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Surface Speed & Cutting Physics

SFM & Cutting Speed Calculator

Calculate peripheral surface cutting speed in Surface Feet per Minute (SFM) or meters per minute (m/min) from tool diameter and spindle RPM.

End mills, face mills & CNC routers

RPM
mm
Primary Calculated Result✓ VERIFIED RESULT
Cutting Speed
94.2m/min
How This Was Calculated
Vc = (π × Tool Diameter × RPM) / 1,000
(π × 10 mm × 3,000 RPM) / 1,000
= 94.2 m/min

Machining Safety Notice: Calculated values are theoretical mathematical starting points and not guaranteed safe machining parameters. Actual feeds and speeds depend heavily on machine rigidity, spindle power, workholding stability, tool material and coating, workpiece alloy hardness, coolant application, and vibration characteristics. Always consult tooling manufacturer catalog recommendations before running parts on CNC equipment.

Surface Feet per Minute (SFM) & Cutting Speed (Vc)

Surface speed measures how much material length passes the cutting edge every minute. Because heat generation occurs during chip shearing, maintaining optimal surface speed is fundamental to tool life.

Imperial SFM Formula

SFM = (π × D × RPM) / 12

Where D is tool or workpiece diameter in inches, and RPM is spindle rotational speed.

Metric Vc Formula

Vc = (π × D × RPM) / 1,000

Where D is diameter in millimeters, and result Vc is in meters per minute.

Typical Cutting Speed Starting Ranges

Workpiece Material Carbide SFM (ft/min) Carbide Vc (m/min) Machinability Notes
Aluminum (6061-T6) 600 – 2,500+ 180 – 750+ High speed machining, flood coolant or mist
Mild Carbon Steel (1018) 350 – 650 100 – 200 Standard TiAlN or AlTiN coated carbide
Alloy Steel (4140 Annealed) 250 – 450 75 – 140 Rigid setup, controlled chip formation
Stainless Steel (304 / 316) 180 – 350 55 – 110 Work-hardens easily; never let cutter dwell
Titanium (Ti-6Al-4V) 120 – 220 35 – 70 Low thermal conductivity; high-pressure coolant
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FAQ & MACHINING REFERENCE

Cutting Speed Questions & Answers

What is SFM (Surface Feet per Minute)?

SFM is the linear cutting speed of the outer circumference of a cutting tool or rotating workpiece in feet per minute. It measures how fast the cutting edge shears material at the point of contact.

How do you calculate SFM from RPM and cutter diameter?

SFM = (π × Tool Diameter in inches × Spindle RPM) / 12. For example, a 0.5-inch end mill running at 3,000 RPM produces (π × 0.5 × 3,000) / 12 = 392.7 SFM.

What is the metric equivalent of SFM?

The metric equivalent is cutting speed (Vc), expressed in meters per minute (m/min). The formula is: Vc = (π × Tool Diameter in mm × Spindle RPM) / 1,000. 1 m/min equals approximately 3.28084 SFM.

Why does cutting speed matter more than RPM for tool wear?

Cutting temperature is directly proportional to surface cutting speed. Tool coatings and carbide grades have specific thermal breakdown thresholds. Operating above the recommended SFM causes rapid crater wear and premature edge degradation.