Figure 21.4 (a) Manually operated milling

• CNC machines can be used continuously and only need to be switched off for occasional maintenance.
  
• These machines require less skilled people to operate unlike manual lathes / milling machines etc.
  
• CNC machines can be updated by improving the software used to drive the machines.
  
• Training for the use of CNC machines can be done through the use of 'virtual software'.
  
• The manufacturing process can be simulated virtually and no need to make a prototype or a model. This saves time and money.
  
• Once programmed, these machines can be left and do not require any human intervention, except for work loading and unloading.
  
• These machines can manufacture several components to the required accuracy without any fatigue as in the case of manually operated machines.
  
• Savings in time that could be achieved with the CNC machines are quite significant.
  
  Some of the disadvantages of the CNC machines are:
  
  
• CNC machines are generally more expensive than manually operated machines.
  
• The CNC machine operator only needs basic training and skills, enough to supervise several machines.
  
• Increase in electrical maintenance, high initial investment and high per hour operating costs than the traditional systems.
  
• Fewer workers are required to operate CNC machines compared to manually operated machines. Investment in CNC machines can lead to unemployment.