Rotational Molding worked example
Part Shrinkage Allowance with oversized cavity dimension of 310 units: a worked example
What does the result look like when oversized cavity dimension reaches 310 units? The full calculation is worked below with real intermediate numbers. Use it when part shrinkage allowance in rotational molding needs a clean margin number for a rotational molding go / no-go review.
The inputs for this scenario
- Oversized cavity dimension: 310 units (raised for this scenario; the documented default is 125)
- Target finished part dimension: 100 units (unchanged)
- Reference (nominal) dimension: 100 units (unchanged)
Working through the calculation
- Applying the documented formula (Part Shrinkage Allowance margin = available value - required value) to the inputs above produces each figure below.
- At this operating point the engine returns 210 % for margin, the number this scenario is built around.
- At this operating point the engine returns 210 value for absolute margin.
- At this operating point the engine returns 310 value for available amount.
- At this operating point the engine returns 100 value for required amount.
How this compares with the baseline
- Against the tool's baseline example, where oversized cavity dimension sits at 125 units and the headline result is 25 %, this scenario comes in 740% above the baseline at 210 %.
- A figure at this level is achievable when oversized cavity dimension is genuinely sustained, not just peaked for a shift. Rotomolding shrinkage is anisotropic and varies with wall thickness, resin grade, and cooling rate, so a single percentage is an approximation that should be validated on a first-article part.
Results at a glance
- Margin: 210 % (headline result)
- Absolute margin: 210 value
- Available amount: 310 value
- Required amount: 100 value
Run it with your numbers
- Every input above is editable in the live Part Shrinkage Allowance calculator, which recalculates instantly and can be shared with the inputs intact.
Last reviewed 2026-05-12.