Abstract: Apparatus for facilitating drilling or similar machining operations upon a workpiece, the apparatus including a vertically directed vee shaped recess (15) for interchangeably receiving and centring tool guide arrangements (18) for the tools required to be used for machining the workpiece; and means (19) for cramping a selected tool guide arrangement (18) against the mutually inclined faces of the vee shaped recess (15); and with a vee shaped recess (14) whose apex (17) is directed transversely of the apex (16) of the vee shaped recess (15) and intersects the apex (16) of the vee shaped recess; a workpiece support means (26) mounted for displacement towards and away from the vee shaped recess (14) in such manner that a workpiece (27) placed upon the workpiece support means (26) can be brought into firm contact with the faces of the vee shaped recess (14), and means for positionally locating a workpiece upon the workpiece support means (26).