Enter your Cutting Speed, Tool Diameter, and Unit System into the Spindle Speed Calculator to get your target RPM — then add Feed Per Tooth and Number of Teeth to also calculate your Feed Rate and Material Removal Rate.
Spindle Speed
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Feed Rate
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Material Removal Rate
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Spindle speed is the rotational speed of the machine spindle measured in revolutions per minute (RPM). It determines how fast the cutting tool rotates during machining operations like milling, turning, and drilling.
Spindle speed is calculated using the formula: RPM = (Cutting Speed × 1000) / (π × Tool Diameter). For imperial units, RPM = (SFM × 12) / (π × Tool Diameter in inches).
Feed rate is the speed at which the cutting tool advances through the material, typically measured in inches per minute (IPM) or mm/min. It's calculated as: Feed Rate = RPM × Feed per Tooth × Number of Teeth.
For milling steel with HSS tools, typical cutting speeds range from 50-150 SFM, resulting in RPMs that vary based on tool diameter. A 1/2 inch end mill would typically run at 400-1200 RPM for steel.
Larger diameter tools require lower RPM to maintain the same surface speed (SFM). This is because the cutting edge travels a greater distance per revolution on larger tools, so fewer revolutions are needed to achieve the desired cutting speed.
SFM is the linear speed at which the cutting edge moves past the workpiece material. It's a critical parameter that determines tool life and cutting quality, typically specified by tool manufacturers for different materials.
Correct speeds and feeds ensure optimal tool life, surface finish quality, dimensional accuracy, and machining efficiency. Running too fast can cause premature tool wear or breakage, while running too slow reduces productivity and can cause poor surface finish.