Metrology for patterns — a pattern maker’s shrinkage rule is designed to account for which allowance during pattern making for metal castings?

Introduction / Context:
When molten metal solidifies and cools to room temperature, it contracts. Patterns must therefore be made slightly larger than the final required size to compensate for this linear shrinkage. Pattern maker’s shrinkage rules are modified scales used to build this compensation directly into layout and measurement.

Given Data / Assumptions:

• Shrinkage varies by casting alloy (e.g., grey iron versus aluminium).
• Other allowances also exist: machining, draft, shake (rapping), and distortion allowances.
• The question asks specifically what the shrinkage rule “considers”.

Concept / Approach:

A shrinkage rule has graduations that are slightly enlarged relative to a standard scale by a factor corresponding to the alloy’s linear contraction. It does not inherently include machining, draft, or other allowances, which the pattern maker must add separately in the pattern design or by documentation on the drawing.

Step-by-Step Solution:

Verification / Alternative check:

Foundry standards provide different shrinkage rule factors for different alloys, confirming the rule’s dedicated function.

Why Other Options Are Wrong:

“All pattern allowances” overstates the function; “all materials to be cast” and “all materials of the pattern” are irrelevant to what the rule’s graduations encode.

Common Pitfalls:

Assuming the rule magically includes draft or machining stock; those allowances must be added separately during pattern design.

Final Answer:

only shrinkage allowance