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1895, German overtone made the world's first DC electric drill. The shell is made of cast iron and can drill 4mm holes in the steel plate. A three-phase power-frequency (50Hz) electric drill followed, but the motor speed failed to break through the 3000r/min. 1914, the emergence of single-phase series of motor-driven electric tools, motor speed up to 10000r/min above. 1927, the emergence of a power supply frequency 150~200hz medium frequency electric tool, which has the advantages of high speed of Single-Phase series Motors, but also has three-phase power-frequency motor structure simple, reliable advantages, but the need for medium-frequency current supply, use is limited.