Drilling Machine Operations: Drilling, Reaming, Boring, Counter boring, Countersinking, Spot facing, Tapping, Lapping, Grinding, Trepanning


Drilling Machine Operations: Drilling, Reaming, Boring, Counter boring, Countersinking, Spot facing, Tapping, Lapping, Grinding, Trepanning

                      
Drilling
Machine Operations:-

·       
The different operations that can be performed in a drilling
machine are:

Ø
Drilling

Ø
Reaming

Ø
Boring

Ø
Counter boring

Ø
Countersinking

Ø
Spot facing

Ø
Tapping

Ø
Lapping

Ø
Grinding

Ø
Trepanning

     Drilling:- 


·      
Drilling is the operation of producing a cylindrical hole by removing
of metal by the
rotating edge of cutting tool called the drill.

·      
The drilling is the simplest
method of producing
a hole.

·      
Before
drilling, the centre
of hole is located on the workpiece by drawing two
lines at right angles
to each other and then center punch
is used to produce an indentation
at the centre.

·      
Drill
point is pressed
at this centre
point to produce
the required hole.

·      
Drilling does not produce
an accurate hole
in a workpiece and the hole is generated
by drilling becomes rough and the hole
is always slightly
oversize than drill
used due to vibration of the spindle
and drill.

·      
A 12 mm drill may produce a hole as much as 0.125 mm oversize and 22 mm drill
may produce 0.5 mm oversize.




Drilling
Drilling




          
Reaming:-

·       Reaming is an accurate way of sizing
and finishing a hole which
has been previously drilled.

·       To
finish a hole and to boring it to the accurate size, the hole is drilled
slightly undersize.

·       The speed
of spindle is made half
of drilling and automatic feed may be produced.

·       Reamer tool is used which has multipoint cutting
edges.



·       It can not originate hole, it simply
follow the path which has
been previously drilled.

·       The material
removed by this process is around 0.375 mm and for accurate
work it should not exceed 0.125 mm.




Reaming
Reaming




           Boring:-

·       Boring is performed in a drilling
machine for reasons
stated as under.

1.    
To enlarge a hole by means of an adjustable cutting tool with only one cutting
edge.

2.     To finish
a hole accurately and to bring it to the required size.

3.     To machine
internal surface of a hole already produced
in casting.

4.     To correct
out of roundness of the hole.

5.    
To correct the location of the hole as
the boring tool follows an independent path with respect
to the hole.

·       In precision machine the accuracy
is as high as ± 0.00125 mm.


Boring
Boring





          
Counter boring:-

·       Counter boring is the operation of enlarging the end of hole cylindrically.

·       The enlarged
hole forms a square shoulder
with original hole.

·      
This
is necessary in some cases
to accommodate the heads of bolts, studs
and pins.

·      
Counter
boring can give accuracy of about ± 0.050 mm.

·      
The cutting speed for counter
boring is 25% less than that of drilling operation.


Counter boring
Counter boring





           Countersinking:-


·      
Counter
sinking is the operation of making a cone shaped
enlargement of the end of a
hole to provide
a recess for a flat head screw or countersunk rivet fitted into the
hole.

·      
Standard countersinks have 60o, 82o or 90o inclined angle.

·      
Cutting
speed is 25% less than that of drilling.



Counter sinking
Counter sinking





           Spot facing:-

·       Spot facing
is the operation of smoothing and
squaring the surface area
and a hole for the seat for a nut or the head of the screw.

·       Counter bore
or a special facing tool
may be employed for this purpose.



Spot facing
Spot facing




          
Tapping:-

·       Tapping is the operation of cutting internal
threads by means
of a cutting tool called a
tap.

·       Tap may be considered as a bolt with accurate
threads cut on it.

·       The threads
act as cutting edges which
are hardened and ground.

·       When tap is screwed
into the hole it removes
metal and cuts
internal threads which will fit into external
threads of the same size.



Tapping
Tapping




  Lapping:-


·       Lapping
is the operation of sizing and finishing a small diameter hardened by removing a very small
amount of material
by using a tap.

           Grinding:-

·       Grinding operation may be performed in a drilling machine to finish
a hardened hole.

·       Grinding wheel
is made to revolve with the spindle
and is fed up and down.

·       Accuracy in grinding operation
is ± 0.0025 mm.

           Trepanning:-

·       Trepanning
is the operation of producing a hole by removing metal along the circumference of a hollow
cutting tool.

·       Trepanning operation is performed for producing large
holes.

·       Fewer chips
are removed but tool may be operated at higher speeds
as the variation in diameter of tool is limited
by narrow cutting
edge.


Trepanning
Trepanning

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