Drill Tool Nomenclature
When it comes to machining operations, Drill Tool Nomenclature is a collection of principles that allows you to establish systematic names for drill bits that are used in that specific activity. A drill or twist drill is a grooved end-cutting tool used for manufacturing holes in firm material. It basically consists of two parts.
- The body consisting of the cutting edges, and
- The shank used for holding purposes.
The various parts and angle of the twist drill are shown below
The body of the twist drill spiral grooves cut on it. These grooves serve to offer clearance to the chips formed at the cutting edge. They also permit the cutting fluid to spread to the cutting edges.
It is a part that gets fitted into the drill chuck or sleeve. It might be parallel shank or taper shank. Smaller diameter drills have straight shank. Morse taper is generally provided for large diameter tapered drills. The taper shank brings the tang at the end of shank. This fits into a slot in the machine spindle, sleeve or socket and gives a positive grip.
It is the undercut portion between the body and the shank. Usually, size and other details are marked at the neck.
It is the cone fashioned end of the drill. The point is shaped to produce lip, face, and flank and chisel edge or dead center.
Land or Margin
It is a narrow strip. It ranges back on the edge of the drill flutes. The size of drill is measured across the lands at the point end. Land retains the drill aligned.
It is the central portion of drill located between the roots of the grooves and lengthening from the point towards the shank.
The intersection of flank forms the chisel edge. This acts as a flat drill. It cuts a small hole in the work piece at the beginning. Therefore cutting edges removes further materials to complete the hole.
The cutting edges of a drill are known as lips. Both lips should have equal length, same angle of inclination and correct clearance.
The surface behind the lip to the following flute is called flank.
This is the portion of the flute surface adjacent to the lip. The chip impinges on it.
The edge which is formed by the intersection of the flute surface and the body clearance is known as heel.
It is the angle between the cutting edges. It is generally 118 degree. Its value depends upon the hardness of the work piece to be drilled. For harder material, larger angles are used.
It is the angle between the face and the line parallel to the drill axis. At the periphery of the drill, it is equal to the helix angle.
It is the angle between the leading edge of the land and the axis of the drill. It is also called as spiral angle.
Lip clearance angle
It is the angle formed by the portion of the flank adjacent to the land and a plane at right angles to the drill axis measured at the periphery of the drill.
Chisel edge angle
It is the obtuse angle between the chisel edge and the lip. Generally, this angle is 120 and 135 degree.
The length of the flute is represented by the depth of the hole, the length of the bush, and the amount of regrinding allowance. Because the effect on the tool’s life is significant. It is vital to keep it to a bare minimum as much as feasible.
The cutting edge shape of a drill bit and their applications:
This kind of flank has a conical form, as illustrated in the diagram, and the clearance angle increases as the drill moves toward the centre of the hole. It is referred to as the all-purpose drill bit.
As seen in the illustration, this form of flank has a flat contour. Grinding is a simple method of creating this sort of drill bit. It is mostly used in the production of tiny diameter drills.
Three flank angles:
A specific grinding machine is necessitated for machining of this sort of flank, since it has three angles on each side. Surface grinding is carried out on three sides in this instance. Because there are no chisel edges, there is a strong centripetal force and a minor hole oversize as a consequence of this. Drilling procedures requiring a great hole precision as well as precise placement are the primary applications for this drill bit.
The shape of this chisel edge is in the shape of a ‘S’. These unique drilling bits are used for drilling operations that need exceptional precision. The chisel edge generates a large amount of centripetal force while maintaining good machining precision. In order to machine this unusual helix angle cutting edge, conical grinding is used. This procedure raises the clearance angle at the centre of the drill, which is important for drilling.
This kind of flank has a radial cutting edge that has been honed to spread the machining loads. Cast iron, aluminium alloy, and steel plates are among the materials on which these drill bits are most often used because of their high machining precision and excellent surface polish. The radial lip in the cutting tool is created with the help of a specialised grinding machine.
Center point drill:
This kind of flank has a two-stage point angle geometry, which allows for improved concentricity and a decrease in shock vibration when the tool retracts. Thin sheet drilling activities are carried out with the help of this kind of drill bit.