Machine tool main shaft speed changing box

The invention relates to a machine tool main shaft speed changing box which comprises a box body, an input shaft and an output shaft. The input shaft is fixedly connected with a main input gear. The output shaft is fixedly connected with a main output gear. A speed changing group comprises a clutch, a hollow shaft and a solid shaft. The upper portion of the hollow shaft and the lower half side of the clutch are fixed. The lower portion of the hollow shaft is fixedly provided with a hollow shaft gear meshed with the main input gear. The upper portion of the solid shaft is fixedly connected with the upper half side of the clutch. The lower portion of the solid shaft is provided with a solid shaft gear meshed with the main input gear. The solid shaft is connected into the hollow shaft in a sleeved mode through a bearing, and the solid shaft and the hollow shaft are coaxial. Transmission chain rigidity is improved, the service life of the gears and a supporting bearing on a shaft is prolonged, the cavity size in the speed changing box is reduced, so that a gear box is stable, the design of an inner-outer sliding spline in the transmission main shaft speed changing box is avoided, the machining difficulty of the shaft gears is lowered, and reliability is improved.