Spindle Speed (RPM) Calculator for Threading

Optimize your machining processes with our online cutting parameters calculator. Select the operation type (turning, milling, drilling or threading) and instantly get the critical calculations for your shop: cutting speed (Vc), revolutions per minute (RPM), feed per revolution or per tooth, machining time and the theoretical roughness (Ra / Rz) based on the insert nose radius. To fine-tune those values live at the machine, use the interactive machining calculator.

Cutting calculator

Step 1

Which operation are you machining?

TurningRPM per part diameter and feed per revolution.MillingRPM per cutter diameter and feed per number of teeth.DrillingRPM per drill diameter and axial feed per turn.ThreadingRPM, synchronised feed, lead and time for tap, lathe threading or thread mill.

Paso 2

What do you want to calculate?

Cutting speed VcCalculate Vc from diameter and RPM.RPMCalculate revolutions from Vc and diameter.FeedWork out the programmable feed or its linear equivalent.Theoretical roughnessGuideEstimate Ra/Rz with feed and tip or edge radius.

Paso 3

Introduce Vc y diámetro

Cutting speed (Vc)Diámetro rosca / pieza

Formula

n=1000 × Vcπ × D

Result

RPM calculadas

0rpm

Where Vc is the cutting speed in m/min and D is the reference diameter in millimeters (mm).

Material, power and warnings

Pick material and tool: that gives you the Vc and feed ranges, and also whether your machine can take the cut.

ToolingCut typeCondition

Do you want to adjust these values live?

Here you get the recommendation (Vc, feed, roughness, threading). In the interactive machining calculator you can move Vc, diameter, RPM and feed with linked scales, locks and time/power estimation.

Open interactive calculator →

Spindle speed in threading: formula, example and table

n = 1000 × Vc / (π × D)

Vc is the cutting speed in m/min, D the thread diameter in mm and n the spindle speed in rpm. In threading the diameter that counts is the thread diameter.

Worked example: Medium-carbon steel C45 / 1045 in threading, Ø20 mm, Vc 95 m/min → n = 1000 × 95 / (π × 20) = 1512 rpm.

When threading on a lathe with G76 or G92 the rpm must be fixed (G97), never G96: the control synchronises the feed with the spindle and a speed change mid-pass shifts the thread. Also check that the resulting feed (pitch × rpm) does not exceed the Z-axis maximum.

Speeds for coated carbide at mid Vc of the range; with HSS use about a third. Diameters typical for threading.
Material	Vc (m/min)	n Ø10 (rpm)	n Ø20 (rpm)	n Ø36 (rpm)
Low-carbon steel S235 / St37	114	3629	1814	1008
Medium-carbon steel C45 / 1045	95	3024	1512	840
Alloy steel 42CrMo4 / 4140	81	2578	1289	716
16MnCr5 carburizing steel	85	2706	1353	752
Austenitic stainless 304 / 1.4301	66	2101	1050	584
Austenitic stainless 316 / 1.4401	58	1846	923	513
Martensitic stainless 420 / 1.4021	60	1910	955	531
Gray cast iron GG25 / EN-GJL-250	83	2642	1321	734
GGG50/EN-GJS-500 nodular cast iron	73	2324	1162	645
Aluminum 6082 / AlMgSi1	295	9390	4695	2608
Aluminum 7075 / AlZnMgCu	264	8403	4202	2334
Brass CuZn39Pb3	148	4711	2355	1309
Titanium Ti6Al4V	25	796	398	221
Inconel 718	15	477	239	133
Hardened steel 50-55 HRC	48	1528	764	424

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