PowerPoint to accompany
Technology of Machine Tools
6th Edition
Krar • Gill • Smid
Cutting Speeds and
Feeds
Unit 41
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
41-2
Objectives
• Calculate the revolutions per minute
(r/min) for inch and metric size drills
• Select the feed to be used for various
operations
• Calculate the revolutions per minute for
the reaming operation
41-3
Cutting Speeds and Feeds
• Two important factors
– Diameter and material of cutting tool
– Type of material being cut
• Speed of twist drill referred to as cutting
speed, surface speed or peripheral speed
– Distance point on circumference of drill will
travel in 1 min
41-4
Recommended Cutting Speeds
For every job, choose the drill speed that will
result in the best production rates!
Steel Casting
Tool Steel
Drill Size Cutting Speeds in Feet per Min or Meters per Min
in mm
40 ft/min 12 m/min 60 ft/min 18 m/min …
1/16 2
2445
1910
3665
2865
1/8 3
1220
1275
1835
1910
3/16 4
815
955
1220
1430
Portion of Table 41.1 from text
41-5
Economical Drilling Speed
Variables
•
•
•
•
•
•
•
Type and hardness of material
Most important!
Diameter and material of drill
Depth of hole
Type and condition of drill press
Efficiency of cutting fluid employed
Accuracy and quality of hole required
Rigidity of work setup
41-6
Revolutions per Minute
• Compute correct number of r/min of drill
press spindle for given size drill
– Type of material to be drilled
– Recommended cutting speed of material
– Type of material from which drill is made
41-7
Formula (Inch)
CS (feet per minute) x12
r / min 
 D(drill circumfere nce in inches)
where CS = recommended cutting speed in
feet per minute for the material being drilled
D = diameter of drill being used
Revolution per minute = number of revolutions
of the drill necessary to attain proper cutting
speed for metal being machined.
41-8
Simplified Formula
• Since not all machines can be set to exact calculated
speed, pi (µ) divided into 12 to simplify formula
CS x 4
r / min 
D
Example: Calculate r/min required to drill a ½ in hole
in cast iron (CS 80) with a high-speed steel drill.
80 x 4 320
r / min 

 640
1/ 2
1/ 2
41-9
Formula (Metric)
CS (m)
r / min 
 D(mm)
Convert so all units are in mm
CS x 1000
r / min 
D
CS x 320
r / min 
D
Example: Calculate r/min required to drill 15 mm hole in
tool steel (CS 18) using a high-speed steel drill.
18 x 320 5760
r / min 

 384
15
15
41-10
Feed
• Distance drill advances into work for each
revolution
• May be expressed in decimals, fractions of
an inch, or millimeters
• Three factors govern rate of feed
– Diameter of drill
– Material of workpiece
– Condition of drilling machine
41-11
Drill Feeds
General –purpose Work
Drill Size
in.
Feed per Revolution
mm
in.
mm
1⁄8 and smaller 3 and smaller .001 to .002
0.02 to 0.05
1⁄8 to ¼
3 to 6
.002 to .004
0.05 to 0.1
¼ to ½
6 to 13
.004 to .007
0.1 to 0.18
½ to 1
1 to 1 ½
13 to 25
25 to 38
.007 to .015
.015 to .025
Table 41.2 Drill feeds
0.18
0.38 to 0.63
41-12
Drill Feeds
• General rule: feed rate increases as drill size
increases
– Too coarse – chip cutting edges
– Too light – chattering noise, dulls cutting edge
• Hard steels or alloys use slower feed
• Softer metals drilled with faster feed
• Blue steel chips indicate too much heat at
cutting edge
– Dull cutting edge or too high speed
41-13
Cutting Fluids
• Provide both cooling and lubrication
• Properties of an effective liquid in
dissipating heat
– Able to absorb heat rapidly
– Have good resistance to evaporation
– Have high thermal conductivity
Oil: good lubricant, poor coolant
Water: best coolant, no lubricating value (promotes rust)
41-14
Good Cutting Fluid
•
•
•
•
•
•
Cool workpiece and tool
Reduce friction
Improve cutting action
Protect work against rusting
Provide antiweld properties
Wash away chips