What a Gate Vestige Is and Why It Matters

Once the part ejects, someone cuts the sprue, runner, and gate away. What stays behind is the gate vestige, also called a witness mark. Most gates leave a mark so small you have to look for it. A bad gate choice turns it into a bump a customer will feel with a thumb.

For cosmetic parts, the vestige is a pass-or-fail item at visual inspection. It can also sit on a sealing face or a mating surface, where height matters more than looks. This is why the gate is not a mold detail for the toolmaker to pick alone. It belongs in the sourcing discussion before the mold is cut.

Gate Vestige Control Starts With Placement

Put the gate where no one will see it. That rule beats every nozzle trick. A back face, a rib, a mounting boss, or a hidden cavity side all work.

Sometimes the flow pattern forces a gate onto a visible face. Glass-filled resins need bigger gates than unfilled ones, which makes the mark harder to hide. When that happens, pick a gate type whose residual is small and whose mark can be flattened.

Ask your supplier about deciding where the gate goes before the mold design is frozen. Moving it later means welding steel, and welds never quite match the original surface. Our DFM guide covers gate, cooling and runner strategy together, since the three interact.

Tab Gates Leave the Largest Vestige

A tab gate is the most common and the largest side gate. Protolabs’ gating design tips flag it as the option with the most visible residual. The gate looks like a tapered rectangle jutting from the part edge. It sits at the parting line, easy to reach.

That easy access is the tab gate’s real virtue. Trimmers cut it with standard nippers. The mark usually sits at the thickest wall, away from stress risers. But on a show surface, easy trimming does not mean invisible.

Use tab gates for large parts where the edge will be hidden, or for parts that need big gates to fill. On a cosmetic face, they are the wrong pick.

Edge and Fan Gates Keep the Mark Small

Edge gates enter through the parting line at 0.5–2.0 mm thick and 2–6 mm wide. Zetarmold notes they go on roughly six of every ten molds its engineers design. The residual is modest: a 0.1–0.5 mm bump that a deburring tool usually erases.

A fan gate is the edge gate’s wide cousin. It spreads the melt across a broad front, which suits flat parts and lowers gate blush. The vestige runs along the edge as a thin line rather than a single bump. It stays discreet where the edge is not a show face.

Both edge and fan gates need manual trimming. Budget labor time per part, and specify the trimming tool in the purchase order. A dull blade tears the mark and leaves white stress marks on PC or ABS. A gate that is too small also traps air. Our venting depth and placement guide covers the other half of that problem.

Tunnel Gates Trim Themselves on Ejection

A tunnel gate dives under the parting line and breaks off when the part ejects, untouched by any operator. For high-volume cosmetic parts, that automatic separation is the whole pitch.

Typical tunnel gates run 0.8–1.5 mm in diameter and leave 0.05–0.2 mm of residual. The catch is the tunnel geometry. The tunnel should be two to three times as long as the gate diameter, as Zetarmold’s gate removal guide details. Get the break angle wrong and the vestige comes out rough.

Resin choice matters here too. Brittle materials like PS snap off cleanly, while tough materials like PC are more likely to leave a ragged edge. If your part runs in PC, ask for a T1 sample to check the vestige before the mold goes to production.

Hot Tip Versus Valve Gate on Cosmetic Parts

Hot tip and valve gate are the two hot runner answers to the vestige problem. If you are new to the hardware, start with our hot runner system overview before comparing nozzles. A hot tip relies on the gate freezing and breaking open each cycle. The mark is a small dome, 1.5–2 mm across and 0.25–0.5 mm high. It can be flattened to about 0.1 mm.

The hot tip suits tapered or domed parts where the melt flows outward in all directions. MoldMaking Technology’s valve gate guide gives the sizing rule. A thermal gate vestige stands one-third to one-half as tall as the gate diameter. Bigger gates leave bigger domes, so nozzle size affects cosmetics as much as fill.

A valve gate replaces the thermal break with a pin that seals the orifice mechanically. The witness mark is flat and roughly the size of the gate diameter, with no protrusion. No stringing, no drool, and the same mark from the first shot to the last. For high-viscosity resins like PC, PEI, or glass-filled PA66, it is the standard answer on cosmetic parts.

The gap between them is money. An open hot tip nozzle runs about $500–$1,500 per drop, while a valve gate nozzle runs about $1,500–$4,000. Multiply by the cavity count and the premium shows up fast. For cosmetic parts at volume, the mark quality usually pays for the pin.

Trimming and Inspection Rules for the Mark

Trimming is a controlled operation, not an afterthought. Set the cut depth limit at ±0.1 mm from the part surface. Anything deeper leaves a divot, and anything shallower leaves a bump a thumb will find.

Inspect the mark like a dimension. On tight-tolerance parts, recheck critical dimensions near the gate after trimming, because the cut can pull the surface. White stress marks, drag lines, or a glossy ring around the mark all mean the trimming needs work.

Write the standard into the purchase order: gate location, gate type, maximum vestige height, and who signs off the first article. A supplier that can answer those four questions will not surprise you at the loading dock.