471Machinability
• Sharpening should be performed using suitable xtures, and free-
hand sharpening should be avoided.
• Depth of cuts should be substantial enough to prevent the tool from
riding the work surface—a condition that promotes work hardening.
• Tools should be as large as possible to enhance heat dissipation.
• Tools of sufcient clearance angle and having chip breakers should
be used.
• Proper coolants and lubricant are essential. They must be used in suf-
cient quantities and directed so as to ood the tool and workpiece.
15.2.4.2 Machinability of Cast Irons
The presence of primary cementite makes white cast irons very difcult
to machine. Chill zones in castings reduce machinability and cause tool
chipping or fracture, thus requ ...