A CNC machining center has a table-mounted referencing device having two pedestals, each separately engageable by a tool in a Z-axis drive tool holder to establish a zero reference for vertical machining operations on a work-piece mounted on the table. The first of the pedestals has a relatively soft top so that rapid Z-axis advance of the tool onto the pedestal will not damage the tool tip. A spring load on the pedestal also accommodates limited downward movement from a rest position for the pedestal to operate a Z-axis drive stop switch to further avoid tool damage and to save in the computer controller memory, the height of the tool tip from the table. The second pedestal is provided with a hard top so that when the tool tip is touched on it and moves the hard pedestal to operate the switch 34, the Z-axis drive recorder records in controller memory a number that is precisely related to the height of the tool tip from the table.