• CNC is the acronym for computer
• It is an outgrowth of the older term
"NC", which stands for just "numerical
• Numeric control is a programmable
automation in which process is
controlled by numbers, letters and
(Computer + NC=CNC)
• CNC refers to the idea of controlling
machine tools programmatically via
computer. With the older "NC" term, A
computer need not be involved. The
• This means a computer converts
the design produced by Computer
Aided Design Software (CAD), into
numbers. The numbers can be
considered to be the coordinates of
a graph and they control the
movement of the cutter. In this way
the computer controls the cutting
and shaping of the material.
• CNC can control the motions of the
work piece or tool, the input
parameters such as feed, Depth of
cut, speed, and the functions such
as turning spindle on/off, turning
• The applications of CNC include
both for machine tool as well as
non-machine tool areas. Some are
sheet-metal press working
tube bending machine etc.
5. welding machines (arc and resistance),
tape laying and
filament winding machines for Composites etc.
• This Technology is applied to Prosthetics and Orthotics field as well.
• The first NC machines were built
in the 1940s and 1950s by Prof.
John T Parson.
• Conceived method of using
punched cards containing
coordinate position data to
control the machine tool.
• In 1948, Parson demonstrated
his concept to U.S Air Force
Fig: punched card which contains
command to control automated machinery
• CNC machine came to existence
after evolution of computer
• Modern CNC Machine are
improving further as the
technology is changing with
variety of functions according to
1959 CNC Machine: Milwaukee-Matic-II
was first machine with a tool changer...
8. COMPUTER NUMERICAL CONTROL
• Easier to program
• Easy storage of existing
• Easy to change program
• Avoid human error
• CNC machines are safe to
• Complex geometry is
produced as cheaply as
• Costly setup than manually
• Skilled operators
• Computers, programming
• Maintenance is difficult.
10. DIRECT NUMERICAL CONTROL
• Greater computation and flexibility.
• Eliminates use of punched tapes.
• Convenient storage of NC Part Programme
in computer file.
• Direct conversion of data from CAD to NC
• Increases Productivity
• Save time.
• The only disadvantage of the DNC is
if the computers breaks down, but
the computer is so reliable that this is
unlikely to occur..
• Some type like Terminal-based DNC
system and Network-based DND
system are expensive.
11. NUMERICAL CONTROL
• Higher productivity- reduction in time of
set up, work piece handling time, tool
• Reduced non-productive time.
• Reduced fixturing.
• Greater accuracy and repeatability
• Reduced inventory
• Reduced floor requirements.
• Operator skill level reduced
• NC machine are safer to operate.
• high investment cost.
• High maintenance effort.
• Need for skilled programmers.
• High utilization required.
12. ELEMENTS OF CNC MACHINE
• A CNC machine consists of following 6 major elements:
i. Input device
ii. Machine control unit
iii. Machine tool
iv. Driving system
v. Feedback devices
vi. Display unit
16. DRIVER SYSTEM
• The driving system is an
important component of
CNC machine as the
accuracy and repeatability
depend very much on the
performance of the
• The driving system is
classified as Spindle
drives and feed drives.
• The spindle drives are
used to provide angular
motion to the work piece
or cutting tool.
• Feed drives are used to
drive the slide or a table.