1. CNC Machines
Computer numerical control (CNC) machines are automated milling machines that make industrial
components without human assistance. This is possible because CNC machines are fed a series of
instructions that are delivered to an internal computer controller. These instructions are in the form of
codes that belong to the numerical control programming language.
The code used to program CNC machines is generically called G­code. However, G­code instructions
are only part of the programming language. Specifically, G­codes give CNC machines the coordinates
from which to hold and engage the machining tool in order to cut and shape metal to certain
specifications. The entire series of codes used to operate CNC machines also include M­codes and T­
Codes, which manage the CNC machine and drill tool, respectively. Tooling speed and feed controls
are dictated by S­Codes and F­Codes, while X, Y, and Z­codes determine absolute position.
A standardized set of control codes for CNC machines was developed in the early 1960s in the U.S. by
a trade organization known as the Electronic Industries Alliance. Roughly 20 years later, the system
was revised and dubbed RS274D. Although these codes are still used across the country to assist
computer­aided manufacturing (CAM), variations and additions exist among operators and
manufacturers of CNC machines. In fact, operators of specific CNC machines need to be educated
about the differences between manufacturer’s models to avoid a conflict in programming compatibility.
CNC machines have evolved considerably since their initial introduction into the manufacturing
industry. The earliest CNC machines received code instructions through hard­wired controllers, which
meant that the programming format could not be altered. However, later models were programmed via
mainframe cables and floppy disks, which permitted variations in programming. At present, most CNC
machines are tied into a network of computers and receive operating and tooling instructions via a
software file containing the ".NC" extension. Although, the file extension varies with each machine
shop, depending on its ISO certification protocols.
Today, CNC machines have graduated to encompass entire "cells" of tooling machines that can operate
independently of each other. They are driven by the direct upload of CAM software files, eliminating
the need for design plans to be physically drawn up. Modern CNC machines are also capable of
running overnight or for several days without human supervision. In fact, CNC machines are now so
sophisticated that they can dial the chief operator’s cell phone to notify him or her when a tool part
breaks, and still complete other parts of the program. These features make it possible to produce
thousands of parts while the machine shop is closed or while the operator is performing other tasks.
Advantages and disadvantages of using CNC machines
Advantages:­

2. *Accuracy
When programmed correctly, CNC machines are usually 100% correct with what they produce. They:
1. produce parts to maximise accuracy
2.provide good positional accuracy and repeatability
3.provide a high degree of quality because of their accuracy and their ability to reuse programs.
*Simplicity
CNC machines are not all that difficult to use once you learn how. For example:
1.complex jigs and fixtures are not required in all areas
2.since fewer jigs are used, the actual storage requirements are reduced
3.lower tooling costs since there is less need for complex jigs and fixtures
4.once the first piece has passed inspection, minimal inspection is required on subsequent parts
5.advanced machine control and programming capabilities allow for complex machining operations
to be more easily accomplished.
*Time
Using CNC machines effectively reduces the amount of time take to produce furniture items. CNC
machines:
1. enable the operator to make changes or improvements with a minimum of delay or expense
2.reduce waste as errors due to operator fatigue, interruptions and other factors are less likely to
occur
3.improve production planning as they can often perform work at one setting that would normally
require several conventional machines
4.reduce lead time as a result of lower tooling costs.
Disadvantages:­
*Cost
As with any business, costs are always a factor. CNC machinery:
1.costs quite a lot more than conventional machinery
2.does not eliminate the need for expensive tools
3.parts (ie machines and tooling) are costly and their purchase requires extensive justification.
4.is expensive to repair.

3. *Errors
CNC machines do not totally eliminate errors. Operators can still push the wrong buttons, make
incorrect alignments and fail to locate parts properly on a jig.
Conventional Machines:­
Conventional machining is collection of material­working processes in which
power­driven machine tools, such as saws, lathes,milling machines, and drill presses,are used with a
sharp cutting tool to mechanically cut the material to achieve the desired geometry. Machining is a
part of the manufacture of almost all metal products, and it is common for other materials, such as
wood and plastic, to be machined. A person who specializes in machining is called a machinist . A
room, building, or company where machining is done is called machine shop.Much of modern day
machining is controlled by computers using computer numerical control (CNC) machining.