# Lathe Machine | Speed ,Depth of Cut ,Feed , Machining Time

Lathe is a machine tool which causes workpiece to revolve so that when cutting tool comes in contact with the workpiece it removes the metal in the form of  chips. Workpiece can be held securely and rigidly on the machine tool between centres or by means of chuck. To cut the material easily the cutting tool should be harder than the material of workpiece. It should be rigidly held on the machine or  should be fed in a definite way relative to the workpiece.
Arrangements for setting the direction of tool advancement and its rigid holding, are already provided on lathe machine.

Cutting speed, feed, depth of cut and machining time are the terms which are used in cutting operation. Study of all these terms is necessary to calculate the machining cost.

### Cutting Speed

Cutting speed of a tool is the speed at which the metal is removed from any surface by the cutting tool. In lathe, it is the peripheral speed of the work past the cutting tool expressed in meter per minute

Cutting speed meter / minute = π d n /1000

where d = diameter of job in mm, and
n = revolution per minute (rpm) of the work.

### Feed

Feed is the displacement of the tool along the workpiece for each revolution of  the work. It is expressed in millimeter per revolution.

### Depth of Cut

It is the perpendicular distance measured from the machined surface to the uncut surface of the workpiece. For lathe the depth of cut is expressed as follow

Depth of cut = (D − d ) /2 mm

where D = dia of job in mm, and
d = finished dia in mm (in single cut)

### Machining Time

In lathe work, if the speed of job, feed of tool and the length of job are given, we can calculate the machining time by the following formula

Machining Time for a Complete Cut minute
= l / (s * n)  Minutes

where l = length of job to be cut in mm,
s = feed in mm / revolution, and
n = rpm (revolution per minute).