Abstract: An apparatus for connection to a machine tool having a rotating head and a fixed part is capable of automatically moving a cutting tool radially while a spindle carrying the cutting tool rotates. The apparatus includes a body which is engageable to the tool machine so as to remain fixed with respect to a central axis. A spindle is rotatably mounted to the body and is connected to the head of the tool machine for rotation. A slide holder is fixed to the spindle and carries a toolholder for sliding movement in a radial direction with respect to the central axis. An electric motor is mounted in the non-rotating body and drives a gear train which can radially move the toolholder while the spindle, slide holder and toolholder rotate. A position transducer is engaged with the electric motor for determining its position and thus the position of the toolholder on the spindle.