Read the texts and decide if the following sentences are true (T) or false (F).A machine
tool uses a power source to modify the shape of metal components of machines. It is a sort of
machine used as a tool in the making of other machines. Machine tools were powered
in the Middle Ages by humans and animals, and later by the energy captured by
waterwheels. After the Industrial Revolution, most machine tools were powered
by steam engine
and nowadays by electricity. Machine tools can be operated manually, or under automatic control.
In the 1960s, computers
gave more fl exibility to the process. Such machines became known as computerized numerical
control (CNC) machines.
They could precisely repeat sequences, and could produce much more complex pieces than even the most skilled tool operators. Let's examine the main
features of some of the most commonly used
machine tools.
Turning machine
The
engine lathe is the most important of all the machine tools. It
is used to produce external or internal
cylindrical surfaces. The piece is held by the
machine and is rotated while a cutting tool
removes excess metal from the external
diameter. Internal turning consists of enlarging
and finishing a hole.
Shaper
This
is a metal-cutting machine used to produce or modify
flat surfaces. The cutting tool moves cutting on
the forward stroke, with the piece feeding
automatically towards the tool during each
return stroke. Shapers can be horizontal or
vertical.
Drilling machine
It
is used to produce circular holes in metal with a twist drill. It also uses a variety of other
cutting tools to perform the basic
hole-machining operations.
Milling machine
This cuts flat metal surfaces. The piece is fed against a rotating cutting tool. Cutters
of many shapes and sizes are available for a wide variety of milling operations. Milling
machines may be manually operated, mechanically automated, or digitally automated via
computer numerical control (CNC).
Grinding
machine
This
removes excessive material from parts that are brought into contact
with a rotating abrasive wheel. Grinding is the most
accurate of all the basic machining processes, but also
the most time consuming.
Press
This
is a machine tool that changes the shape of a workpiece. Historically, metal was shaped by hand using a hammer. Machine presses can be dangerous. Bi-manual controls (controls Band saw which require both hands to be on the buttons to operate) are a very good way to prevent accidents.
Band
saw
It
is a power tool which uses a blade consisting of a continuous band of metal with teeth along one edge. The band
usually rides on two wheels rotating in the same
plane. Band saws are used for woodworking, metalworking, or for
cutting a variety of other materials, and are particularly useful for cutting irregular or curved
shapes. A constant flow of liquid is poured over the
blade to keep it cool and preventing it flom overheating.1) Turning machines remove excess metal from the external diameter and enlarge and finish a hole. TF 2) Shapers can only be vertical. TF 3) Drilling machines use a twist drill to make circular holes. TF 4) Milling machines can only be manually operated. TF 5) Grind ing machines remove excessive material from parts. TF 6) Band saws use a band of metal with teeth to cut various parts. TF 7) Presses are not dangerous if operated by both hands. TF