During　the　turning　process,　if　the　feed　rate　too　high,　or　the　feed　rate　too　large,　chattering　will　be　occurred.　The　variable　stiffness　tip　can　change　the　system　stiffness　during　the　machine　work,　so　as　to　increase　the　limit　depth,　but　the　stability　of　time-varying　systems　is　difficult　to　predict.　This　article　will　be　explained　in　as　follows:　Firstly,　in　this　paper,　the　turning　stiffness　is　studied,　and　the　turning　dynamics　model　is　established.　Secondly,　it　predicts　the　limit　depth　of　cut　by　changing　the　time　domain　model　parameters,　and　using　the　variable　stiffness　method　to　optimize　the　ultimate　depth　of　cut.　Finally,　verify　the　correctness　of　the　limit　depth　of　cut　through　experiments.　©　Published　under　licence　by　IOP　Publishing　Ltd.