The auger bit is one of the most delicate tools in the woodworker's kit. It must be of high-grade manufacture to begin with; even so, it will stand little abuse, and if it is not kept in first-class condition there is no pleasure in using it.
Cutting into nails with a bit is probably the most common cause of damage. In many instances, however, a bit that has apparently been ruined can be restored by proper treatment.
Auger bits of various types may be had for different kinds of work, but the principal specification in which the average user is interested concerns the speed with which the bit is drawn into the wood. The boring speed depends upon the pitch or twist of the thread at the screw point. In this regard auger bits usually are classified as slow screw, medium screw, and fast screw. For all ordinary work the medium screw is most satisfactory, but it is well to get advice from the tool dealer before making the purchase.
Fig. 3. - An auger bit file and the cutting end of a typical bit. showing screw point, spurs, and lips.
It is well to remember also that the original cost of an auger bit, or any other tool, is not the sole consideration, but that it is more important to obtain a tool that will "stand up" and give satisfactory service.
There are three principal parts of the auger bit (Fig. 3) that may receive injury through contact with foreign substances in the wood - (1) the screw point (the screw that feeds the bit); (2) the lips (horizontal cutting surfaces); (3) the spurs (vertical cutting edges). All of these can be reconditioned, provided the damage done has not been too great.
Fig. 4 (above). - How the lips of the bit are sharpened on top by means of an auger bit file.
Fig. 5 (at right). - Filing the spur on the inside. To tile the outside would ruin the bit.
For sharpening auger bits, either a file or a small sharpening stone may be used. A suitable file is one about 4 in. long, very fine cut ("dead smooth"), and half round in shape. It is better, however, to use a special auger bit file (Fig. 3), which can be obtained in any large hardware store. Such a file is made with "safe" edges adjacent to the cutting surfaces, and there is no danger of filing in the wrong place.
The lips are filed or sharpened with a stone on the top side, the bit being held in the position indicated in Fig. 4. The edge must be kept thin, and filing should not be carried beyond the point wh a fine wire edge or burr appears. If small sharpening stone is available, it should be used for a very light stroke or two on the underside of the lip in order to remove the wire edge; if no stone is at hand, the file may be used for the same purpose. For this delicate operation, the bit is turned with the spurs upward and laid against the edge of the workbench. Care must be taken not to file too much and to follow the original surfaces.
The spurs are sharpened with the bit in the left hand and held against the edge of the bench as shown in Fig. 5. It should be kept in mind that the spurs must be long enough to cut deeper into the wood than the lips when the bit is in operation, hence no wasteful strokes should be made at this point. If they are worn too short, the lips probably can be filed back in order to relieve the difficulty. Needless to say, all filing on the spurs must take place on the inside, except the smoothing up or removing the burr, as previously described.
Sometimes, after striking a nail at a certain angle, the spurs are bent inward very decidedly. In such cases, instead of removing all the distorted metal with the file and thus losing a large part of the nibs, it is possible to reshape the bit by ending the point back into position with i pair of small pliers. In doing this care must be taken not to break off any part.
After the tip is put into position, it is sharpened in the usual way.
The screw point is probably the most difficult part to put into condition after it has been injured. Patient work with a special oilstone having a very thin edge as shown in Fig. 6 will usually give satisfactory results. If considerable injury has been received at this point, the bit may afterwards require a slight pressure to assist the screw in feeding; but since that requirement can be met with in all ordinary work, its efficiency is not materially reduced.
Fig. 6. - Doctoring the screw point with an oilstone (usually called a "slip") that has a thin edge.
Fig. 7. - To straighten a bit, lay it on a hardwood block and drive another block heavily against it with a hammer or mallet.
An auger bit which has been bent out of shape may be straightened as in Fig. 7. A block of wood, preferably some hard variety, is used as a support, and a wooden block, held on end, makes contact from above. A smooth-faced wooden mallet may take the place of both hammer and block. A good way to test an auger bit for straightness is to lay it on a straight surface and revolve it slowly while watching for irregularity in the space between the bit and the surface at various points.