Lathe spindle standard: The built-in spindle taper commonly provided in engine lathes is approximately

Introduction / Context:
Lathe spindles incorporate a self-holding taper to accept centres, drive plates, and tool holding attachments. Recognizing the typical taper ratio helps with accurate setup and compatibility across standard tooling.

Given Data / Assumptions:

• Conventional engine lathe, internal spindle nose taper is of the self-holding type.
• Approximate ratio is sought (on diameter basis).
• Focus is on typical practice rather than a specific manufacturer variant.

Concept / Approach:
Self-holding tapers like Morse tapers are widely used. Their included angles and taper ratios are such that they wedge securely under light load but can be released when needed. A commonly remembered approximate taper magnitude is close to 1 in 20 on diameter for these applications, aligning with many shop exam conventions.

Step-by-Step Solution:

Verification / Alternative check:
Handbooks list exact Morse taper data varying by size; the approximate value aligns best with 1 in 20 among the options provided.

Why Other Options Are Wrong:
Ratios such as 1 in 10 or 1 in 30 do not match the widely cited approximate spindle self-holding taper for general engine lathes.

Common Pitfalls:
Confusing different taper systems (self-releasing vs self-holding) or mixing angle vs ratio on radius vs diameter.

Final Answer:
1 in 20