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
Revolutions per Minutes
Tool Diameter
Cutting Speed Obtained From
Machinist Handbook
RPM = CS x 4
Diameter
Recommended Cutting SpeedsMilling 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
ExampleWhat spindle speed should be used to Mill Aluminum with a ½ inch End Mill?
CS x 4DiameterRPM =
Cutting Speed for Aluminum is 250 surface ft./min.
ExampleWhat spindle speed should be used to Mill Aluminum with a ½ inch End Mill?
CS x 4DiameterRPM =
Cutting Speed for Aluminum is 250 surface ft./min.
250 x 4
.5RPM = = 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
DiameterRPM =
Cutting Speed for Soft Cast Iron is 80 surface ft./min.
80 x 4
.250RPM = = 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 FeedTool 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 RateCalculate 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 RateCalculate the Feed Rate for End Milling
Aluminum with a 2 flute, ½ inch HSS end mill.
Fm = ft x nt x Nft=.005 in. / tooth nt= 2 teeth
N = = 2000 rpm250 x 4
.5=
Fm = .005 x 2 x 2000
Fm = 20 in/min.
Your turn, ex. Feed RateCalculate the Feed Rate for Face Milling
Aluminum with a 4 flute, ¾ inch HSS end mill.
Fm = ft x nt x Nft=.005 in. / tooth nt= 4 teeth
N = = 1333.33 rpm250 x 4
.75=
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
Tool Feed Rate (ipm) = ipr x rpm
Feed in inches/min.
Penetration rate in inches/rev.
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
250 x4.375
RPM = 2,666 RPM
Drill feed: ¼ - ½ diameter: .004 - .007
Tool Feed Rate (ipm) = .005 x 2,666
ipm = 13.33
What tool feed rate should be used for drilling a .375 inch hole in aluminum?
Tool Feed Rate (ipm) = ipr x rpm
Your Turn, Ex. Drill Feed
1,600 RPM
Drill feed: ¼ - ½ diameter: .004 - .007
Tool Feed Rate (ipm) = .004 x 1,600
ipm = 6.4
What tool feed rate should be used for drilling a .25 inch hole in copper?
100 x4.25
RPM =
Tool Feed Rate (ipm) = ipr x rpm
Special Operations
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)
CS x 4DiameterRPM =
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
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