Development of a Top/Bottom Chamfering Tool with a Clip Spring-Based Force Dip Mechanism

Conventional hole finishing requires separate drilling and top/bottom chamfering, and excessive insert pressure can leave scratch-type marks on the hole wall. This study develops a clip-spring-based tool that performs drilling and top/bottom chamfering in a single machining cycle, with the chamfer depth passively set by equilibrium between the hole-wall reaction and the restoring force of a replaceable clip spring. A dual-angle insert–clip-spring interface produces a non-monotonic force drop followed by a low-incremental-stiffness plateau, separating high-force burr engagement from lower-force hole passage. Four insert-geometry and spring-bottom-shape combinations were analyzed by nonlinear finite element analysis, and the two embossed-bottom cases were supported by compression tests. The dual-angle/embossed case showed a 72% Force Dip, which compression testing reproduced together with the low-force plateau, and one-step machining confirmed process feasibility. The measured hole-wall roughness decreased fourfold, from Ra 1.7 μm to 0.4 μm. These results demonstrate a passive geometric route to Force Dip generation and self-equilibrating depth setting under the tested condition.