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Runner Weight and Shot Waste

Back-calculate discharged runner and sprue weight from a measured shot, part weight, and active cavities.

Example starting values are prefilled to demonstrate the calculation. Replace them with your measured, quoted, or job-specific inputs before relying on a result.

Inputs

Inputs

Range: at least 0.001 lb

Enter the measured mass of all material discharged in one shot, including parts and cold runner/sprue. Do not include hot-runner material remaining in the mold.

Defaults to lb; the part-weight measurement may use a different unit.

Range: at least 0.0 lb

Enter measured finished-part mass for one producing cavity from the same shot. Positive mass is required.

Defaults to lb; may differ from the total-shot unit.

Range: at least 1 cavities

Enter a whole-number count; decimal values are rejected during calculation.

Result

Total cavity part mass (lb/shot)
0.0882
Estimated runner/sprue mass (lb/shot)
0.026
Runner/sprue share of total shot
0.23
Estimated runner/sprue mass (oz/shot)
0.42
Measured total discharged shot (lb)
0.1146
Mass-balance assumptions and limits
Estimated runner/sprue mass is the residual from the measured discharged shot after subtracting all active-cavity part mass. This only represents material discharged with that shot and assumes both weight inputs describe the same cycle. A negative residual is invalid; recheck measurements, cavity count, and unit selection.

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