Drilling practice with high-speed steel (HSS) drills: What is the typical cutting-speed range (m/min) used when drilling aluminium, brass, and bronze?

Introduction / Context:
Choosing an appropriate cutting speed is fundamental to successful drilling. For high-speed steel (HSS) drills, the recommended speed depends strongly on the work material. Aluminium, brass, and bronze generally permit higher speeds than steels because they are softer (in many grades) and have better thermal conductivity, which reduces edge temperature. This question tests recognition of the commonly used speed band for these nonferrous alloys.

Given Data / Assumptions:

• Tool: HSS twist drill in good condition.
• Work materials: aluminium, brass, bronze (general-purpose grades).
• Conventional drilling on a drill press or machining center with standard flood or mist coolant.

Concept / Approach:
HSS drills are limited by edge softening temperature and wear. Nonferrous alloys such as aluminium and brass allow higher speeds than steels. Typical shop charts cluster recommended speeds for these materials roughly in the medium-to-high range for HSS. A practical, conservative range used across many shops for aluminium/brass/bronze is about 60 to 90 m/min, with the exact value tuned for alloy, hole size, coolant, and rigidity.

Step-by-Step Solution:

Verification / Alternative check:
Reference machinability tables often show aluminium at even higher speeds with HSS under ideal conditions; however, a safe, broadly applicable range is 60–90 m/min, especially for general shop settings and mixed nonferrous materials. Fine-tuning above 90 m/min is possible for free-machining aluminium with excellent cooling.

Why Other Options Are Wrong:

• 10–20 and 18–30 m/min: too low for these materials with HSS; leads to poor chip evacuation and built-up edge.
• 24–45 m/min: still below common practice for aluminium/brass/bronze.
• 110–150 m/min: aggressive for general HSS drilling and not universally safe across all three materials and setups.

Common Pitfalls:
Confusing HSS recommendations with carbide; ignoring larger drill diameters (which require lower rpm for the same surface speed); using dry drilling on gummy aluminium causing built-up edge despite correct speed.

Final Answer:
60 to 90 m/min