4 drilling

7/30/2019 4 Drilling

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Assistant Professor

and not for any commercial use.

Drilling

T. SADASIVA RAO

Mechanical Engineering Department

NIT Warangal 506 004

Disclaimer

The content presented here is not entirely my own. Some portions are taken from

different sources with great regard. This content is solely for class room teaching


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Creates a round hole in a workpart

Compare to boring which can onlyenlarge an existing hole

Drilling is most common singlemachining operation

Drilling makes up 25% of machining

Cutting tool called a drillor drill bit

Machine tool: drill press

Fig.: Drilling

Drilling


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- drill exits opposite

side of work

Throughholes

does not exit work

opposite side

Blindholes

Figure: Two hole types: (a) through-hole, and (b) blind hole.

Through Holes vs. Blind Holes


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Drilling machines are generally used to originate through

or blind straight cylindrical holes


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Various types of drills anddrilling operations.


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Drilling

Boring

Reaming

Tapping

Counterboring

Countersinking

Spot-facing


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Fig.: ReamingTool called a reamer


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Fig.: Tapping


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Fig.: Counterboring

Counterboring: Follows a drilling operation, or in with drilling with a

custom tool. Purpose is to produce a flat bottom so that bolt head or

nut is below the surface with enough clearance for a tool.


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Countersinking: Similar to counterboring, but with a 60,

82, or 90 beveled bottom to accommodate flat-head

screw or rivet.


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Spot facing: Machine minimum depth and diameter around hole

to ensure full seating of a bolt head. Used on rough stock

surfaces where corrosion or fatigue requirements require fullseating


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Can be operated with ease any

where and in any position which

cannot be drilled in a standard

drilling machine

Driven by high speed electric motor

The maximum size of the drill it can

accommodate is not more than 12 to18 mm.

In fire hazardous areas the drill is

often powered by compressed air.


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Small machine, designed for drilling

small holes at high speed in light jobs.

The base of the machine may be

mounted on a bench or on a floor.

Capable of holding drills of size from

1.5 to 15.5 mm rotating at 20,000 rpm.

Fig. Table top sensitive drilling machine


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For handling1. Bevel gear drive to spindlemedium sized2. Spindle

workpieces. 3. Overhead shaft4. Back stay

5. Counter shaft cone pulley

6. Fast and loose pulleySimilar to a 7. Foot pedalsensitive drilling 8. Base

9. Table elevating handlemachine but larger 10. Rack on column

11. Table elevating clamp handleand heavier in size12. Table clamp

13. Tablewith power feed14. Columnarrangement. 15. Hand wheel for quick feed16. Hand wheel for sensitive feed.

More no. of feeds

and speeds


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Intended for drilling medium to large andheavy workpieces.

Movements:

Radial arm - up and down, radial motion

Drill head - horizontal motion

These movements permit the drill to be

located at any desired point on a large

workpiece for drilling number of holeswithout disturbing the workpiece set up.

Fig.: Radial Drill Press


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Specialized Drill Presses Radial drilling

machines: used on

large workpieces,

spindle mounts on

radial arm, allowing

drilling operations

anywhere along thearm length


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Number of single spindle drilling machinecolumns are placed side by side on a

common base and have a common work table

The speeds and feeds of the spindles are

controlled independently.

Specially adapted for production work. A

series of operations may be performed on the

work by simply shifting the work from one

position to the other on the work table.

Each spindle may be setup properly with

different tools for different operations.


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Structurally rigid column type and are moreproductive like gang drill by having a

pentagon or hexagon turret

The turret bearing a number of drills and

similar tools is indexed and moved up anddown to perform quickly the desired series

of operations progressively.

These drilling machines are available with

varying degree of automation both fixed

and flexible type.


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Large number of drills worksimultaneously on a blank

through a jig specially made

for the particular job.

The entire drilling headworks repeatedly using the

same jig for batch or lot

production of a particular

job.

Drills are driven by a main

spindle and the central gear

through a number of

planetary gears and the

corresponding flexible

shafts.


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Nomenclature of a Drill

FIG.: Chisel-point drill


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Nomenclature and Geometry of a

Twist Drill

FIGURE : 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.


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Steps to High Accuracy Holes with

Conventional Drills

FIGURE To obtain a

hole that is accurate as to size

and aligned on center (located),

this 4 step sequence of

operations is usual.


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