你要想你这块金属光滑，必须用锉刀不停地锉上几小时。

You have to file away for hours to get this metal smooth.

youdao

顺着他指的方向我们看到在界墙上有个锉刀头在一进一出地锉动，将砖头锯断。

There, on the outside wall, we saw the end of file, sawing in and out, cutting through the brick.

youdao