Ultrasonic testing is done in materials to determine

Cubic Boron Nitride

top rake angle decreases

Type N

The type of drill used for general purpose drilling work is Type N.

The helix angles vary according to the material being drilled. According to indian standards, three types of drills are used for drilling various materials.
Type N - For normal low carbon steel.
Type H - For hard and tenaceous materials.
Types S - For soft and tough materials.

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