The spindle is the rotating heart of a machine tool — the assembly that holds and turns either the cutting tool (on a mill) or the workpiece (on a lathe). Its bearings, drive and taper determine how fast, how accurately and how hard the machine can cut.
Spindles are rated by maximum speed (RPM), power and torque, and by the tool interface (taper). Higher speeds suit small tools and aluminum; more torque at low speed suits large tools and steel.
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