text: 1. Field of the Invention
  The present invention relates to a structure for detachably mounting a horizontal drill head on a drill head of a machine tool such as a wood working machine.
  2. Description of Background Art
  In a conventional mounting structure, the detachable horizontal drill head is mounted on the drill head of the machine tool by securing the driving shaft of the horizontal drill head to the spindle of the machine tool as well as by securing the guide pin slidably inserted into the pin bore formed in the head case of the machine tool to the horizontal drill head. That is, the horizontal drill head is secured to the machine tool by the driving shaft and the guide pin slidable in the pin bore formed in the head case of the drill head of the machine tool.
  In such a manner, the detachable horizontal drill head can be mounted on the drill head of the machine tool when horizontal drill working is required and the mounted horizontal drill head can be vertically advanced toward and retracted from the work placed on the work table by the vertical actuation of the driving spindle of the machine tool.
  However, since the pin bore for slidably receiving the guide pin is formed in the bead case of the drill head of the machine tool, it is very expensive to form the pin bore with the required high accuracy of parallelism to the direction of sliding motion of the driving shaft of the horizontal drill head.
  Also in the conventional detachable horizontal drill head, since the pin bore is formed in the head case of the drill head, the size of the head case is necessarily increased and thus the overall size of the machine tool is increased.