Abstract: Disclosed is a balancer attachment for the spindle of a machining apparatus using two primary and secondary balancers operatively coupled so as to allow the primary balancers to take major part in balancing while an associated tool traverses a short distance, and allow the secondary balancers to take major part in balancing while the tool traverses a long distance. These balancers follow circular arcs to bring their weights in the direction which is opposite to the linear displacement of a tool-carrying slide, thereby maintaining equilibrium in the rotating mass.