3. Types of Bore Bits

Bore bits have a wide field of application.

The different properties of wood cut parallel with or across the grain or of cross-grained wood and wood fibreboards call for different types of boring tools.

- The types of bore bits described in Table 1 are tools which can be used in manually operated boring appliances only, except for the Forstner auger bits and twist drills which can be operated manually and on machines.

Figure 4-1 Types of bore bits: auger bit (Douglas type),

Figure 4-2 Types of bore bits: auger bit (Irwin type),

Figure 4-3 Types of bore bits: centre bit,

Figure 4-4 Types of bore bits: expansive centre bit,

Figure 4-5 Types of bore bits: Forstner auger bit,

Figure 4-6 Types of bore bits: gimlet with ring handle,

Figure 4-7 Types of bore bits: twist drill,

Figure 4-8 Types of bore bits: spoon bit,

Figure 4-9 Types of bore bits: wood countersink (rose bit),

Figure 4-10 Types of bore bits: depth setter

Table 1: Types of Bore Bits

Designation	Features	Application
Auger bit	- Diameter 6 mm ... 30 mm	- Boring of long-grained wood - Boring of end-grained wood
	- Length 185 ... 250 mm - Brad point with draw-in thread - Two pre-cutters	- Deep holes
	- Douglas double twist type - Irwin single twist type	- Particularly for holes in hard wood - Particularly for holes in wet wood
Centre bit	- Diameter 10 mm ... 40 mm - Brad point without draw-in thread - One pre-cutter	- For holes of small depth in cross-grained wood (not suitable for end-grained wood)
Expansive centre bit	- Diameter 16 mm ... 40 mm - Brad point with draw-in thread - Pre-cutter and cutting edge are adjustable inserts - Pre-boring bit	- For holes of varying sizes (not suitable for hard wood)
Forstner auger bit	- Diameter 8 mm ... 40 mm - Length 80 mm ... 125 mm - Minimum brad point - Cylinder circumference serves as pre-cutter - Two cutting edges between brad point and pre-cutter	- For flat and very clean-cut holes with plane bottom for mounting of fittings - For boring out of defective spots
Gimlet with ring handle	- Diameter 2 mm... 10 mm - Length 110 mm ... 200 mm - No pre-cutter - Helical transition from draw-in point to main cutting edge removes chips at hole circumference	- Pre-boring of nail and screw holes in end-grained wood and long-grained wood
Twist drill	- Diameter 2 mm ... 12 mm - Length 120 mm ... 170 mm - Taper brad point - No pre-cutter	- For holes in thin material - Dowel holes
Spoon bit	- Diameter 10 mm ... 60 mm - Length 220 mm ... 490 mm - No brad point - No pre-cutter - Spoon type cutting body - Cutting edge removes chips at hole circumference - No pre-cutter	- For producing conical holes - For enlarging conical holes - Boring of end-grained wood
Rose bit	- Diameter 16 mm and 20 mm - Length 100 mm - Conical arrangement of main cutting edges	- For reaming of screw holes - Holes are provided with a chamfer
Depth setter	- Appliance as boring aid - Is bolted to the bit	- Helps to observe the required depth of hole

All bore bits specified in the table are to be classified according to the following criteria!

without	with	without	with	without	with
brad point		thread		pre-cutters

In addition to the various types of bore bits, auxiliary tools are used for boring to safely guide the boring tool in the desired position of the bore hole axis.

Figure 5 Piece of wood as boring aid

1 bit center line

Depth setters guarantee that the specified depth of the hole is not exceeded.