Mechanical fixed-size machine

The invention provides a mechanical fixed-size machine. The fixed-size machine comprises bases, rails arranged on the bases, a fixed-size trolley, transmission racks, a detection rack, transmission gears, a detection gear and an encoder. The fixed-size trolley at least comprises a trolley body. The transmission racks are arranged on the bases and on the outsides of the rails. The detection rack is arranged on the base and on the outside of the rail and disposed above the transmission racks and parallel to the transmission racks. The transmission gears are arranged on the trolley body of the fixed-size trolley and meshed with the transmission racks. The detection gear is arranged on the trolley body of the fixed-size trolley and meshed with the transmission rack, and the detection gear is arranged above the transmission gears. The encoder is arranged on the detection gear. By means of the machine, the fixed-size accuracy is improved.