Tool materials – permissible cutting speed: High-speed steel (HSS) twist drills can be operated at approximately what multiple of the speed used for high-carbon steel (HCS) drills, for similar conditions?

Introduction / Context:
Cutting speed limits are governed by hot hardness and wear resistance of tool materials. HSS retains hardness and edge strength at significantly higher temperatures than high-carbon steel (HCS), enabling higher practical surface speeds.

Given Data / Assumptions:

• Comparable work material and coolant conditions.
• Similar tool geometry for HSS and HCS twist drills.
• Focus on order-of-magnitude speed capability, not an exact recommended value chart.

Concept / Approach:
HSS maintains cutting performance at elevated temperatures due to alloying (W, Mo, V, Cr, Co). Typical shop rules of thumb allow roughly twice the cutting speed (or more) with HSS compared to HCS while maintaining tool life.

Step-by-Step Solution:

Verification / Alternative check:
Machining handbooks and tool catalogs list higher recommended speeds for HSS than for HCS; the ratio commonly falls around two or more depending on alloy and coolant.

Why Other Options Are Wrong:
One-half or one-fourth contradict improved hot hardness; four times can be excessive under many shop conditions; “exactly the same” ignores material science differences.

Common Pitfalls:
Forgetting to also adjust feed, coolant, and peck cycles; exceeding machine power limits when increasing speed with large diameters.

Final Answer:
Double