An old style of wood boring bit, the auger drills deep holes across the grain of boards and beams without wandering. Designed for the manually powered bit brace and for a number of boring machines which now exist only as antiques, Jennings auger bits are important to any carpenter who occasionally works away from a constant electrical source. The Irwin auger converts the old design to use in power drills.
The Jennings auger is a uniform steel spiral around a central shaft, ending in a conical threaded tip and with two cutting edges. Each cutting edge has a sharp flange which scores the wood just ahead of the blade. When the bits are properly sharpened, the Jennings auger efficiently cuts a very clean edged hole. Wood shavings are propelled up the shaft by the spiral. The Irwin pattern has one cutting edge. Still led into the wood by the threaded tip, this power auger cuts fast but not so clean as the older style.
Other common drill bits may do rough work, but can be deflected by tough wood grain patterns. This makes them inappropriate for truly deep holes--which is the best application of the auger bit. Often used in mortising, auger bits flex very little and clear waste shavings quickly. While a twist drill might have to be withdrawn and cleaned several times in the course of drilling one hole, an auger often cuts the entire distance on one pass.
In timber frame construction, cutting deep mortises requires quick removal of waste wood. The old tools still find practical application in this popular style of construction. Auger bits as large as four inches in diameter can still be found. With horizontal handles designed for manual twisting, using these larger auger bits can still be faster than drilling multiple smaller holes with power drills. Older manual machines like the beam brace--designed for heavy auger work--are now rarely seen.
Augers must be sharp and balanced for the bit to cut efficiently and accurately. A dull auger may break or simply jam in the hole. Once the auger stops rotating, it may be impossible to withdraw.
In cramped spaces where power drills won't fit, a bit brace often will. The ratcheting handle drives the bit even in situations where a full turn isn't possible. Auger bits cut clean, large holes appropriate for running pipe, as well as for traditional mortising applications. Augers quickly remove waste wood from mortises; mortising chisels finish the work.