A gating system allows molten metal to flow into the casting cavity. The system also provides a reservoir of molten metal to counteract shrinkage of the metal during solidification.

When most metals go from a liquid phase to a solid phase, they shrink in volume. This volume contraction requires a reservoir (riser) of molten metal to backfill so that as the metal shrinks, more molten metal is fed into the casting cavity.

Calculations must be done for the gating system so that the gating freezes before the molten reservoir (riser) freezes. If that riser freezes off before the casting cavity does, there will be porosity or voids in the casting, and it will be defective.

The risers are large hollow tubes placed on top of the cope half of the pattern. After the casting is complete, these tubes will have formed solid metal appendages attached to the casting. Once the casting has fully solidified and cooled, the risers will be removed with a rotary saw, and hand grinders and hand sanders will be used to smooth out the surface.