Machine tool

A method of controlling the position of a machining tool relative to a workpiece mounted on a worktable itself slidable in a straight line along a worktable axis (the Z axis) relative to a machine bed, in a direction generally perpendicular to the direction of movement of the machining tool, comprising mounting a reference straight edge to the worktable and for cooperation with sensing means fixed to the machine bed and located so as to be generally opposite the point of application of the machining tool, for determining any non straight line movement of the worktable, storing a calibration signal in the form of a look up table for a plurality of positions of the worktable along the Z-axis;

• generating an error signal indicative of any non straight line movement of the worktable;
• adjusting said error signal using the stored calibration signals;
• mounting a tool position indicating means at the same height as the sensing means and in line with the X-axis, adjusting a signal defining the target position for the tool along the X-axis (or the feedback signal for the tool position indicating means indicating the actual position of the tool), by the adjusted error signal, thereby to cause tool positioning means to position the tool relative to the worktable and any workpiece positioned thereon taking into account errors affecting the accuracy of the tool position relative to the worktable axis such as yaw or roll or non parallelism of the straight edge to the Z-axis.