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To seek experience first hand
[]
 
See also: 
Recreation
 and 
Learning
 
Exploration as the pursuit of first hand experience and knowledge is often an example 
of diversive and intrinsic exploration when done for personal satisfaction and 
entertainment, though it may also be for purposes of learning or verifying the 
information provided by others, which is an extrinsic motivation, and which is likely to be 
characterised by a relatively systematic approach. As the personal aspect of the 
experience is central to this type of exploration, the same region or range of 
experiences may be explored repeatedly by different people, for each can have a 
reasonable expectation of personal discovery.

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Drilling 
For drilling in the earth, see 
Boring (earth)
. For other uses, see 
Drilling (disambiguation)
. 
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"Drilling"
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(June 2008) (
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Titanium drilling 
Drilling
is a 
cutting
 process where a 
drill bit
 is spun to cut a hole of circular 
cross-
section
 in solid materials. The drill bit is usually a rotary 
cutting tool
, often multi-point. 
The bit is 
pressed
 against the work-piece and rotated at rates from hundreds to 
thousands of 
revolutions per minute
. This forces the cutting edge against the work-
piece, cutting off 
chips (swarf)
 from the hole as it is drilled. 
In 
rock
 drilling, the hole is usually not made through a circular cutting motion, though the 
bit is usually rotated. Instead, the hole is usually made by hammering a drill bit into the 
hole with quickly repeated short movements. The hammering action can be performed 
from outside the hole (
top-hammer drill
) or within the hole (
down-the-hole drill
, DTH). 
Drills used for horizontal drilling are called 
drifter drills
. 
In rare cases, specially-shaped bits are used to cut holes of non-circular cross-section; 
a 
square
 cross-section is possible.
[1]
 
Process
[]
Drilled holes are characterized by their sharp edge on the entrance side and the 
presence of 
burrs
 on the exit side (unless they have been removed). Also, the inside of 
the hole usually has helical feed marks.
[2]
 
Drilling may affect the mechanical properties of the workpiece by creating low 
residual 
stresses
 around the hole opening and a very thin layer of highly 
stressed
 and disturbed 
material on the newly formed surface. This causes the workpiece to become more 
susceptible to 
corrosion
 and 
crack propagation
 at the stressed surface. A finish 
operation may be done to avoid these detrimental conditions. 
For 
fluted
 drill bits, any chips are removed via the flutes. Chips may form long spirals or 
small flakes, depending on the material, and process parameters.
[2]
 The type of chips 
formed can be an indicator of the 
machinability
 of the material, with long chips 
suggesting good material machinability. 
When possible drilled holes should be located perpendicular to the workpiece surface. 
This minimizes the drill bit's tendency to "walk", that is, to be 
deflected
 from the intended 
center-line of the bore, causing the hole to be misplaced. The higher the length-to-
diameter ratio of the drill bit, the greater the tendency to walk. The tendency to walk is 
also preempted in various other ways, which include: 

---


Establishing a centering mark or feature before drilling, such as by: 
o
Casting
, 
molding
, or 
forging
 a mark into the workpiece 
o
Center punching
 
o
Spot drilling
 (i.e., center drilling) 
o
Spot facing
, which is machining a certain area on a casting or forging to 
establish an accurately located face on an otherwise rough surface. 

Constraining the position of the drill bit using a 
drill jig
 with 
drill bushings
 
Surface finish
 produced by drilling may range from 32 to 500 microinches. Finish cuts 
will generate surfaces near 32 microinches, and roughing will be near 500 microinches. 
Cutting fluid
 is commonly used to cool the drill bit, increase tool life, increase 
speeds 
and feeds
, increase the surface finish, and aid in ejecting chips. Application of these 
fluids is usually done by flooding the workpiece with coolant and lubricant or by applying 
a spray mist.
[2]
 
In deciding which drill(s) to use it is important to consider the task at hand and evaluate 
which drill would best accomplish the task. There are a variety of drill styles that each 
serve a different purpose. The subland drill is capable of drilling more than one 
diameter. The spade drill is used to drill larger hole sizes. The indexable drill is useful in 
managing chips.
[2]