Drill geometry selection: The preferred point angle for drilling stainless steel is typically ________.

Introduction / Context:Stainless steels are tough and work-harden readily, demanding robust drill geometry to reduce chisel edge thrust and improve penetration. Point angle choice directly affects cutting action and heat generation.

Given Data / Assumptions:

• A standard twist drill is used (not a split-point or special geometry).
• Appropriate cutting fluid is applied.
• Machine rigidity and feeds/speeds are suitable for stainless steel.

Concept / Approach:Larger point angles (e.g., 135°) create a shorter chisel edge and a stronger point, which helps when drilling tough, work-hardening materials. General-purpose drills for mild steel often use 118°, but stainless benefits from 135° with proper lip relief and possibly split-point to lower thrust and wandering.

Step-by-Step Solution:

Verification / Alternative check:Machining handbooks routinely recommend 135° for tough alloys including stainless, often combined with split-point geometry.

Why Other Options Are Wrong:90°/100°: too acute for stainless; weak point and increased wandering.118°: common for mild steel, but not optimal for stainless.150°: excessive and may increase rubbing without special setups.

Common Pitfalls:Running too fast causing work-hardening; inadequate coolant; dull drills leading to burnishing rather than cutting.

Final Answer:

135°