Inner expanding-tightening clamping device for main shaft box

The invention discloses an inner expanding-tightening clamping device for a main shaft box. The clamping device is used for clamping and locating the main shaft box when small holes are drilled in the main shaft box. The inner expanding-tightening clamping device comprises a clamp body in the shape of a horizontal plate. A locating pillar protruding downwards is arranged on the lower portion of the clamp body. A force application rod capable of moving axially is arranged on the axial line of the locating pillar. A floating steel ball is arranged below the driven end of the force application rod. A magnet is arranged in the steel ball. The steel ball is located in the center of the locating pillar. Plungers with the radial movement freedom degree are arranged in the locating pillar. The driving ends of the plungers are bevels and supported on the lower surface of the steel ball. The driven ends of the plungers penetrate into a big hole of the workpiece from the side of the locating pillar and are used for clamping the inner wall of the big hole of the workpiece. The lower portion of the clamp body is provided with a supporting nail used for locating the upper surface of the workpiece. The clamp body is provided with drill bit locating holes. After clamping, the small holes can be drilled through the multiple preset drill bit locating holes in the clamp body. Through the inner expanding-tightening clamping device, the main shaft box can be clamped stably.