Twist drills are the most popular drill type that users choose for their daily routine drilling purpose. A key reason why this drill type is popular among users is that they can cut a wide variety of materials, from concrete to plastic and sometimes even wood. Do you want to learn more about twist drills? Please read on.
Table of Contents
8 Features of a Twist Drill and its functions
Web Thickness (Core)
Chisel Edge Angle
What is a twist drill?
A twist drill is a tool with a definite cross-sectional diameter with spiral flutes that take up about 80 percent of the entire body of the drill bit. The number of pipes on a typical drill describes the type of hole it makes. When the twist drill has a two-flute drill, they are applicable for primary drilling. However, for three flutes and above, such drills are best suitable for enlarging cast or punched holes.
Another critical characteristic of this tool that makes it popular among professionals is its bit size range. It makes it the perfect fit for cutting different types and thicknesses of materials. They contain the M2 high-speed steel structural build-up. This attribute makes them excellent for cutting metals even though they can also cut numerous materials.
The twist drill comes in different forms for different applications. The Jobber length drill is a variation of the twist drill with a standard average length. Specialty twist drills of longer lengths are also a variation of the regular twist drill, popularly known as the extra-length drill. Finally, the variety is known as the screw machine drill for short twist drills. These twist drills are mostly carbide-tipped, with their entire structure also of solid carbide makeup.
8 Features of a Twist Drill and its functions
The helix or spiral angle is a vital feature of the twist drill as it helps determine the chip formation process. The varying degree range of the helix angle is responsible for either long or short-tipping materials. This information helps the user of this tool determine the perfect angle that suits the application for cutting.
The helix angle also helps to determine the rake angle. As the helix angle decreases, the rake angle follows suit. This correlation between the helix angle and the rake angle determines how strong the cutting edge will be for the drill. Most helix angles are usually 16° to 30° for diameters between 0 – 0.6 mm. However, these helix angles become smaller to the tune of 10° to 13° for harder materials and 35° to 45° for softer materials.
Figure 2: Helix AngleFlute Profile
It is an essential portion of the twist profile, with the flute holding the sole responsibility of absorbing and removing the chip. The wider the flute profile is, the better the chip removal. A good and more extensive flute profile design enables the twist drill to work longer on harder surfaces. It is possible since the design provides a higher accommodation of heat generated by the friction of the surfaces in contact.
Creating a flute profile follows the sequence of either a “wider profile-flatter flute” or a “thinner profile-deeper flute.” The flute profile also helps make the cutting lips and provides a marginal space to accommodate the withdrawal of the swarf from the hole.
Figure 3: Flute ProfileWeb Thickness (Core)
The region along the cross-section of the flutes is the Web. The thickness of this Web varies to suit the application of the twist drill. Its entire scope ranges through the twist drill’s whole length, making it a very integral part of the drill.
The sole function of the web thickness is to help ensure the stability that the drill requires to work effectively. They often have a sequence of producing higher stability. It is necessary to allow more torque by the twist drill for cutting harder and thicker materials.
The cutting edge has a self-evident function, ensuring the drilling of the workpiece. Twist drills also have a cutting performance, which is determined by the cutting-edge ratio of the drill. Twist drills with longer cutting edges have a higher cutting performance.
The cutting edge is the part of the drill responsible for the actual cutting away of the material in the drilling process. Each drill flute has its cutting edge and is mostly razor sharp.
Figure 4: Cutting EdgeChisel Edge Angle
It is a part of the twist drill that is mostly responsible for its sharpness. It is the angle between the chisel edge and the cutting lip. This angle also relates directly with the clearance, with larger angles producing larger clearances. These angles range from 130° to 145°.
The edge width is the part of the twist drill responsible for the type of surface finish the holes have with twist drills. The wider edge drills have higher stability, the perfect fit for materials with high impurity content.
The twist drills with narrow edge lines have lower strength but higher sharpness for a better surface finish, which makes the narrow edge line the perfect tool for drilling material with an expected exquisite surface finish.
The point angle of the twist drill sits at the top of the conical-like surface at the cutting end of the drill. It is an essential part of the twist drill and sits at the top (head) of the drill. The very fundamental function of the point angle is that it helps to position the twist drill at the center. These point angles affect the cut of the twist drill because a small point angle makes it easier to position the drill at the center, and the reverse is the case for a large point angle. Hence, posing a more significant challenge in positioning the drill.
However, the larger point angle will have a shorter tapping time than the smaller one. Nevertheless, the lower point angle makes long main cutting edges, and the larger point angle makes a short main cutting edge.
The standard or typical point angle of the twist drill is 118 degrees, and this is so because, over time, this specific angle gives satisfactory results for different materials. The point angle also has an inverse correlation with the width of the cut, with a lesser point angle increasing the cut width and vice versa. Nevertheless, the point angle doesn’t always come at the regular 118°, and the different material application requires a different point angle. For example
• 0°-point angle- laminated plastic and marble.
• 140°-point angle-copper, aluminum alloys, and stainless steel
Figure 5: Point AngleRake Angle
The rake angle is what most will define as the relationship between the workpiece and the angle of the flute. In most typical drilling cases, the manufacturer sets the rake angle during the design, and end-users are not allowed to change it. An angle of 90 degrees or those close to this range will usually not give a sharp cutting edge. A small angle creates cutting edges that are too thin to withstand stress and strain. This invariably leads to a breakdown.
The rake angle also plays a significant part in chip formation as it directly impacts the tightness of the chip curl, which invariably determines the space this chip occupies. The size of the rake angle also determines the type of chip when drilling with larger rake angles producing a tightly rolled chip, while a smaller rake angle curly chip.
By now, you must have seen the key features of the twist drill and its functions. Although it becomes easier to explain your twist drill requirements to manufacturers, you can trust only a few manufacturers with top-notch tools. NC Cutting Tools has a proven track record of manufacturing the best twist drills. Besides, this video will help you to understand the twist drill anatomy better.