Spindles used in Turning

A very important function of spindles is turning. Like drilling, milling, grinding, turning is another important basic machining processes. Turning as a machining process produces cylindrical parts. Turning produces cylindrical components in a lathe and this is done manually or by using a CNC (computer numerical control) machine. The manual turning is done on conventional machines or lathes which are not computerized, requiring constant supervision. Turning can also be done using automatic lathes operated by skilled fitters and turners. With advance technology, modern turning is moving towards the use of CNC controls.

Turing process
Turning process produces solids of revolution which can be adjusted because of the specialized nature of the operation. This machining is done on a machine called a lathe in which the tool is stationary and the part is rotated. When turning, a cylindrical piece of material, made of wood, metal, etc. is rotated. The cutting tool moves along two axes of motion, thereby producing precise depths and diameters. Turning is done either on the inside of the cylinder or outside to produce tubular components to various measurements.

Diagrammatic representation:The cutting is done as shown below


Features of turning
Turning is the machining of an external surface with the following features:

• Turning with the workpiece rotating.
  
  
• Turning with a single-point cutting tool.
  
  
• Turning with the cutting tool feeding parallel to the workpiece's axis and at a distance that will remove the work's outer surface.
  
  
• There is a type of turning known as taper turning where the cutter path is at an angle to the work axis.
  
  
• Contour turning is another type of turning where the distance of the cutter from the work axis is changed to produce the desired shape.

Adjustable cutting factors available in turning
There are three primary factors in any turning operation. They are as follows:

Speed
This factor generally refers to the spindle and the workpiece. It tells their rotating speed in revolutions per minute(rpm). The most important figure for a particular turning operation is the surface speed. This is the speed where the work piece material moves past the cutting tool. This is measured by multiplying the rotating speed with the circumference of the workpiece before the cut is started and this is expressed as sfpm (surface feet per minute). Every workpiece with different diameter will have a different cutting speed, even though the rotating speed is the same. Depending on the spindle used, the speed varies.

Feed
This is the cutting tool, and here the rate is that at which the tool advances along its cutting path. On many lathes, the feed rate is directly related to the spindle speed and is expressed in ipr (inches per revolution).

Depth of Cut
This refers to the thickness of the layer being cut from the workpiece or the length of the uncut surface of the workpiece to the cut surface, expressed in inches. The important fact out here is that the diameter of the workpiece is reduced by two times the depth of cut. The reason behind this is that this layer is being removed from both sides of the work.