Twist drill is the most widely used drill in industrial manufacturing, and we generally use twist drill. The length to diameter ratio of the bit is calculated when the technician selects the most appropriate bit type for a specific hole machining task. The length-diameter ratio is the ratio of the depth of the hole to be machined to the diameter of the drill. For example, if the drill diameter is 12.7mm and the hole depth to be machined is 38.1mm, the length-diameter ratio is 3:1. When the length to diameter ratio is about 4:1 or less, the chip removal groove of most standard twist drill bits can remove the chip removed by the bit cutting edge fairly smoothly. When the length-diameter ratio exceeds the above range, a specially designed deep hole drill is needed to achieve effective machining. Twist drill standard products are adopted national standards, and equivalent to the use of international standards. Once the length to diameter ratio of the machining hole is greater than 4:1, the standard twist drill is difficult to remove the chip from the cutting area and out of the hole, the chip will soon block the drill chute, at this time you need to stop drilling, exit the drill from the hole, remove the chip in the chute, and then re-drill to continue cutting, the above operation needs to be repeated many times to process the required hole depth. This type of drilling is often referred to as the "pecking" method. Using "pecking" method to process deep holes will shorten the tool life, reduce the processing efficiency and affect the quality of the machined holes. Each time the bit is removed from the hole and re-inserted after the chip is removed, it is possible to deviate from the center line of the hole, thereby increasing the aperture beyond the specified dimensional tolerance. In order to solve the problem of deep hole machining, in recent years, the drill manufacturers have developed two new types of deep hole machining bits - ordinary parabolic bit and wide blade parabolic bit.

Twist drill specifications and dimensions:

Φ Φ 1.0, 2.5, 1.5, 2.0, Φ Φ Φ Φ 3.0, 3.2, 3.3, 3.5 and 3.8, Φ Φ Φ Φ 4.0, 4.2, 4.5 and 4.8, Φ Φ Φ Φ 5.5, 5.0, 5.2, Φ Φ Φ 5.8, Φ Φ 6.0, 6.2, 6.5, 6.8 and 7.0, Φ Φ Φ Φ 7.2, Φ 7.5, Φ Φ 7.8, 8.5, 8.0, 8.2, Φ Φ Φ Φ 8.8, 9.0, 9.2, 9.5 and 10.0, Φ Φ Φ Φ 10.2, 10.5, 11.0 and 12.0, Φ Φ Φ Φ 13.5, 12.5, 13.0, Φ Φ Φ 14.

Twist drill specification table:

Straight shank twist drill GB/T 6135.3-1996 Φ3-Φ20

Straight shank long twist drill GB/T 6135.4-1996 Φ3-Φ31.5

Morse taper shank twist drill GB/T 1438.1-1996 Φ6-Φ100

Standard handle, thick handle Morse taper shank long twist drill GB/T 1438.2-1996 Φ6-Φ50

Morse taper shank lengthened twist drill GB/T 1438.3-1996 Φ6-Φ30

Carbide straight shank twist drill, specification 16

The specifications of twist drill bits are as small as 3.5MM diameter, and there are 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 32 and other specifications.