Objects which are cast or forged so that only a very little filing will reduce them to the required dimensions, must be properly treated previous to filing, to avoid an unnecessary waste of files through rubbing them upon the hard sandy surfaces of the work. A piece which is too small for chipping should have its hard skin removed by holding it to a grindstone; and if the object is too small to be held in the hands, it is held either with tongs, bolts and plates, or with a lathe-chuck. After grinding, the filing proceeds in an easy manner, because the clean surface of the metal is exposed to the file. Objects having irregular surfaces can be only partly ground with the stone; and small pieces of such shapes may have their surfaces entirely cleansed from sand, if required, by allowing them to remain a few hours in sulphuric acid and water, which is provided in a proper vessel of suitable length and depth. This treatment allows the acid to slightly corrode the metal and remove the sand at the same time.

To avoid an unnecessary consumption of rough files, they are first used for filing brass and gun-metal, for which the files are suitable while their teeth are sharp. They are next applied to clean cast iron and forged iron; and when found to be blunted by these comparative soft metals, the files are applied to steel, and will then cut without being so liable to break their teeth as when they were new and sharp.