Drilling Machine

Drilling

Drilling is the operation of producing circular hole in the work-piece by using a rotating cutter called DRILL.The machine used for drilling is called drilling machine.The drilling operation can also be accomplished in lathe, in which the drill is held in tailstock and the work is held by the chuck.The most common drill used is the twist drill or drill bit.

Drilling Machine

It is the simplest and accurate machine used in production shop.The work piece is held stationary ie. Clamped in position and the drill rotates to make a hole.Types :-

a) Based on construction:

Portable, Sensitive,Radial, up-right, Gang, Multi-spindle

b)Based on Feed:

Hand and Power driven

Portable drilling machine

Sensitive Drilling Machine

Drill holes from 1.5 to 15mmOperator senses the cutting action so sensitive drilling machine

Up-Right Drilling Machine

Drill holes upto 50mmTable can move vertically and radially

Radial Drilling Machine

It the largest and most versatile used fro drilling medium to large and heavy work pieces.

Gang Drilling Machine

Multi spindle Drilling Machine

Based on Feed:

Hand and Power driven

Driving mechanism

Drill Materials

The two most common types are

1. HSS drill

- Low cost

2. Carbide- tipped drills

- high production and in CNC machines

Other types are

Solid Carbide drill, TiN coated drills, carbide coated masonry drills, parabolic drills, split point drill

Drill Bit

Fit in chuck

Fit direct into spindle

Tool Nomenclature

Drill Bit Features

The point of the drill is ground to an angle of 118 degrees each side is ground back to give " relief " of about 12 degrees to each cutting edge as shown

The nomenclature of the twist drill is shown

Drilling And Drills

Types of drills

Twist drill: most common drillStep drill: produces holes of two or more different diametersCore drill: used to make an existing hole bigger

Drilling And Drills

Drilling operationsCounterboring & countersinking: produce depressions on the surface to accommodate the heads of screwsCenter drill: is a short and is used to produce the hole at the end of a piece of stockSpot drill: is used to spot (start) a hole at the desired locationGun Drilling - used fro drilling gun barrels and deep holesThrust Force and TorqueThrust force acts perpendicular to the hole axisCan cause the drill to bend or break if excessiveDrilling PracticeHeld in drill chuckswalking can be a problem when starting a holeThe drill should be guidedUsed a center drill to start a holeDrills can be reconditionedDrill life is measured by the number of holes drilled.

Drill point Geometries

Fig : Standard chisel-point drill indicating various features. The function of the pair of margins is to provide a bearing surface for the drill against walls of the hole as it penetrates into the workpiece; drills with four margins (double-margin) are available for improved drill guidance and accuracy. Drills with chip-breaker features are also available. (b) Crankshaft-point drill. (c) Various drill points and their manufacturers: 1. Four-facet split point, by komet of America. 2. SE point, by Hertel. 3.New point, by Mitsubishi materials. 4. Hosoipoint, by OSG Tap and Die. 5. Helical point.

Reaming And Reamers

Operation used to make an existing hole dimensionally more accurate than by drilling aloneThe hole making sequence isCenteringDrillingBoringreaming

Fig : various types of drilling and reaming operations.

Twist drills - Helix Types

The helix angle of the twist drill is the equivalent of the rake angle on other cutting tools and is established during manufacture. The standard helix angle is 30 degrees, which, together with a point angle of 118, is suitable for drilling steel and cast iron.

Helix types

Standard

quick helix

slow

Helix types

Drills with a helix angle of 20 known as slow-helix drills are available with a point angle of 118 for cutting brass and bronze and with a point angle of 90 for cutting plastics materials.Quick-helix drills, with a helix angle of 40 and a point angle of 100, are suitable for drilling the softer materials such as aluminium alloys and copper

Drill Bit

Wood bits

masonry

steel

Drill fixed to the spindle

Drilling operations

Drilling Deep HolesDrilling Thin Material

Tool Holding devices

The different methods used for holding drill in a drill spindle areBy directly fitting in the spindle hole.By using drill sleeveBy using drill socketBy using drill chuck

Work Holding Devices

Nomenclature and geometry of conventional twist drill. Shank style depends upon the

method used to hold the drill. Tangs or notches prevent slippage:

(a) straight shank with tang,

(b) tapered shank with tang,

(c) straight shank with whistle notch,

(d) straight shank with flat notch.

Tool Holding

Holding taper shank drills

Morse Taper Sleeve

Drill Drift

To remove a shank from the spindle, a taper key known as a drift is used.

Using the drill drift

The drift is inserted through a slot in the spindle

Strike here to remove

Most modern machines have a built-in drift

Drilling operations

Operations that can be performed in a drillin g machine are

Drilling

Reaming

Boring

Counter boring

Countersinking

Tapping

Operations in drilling machine

Reaming

A reamer enters the workpiece axially and enlarges an existing hole to the diameter of the tool. A reamer is a multi-point tool that has many flutes, which may be straight or in a helix. Reaming removes a minimal amount of material and is often performed after drilling to obtain both a more accurate diameter and a smoother internal finish.

