In the finishing process of turninglarge pitch thread

the system vibration causes the instantaneous change of thecontact relationship between the tool and workpiece The axial change of thetool and workpiece contact relationship causes the thickness of the cuttinglayer to change

which is the cause of the instantaneous cutting force In thispaper

the ratio between vibration displacement and instantaneous cutting forceis used to describe the dynamic flexibility of the cutting system andcharacterize the stability of the large pitch thread system The vibration andcutting force signals are processed by using wavelet packet decomposition andreconstruction

wavelet packet denoising and curve fitting The method forobtaining the dynamic flexibility of the cutting system can quickly andaccurately represent the relationship between the vibration displacement andthe instantaneous cutting force

and judge the system stability in the cuttingstroke