Drill helix selection Low-helix-angle (slow spiral) twist drills are preferred for drilling which of the following materials to reduce grabbing and improve chip control?

Introduction / Context:
Helix angle (spiral) in a twist drill governs chip evacuation and the cutting action at the lip. In certain ductile, gummy materials the drill tends to “grab,” causing oversize holes, poor finish, or tool breakage. Adjusting helix helps stabilize cutting.

Given Data / Assumptions:

• Conventional twist drill, right-hand cut.
• Material choices include ductile nonferrous metals and steels.
• Goal is to minimize grabbing and improve hole quality.

Concept / Approach:
Low-helix (slow spiral) drills are recommended for copper, brass, and some bronzes because a steep helix can pull the tool into the work (self-feeding), increasing the risk of grabbing. A slower spiral reduces the axial component of cutting force and stabilizes chip flow. For steels, a standard or higher helix may be used to aid chip evacuation.

Step-by-Step Solution:

Verification / Alternative check:
Tool catalogs list special “slow spiral” or modified point geometry for copper and brass to minimize grabbing and improve roundness.

Why Other Options Are Wrong:
Plastics: often require special points and high rake; helix choice varies widely.Cast/Carbon steel: normally use standard or higher helix for chip evacuation.Hardened tool steel: requires carbide and different geometries, not slow spiral HSS drills.

Common Pitfalls:
Using a standard high-helix in copper can cause the drill to screw in, creating oversize/tapered holes. Control feed and use split-point geometry where appropriate.

Final Answer:

Copper