Method of operating a numerically controlled machine tool having a worktable capable of rotation about two intersecting axes

In a numerically controlled machine tool of the kind having a tool mounted to a spindle for movement therewith along an x axis extending horizontally, a y axis extending vertically, and a z axis extending horizontaly and at right angles with the x axis, the tool being rotatable with the spindle about an axis parrel to the z axis, a worktable disposed forwardly of the tool in the direction of the z axis and revolvable both about a fixed axis A set at 45 degrees with respect to the horizontal in the z-y plane and about its own axis B set at 45 degrees with respect to the axis A in the same plane, and numerical control means for controlling the movement of the tool along the x, y and x axes and for controlling the rotation of the worktable about the axes A and B, a method of creating holes in two predetermined different positions on, and in a direction perpendicular to, a sloping surface of a workpiece on the worktable, which method comprises the steps of:

• inputting into the numerical control means coded data concerning the angle .theta. of the sloping surface of the workpiece on the worktable relative to the axis B, the distance h between the intersection O of the axes A and B and the intersection of the axis B with the axis of rotation of the tool being held perpendicular to the sloping surface of the workpiece in one predetermined position thereon where the first hole is to be formed, the distance l between the sloping surface of the workpiece and a plane parallel to the sloping surface of the workpiece and passing through the intersection O of the axes A and B, and the positional relationship (m, n) between the two predetermined positions on the sloping surface of the workpiece where the holes are to be formed,
• programming the numerical control means to put out instructions for rotating the worktable about the axis A through an angle defined as
• Ao=cos.sup.-1 (1-2 sin .theta.)
• and for positioning the tool at a point given by ##EQU18## machining the first hole in one predetermined position in the sloping surface of the workpiece,
• further programming the numerical control means for positioning the tool at another point displaced m and n along X and Y axes from the point (x, y), the X and Y axes constituting a coordinate system at an angle ##EQU19## with respect to a coordinate system of the axes x and y, and machining the second hole in the sloping surface of the workpiece.