In a standard engine lathe, the internal taper provided on the lathe spindle nose corresponds approximately to which taper ratio?

Introduction / Context:
In manufacturing and machine tool technology, tapered holes and shafts are used to align and hold tools accurately. Engine lathes have a tapered hole in the spindle nose and tailstock to accept standard taper shanks for centres and tooling. This question asks about the approximate taper ratio provided on a typical lathe spindle, which is linked to a commonly used standard taper system.

Given Data / Assumptions:

• The machine under consideration is a standard engine lathe used in workshops.
• The spindle nose has an internal taper to receive centres or tool holders.
• Several taper ratios like 1 in 10, 1 in 20, 1 in 15, and 1 in 25 are listed.
• We assume reference to common self holding tapers such as Morse taper.

Concept / Approach:
Morse taper is widely used in machine tools for holding drills, centres, and other tools. The approximate standard taper for Morse tapers is about 1 in 20, meaning that for every 20 units of length, the diameter changes by 1 unit. This gentle taper provides a good balance between self holding friction and easy removal. Lathe spindles and tailstock sockets typically use such a taper for proper alignment and torque transmission.

Step-by-Step Solution:
Step 1: Recall that Morse tapers are common in lathe spindle and tailstock design for holding centres and tool shanks. Step 2: The Morse taper system has a standard taper of approximately 1 in 20 for its self holding tapers. Step 3: A 1 in 10 taper would be much steeper and may not provide the same self holding characteristics suitable for general lathe spindle applications. Step 4: Ratios like 1 in 15 or 1 in 25 are not standard for Morse tapers and do not match the common workshop reference. Step 5: Therefore, the closest correct taper ratio for the lathe spindle is 1 in 20.

Verification / Alternative check:
Machine tool handbooks and engineering data tables list Morse taper specifications, with the taper per unit length corresponding approximately to 1 in 20. The slight variations in exact angles and diameters among different Morse sizes do not change the general approximation used in many examination questions. Since engine lathes almost universally use these standard tapers, this value is considered correct for general knowledge questions.

Why Other Options Are Wrong:
1 in 10: This is a much steeper taper, more common in quick release or non self holding applications, and not typical of standard Morse taper spindles. 1 in 15: This does not match the widely accepted Morse taper approximation and is not the standard training value. 1 in 25: This is a milder taper than most self holding tapers used in spindles and is not the common reference value.

Common Pitfalls:
Learners may try to memorise many different taper ratios used in machine tools and then mix them up in exams. A practical strategy is to remember the approximate 1 in 20 value associated with Morse taper, since it appears frequently in lathe related questions. It is also helpful to distinguish self holding tapers like Morse from self releasing tapers used in milling machine spindles, which have different standard angles.

Final Answer:
The taper on a standard lathe spindle is approximately 1 in 20.