Mechanical Engineering - Production Engineering - Discussion

Low angles (<30deg) are best for hard, high-rigidity materials, while high angles (>45deg) excel at shearing soft, ductile materials.

But in case of plastic due to higher helix angle chip wrap around the tool. So it is difficult to machine.

Low helix angle is the right answer.

Explanation:

Helix angle of a drill refers to the angle between the leading edge of the flute and the drill axis.

A low helix angle (15°–20°) means the flutes are less twisted.

Material Preferred: Helix Angle - Reason.

Plastics : Low helix angle - Prevents excessive cutting and reduces the tendency to grab or chip the soft material.
Copper/Aluminium (soft, ductile metals) : High helix angle (35°–45°) - Improves chip removal.
Cast steel/Carbon steel (hard materials): Medium helix angle (25°–30°) - Balanced cutting and chip evacuation.

Therefore, low helix angle drills are best for plastics.

Small helix for hard material and large helix for ductile material.

D. carbon steel is correct.

Carbon steel 0.1 to 1.5%.
Cast steel 0.1 to 0.75%.

The helix angle is inversely proportional to strength. CARBON STEEL has the highest strength here.

Low Helix for Soft.

High Helix for Hard material.

So, Option C is correct.

Low helix angle for soft material.

High helix angle for hard material.

D is the right answer because low helix angle is 10-13 degree that is called the normal material.

C is the correct answer.

D is correct as per Sadhu Singh. It was of 1992IES.

Low helix angle used for Hard & brittle material, so "C "is Right answer.