What Speed (RPM) Should I Run a Thread Forming Tap?

If you’re switching from cutting taps to forming (extrusion) taps, the first surprise is the spindle speed. Forming taps don't cut chips—they cold-displace ductile metal—so they're normally run faster than a cutting tap of the same size, but torque-limited by material and machine rigidity. There is no single RPM; you pick a surface speed (Vc), then convert it to RPM from the taup diameter.
The formula you actually use
Metric shops:
RPM = (Vc × 1000) ÷ (π × D)​ — Vc in m/min, D in mm.
Inch shops:
RPM = (SFM × 3.82) ÷ D(inch).
Rule of thumb from tap makers: run a forming tap at roughly 1.5×–2× the SFM of a cutting tap​ in the same material—but cap it where torque, heat, or galling shows up.
Starting Vc / SFM for forming taps
Practical starting points for HSS-E forming taps:
•Aluminum / brass: 40–80 m/min​ (130–260 SFM)
•Low-carbon steel: 15–30 m/min​ (50–100 SFM)
•304/316 stainless: 8–20 m/min​ (25–65 SFM)
•Copper: 20–40 m/min​ (65–130 SFM)
Always start at the low end, check torque and thread finish, then ramp up 10–15%.
Real-number exampleses
•M6 × 1.0 forming tap in 6061 aluminum​ at Vc = 60 m/min → RPM = (60×1000)÷(3.1416×6) ≈ 3,180 RPM. Shops commonly run 2,500–3,500 RPM with MQL or emulsion; feed is locked to pitch = 1.0 mm/rev → 3,180 mm/min.
•M10 × 1.5 forming tap in 1018 mild steel​ at Vc = 22 m/min → RPM = (22×1000)÷(3.1416×10) ≈ 700 RPM​ (many run 500–700 RPM). Feed = 1.5 × 700 = 1,050 mm/min.
•M8 × 1.25 forming tap in 304 SS​ at Vc = 12 m/min → RPM ≈ 300 RPM​ (typical shop range 200–320 RPM). Push past 350 RPM and you’ll see work-hardening, heat, and twisted taps.
What changes the number
•Blind hole​ → drop 10–20%; form taps can't relieve pressure out the bottom.
•Soft aluminum + rigid CNC + good lube​ → you can exceed the chart.
•Old manual machine / floating holder​ → cut RPM 30–40%, synchronization matters more than peak speed.
•Wrong pilot-hole diameter​ → forming torque spikes regardless of RPM. Forming taps need a tighter, larger-than-cut-tap drill (≈ D − pitch/2 for metric).
Don't copy a cutting-tap RPM and don't maxe the spindle. Pick Vc from the material, convert with the formula, start low, and let torque tell you when to climb. For an M6 in aluminum think ~3,000 RPM, M10 in steel ~600–700 RPM, M8 in stainless ~250–300 RPM—then tune from there.
Neeod a printable M3–M20 forming-tap RPM chart​ (aluminum / steel / stainless, HSS-E vs. PM) to drop into your quoting sheet? I can put one together.