Auger Bits

Auger bits

The cutting principles of the auger bit are the same as those of the center bit. The auger adds a long deep spiral flute for effective chip removal.

Two styles of auger bit are commonly used in hand braces: the Jennings or Jennings-pattern bit has a self-feeding screw tip, two spurs and two radial cutting edges. This bit has a double flute starting from the cutting edges, and extending several inches up the shank of the bit, for waste removal. This pattern of bit was developed by Russell Jennings in the mid-19th century.

The Irwin or solid-center auger bit is similar, the only difference being that one of the cutting edges has only a “vestigal flute” supporting it, which extends only about 1⁄2 in (13 mm) up the shank before ending. The other flute continues full-length up the shank for waste removal. The Irwin bit may afford greater space for waste removal, greater strength (because the design allows for a center shank of increased size within the flutes, as compared to the Jenning bits), or smaller manufacturing costs. This style of bit was invented in 1884, and the rights sold to Charles Irwin who patented and marketed this pattern the following year.

Both styles of auger bits were manufactured by several companies throughout the early- and mid-20th century, and are still available new from select sources today.

The diameter of auger bits for hand braces is commonly expressed by a single number, indicating the size in 16ths of an inch. For example, #4 is 4/16 or 1/4 in (6 mm), #6 is 6/16 or 3/8 in (9 mm), #9 is 9/16 in (14 mm), and #16 is 16/16 or 1 in (25 mm). Sets commonly consist of #4-16 or #4-10 bits. (Wiki)

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