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Twist Drill Definition Nomenclature Types & its 10 Applications

In this post, you’ll learn about Twist Drill Definition Nomenclature Types & its 10 Applications

Twist Drill

It is the most popular type of drill in used today . It was basically formed by twisting a flat piece of tool steel longitudinally for several revolutions, then grinding the diameter and point. Currently, twist drills are manufactured by two machining spiral flutes or grooves that run lengthwise around the body of the drill.

twist drill consists of a cylindrical piece of steel with special grooves. One end of the cylinder is pointed and the other end is so shaped that it can be attached to the drilling machine. The grooves are called flutes. Flutes are formed by twisting a flat piece of steel into a cylindrical shape and such types of cylindrical shape drills are called twist drills.

Now let us discuss the various parts or Nomenclature of the twist-drill bits:

Twist Drill Nomenclature:

 

Twist drill nomenclature min
Twist Drill Nomenclature

 

Nomenclature of twist drill parts and their functions

  • Axis
  • Body
  • Shank
  • Dead Center
  • Point
  • Lips
  • Body clearance
  • Chisel edge
  • Chisel edge corner
  • Face
  • Flank
  • Flutes
  • Heel
  • Neck
  • Tang
https://youtu.be/QDg832tFIOg
Watch this video to get clear concept.

Axis: It is the longitudinal centre line of the drill.

Body: The portion between the shank and the drill bit tip is called ‘Body. The body is mostly fluted and relieved.

Shank: The part of the drill bit that holds into the holding is called the ‘shank’.

Dead Centre: 

It is the sharp edge at the extreme tip end of the drill, formed by the intersection of the cone-
shaped surfaces of the point. It should always be in the exact centre of the axis of the drill.

Point: The entire cone-shaped surface at the cutting end of the tool.

Lips: The main cutting edges of the drill are formed by the intersection of the flank and the flute surfaces. For a good cutting, it should be straight, symmetrical with the axis of the shaft and equal in length.

Body clearance: To provide diameter clearance the body surface diameter is reduced.

Chisel edge: The chisel edge is the point. Here two cutting lips meet at extreme tip.

Chisel edge Angle: The chisel edge angle is the angle between the chisel edge and cutting lip measured plane normal to the axis.

Face: The flute surface portion adjacent to the lip, when it is cut from the work the chip impinges.

Flank: Drill surface which extends behind the lip to flute.

Flutes: The Twist Drill body has grooves and it is known as flutes.The groove in the body of the drill that gives lip.

The uses of the flutes are:

To From the cutting edges on the point.

To allow the chips to escape.

For to cause the chips to curl.

To allow the cutting fluid to enter the cutting edges.

 

Heel: The Heel is the intersection of the flute surface and the body clearance.

Neck: Neck is the portion of the body with reduced diameter between body and shank.

Tang: The tang is flattened end of the taper shank.

Types of Twist Drill

Following are the types of twist drill:

1.Short Series or Jobbers Parallel Shank Twist Drill

2.Sub Series Parallel Shank Twist Drill

3.Long Series Parallel Shank Twist Drill

4.Taper Shank Twist Drill

5.Taper shank Core Drill (Three or Four Fluted)

6.Oil Tube Drill

7.Centre Drills

1. Short Series or Jobbers Parallel Shank Twist Drill

Parallel Shank (Short Series or Jobbers) Twist Drill
Parallel Shank (Short Series or Jobbers) Twist Drill

The drill has two parallel shank of approximately the same diameter as the cutting end. The diameter of the drill ranges from 0.2 to 16 mm increasing by 0.02 to 0.03 mm in lower series to 0.25 mm in higher series. The figure illustrates the drill.

2. Sub Series Parallel Shank Twist Drill

Parallel Shank (Stub Series) Twist Drill
Parallel Shank (Stub Series) Twist Drill

The drill is a shortened type of the parallel shank twist drill, the shortening being on the flute length. The diameter of the drill ranges from 0.5 to 40 mm increasing by 0.3 m in lower series to 0.25 to 0.5 mm in higher series. The figure illustrates the drill.

3. Long Series Parallel Shank Twist Drill

The drill has two helical flutes with a parallel shank of approximately the shank diameter as the cutting end, which however does not exceed the diameter at the drill point.

parallel-shank-long-series-twist-drill
Parallel Shank (Long Series) Twist Drill

The overall length of this drill is the same as the of a taper shank twist drill of the corresponding diameter. The diameter varies from 1.5 to 26 mm increasing by 0.3 mm in lower series to 0.25 mm in higher series. The figure illustrates the drill.

4. Taper Shank Twist Drill

The drills have two helical flutes with a tapered shank for holding and driving the drill. The shank for these drills conforms to Morse tapers. The diameter ranges from 3 to 100 mm.

Taper Shank Twist Drill
Taper Shank Twist Drill

The diameter increases by 0.3 mm in lowest series having Morse taper shank No. 1, by 0.25 mm in Morse taper shank number 2 and 3, by 0.5mm in Morse taper shank No. 4, and by 1 mm in Morse taper shank number 5 and 6.

The Morse taper shank is used below 6 mm size is not preferred. A drill gauge allows any drill to be easily selected by truing into the holes of the gauge. The figure illustrates the drill.

5. Taper Shank Core Drill (Three or Four Fluted)

These type so drills are designed for enlarging cored, punched or drilled holes. These drills cannot originate a hole in solid material because the cutting edges do not extend to the centre of the drill. The metal is removed by a chamfered edge at the end of each flute.

Taper Shank Core Drill (Three or Four Fluted)
Taper Shank Core Drill (Three or Four Fluted)

Cored drills provide better-finished holes than those cut by normal two fluted drills. The cutting action of a core drill is similar to that of a rose reamer and is used as a rough reamer. In some cases, a two fluted twist drill is chosen to originate a hole half the required size and the rest is finished by a three or four fluted drills. The figure illustrated the drill.

6. Oil Tube Drill

Oil Tube Drill

The oil tube drills are utilised for drilling deep holes. Oil tubes run lengthwise spirally through the body and to carry the oil directly to the cutting edges.

Cutting fluid or compressed air is pushed through the holes to the cutting point of the drill to separate the chips, cool the cutting edge and lubricate the machined surface. The figure illustrates the oil tube drill.

7. Centre Drills

Centre Drill

The centre drills are straight shank, two fluted twist drills used when centre holes are drilled on the ends of a shaft. They are made in finer sizes. The figure illustrates the drill.

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