Centre lathe turning operations - Taper turning
 
When the diameter of a piece changes uniformly from one end to the other, the piece is said to be tapered. Taper turning as a machining operation is the gradual reduction in diameter from one part of a cylindrical workpiece to another part. Tapers can be either external or internal. If a workpiece is tapered on the outside, it has an external taper; if it is tapered on the inside, it has an internal taper.

There are three basic methods of turning tapers with a lathe. Depending on the degree, length, location of the taper (internal or external), and the number of pieces to be done, the operator will use either one of the following methods:

With any of these methods the cutting edge of the tool bit must be set exactly on centre with the axis of the workpiece or the work will not be truly conical and the rate of taper will vary with each cut.
 

Form tool method Videos Additional website

  
   

The tool is ground and shaped at a particular angle which is needed in taper turning. This method is used in mass production for producing a small length of taper where accuracy is not
a criterion. The form tool should be set at right angle to the axis of the work. The carriage should be locked while taper turning by this method.

Advantage

  • Once the tool is made with cutting edge at particular angle, as long as tool is aligned perpendicular to the axis of the lathe, one can easily turn the jobs at required angle.

Disadvantage

  • There is only one angle value possible for the tool to be ground at a time.
 

Compound slide method Videos Additional Website
   

Generally short and steep taper are produced using this method. In this method the work piece is held in the chuck and it will be rotated about the lathe axis. The compound rest is swivelled to the required angle and then it will be clamped in position.

Advantage:

  • Both internal and external taper can be produced

  • Steep taper can be produced

  • Easy setting of the compound slide

Disadvantages:

  • Only hand feed can be given

  • Threads on taper portion cannot be produced

  • Taper length is limited to the movement of the top slide.

Calculations

External taper

Internal taper
 

Tailstock method Videos
   

In this method the job is held at an angle and the tool moves parallel to the axis. The body of the tailstock is shifted on its base to an amount corresponding to the angle of taper. This method. The taper can be turned between centres only and this method is not suitable for producing steep tapers.

ADVANTAGES

  • Power feed can be given

  • Good surface finish can be obtained

  • Maximum length of the taper can be produced

  • External threads on taper portion can be produced

  • Duplicate tapers can be produced

DISADVANTAGES

  • Only external taper can be turned

  • Accurate setting of the offset is difficult

  • Taper turning is possible when work is held between centres only

  • Damages to the centre drilled holes of the work

  • The alignment of the lathe centres will be disturbed

  • Steep tapers cannot be turned

Calculations - to be done

 

Diagram ‘C’ shows the scale at the back of the tailstock. To adjust the tailstock so that it is off centre usually means loosening a number of allen screws, offsetting the tailstock and then tightening the screws back in position.
   
 

Taper turning attachment method Videos Additional website
 
Taper Turning Attachment is very much popular and fits on all lathe machines. In ordinary straight turning, the cutting tool moves along a line parallel to the axis of the work, causing the finished job to be the same diameter throughout.

When the diameter of a piece changes uniformly, from one end to the other, the piece is said to be tapered. Taper turning as a machining operation is the gradual reduction in diameter from one part of a cylindrical workpiece to another part. Tapers can be either external or internal. If a workpiece is tapered on the outside, it has an external taper; if it is tapered on the inside, it has an internal taper.

Advantages of Using Taper Attachment for Tapers:

  • Both internal and external tapers can be produced.
  • Threads on both internal and external taper portions can be cut.
  • Power feed can be used.
  • Lengthy taper can be produced.
  • Good surface finish is obtained.
  • The alignment of the lathe centres is not disturbed.
  • It is most suitable for producing duplicate tapers because. the change in length of the job does not affect the taper.
  • The job can be held either in chuck or in between centres.

Disadvantages of Taper Turning Attachment:

  • Only limited taper angles can be turned.
  • Cross feed must be disengaged for operation, time consuming.
  • Only viable for large production runs.