Twisted Drill

1. Overview

A twist drill is a cutting tool used to create holes directly in solid materials, and it’s also the most widely used type of tool for hole-making operations. A twist drill consists of three main parts: the working section, which is further divided into the cutting portion and the guiding portion. The cutting portion performs the primary cutting task, while the guiding portion ensures accurate positioning once the cutting edge has entered the workpiece—and it also serves as a reserve area for sharpening the cutting edges. To enhance the drill’s rigidity and strength, the diameter of the drill’s core gradually increases toward the shank along its working section, with an increment of 1.4 to 2 mm per 100 mm of length.

The shank—the gripping part of the drill bit, designed to transmit torque. Shanks come in two types: straight shanks, used for small-diameter drills, and tapered shanks, which are suitable for larger-diameter drills.

The neck—located between the working part and the shank—serves to retract the grinding wheel when sharpening the shank, and it’s also where the drill bit is marked.

The twist drill has been subject to an export product quality licensing system; products without an export quality license are prohibited from being exported.

2. Testing Standards

All twist drill products comply with national standards and also adopt international standards on an equivalent basis, as shown in Table 6–10–56.

3. Inspection items and technical requirements:

(1) Appearance: No cracks, chipped edges, burns, dull cutting edges, or other defects that could impair performance are allowed.

(2) Refer to Table 6–10–57 for the surface roughness of twist drills.

(3) Dimensional tolerances for the working parts shall comply with national standards.

(4) For general-grade twist drills, positional tolerances are specified according to Table 6–10–58; for precision-grade twist drills, positional tolerances are defined in accordance with Table 6–10–59.

(5) Taper of the drill’s working section: 0.03 to 0.10 mm per 100 mm length.

(6) Increment in the drill core of the twist drill's working section: 1.4 to 2.0 mm per 100 mm length.

(7) Materials: Twist drills shall be made from W6Mo5CR4V2 high-speed steel or other equivalent-grade material with comparable performance; the shank portion of welded twist drills must be manufactured from 45 or 60 steel, or from alloy steel of equal or superior quality.

(8) Hardness: The quench-hardened area, hardness, and shank hardness of the twist drill's working section. For solid twist drills, the quench-hardened area extends along 4/5 of the length from the drill tip into the flute; for welded twist drills, it spans 3/4 of the flute length from the drill tip.

Hardness: Not less than 63 HRC

Flat-tail hardness: 30-45 HRC.

(9) Standard twist drills should undergo steam surface treatment or other surface-enhancing processes.

(Helicoils with a diameter d ≤ 3 mm are permitted to remain untreated with steam surface treatment or other surface enhancement processes.)

(10) Performance Testing: Before leaving the factory, twist drills shall undergo cutting performance tests in accordance with the provisions of this standard. After testing, the drills must show no chipping or significant wear and must retain their intended operational performance.

① Twist drill performance tests shall be conducted according to the specifications in Table 6–10–60, using equipment that meets the required precision standards. Drill press Taking place upstairs.

② The test material shall be made of 45 or 50 steel, treated by annealing or normalizing, with a hardness ranging from 170 to 200 HB. The surface intended for drilling must be pre-machined and ensured to be perpendicular to the machine tool spindle’s centerline.

③ The coolant is an emulsified oil-in-water solution.

④ Drilling non-through holes.

(11) Labels and Packaging:

① Twist drills should be marked (twist drills with a diameter d < 3 mm may omit marking):

a. Manufacturer's trademark;

b. Twist drill diameter;

c. Material code (HSS).

② The packaging box should bear the following markings:

a. Manufacturer's name and trademark;

b. The markings specified in this standard;

c. Material grade or designation;

d. Quantity;

e. Manufacturing year and month.

③ Packaging: Twist drills should undergo rust-proof treatment before packaging. The packaging must be secure and designed to prevent damage during transportation.