Regenerative chatter is a well-known form of self-excited vibration that limits the productivity of machining operations, in particular for milling. Variable helix tools have been previously proposed as a means of avoiding regenerative chatter, and although recent work has analysed the stability of such tools there has not always been a strong agreement with experimentally observed behaviour. Furthermore, the analysis of variable helix tool stability can be tedious and numerically slow, compared to standard tools. Consequently it has been difficult to gain insight into the potential advantages of variable helix tools. The present work attempts to address these issues, by first developing an efficient approach to variable helix tool stability based upon the Laplace transform. Then, this new analysis method is used to demonstrate the importance of multi-frequency effects and nonlinear cutting stiffness. The work suggests that whilst variable-helix tools can have more operating regions that are stable, un-modelled behaviour (such as nonlinearity and multi-frequency effects) can have a critical influence on the accuracy of model predictions.
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