Lathe capacity terminology — swing over bed The swing diameter over the bed of a lathe is how many times the centre height (centre above bed)?

Introduction / Context:
Lathe capacity is commonly specified by ‘‘swing over bed’’ and ‘‘distance between centres.’’ Understanding the geometric relationship between swing and centre height is essential for checking whether a workpiece diameter can clear the bed.

Given Data / Assumptions:

• Centre height H is the vertical distance from bed top to spindle centreline.
• Swing over bed is the maximum work diameter that can rotate without hitting the bed.

Concept / Approach:
If the spindle centre is H above the bed, a circle of radius H can rotate without interference, so the maximum diameter equals 2H. Hence, swing over bed equals twice the centre height.

Step-by-Step Solution:
Let centre height = H.Clearance radius = H ⇒ maximum diameter = 2H.Therefore, swing over bed = 2 × centre height.

Verification / Alternative check:
Machine nameplates often list, e.g., ‘‘Swing over bed 400 mm’’ which implies centre height of 200 mm.

Why Other Options Are Wrong:
Other multiples do not match the simple geometry of radius versus diameter; one-half would correspond to radius, not diameter.

Common Pitfalls:
Confusing ‘‘swing over carriage’’ (smaller) with ‘‘swing over bed.’’ Accessories reduce practical swing further.

Final Answer:
Twice the centre height