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Blind Holes: Injection Molding Design Rules
Blind holes need vent paths and draft like any pocket closed on one end.
DFM
Blind holes trap air and need vent paths or coring
Pockets closed on one end are common burn and short fill sites.
Blind holes in bosses must vent to atmosphere or parting line through steel details.
Deep blind pockets need draft on side walls for release without scuff.
Through holes vent naturally when both ends are open to the mold split.
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.
Pockets
Blind hole review on CAD
Mark these before T1 short fills.
Depth to diameter ratio on each blind pocket
Vent path sketch or suspected air trap flag
Cosmetic face opposite thick blind boss
Core pin steel support for deep holes
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
DFM article
Long form engineer guide.
DFM articleVenting
Air trap DFM.
VentingBoss design
Blind holes in bosses.
Boss designFillets and radii
Radius at pocket floors.
Fillets and radiiVisual 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
Blind hole questions
Can blind holes be threaded?
See molded in threads and boss design spokes for thread strategy.
Do blind holes always need vent pins?
Deep blind features often need vent detail in steel.
Are blind holes ok on thin walls?
Aspect ratio and vent path decide. Upload sections for DFM.
Next step
Flag blind pockets on upload
Highlight deep blind holes and suspected air traps on CAD.