Pin-Point Gate vs. Direct Sprue: Key Differences for Mold Engineers

How Each Gate System Works

A direct sprue gate delivers resin straight from the injection machine nozzle through a tapered channel into a single cavity. The sprue bushing is the only flow component — there is no runner system. The solidified sprue remains attached to the part and must be trimmed after ejection.

A pin-point gate uses a three-plate mold structure. Resin flows from the sprue bushing into a runner plate, then through a small-diameter gate bushing (0.5–2.0 mm tip) into the cavity. During mold opening, the runner plate separates first, automatically shearing the gate from the part. The runner and gate vestige are ejected separately.

Side-by-Side Comparison

Gate Vestige and Part Quality

Gate vestige is often the deciding factor. Pin-point gates leave a small circular mark, typically 0.3–0.5 mm raised, that is barely visible on finished parts. Direct sprue gates leave the full diameter of the sprue channel — usually 4–8 mm — which requires secondary trimming and may leave a visible scar.

For cosmetic parts such as consumer electronics housings, automotive interior trim, and medical device enclosures, pin-point gating is the industry standard. According to ScienceDirect's injection moulding reference, gate mark size directly influences perceived part quality in consumer applications.

Mold Complexity and Cost

Three-plate molds for pin-point gating require additional components that increase both initial cost and maintenance complexity:

• Runner lock pins — hold the runner plate in position during the first stage of mold opening
• Runner ejector sets — push the solidified runner out of the runner plate
• Runner change pins — redirect resin flow in multi-cavity layouts
• Pin-point gate bushings — precision components with hardened tips that define gate diameter and geometry

A typical four-cavity three-plate mold costs 30–50% more than an equivalent two-plate mold. However, the per-part cost drops significantly at high volumes because automatic degating eliminates manual trimming labor.

When to Choose Each Gate Type

The decision follows a straightforward logic based on three factors:

• Cosmetic requirement? — If the gate mark must be invisible or minimal → pin-point gate
• Multi-cavity? — If the mold has 2+ cavities → pin-point gate (direct sprue cannot feed multiple cavities)
• Single-cavity, non-cosmetic, low volume? — Direct sprue is simpler and cheaper

According to the ISO 294 series on injection moulding of test specimens, standardized test molds typically use direct sprue gates for simplicity, but production molds for the same parts often switch to pin-point gating for higher throughput.

Material Considerations

Not all resins work well with small pin-point gates. High-viscosity materials like polycarbonate (PC) at low melt temperatures or glass-filled nylon (PA6-GF30) may require larger gate diameters to fill properly. The gate diameter must balance two competing requirements:

• Too small — excessive shear heating, jetting, and incomplete fill
• Too large — longer freeze-off time, larger vestige, potential sink marks near the gate

A practical starting point for pin-point gate diameter is 60–80% of the part wall thickness. For direct sprue gates, the sprue port diameter (P) is typically 1.5–3.0 mm larger than the machine nozzle orifice to prevent hang-up.