The MILWAUKEE-MATIC II, introduced by the Kearney & Trecker Corporation in 1959, was the first machine offered commercially with automatic tool changing. The machine included a tool storage magazine that carried a selection of tools for insertion into the rotary spindle. All movements of the machine were under numerical control.

The tool storage magazine rotated the selected tool into a tool change station. A double grip tool change arm then rotated into engagement with the selected tool at the tool change arm moved axially to extract the two tools from the magazine and spindle, respectively, rotated 180 degrees to interchange the positions of the two tools, and then moved axially to insert the previously used tool into the magazine and the new tool into the spindle. The new tool was automatically locked in the spindle or the performance of the next machining operation and the tool change arm moved into a parked position.

The numerical control circuit designated the tool to be used in the next machining operation. All of the tool holders were provided with code rings, which identified the tools. As the magazine rotated the tools in a circle, the code rings actuated a plurality of switches to individually identify the tools, and when the selected tool was identified, it moved into the tool change station for transfer to the spindle by the tool change arm.

Automatic tool changing and numerical control rendered the machine tool fully automatic and constituted an outstanding advance in machine tool design. It greatly reduced the amount of human labor needed in machining operations and resulted in very substantially reducing error in machining.

Because the machine was capable of performing a variety of machining operations on a workpiece, decreased the requirement to move workpieces from one machine to another in completing its manufacture. This also resulted in reducing inventory inasmuch as it lessened the lead-time for parts manufactured in this manner.