Permanent-way maintenance: Gauge adjustment with pot sleepers By interchanging the gibs and cotters of a cast-iron pot sleeper assembly, by how much can the track gauge be slackened (reduced or increased stepwise)?

Introduction / Context:
On older permanent-way layouts using cast-iron pot sleepers, small adjustments to track gauge are made without re-drilling or re-boxing. The fastening system with gibs and cotters provides discrete steps of gauge tightening or slackening for routine maintenance and keeping within tolerances.

Given Data / Assumptions:

• Cast-iron pot sleeper with chairs/keys fastened by gibs and cotters.
• Standard practice uses interchange of gibs and cotters to obtain a fixed incremental change.
• Goal: quantify the gauge change achieved by interchanging these components.

Concept / Approach:
Gibs and cotters are shaped so that reversing or interchanging them shifts the running face of rail seating by a known amount. This creates a predetermined, repeatable gauge change used for centering, correcting tight gauge in curves, or compensating wear at rail seats.

Step-by-Step Solution:
Identify the fastening geometry that provides a discrete offset per interchange.Maintenance manuals standardize this offset for pot sleepers as approximately 3.2 mm per interchange.Thus, a single interchange yields a 3.2 mm gauge slackening (or tightening, depending on direction).

Verification / Alternative check:
Track inspection templates and feeler gauges confirm the post-adjustment gauge against specified tolerances for the route class and curvature, validating the expected 3.2 mm step.

Why Other Options Are Wrong:
1.2 mm, 2.2 mm: Too small; not the standardized step.4.2 mm, 5.0 mm: Exceed typical fine-adjustment increments and risk exceeding limits.

Common Pitfalls:

• Confusing pot sleeper adjustments with timber sleeper adzing or rail-seat packing.
• Attempting multiple interchanges without re-checking gauge at both rails.

Final Answer:
3.2 mm