Tap Speed and Feed Formulas:
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Definition: This calculator determines the optimal RPM and feed rate for tapping operations based on material speed (SFM), tap diameter, and thread density.
Purpose: It helps machinists and CNC operators achieve proper thread cutting while maximizing tool life and efficiency.
The calculator uses two formulas:
Where:
Explanation: First calculate RPM from SFM and diameter, then derive feed rate based on the thread pitch.
Details: Correct calculations prevent tap breakage, ensure thread quality, and optimize machining time. Too fast can break taps, too slow reduces productivity.
Tips: Enter the material's recommended SFM, tap diameter in inches, and threads per inch. All values must be > 0.
Q1: Where do I find SFM values?
A: Refer to material/tap manufacturer charts. Example: 30 SFM for aluminum, 10 SFM for mild steel, 5 SFM for stainless.
Q2: Why is 3.82 used in the formula?
A: It's the conversion factor (12/π) to convert SFM (feet) to RPM (inches).
Q3: How does TPI affect feed rate?
A: Higher TPI (finer threads) requires slower feed to maintain proper thread engagement.
Q4: Should I adjust for different tap materials?
A: Yes, carbide taps can run 2-3× faster than HSS at the same SFM.
Q5: What about thread percentage?
A: For less than 75% thread engagement, you may increase feed by 10-20%.