cutting

Cutting in machining means rotating a tool against a workpiece to peel away metal chips and expose a finished surface. A lathe spindle might spin a steel rod at 400 rpm while a carbide insert moves steadily across it, or a milling machine's endmill might rotate at 2000 rpm to plunge vertically into aluminum. The tool geometry, feed rate, spindle speed, and coolant all work together to control the size and shape of the chip being removed.

The workpiece material and desired finish determine the cutting parameters. Harder materials like cast iron demand lower speeds and heavier feeds; soft materials like aluminum tolerate higher speeds and can produce long stringy chips that jam machines if not managed. Surface finish ranges from rough cuts that remove material quickly to finishing cuts that take tiny depths of cut, often 0.005 to 0.010 inches, to hit tight tolerances and dimensional specs.

Cutting tools wear progressively. The tool's cutting edge flattens and develops a crater or flank wear; eventually it fails by chipping, breaking, or becoming too dull to cut cleanly. High-speed steel (HSS) tools are cheap but wear quickly and need frequent regrinding. Carbide tools cost far more but withstand higher temperatures and last much longer, especially for production runs. Coated carbides with titanium nitride or aluminum oxide extend tool life further and allow even higher speeds.

Cutting fluid cools the tool and carries away chips. In rough work on a lathe, a simple soluble oil (water mixed with emulsifier) suffices. High-speed milling often demands straight mineral oil or synthetic cutting fluid sprayed through the tool itself. Dry cutting is possible for some materials and speeds but risks tool breakage and poor surface finish if conditions slip.

The cutting process generates significant heat where tool meets workpiece. Tool temperature at the cutting edge can exceed 1500 degrees Fahrenheit in steel machining. This heat weakens the tool and can soften the workpiece near its surface, changing hardness or dimensional stability. Rigid machine tools, sharp tools, correct speeds, and adequate coolant all help manage the thermal load and keep the operation stable and repeatable.