Figure 5
Feed and rotation axes
in Cartesian coordinate system
Often further controllable feed axes are needed. These are then marked as U, V, W. Additionally there are
the adjustable rotation axes around which the machining table, head stock and tool holder can rotate independent
of the feed axes. They are marked as A, B and C.
The required tool and work part carriers are moved by feed drives. The feed drives meet the highest requirements
due to high machining and iteration precision. The individual axis movements must be carried out with
maximum feed speed and minimum positioning time. To meet these requirements a modern feed drive
(see figure 6) consists of the following components:
• motor, mechanical gears against overload as well as electronic control
• ball screw drive for power transfer free from play
• sensor as path measuring system, mostly located at the free end of the axis
• power amplifier with analog or digital interfaces for CNC control
For exact positioning the feed drives are connected with the measuring facilities. Each controllable axis of a
CNC machine needs a path measuring system with automatic interpretation of the measuring signal. The
most frequently used resolution for length measuring is 0.001 mm, however for the X axis of the lathe
(diameter dimension) 0.0005 and for the precision grinding machine up to 0.0001 are customary.