When a wheel clamp is used, width of a wheel is detected first, a first servo motor drives a lead screw to rotate, a supporting block and a lifting plate are automatically adjusted to appropriate heights via a nut, a manipulator puts the wheel onto end face blocks, air-tight devices are pressed down, an oil cylinder drives a chuck so that clamping jaws expand the central hole of the wheel, meanwhile, four air cylinders drive clamping blocks to compact outer side of the wheel, and the wheel is completely positioned; at this moment, a bolt hole of the wheel can be drilled; after machining, second servo motor drives right shaft, right lug plate and a turnover part to rotate certain angles via second decelerator; high pressure oil is introduced into cavities between ipsilateral expansion sleeves and end covers, and left and right shafts are separately locked by ipsilateral expansion sleeves.

A work holder includes: a first holding part having three attracting members that are arranged circumferentially apart from each other to attract an axial end face of an annular work; and a second holding part having a contacting member that is held in contact with an inner periphery or outer periphery of the work and restricts radial movement of the work.

When a wheel clamp is used, width of a wheel is detected first, a first servo motor drives a lead screw to rotate, a supporting block and a lifting plate are automatically adjusted to appropriate heights via a nut, a manipulator puts the wheel onto end face blocks, air-tight devices are pressed down, an oil cylinder drives a chuck so that clamping jaws expand the central hole of the wheel, meanwhile, four air cylinders drive clamping blocks to compact outer side of the wheel, and the wheel is completely positioned; at this moment, a bolt hole of the wheel can be drilled; after machining, second servo motor drives right shaft, right lug plate and a turnover part to rotate certain angles via second decelerator; high pressure oil is introduced into cavities between ipsilateral expansion sleeves and end covers, and left and right shafts are separately locked by ipsilateral expansion sleeves.

A work holder includes: a first holding part having three attracting members that are arranged circumferentially apart from each other to attract an axial end face of an annular work; and a second holding part having a contacting member that is held in contact with an inner periphery or outer periphery of the work and restricts radial movement of the work.