Drilling Operation and 

Drilling Machines

Drilling • Drilling is a process of making a hole or enlarging a hole in

an object by forcing a rotating tool called “ Drill”.• The drill is generally called a twist drill, since it has sharp

twisted edges formed around a cylindrical tool providedwith a helical groove along its length to allow the cutmaterial to escape through it.

• The sharp edges of the conical surfaces ground at lowerend of the rotating twist drill cut the material by peeling itcircularly layer by layer when forced against a workpiece.

• The removed material chips get curled and escape throughthe helical grooves provided in the drill.

• A liquid coolant is generally used while drilling to removethe heat of friction and obtain a better finish for the jobdone.

Drilling Operation

Drilling Machines

• A power operated machine tool which holds the drill in itsspindle rotating at high speeds and when it move linearlysimultaneously against the workpiece produces a hole iscalled a drilling machine.

• Drilling machine is one of the simplest, moderate andaccurate machine tool used in production shop and toolroom.

• It consists of a spindle which imparts rotary motion to thedrilling tool, or mechanism for feeding the tool into thework.

• It is considered as a single purpose machine tool since itschief function is to make holes.

Specifications of a Drilling Machine

A drilling machine is specified as follows:

• Size of the drilling machine table.• Largest bit the machine can hold.• Maximum size of the hole that can be drilled.• Maximum size of the workpiece that can be held.• Power of the motor, spindle speed or feed.

Types of Drilling Machines

• Portable drilling machine.• Sensitive or bench drilling machine.• Upright drilling machine.• Radial drilling machine.• Gang drilling machine.• Turret machine.• Deep hole drilling machine.• Multiple spindle drilling machine.• Automatic drilling machines.

Portable Drilling Machines

Sensitive or Bench Drilling Machine

Radial Drilling Machine

Turret Drilling Machine

Gang Drilling Machine

Gun Drilling Machine

Classification of Drills

• According to the type of shank:• Parallel shank.• Tapered shank.• According to the type of flutes:• Flat or spade drills ( Parallel longitudinal flutes).• Twist drills ( Spiral/ Helical flutes).

• According to length:• Short series drills.• Stub series drills. • Long series drills.

Classification of Drills

• According to Applications:• Core drills.• Drills for long hole drilling.• Centre drills.• Masonry drills.

• According to the tool material:• High speed steel drills.• Carbide tipped drills

Drilling Machine Tools

• Flat drill.• Straight drill.• Twist drill.• Taper shank core drill.• Oil tube drill.• Centre drill.• Reamer.• Centre punch.• Drift.• Hammer.

Twist Drill Nomenclature• Body:• The body is the portion of the drill which extends fromits extreme point upto the neck or shank of the drill.Itconsists of body clearance, chisel edge, face, flank,flutes, heel, land or margin, point, lip and web.

• Body Clearance: It is the portion of the body surfacewith reduced diameter which provides diametricalclearance.

• Face : It is the portion of the flute adjacent to the lipon which chip flows as it is cut from the workpiece.

• Flank : It is the conical surface of a drill point whichextends behind the lip to the following flute

Elements of a twist drill

Drilling Machines

Drilling Machines

Drilling Machines

Twist Drill Nomenclature

• Flutes : These are helical grooves cut on the cylindrical surfaceof the drill and provide the lip. They serve the followingpurpose:‐

• Ensure easy escape and flow of chips.• Cause the chips to curl and provide passage for the flow.• Form the lips and cutting edges on the point.• Allow the cutting fluids to reach the cutting edges thus reducing

their friction.• Heel : It is the edge formed by the intersection of flute surface

and the body clearance.• Land : It is the cylindrical ground narrow strip on the leading

edges of drill flutes. It keeps the drill aligned. It is also known as“Margin”.

Twist Drill Nomenclature• Point : It is the cone shaped sharpened end of the drill that

produces lips, faces, flanks and chisel edge of the drill.• Lips : The lips, also known as “Cutting edges”, are the edges

formed by the intersection of flanks and faces. They are two innumber with identical length and angle.

• Web : It is the thickness of the drill between the flutes whichextends from point towards the shank. The point end of theweb forms the chisel edge.

• Shank :• The shank is the cylindrical portion of the drill which is used to

hold and drive the drill. It extends from the neck and it may beeither straight or tapered.

• Tang : It is the flat end of the taper shanks which fits into socketor drill holder. It ensures positive drive of the drill from the drillspindle.

Advantages of twist drills

• For the same size and depth of the hole they need lesspower in comparison to other forms of drills.

• Cutting edges are retained in good condition for afairly long time, thus avoiding the frequent regrindingof the drill.

• The chips and cuttings of the metal are automaticallydriven out of the hole through the flute.

• Heavier feeds and speeds can be employed quitesafely, resulting in a continuous saving of time.

Drilling Machine Operations

• In addition to drilling, the following operations are carried out on a drilling machine :

• Reaming.• Boring.• Counter boring.• Counter sinking.• Spot facing.• Tapping.• Trepanning.

Drilling Machine Operations• Reaming: It is the operation of finishing an existing hole very

smoothly and accurately in size. A reamer is a multi tooth cutterwhich rotates and moves linearly into an already existing hole.

• Boring : It is an operation of enlarging an existing hole.• Counter‐boring : An operation of enlarging a drilled hole

partially that is for a specified length.• Counter‐sinking : It is an operation of forming a conical shape at

the end of a drilled hole.• Spot facing : It is the operation of smoothing and squaring the

surface around a hole for the seat of a nut or the head of ascrew.

• Tapping : An operation in which external threads are cut in theexisting hole.

• Trepanning : It is the operation of producing a hole by removingthe metal along the circumference of a hollow cutting tool.

Reaming

Hand Reamer

Machine Reamer

Boring

Counterboring

Countersinking

Spot Facing

Tapping

Trepanning