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Technical Reference
CNC Cycle Time Formulas
The mathematical foundation of quoting and scheduling. Precise formulas for Milling, Turning, and Drilling.
Don't Do This By Hand
These formulas are complex. Our Machining Time Calculator handles the math, including approach and over-travel distances.
Key Variables
LLength of Cut (in)
fFeed Rate (IPM or IPR)
NRPM
DTool/Part Diameter (in)
Milling Formulas
Standard Side/Slot Milling
Time (min) = L / f
Where f = IPM (Inches Per Minute). Calculate IPM first using: RPM × IPT × Flutes.
Face Milling (with Approach/Overtravel)
Time = (L + A + O) / f
A (Approach Distance): Typically 50% of cutter diameter to ensure full engagement before cutting.
O (Overtravel): Typically 10-20% of cutter diameter to clear the part.
Turning (Lathe) Formulas
Turning / Boring (Constant RPM)
Time (min) = L / (f_n × N)
- f_n: Feed per revolution (IPR). Usually 0.005" - 0.015".
- N: RPM.
⚠️ Note: CSS (Constant Surface Speed) changes RPM as diameter changes, making this formula an approximation for facing cuts.
Drilling / Tapping
Drilling (Standard)
Time = Depth / (N × IPR)
Peck Drilling (Deep Holes)
Time = (Depth / (N × IPR)) × Efficiency Factor
Deep holes (>3xD) require retracts. Multiplier typically ranges from 1.5x to 3.0x depending on hole depth.