In this talk I will discuss our current research on the chatter instability in drilling. Chatter is a self-excited oscillation between the machine tool and the workpiece that limits productivity of machining operations, reduces the quality of the product and shortens machine tool life. Up until recently all models of chatter have been linear, with delay effects

in the case of regenerative chatter. These models only partially explain the instabilities observed in the machining process.

In aircraft manufacture drilling is a critical machining process: over a million holes may be drilled in the creation of a commercial passenger jet. To address the problem of chatter in drilling, we are developing a suite of nonlinear models of metal cutting that can be merged with finite element studies of drill vibration modes and informed by large scale of

simulations of metal cutting operations. Typically, engineering studies of chatter have restricted themselves to the question of linear stability of a steady cutting solution; in addition to that we are studying the effects of the nonlinear terms in the model on the resulting dynamics. Ultimately contact will be made with laboratory results from experiments conducted in Seattle and St. Louis, with the goal of directing tool design and allowing machine operators to avoid chatter regimes in drilling.