Filing. It is of great importance that the saw be properly supported during the operation of filing. An unusual amount of noise shows that the blade is not properly clamped, or that the file is not being properly handled; it is also a sure indication that the filing is not going on as fast as it might, and that the file is being injured. If the file is new, let the pressure be very light. Carry it across the work with a slow, steady movement. Never take short, quick strokes, as but little will be done in this way, and the file will suffer beyond repair. In filing a ripping-saw, the movement should be exactly perpendicular to the plane of the blade, as indicated by plan, Fig. 81, and the outline of the teeth maintained by an even contact, as shown by the elevation in the same figure. But if the form of the teeth is to be changed, the file must be turned either in the direction indicated by the arrow, Fig. 81, or in the opposite direction.

In filing a cross-cutting-saw, the angle between the file and the blade must be varied in accordance with the following considerations: first, the outline of the teeth may be preserved or changed in the manner just described in connection with the ripping-saw; secondly, the angle of the advancing face (e'ef, Fig. 64) is determined by the inclination of the file to the blade, as shown by the plan, Fig. 82; thirdly, the angle of the point (iaj, Fig. 64) is determined by the inclination of the file to the blade, as shown by the end elevation, Fig. 82. The form of the teeth having been decided upon from principles already given, it may be produced without difficulty by attending to the foregoing directions.

Fig. 80

Elevation.

Plan.

Fig. 81

Elevation.

Plan.

In filing any of the teeth herein discussed, the file should always be in gentle contact with the face of one tooth, as b, Fig. 81, while most of the cutting is done on the back of the next one a, which, as usually considered, is the tooth that is being filed. This tooth should be one which, by its set, bends away from the operator. Beginning at one end of the blade, he files every second tooth until the opposite end is reached, when the blade is turned, and the remaining teeth filed from the other side.

No saw, even though the teeth are not bent, should be filed wholly from one side, for the file turns a slight edge, or bur; and, since this increases the set, it should be evenly distributed on both sides of the blade.

The filing on each tooth should continue until the facet produced by the jointing disappears. After this is accomplished, a single stroke will make the tooth receiving it lower than the others. To avoid this, it will be found best to leave the teeth filed from the first side a little dull, for, in filing the intermediate teeth after the saw has been turned, the advancing faces of the others (the teeth first filed) are somewhat reduced. After every tooth has been passed over, if dull points are still to be seen, they may be sharpened from either side as their proportions may dictate. Regularity in the size and form of the teeth, and a similarity of appearance when viewed from either side of the blade, are the tests of good workmanship.

Plan.

Fig. 82

Side Elevation.

End Elevation.