I need information about a tool set block. I have seen only one in operation. The one I'm speaking of is, a block of Alum. with a wire attached to it and set to ground point. When setting the Z axis the tool is joged to meet it, and when it does, the tool and the axis stops so that the tool is at the same height as all the rest. Is there a real simple way to make one or is it a buy only accessory??