Countersinking

A countersink tool enlarges the top portion of an existing hole to a cone-shaped opening. Countersinking is performed after drilling to provide space for the head of a fastener, such as a screw, to sit flush with the workpiece surface. Common included angles for a countersink include 60, 82, 90, 100, 118, and 120 degrees.

Counter bore and spot facing

Countersinking Bits

Counterboring

A counterbore tool enlarges the top portion of an existing hole to the diameter of the tool. Counterboring is often performed after drilling to provide space for the head of a fastener, such as a bolt, to sit flush with the workpiece surface. The counterboring tool has a pilot on the end to guide it straight into the existing hole

Counterboring Bit

Spotfacing

Spotfacing provides a seat or flat surface at the entrance and surrounding area of a hole. This flat surface allows the bottom of a screw or bolt to seat squarely with the material. Spotfacing is commonly done on castings where irregular surfaces are found. Spotfacing may be performed on a drill press with a counterbore of suitable size for the operation. A proper size pilot must be used whenever this is done on the drill press.

Spotfacing

spotface

Making a sloped surface flat

To seat a nut

Back spotface

The holes in the bottom part are transferred by spotting through from the top part.

Drilling of the bottom part can then proceed in the knowledge that both sets of holes are identical, which may not be the case if both parts are marked out and drilled individually.

Spotting

Drilling holes to depth

Holes can be drilled to a particular depth by setting the depth stop on the machine

e.g. 15mm

Operations in drilling machine

Types of cutters

Reamers :-

Multi tooth cutting tool

Accurate way of sizing and finishing the pre-existing hole.

Accuracy of 0.005mm can be achieved

Boring Tool:-

Single point cutting tool.

Boring tool is held in the boring

bar which has the shank.

Accuracy of 0.005mm can be achieved.

Types of cutters

Countersinks :-

Special angled cone shaped enlargement at the end of the hole. Cutting edges at the end of conical surface.

Cone angles of 60, 82, 90, 100, 110, 120

Counter Bore Tool:-

Special cutters uses a pilot to guide the cutting action .

Accommodates the heads of bolts.

Types of cutters

Combined Countersinks and central drill :-

Special drilling tool to start the hole accurately.

At the end it makes countersinks in the work piece.

Gun drill :-

Machining of lengthy holes with less feed rates.

To overcome the heating and short life of the normal drill tool

Gundrills Geometry

The gundrill geometry is very different from

that of conventional drills.

Types of cutters

Types of cutters

Tapping:-

For cutting internal thread

Multi cutting edge tool.

Tapping is performed either by hand or by machine.

Minor dia of the thread is drilled and then tapping is done.

Drilling Machine Vice

The Machine Vice has slots in the side of the base of the vice which enable the user to screw the Machine Vice to the Drilling Machine table.

Work Holding Devices

T-Slot block

Direct Clamping

Clamping set

Vee Blocks & Clamps

used when drilling round bar

Hand Vice

used on drilling machine to clamp sheet metal

Drilling sheet metal

PROBLEMS since the chisel edge can break through before the drill is cutting its full diameter, due to the length of the drill point and the thinness of the material. In this case there is no guide at all the drill will wander and produce a hole to some odd shape. Producing these odd-shaped holes is known as lobing.

Drilling Thin Material

Support acts as thicker material so drill point is guided through work

Drilling plastics

problems associated with producing holes in plastics.

Thermosetting plastics can be drilled using standard high-speed-steel twist drills. The chips from thermoplastic materials tend to stick and pack the flutes and cause overheating, which can effect the composition of the material.

Drilling plastics

To prevent this, slow-helix drills with wide highly polished flutes are available. Point thinning can also be carried out to reduce friction and heat at the centre of the drill point. A better finish on breakthrough can be obtained by sharpening the point angle at 90..

Definitions

Cutting Speed (v):-

Its the peripheral speed of the drill

v = *D*N where

D = dia of the drill in m

N = Speed of rotation in rpm

Feed Rate (f):-

Its the movement of drill along the axis (rpm)

Depth of Cut (d):-

The distance from the machined surface to the drill axis

d = D / 2

Material Removal Rate:-

Its the volume of material removed by the drill per unit time

MRR = ( D2 / 4) * f * N mm3 / min

Machining Time (T) :-

It depends upon the length (l) of the hole to be drilled , to the Speed (N) and feed (f) of the drill

t = L / f N min

Precautions for Drilling machine

Lubrication is important to remove heat and friction.Machines should be cleaned after useChips should be removed using brush.T-slots, grooves, spindles sleeves, belts, pulley should be cleaned.Machines should be lightly oiled to prevent from rusting

Safety Precautions

Do not support the work piece by hand use work holding device.Use brush to clean the chipNo adjustments while the machine is operatingEnsure for the cutting tools running straight before starting the operation.Never place tools on the drilling tableAvoid loose clothing and protect the eyes.Ease the feed if drill breaks inside the work piece.

Drilling And Drills

Types of drills

Twist drill: most

common drill

Step drill:

produces holes

of two or more

different

diameters

Core drill: used

to make an

existing hole

bigger