In this study, an experimental investigation of chatter vibration frequency in CNC turning of AISI 4340 Alloy Steel material was carried out, with uncoated carbide tool insert (TPG 322) on Fanuc 0i TC CNC lathe machine, with two boundary conditions. The experimental design adopted for this study is the Taguchi parameter design with L9 orthogonal array. Turning tests were carried out on nine samples of the test-piece material for the clamped-free (C-F) condition, and the tests replicated on another set of nine test-pieces for Clamped-Pinned, so-called C-SS workpiece boundary condition. Chatter vibration frequencies were measured using MXC-1600 digital frequency counter and the frequency plots continuously analysed through DTO 32105 sound signal and frequency analyzer. The main objective is to investigate the process parameters’ performances on the work-piece material of AISI 4340 alloy steel, and to carry out comparisons between the two different boundary conditions vis-à -vis the effects of process parameters which are cutting speed, feed rate and depth of cut on the chatter vibration frequency for the orthogonal turning operation. Chatter vibration frequency values for the C-SS scenario were found to be up to 30% lesser when compared to the C-F machining scenario. Introduction of the tailstock used in pinning the free-end of the slender work-pieces reduced the chances that workpiece would bend; whereas absence of the pinned end means that workpiece may be skewed at an angle in the chuck with increased dynamic deflections at the free end leading to more aggressive workpiece and cutting tool perturbations which are known to favour cutting instability.