manner, wherein the centre drill can be moved axially in the hollow drill shaft in a limited manner and wherein the centre drill is axially supported against the first spring element;
• a stop element which in a first position prevents the centre drill from a complete axial displacement into the interior of the hollow drill shaft, which allows in a second position a complete axial displacement of the centre drill into the interior of the hollow drill shaft;
• an activation device for activating the first or second positions of the stop element as a function of an axial position of the drill bit relative to the hollow drill shaft, wherein the activation device comprises a sliding sleeve, which is arranged coaxially relative to the hollow drill shaft, and at least one axially extending connecting element;
• a second spring element, wherein the sliding sleeve is supported in an axially displaceable manner against the second spring element on the hollow drill shaft, and can be coupled to the interchangeable drill bit by means of the at least one axially extending connecting element;
• wherein the stop element is supported in a radially displaceable manner in an area of the hollow drill shaft where the sliding sleeve sits radially on an outside of the hollow drill shaft so that the stop element, in a relaxed state of the second spring element, is radially forced by the sliding sleeve towards the interior of the hollow drill shaft, thereby protruding towards the interior, and so that the stop element, in a compressed state of the second spring element, is movable radially to the outside by means of the centre drill when the centre drill penetrates axially deeper backwards into the hollow drill shaft behind the stop element;
• wherein the drill bit comprises at least one groove into which the locking mechanism engages in the inserted state of the drill bit so that the drill bit rotates synchronously, if the hollow drill shaft is rotated, and so that the drill bit is simultaneously supported in an axially displaceable manner relative to the tool holder.

A centre drill comprising a shaft having an axial length for usage with a core drilling machine and a drill bit, wherein the core drill machine comprises:

• a housing;
• an hollow drill shaft extending substantially along an axial direction, which is supported in a rotational manner in the housing of the core drilling machine and which can be rotated by means of a drive unit;
• a coaxial tool holder for receiving a drill bit, which is supported in an axially displaceable manner, wherein the tool holder comprises a locking mechanism adapted for securing the drill bit, if the drill bit is inserted into the tool holder, in a radial direction against axially falling out, wherein the locking mechanism connects the drill bit in a rotationally fixed manner to the hollow drill shaft and allows a limited axial movement of the drill bit relative to the hollow drill shaft;
• a first spring element;
• wherein the hollow drill shaft is suitable for receiving a shaft of an interchangeable centre drill in the front of an interior, wherein the centre drill can be coupled to the hollow drill shaft in a rotationally fixed manner, wherein the centre drill can be moved axially in the hollow drill shaft in a limited manner and wherein the centre drill is axially supported against the first spring element;
• a stop element which in a first position prevents the centre drill from a complete axial displacement into the interior of the hollow drill shaft, which allows in a second position a complete axial displacement of the centre drill into the interior of the hollow drill shaft;
• an activation device for activating the first or second positions of the stop element as a function of an axial position of the drill bit relative to the hollow drill shaft, wherein the activation device comprises a sliding sleeve, which is arranged coaxially relative to the hollow drill shaft, and at least one axially extending connecting element;
• a second spring element, wherein the sliding sleeve is supported in an axially displaceable manner against the second spring element on the hollow drill shaft, and can be coupled to the interchangeable drill bit by means of the at least one axially extending connecting element;
• wherein the stop element is supported in a radially displaceable manner in an area of the hollow drill shaft where the sliding sleeve sits radially on an outside of the hollow drill shaft so that the stop element, in a relaxed state of the second spring element, is radially forced by the sliding sleeve towards the interior of the hollow drill shaft, thereby protruding towards the interior, and so that the stop element, in a compressed state of the second spring element, is movable radially to the outside by means of the centre drill when the centre drill penetrates axially deeper backwards into the hollow drill shaft behind the stop element;
• and wherein the drill bit comprises:
• at least one groove into which the locking mechanism engages in the inserted state of the drill bit so that the drill bit rotates synchronously, if the hollow drill shaft is rotated, and so that the drill bit is simultaneously supported in an axially displaceable manner relative to the tool holder.