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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.

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