A machining device includes a support platform, a machining assembly, a clamping assembly, a driving assembly, and a controlling assembly. The support platform includes a first supporting member, a sliding rail mounted on the first supporting member, and a second supporting member mounted on the sliding rail. The machining assembly mounted on the second supporting member includes a machining tool. The clamping assembly is mounted on the first supporting member, for clamping and rotating the workpiece. The driving assembly is fixed to the second supporting member. The controlling assembly includes a connecting member mounted on the second supporting member and a resisting member mounted on the connecting member. The driving member drives the second supporting member to slide along the sliding rail, to make a gradual and increasing depth of contact by the machining tool on the workpiece, until a preset limit is reached.