Ribs & bosses.
Sink mark prevention.
Stiffening features.
Plastic ribs and bosses design. Stiffening features without sink marks. 60% wall thickness rule, generous fillets, draft for ejection.
Key principles.
60% wall
Rib 60% of base wall. Prevents sink marks.
3× wall max
Rib height ≤ 3× wall thickness.
2× thread
Boss diameter ≥ 2× thread/insert diameter.
60% wall
Boss thickness 60% of wall to prevent sink.
Stress reduction
Generous base fillets reduce stress concentration.
0.5-1°
Draft for ejection. Per side.
FAQ
Why 60% rule?
Rib thicker than 60% causes sink marks at base. Universal rule.
Rib spacing?
Center-to-center 3-5× wall thickness. Tighter = stiffer but more material.
Boss design?
OD 2× thread/insert. Wall 60% of base wall. Generous base fillet.
Cross vs parallel ribs?
Cross (X) ribs 2-3× stiffness vs parallel. Per loading direction.
Demolding?
Sufficient draft (0.5-1° per side). Generous fillets help.
Stiffness gain?
Rib pattern 2-5× plain plate stiffness. Without weight or sink marks.
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