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Thread Milling Speed & Feed Quick Reference

Thread Milling Speed & Feed Quick Reference

Conservative starting values for solid-carbide thread mills. Verify on a test piece; defer to tooling manufacturer’s data sheet.

1. Formulas

Metric:  RPM = (Vc × 1000) ÷ (π × D)    where Vc = cutting speed (m/min), D = thread mill diameter (mm)

Inch:      RPM = (SFM × 3.82) ÷ D          where SFM = surface feet per minute, D = diameter (inch)

2. Recommended Vc / SFM by Material

Material

Vc (m/min)

SFM

Formability

Notes

Aluminum / Brass

80–150

250–500

Excellent

Start high; use light oil/MQL

Low-Carbon Steel

30–55

100–180

Very Good

Use EP tapping fluid

Alloy Steel (4140)

25–45

80–150

Good

Verify with test piece

304 / 316 Stainless

20–35

65–120

Good

High-pressure coolant ideal

17-4 PH Stainless

25–40

80–130

Good

Avoid rubbing; adequate SFM

Hardened Steel (H13/D2)

20–35

65–115

Moderate

PM carbide grade recommended

Note: Values are conservative starting points for HSS-E / solid-carbide thread mills. Increase gradually where torque, finish and chip evacuation are stable.

3. RPM Quick Lookup (M6–M24)

Thread Size

60 m/min

90 m/min

120 m/min

Pitch (mm)

Tap Drill (mm)

M6 × 1.0

3,185

4,775

6,370

1.0

5.0 / 5.1

M8 × 1.25

2,387

3,580

4,775

1.25

6.7 / 6.8

M10 × 1.5

1,910

2,865

3,820

1.5

8.4 / 8.5

M12 × 1.75

1,592

2,387

3,185

1.75

10.1 / 10.2

M16 × 2.0

1,194

1,790

2,385

2.0

13.8 / 13.9

M20 × 2.5

955

1,432

1,910

2.5

17.2 / 17.3

M24 × 3.0

796

1,194

1,592

3.0

20.7 / 20.8

Tap-drill range shown as “forming / cutting” reference. Forming taps require a larger, tighter-tolerance pilot hole than cutting taps.

4. Worked Examples

Example A — M16 × 2.0 in 4140 alloy steel

Choose Vc = 35 m/min.  RPM = (35 × 1000) ÷ (π × 16) ≈ 696 RPM. Feed per tooth locked to pitch = 2.0 mm/rev; use high-pressure coolant and a helical entry ramp.

Example B — 17-4 PH stainless, ~HRC 30

Choose Vc = 30 m/min. For an 8 mm thread mill: RPM = (30 × 1000) ÷ (π × 8) ≈ 1,193 RPM. Keep SFM in the 80–130 range; avoid rubbing by holding adequate cutting speed.

5. Setup Checklist to Prevent Breakage

  • Verify pitch in CAM: Z-step must equal thread pitch (e.g. 2.0 mm/rev for M16×2.0).
  • Use a 3°–5° helical / ramp entry; never plunge straight to depth.
  • Hold tool-holder runout under 0.005 mm (hydraulic / shrink-fit preferred).
  • Peck-thread-mill deep blind holes; retract to clear chips every 180°–360°.
  • Confirm pilot-hole size and material ductility before forming; use cutting taps on brittle materials.