Fig. 2242.
Suppose, for example, that a piece of work requires filing in the middle of its length and half way along its width and half along its length, and a well bellied file may be balanced upon c, [Fig. 2242], and grasped at its two ends a and b, and used with strokes of a sufficient length to file half the work length as required.
In draw-filing the file should be pressed to the cut on the pushing stroke only, and not on the return or pulling stroke.
Draw-filing produces with a given cut of file a smoother surface than cross-filing, but it will not remove so much metal in a given time.
In draw-filing short strokes will produce better work than long ones, because with the latter the file cuttings are apt to become locked in the teeth of the file, and cut scratches in the work. This is called pinning, and the pins cutting deeper than the file teeth produce the scratches.
To avoid this pinning the file surface may be well chalked, which will at the same time cause the file to cut smoother although not quite so freely. It is necessary, however, to clean the file after every ten or twelve draw-filing strokes so as to remove the filings. This removes the chalk also, hence it requires occasional renewal. For this purpose lumps of chalk are employed, but great care is necessary in its selection, because it sometimes contains small pieces of flint or other stones, and these score and greatly damage the file teeth.
To dislodge the chalk and filings the file surface may be rubbed two or three strokes with the hand, and the file lightly tapped on the vice back. But it will also be found necessary to occasionally clean the file with a file-brush or file-card. The file-card is brushed across the width of the file so that the wire may reach the bottoms of the rows of teeth and clean them out.
