The method of processing threaded holes in solid materials using a drill bit is called drilling. Drilling is a rough machining process, with the general accuracy reaching 2 and surface roughness of 7. The tools used for drilling include twist drills, flat drills, center drills, deep hole drills, and countersink drills, among others.

The geometric shape and composition of the helical drill: ①The shank of the helical drill comes in two types: conical and straight shank. Generally, drills with a diameter less than 11mm are made with a straight shank, while those over 13mm are made with a conical shank. The shank is the part of the helical drill that holds it, serving as a centering function during mounting and a torque transmission role during cutting. ②The neck is used as a retraction slot during the grinding of the helical drill. The specifications, materials, and trademarks of the drill head are often marked on the neck. ③The working part of the torque transmitter is the main part of the drill, consisting of the cutting section and the guide section, which perform the functions of cutting and guiding.

2. The geometric components of the twist drill include: ① The working part of the helical slot drill bit features two spiral slots, which serve to form the cutting edge, facilitate chip and coolant evacuation. ② The angle between the tangent of the outer edge spiral line on the helical slot and the axis. As the lead of the spiral slots on the same drill bit is constant, the helix angle varies at different diameters, with a smaller angle closer to the center. The standard helix angle of a twist drill is 18 degrees. The nominal helix angle of the drill bit refers to the helix angle at the outer edge. ③ The leading face refers to the spiral slot surface of the cutting part, from which chips are ejected. ④ The main trailing face is the spiral conical surface of the drill bit, which is the surface opposite the transition surface of the workpiece. ⑤ The main cutting edge is the intersection line between the leading face and the main trailing face, responsible for the primary cutting work. A drill bit has two main cutting edges.

The helix angle of a twist drill is the angle between the two main cutting edges of the drill bit. The standard helix angle for a twist drill is typically 118 degrees. When the helix angle is 118 degrees, the two main cutting edges are shown as straight lines; when the helix angle exceeds 118 degrees, the two main cutting edges are depicted as concave curves; and when the helix angle is less than 18 degrees, the two main cutting edges are shown as convex curves.