Calculating Cutting
Speeds and Feed Rates
for CNC
Computer Integrated Manufacturing
Unit 2 CNC Machining
In this lesson
• Discuss different Cutting Tools.
• Calculate Cutting Speeds and Feed
Rates.
• Practice.
• Download reference materials to share
with your students.
Basic Cutting Tools
Center
Cutting
End Mill
Ball End
Mill
Non- Center
Cutting End
Mill
Indexable Shell
Mill
Obtain Reference Charts
Click here to open Cutting Speed Chart.
Click here to open Tool Feed Chart.
Click here to open Drilling Feed Chart.
Calculating Spindle Speeds
Cutting Speed
Obtained From
Machinist Handbook
CS
x
4
RPM =
Diameter
Revolutions
per Minutes
Tool
Diameter
Recommended Cutting Speeds
Milling Speeds for High Speed Steel Tools
Material
Cutting Speed in surface ft/min.
Magnesium
300
Aluminum
250
Brass and Bronze
150
Copper
100
Cast Iron (Soft)
80
Cast Iron (Hard)
50
Mild Steel
90
Cast Steel
80
Alloy Steel (Hard)
40
Tool Steel
50
Stainless Steel
60
Titanium
50
High Manganese Steel
30
Note: Double Speed for Carbide Cutting Tools
Example
What spindle speed should be used to
Mill Aluminum with a ½ inch End Mill?
CS x 4
RPM = Diameter
Cutting Speed for Aluminum is 250 surface ft./min.
Example
What spindle speed should be used to
Mill Aluminum with a ½ inch End Mill?
CS x 4
RPM = Diameter
Cutting Speed for Aluminum is 250 surface ft./min.
RPM =
250 x 4
.5
= 2000
Your turn, ex. Spindle Speed
What spindle speed should be used to mill
Soft Cast Iron with a ¼ in. End Mill?
CS x 4
RPM = Diameter
Cutting Speed for Soft Cast Iron is 80 surface ft./min.
RPM =
80 x 4
.250
= 1280
Calculating Feed Rates
Fm = ft x nt x N
Fm = Feed Rate in inches/min.
ft = Feed in inches / tooth
nt = number of teeth on the tool
N = Spindle Speed
Recommended Tool Feed
Tool Feed (in/tooth)
Material
Face Mill
Side Mill
End Mill
Magnesium
.005-.020
.004-.010
.005-.010
Aluminum
.005-.020
.004-.010
.005-.010
Brass and Bronze
.004-.020
.004-.010
.005-.010
Copper
.004-.010
.004-.007
.004-.008
Cast Iron (Soft)
.004-.016
.004-.009
.004-.008
Cast Iron (Hard)
.004-.010
.002-.006
.002-.006
Milt Steel
.004-.010
.002-.007
.002-.010
Alloy Steel (Hard)
.004-.010
.002-.007
.002-.006
Tool Steel
.004-.008
.002-.006
.002-.006
Stainless Steel
.004-.008
.002-.006
.002-.006
Titanium
.004-.008
.002-.006
.002-.006
High Manganese Steel
.004-.008
.002-.006
.002-.006
Note: Double Speed for Carbide Cutting Tools
Example Feed Rate
Calculate the Feed Rate for End Milling
Aluminum with a 2 flute, ½ inch HSS end mill.
Fm = ft x nt x N
ft=.005 in. / tooth
Example Feed Rate
Calculate the Feed Rate for End Milling
Aluminum with a 2 flute, ½ inch HSS end mill.
Fm = ft x nt x N
ft=.005 in. / tooth
N=
nt= 2 teeth
= 250 x 4
.5
= 2000 rpm
Fm = .005 x 2 x 2000
Fm = 20 in/min.
Your turn, ex. Feed Rate
Calculate the Feed Rate for Face Milling
Aluminum with a 4 flute, ¾ inch HSS end mill.
Fm = ft x nt x N
ft=.005 in. / tooth
N=
nt= 4 teeth
= 250 x 4
.75
= 1333.33 rpm
Fm = .005 x 4 x 1333.33
Fm = 26.67 in/min.
Factors That Affect Feed Rates
Power of Spindle Motor
Condition of Cutting Tool
Depth of Cut
Quality of surface finish required
Roughing vs. Finish cuts
Condition of the machine
Strength of Fixture
Tool Feed Rate for Holes
Penetration rate in
inches/rev.
Tool Feed Rate (ipm) = ipr x rpm
Feed in
inches/min.
Spindle speed in
rev./min.
Professional Development Lesson ID Code: 6004
Recommended Drilling Feeds
Drilling Feeds
Drill Diameter (in.) Drill Feed Rate (ipr)
<⅛
.001-.002
⅛–¼
.002-.004
¼-½
.004 - .007
½-1
.007 - .015
>1
.015-.025
Drill Feed Example
What tool feed rate should be used for drilling
a .375 inch hole in aluminum?
Tool Feed Rate (ipm) = ipr x rpm
250 x4
RPM =
.375
2,666 RPM
Drill feed: ¼ - ½ diameter: .004 - .007
Tool Feed Rate (ipm) = .005 x 2,666
ipm = 13.33
Your Turn, Ex. Drill Feed
What tool feed rate should be used for drilling
a .25 inch hole in copper?
Tool Feed Rate (ipm) = ipr x rpm
100 x4
RPM =
.25
1,600 RPM
Drill feed: ¼ - ½ diameter: .004 - .007
Tool Feed Rate (ipm) = .004 x 1,600
ipm = 6.4
Special Operations
CS x 4
RPM = Diameter
Other Special Operations require slower speeds:
Reaming – ½ to ⅔ of that used for drilling the material
Counterboring – ¼ of that used for drilling the material
Countersinking – ¼ of that used for drilling the material
Tapping (threading) – determined by many factors
(usually range from 50 to 300 RPM)
Curriculum Alignment:
Unit 2 – CNC Machining
Section 2.5 – Precision Measurement
References:
Kibbe, R.R. & Neely, J.E. & Meyer, R.O. & White,
W.T. (2002). Machine Tool Practices,
Upper Saddle River, NJ: Prentice Hall.
Oberg, E. & Jones F. D. & Horton, H. L. & Ryffell,
H. H. (2000). Machinery’s Handbook, 26th
ed., New York, NY: Industrial Press Inc.
Credits:
Writer: Ken McDermith
Content Editor: Donna E. Scribner
Narration: Donna E. Scribner
PLTW Editor: Ed Hughes
Production: CJ Amarosa
Video Production: CJ Amarosa
Audio: CJ Amarosa
Project Manager: Donna E. Scribner