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

Narration: Donna E. Scribner

PLTW Editor: Ed Hughes

Production: CJ Amarosa

Video Production: CJ Amarosa

Audio: CJ Amarosa

Project Manager: Donna E. Scribner