Centre lathe processes

Facing Off

Before starting to shape the metal bar it is essential to face off the end of the bar. This  basically means to make the end of the bar perfectly square to the sides of the bar.

When facing off a piece of round bar it is essential to ensure the cutting tool is lined up centrally to the piece of bar. If it is not a “Pip ” will develop which means the face of the bar will not be truly flat.

Parallel Turning

This technique moves the tool parallel to the centre axis of the bar as can be seen from the
drawing.  It is used to reduce the diameter of the bar to the desired size.

Taper Turning

This is where the tool moves along the bar at an angle moving further away from the centre axis of the bar.  The angle of the taper can be set using the protractor scale on the compound slide.

Parting off

When all turning work has been completed the final task is to “Part Off” (remove) the  turned piece from the bar secured in the three jaw chuck.

Knurling

Knurling is the process of ‘pressing’, not cutting, a diamond or straight pattern into the surface of a metal bar.  This is usually done to provide a hand grip.  When performing this task the material must be supported with a live centre as well as being secured in the chuck to stop it from bending as pressure is applied to it.

 

Getting a good finish (Parallel turning, taper turning, facing off)!!

There are three things that you can do to get a good surface finish on the metal bar…

  1. Increase the speed that the machine is operating at (Higher RPM)
  2. Take a much finer size of cut from the surface of the material
  3. Slow down the rate that you are ‘feeding’ the tool along the surface of the metal bar.