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CNC Machining Formulas

Cutting Speed Formulas:

RPM = Revolutions Per Minute  

SFM = Surface Feet Per Minute

SMPM = Surface Meters Per Minute

Surface Feet Per Minute (SFM) = 0.262 x Diameter ( Tool or Stock ) x RPM

Revolutions Per Minute (RPM) = 3.82 x SFM ÷ Diameter ( Tool or Stock )

SFM to SMPM = SFM x .3048

SMPM to SFM = SMPM x 3.2808399

Feed Rate Formulas:

RPM = Revolutions per Minute  

IPM = Inches per Minute  

FPR = Feed per Revolution

FPT = Feed per Tooth

T = Number of Teeth in Cutter

MMPR = Millimeters per Revolution

IPR = Inches per Revolution

Inches Per Minute (IPM) = FPT x T x RPM

Feed Per Revolution (FPR) = IPM ÷ RPM

Feed Per Tooth (FPT) = IPM ÷ (RPM x T)

Convert Inches Per Revolution (IPR) to Inches Per Minute (IPM) = IPR x RPM

Convert Inches Per Minute (IPM) to Inches Per Revolution (IPR) = IPM ÷ RPM

Convert Inches Per Revolution (IPR) to Millimeters Per Revolution (MMPR) = IPR x 25.40


Metal Removal Formulas:

TCM = Time Cutting in Minutes

TCS = Time Cutting in Seconds  

IPM = Inches per Minute

MRR = Metal Removal Rate ( Cubic Inches per Minute)

L = Length of Cut

W = Width

D = Depth of Cut

F = Feed in Inches Per Minute

Time Cutting in Minutes (TCM) = L ÷IPM

Time Cutting in Seconds (TCS) = L ÷IPM x 60

Distance Over Time in Minutes (L) = IPM x TCM

Metal Removal Rate (MRR) = W x D x F


Degrees Formulas:

Converting Minutes of a Degree to a Decimal:

Divide Minutes by 60

Example:

35° 42’  

Divide Minutes by 60: 42’ ÷ 60 = .7

Bring Down Degrees: 35.7°


Converting Minutes and Seconds of a Degree to a Decimal:

Divide Seconds then Minutes by 60

Example:

35° 41’ 15”

Divide Seconds by 60: 15 ÷ 60 = .25

Divide Decimal Minutes by 60: 41.25 ÷ 60 = .6875

Bring Down Degrees: 35.6875°












Converting Decimal Degrees to Minutes

Multiply Decimal by 60

Example:

30.7°

Multiply Decimal Degrees by 60: .7 x 60 = 42’

Bring Down Degrees: 30° 42’


Converting Decimal Degrees to Minutes and Seconds

Multiply Decimal Degrees by 60

Example:

30.6875°

Multiply the Degree Decimal by 60: .6875 x 60 = 41.25’

Multiply the Decimal Minutes from Last Calculation by 60: .25 x 60 = 15”

Bring Down Degrees: 30° 41’ 15”


Converting Degrees to Radians

Multiply Degrees by .0174532925 to Obtain Radians


Converting Radians to Degrees

Multiply Radians by 57.29577951 to Obtain Degrees




Drill Point Depth and Countersink Diameter Formulas:

60°

82°

90°

118°

120°

135°

Drill Point Angle:

0.866 X Drill Diameter = Drill Point Length

0.575 X Drill Diameter = Drill Point Length

0.500 X Drill Diameter = Drill Point Length

0.300 X Drill Diameter = Drill Point Length

0.288 X Drill Diameter = Drill Point Length

0.207 X Drill Diameter = Drill Point Length


Use the formulas below to calculate the drill point length for various drill point angles:

Note: you can also substitute the drill diameter with a desired countersink diameter to calculate the depth of cut to make a desired countersink.

Also check out Tapping and Threading Formulas….Click Here

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Web Machinist Software:

Web Machinist Software

“Angles Conversion Calculator”  Convert Angles into Decimal Form and Convert Decimals into Angles.  You can also Convert Degrees into Radians and Radians into Degrees.

Web Machinist Angles Conversion Calculator Web Machinist Software Feeds and Speeds Conversions Calculator

“Speeds and Feeds Conversions Calculator” Calculate the Conversions of 16 Speed and Feed Pairs in both Inch and Metric Measurements.

“Machining Formulas” Reference Guide.  Contains 30+ Formulas for the Machinist!

Machining Formulas Reference Guide Web Machinist Software

Need the formula to check True Position?  Go Here

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