Цахилгаан хэрэгсэл гэж юу вэ?
In 1895, the German overtone made the world's first DC drill. The housing is made of cast iron and can drill a 4mm hole in the steel plate. Then a three-phase power frequency (50Hz) electric drill appeared, but the motor speed failed to break through 3000r/min. In 1914, electric tools drive...