Runner System Design Calculator

More viscous, stiffer-flowing resins (like PC or POM, Material Viscosity = 3) need a larger runner channel to fill the mold without excessive pressure drop, premature freezing, or incomplete cavity filling. Easy-flowing resins (like PE or PP, Material Viscosity = 1) can use a smaller runner because they move through narrower channels with much less resistance.

This calculator steps runner diameter down as melt branches from the main sprue toward each cavity -- Sub-Runner Diameter is 80% of Main Runner Diameter, and Gate-End Runner is roughly 56% of it. Progressively smaller downstream runners follow standard mold-design practice for balancing flow to multiple cavities while limiting wasted material.

Main Runner Length is estimated assuming cavities are arranged in a roughly square grid, with the number of rows approximated as the square root of Number of Cavities. More cavities generally mean a longer overall runner path is needed to reach every cavity from the central sprue, though the actual layout in a real mold can differ from this simplified square-grid assumption.

It compares the estimated Runner Weight to the total weight of all parts produced in one shot (Part Weight times Number of Cavities), expressed as a percentage. A high ratio means a large share of every shot's plastic becomes runner scrap rather than usable part -- the howToUse guidance flags roughly 20% as a rough threshold worth investigating, since higher waste raises material cost and cycle-dependent energy use.

No -- they are empirical starting-point estimates based on common rules of thumb (wall-thickness multiples, fixed branching ratios, and a simplified layout assumption), not the output of a mold-flow simulation. A real tool design should verify runner sizing with flow analysis software or prior production experience with the specific resin before cutting steel.