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Sub Gates: Injection Molding Design Rules
Sub gates hide vestige on parting lines but need steel and ejection planning.
DFM
Sub gates hide vestige on parting but add shear and eject detail
Tunnel, cashew, and similar sub gates break away during ejection.
Sub gates leave less visible vestige when parting line placement allows.
Steel at sub gates erodes on abrasive or glass filled resins.
Ejector motion must clear the sub gate slug without tearing the part.
DFM
Quote this rule with your CAD upload
NetProto DFM review flags these geometry patterns before steel is ordered.
- Call out draw direction and cosmetic faces on the model.
- Note resin family even when the grade is not final.
- Tighten tolerances only on mating features that need them.
Sub gate readiness
Confirm before mold design picks tunnel gates
Sub gates fail when parting or ejection is ambiguous.
Parting line location relative to cosmetic faces
Resin abrasiveness or glass fill callout
Acceptance of small gate scar on hidden edge
Robot or manual degating plan
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
DFM article
Long form engineer guide.
DFM articleGate types
Compare all gate families.
Gate typesGate location
Fill and weld line map.
Gate locationDraft angle
Release before gate steel details.
Draft angleVisual reference
Molding context for this rule
Images from the Forge media library illustrate typical programs.
Injection molded part design review on CAD
Injection molded part design review on CAD
Plastic housing with ribs and bosses
Plastic housing with ribs and bosses
Engineer measuring molded component
Engineer measuring molded component
FAQ
Sub gate questions
Are sub gates automatic degate?
Often yes on ejection, but process must protect the part.
Do sub gates work on soft elastomers?
Very soft materials may tear at tunnel pull.
Can sub gates be added later?
Steel changes at gate are costly after T1 correlation.
Next step
Align gate style with cosmetics
Upload parting line and hidden edge map with your RFQ.