Figure 1-22.—Polishing operations

the surface has been filed flat. Test the flatness with a straightedge or with prussian blue and a surface plate. DRAWFILING.—Drawfiling produces a finer surface finish and usually a flatter surface than crossfiling. Small parts, as shown in view C, are best held in a vise. Hold the file as shown in the figure; notice that the arrow indicates that the cutting stroke is away from you when the handle of the file is held in the right hand. If the handle is held in the left hand, the cutting stroke will be toward you. Lift the file away from the surface of the work on the return stroke. When drawfiling will no longer improve the surface texture, wrap a piece of abrasive cloth around the file and polish the surface as shown in figure 1-22, view A. USE OF FILE CARD.—As you file, the teeth of the file may "clog up" with some of the metal filings and scratch your work. This condition is known as PINNING. You can prevent pinning by keeping the file teeth clean. Rubbing chalk between the teeth will help prevent pinning, too, but the best method is to clean the file frequently with a FILE CARD or brush. A file card (fig. 1-23) has fine wire bristles. Brush with a pulling motion, holding the card parallel to the rows of teeth. Always keep the file clean, whether you're filing mild steel or other metals. Use chalk liberally when filing nonferrous metals. FILING ROUND-METAL STOCK.—Figure 1-21, view D, shows that as a file is passed over the surface of round work, its angle with the work is changed. This results in a rocking motion of the file as it passes over the work. This rocking motion permits all the teeth on the file to make contact and cut as they pass over the work's surface, thus tending to keep the file much cleaner and thereby doing better work. POLISHING A FLAT-METAL SURFACE.— When polishing a flat metal surface, first draw file the surface as shown in figure 1-21, view C. Then, when the best possible drawfiled surface has been obtained, proceed with abrasive cloth, often called emery cloth. Select a grade of cloth suited to the drawfiling. If the drawfiling was well done, only a fine cloth will be needed to do the polishing. 1-16 Figure 1-22.—Polishing operations. Figure 1-23.—File card/brush cleaner.