Machining of large monolithic structures is becoming a standard in today’s aerospace world.  Driven by cost, as well as performance, it is becoming necessary to machine these parts better, faster, lighter and cheaper than ever before.  When machining these large monolithic structures, deformation becomes a large problem.  The typical solution to this problem is machine with lower than optimum material removal rates and do additional fixture rotations which adds unnecessary time and cost to the manufacturing process.  A Finite Element Model has been developed specifically to predict and control these distortions.  The model takes into consideration the machining induced residual stresses as well as the bulk stresses in the material from the manufacturer.  It is the combination of these two residual stress components coupled with the geometry of the part and type of material that allows us to accurately predict, manage and control the shape and magnitude of deformation in large thin walled structures.  The model can be used to determine the ideal cutting conditions for the process as well as determine the best location within the stock plate to machine the part from.  Multiple machining tests have been done in order to validate the accuracy of the model.  Being able to predict distortion will change how parts are machined.  Distortion prediction can be deeply integrated into the manufacturing process as far back as initial part design.