The document discusses the cutting speed for turning on a lathe, which is the speed at which the workpiece rotates and is crucial for effective machining processes. It outlines factors affecting cutting speed, including material hardness, tool rigidity, and machine conditions, as well as the method for setting speeds on different types of lathes. Additionally, it provides formulas for calculating both lathe cutting speed and spindle speed based on the diameter of the workpiece.

1. On the Lathe

2. Cutting speed
Cutting speed for turning is the speed at which the
work rotates. This is also known as surface speed

3. Rate at which point on work circumference travels
past cutting tool
 expressed in meters per minute (m/min)
Important to use correct speed for material
Too high: cutting-tool breaks down rapidly
Too low: time lost, low production rates

4. Cutting speed selection
The softer the work material, the faster the
recommended cutting speed

5. The hardness of the cutting tool material has a
great deal to do with the recommended cutting
speed. The harder the cutting tool material, the
faster the cutting speed. The softer the cutting
tool material, the slower the recommended
cutting speed

6. The depth of the cut and the feed rate will also
affect the cutting speed, but not to as great an
extent as the work hardness

7. Factors that Determine cutting
speed
The material being cut
The rigidity and condition of the machine
The material of which the tool is made
from
The depth of cut and the feed rate
Availability of coolant (cutting fluid)

8. Setting Speeds on a Lathe
Speeds measured in revolutions per minute
Changed by stepped pulleys or gear levers
Belt-driven lathe
Various speeds obtained by changing flat
belt and back gear drive
Geared-head lathe
Speeds changed by moving speed levers into
proper positions according to r/min chart
fastened to headstock
Safety Note!! NEVER change speeds
when lathe is running.

9. Setting Speeds on a
Lathe
Speeds measured in revolutions per minute
Changed by stepped pulleys or gear levers
Belt-driven lathe
Various speeds obtained by changing flat
belt and back gear drive
Geared-head lathe
Speeds changed by moving speed levers
into proper positions according to r/min
chart fastened to headstock
9

10. Lathe Cutting Speeds
Material being cut Cutting speed (metres/minute
Mild steel 20 to 28
Cast iron 18 to 25
High carbon steel 12 to 18
Brass 45 to 90
Bronze 15 to 21
Aluminium Upto 300
47-10

11. Calculating Lathe cutting speed
Given in metres per minute
spindle speed of machine (N) and
diameter of work must be known
S (m/min)= πDN/1000
Where π= 22/7 or 3.142
 D= diameter of material
 N= Spindle speed(rev/min)
47-11

12. Calculating Lathe Spindle speed
(rev/min)
D
xS1000
rev/min
π
=
S (m/min)= cutting speed
Where π= 22/7 or 3.142
D= diameter of material
N= Spindle speed(rev/min

13. Exercise
Calculate the spindle speed required to
turn 200mm diameter piece of high speed
steel, if the cutting speed is 28 m/min.
Find the cutting speed of a 15mm diameter
bar being turned with a spindle of 955
rev/min.
Determine the lathe speed to cut a 40mm
diameter at 30 m/min