CNC Lathe: Precision Machining Quiz

CNC Lathe

• A CNC lathe is an improvement over an automatic lathe by incorporating a computer interface.
• It uses a dedicated stored program to carry out different operations.
• High degree of precision and accuracy can be achieved by carrying out different operations on a workpiece.
• The program can be suitably changed to meet the versatile requirements.
• It is used for mass production work.

Lathe Operations

• All most all the basic machining operations can be performed on a lathe.
• Some of the important and generally performed lathe operations are:
  • Turning
  • Step Turning
  • Facing
  • Taper turning
  • Thread cutting
  • Knurling
  • Chamfering

Turning or Plain Turning

• The process of metal removal from a cylindrical job is called straight or plain turning.
• The plain turning operation is performed using the cross slide and the carriage.
• The workpiece is supported between the two centres which cause the rotation of the workpiece.
• A single point cutting tool is fed perpendicular to the axis of the workpiece with the required depth of cut using the cross slide hand wheel and is moved parallel to the axis of the workpiece towards the headstock using the carriage hand wheel facilitating the metal removal.

Types of Lathes

• Engine Lathe:
  • It has all the basic parts and the headstock is much more robust in construction.
  • It has additional mechanisms for driving the lathe spindle at multiple speeds.
  • It can feed the cutting tool both in cross and longitudinal directions with reference to the lathe axis with the help of carriage, feed rod and lead screw.
• Capstan and Turret Lathe:
  • It is an development over an engine lathe and is used for mass production work.
  • The tailstock is replaced by a hexagonal turret on the face of which multiple tools can be fitted and fed into the work in proper sequence.
  • Several different type of operations can be performed on a workpiece without resetting the work or the tools.
• Tool Room Lathe:
  • A tool room lathe has features similar to an engine lathe but is more accurately built and has wide range of spindle speeds ranging from very low to high speeds.
  • It is mainly used for precision work on tools, dies, gauges and in machining work where accuracy is needed.
• Automatic Lathe:
  • These are high speed, heavy duty, mass production lathes with complete automatic control.
  • Once the tools are set they automatically perform all the operations to finish the job.

Principle of Working of a Lathe

• The work piece is held rigidly using one of the work holding devices, known as chuck and is rotated at high speeds in an anticlockwise direction when viewed from the tailstock end or the right side end.
• A V - shaped cutting tool which is stronger and harder than the work piece is held against the workpiece and is fed or moved parallel to the lathe axis towards the headstock end or the left side end leading to the production of a cylindrical surface.

Major Parts of a Lathe and their Functions

• Bed:
  • The bed is a foundation part of a lathe and supports all its other parts.
  • There are two precision machined guide ways on the top of the bed viz., outer guide ways and inner guide ways.
• Headstock:
  • The housing comprising the stepped cone pulley and feed gear box is called the headstock of the lathe.
  • The headstock is rigidly mounted on the inner guide ways of lathe bed at its left end and is not movable.
  • The main spindle projects out from the headstock and is driven at multiple speeds.
• Tailstock:
  • Tailstock is the movable part of the lathe that carries the dead centre in it.
  • It is mounted loosely on the inner guide ways of lathe bed on the right hand side and can be moved and locked in any position.