用钝刀切削很困难用钝刀工作起来很困难。钝刀只有在这样的情形下才可能工作:用强大的压力加在它上面。用钝锉刀工作起来非常困难,而且需要巨大的力量。完全不可能用钝锉刀去锉软而韧的金属——黄铜、铜等等。在锉这些金属的时候,钝锉刀会打滑,不能切入金属。要想锉软金属,必须用具有锋利刃口的锉刀;因此,新锉刀开始时是用来锉软金属的,后来才用它锉钢和铸铁。 Cutting with a blunt knife is difficult to work with a blunt knife. A dull knife may work only if it is under such conditions: apply strong pressure on it. Working with a blunt file is extremely difficult and requires tremendous power. It is quite impossible to file a soft and tough metal with a blunt file - brass, copper and the like. When filing these metals, the blunt file will slip and can not cut into the metal. To file a soft metal, a file with a sharp edge must be used; therefore, the new file was used to file soft metal at first, and later it was used to file steel and cast iron.