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Gusset Design: Injection Molding Design Rules
Gussets add stiffness between walls and bosses when sized like ribs, not slabs.
DFM
Gussets turn wobbly walls into stable geometry
Triangular ribs support walls and bosses without jumping to full thickness.
Gussets tie perpendicular walls or bosses to a base wall at a controlled thickness.
Oversized gussets act like thick sections and can create sink or air traps at the root.
Draft on gusset side walls must match the mold pull direction.
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.
Gusset checklist
Size gussets like ribs, not like walls
Use the same thickness ratios as rib design.
Gusset thickness versus primary wall
Height and draft on each gusset leg
Root fillet radius to avoid sharp stress corners
Clearance for ejection and vent paths
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
DFM article
Long form engineer guide.
DFM articleRib design
Parallel rules for stiffening ribs.
Rib designFillets and radii
Root radii at gusset intersections.
Fillets and radiiCorner design
External corners near gusset roots.
Corner designVisual 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
Gusset questions
How thick should a gusset be?
Often similar rib guidance: well below primary wall thickness.
Do gussets need draft?
Yes on moldable faces that pull with the core or cavity.
Can gussets cause sink?
Yes when they are too thick relative to the opposite cosmetic face.
Next step
Stiffen parts without thick walls
Upload CAD showing gussets and rib network before tooling.