Keep undercut as designed
- Additional mold components and wear items
- Parting line and flash control on slide shutoffs
- Longer tooling lead on complex actions
DFM
Side Actions: Injection Molding Design Rules
Side actions release external undercuts and add mold complexity you pay for upfront.
DFM
Side actions buy undercut geometry at tooling cost
Every lateral slide adds mold size, maintenance, and qualification work.
Side actions move steel perpendicular to mold open direction to release external undercuts.
Designers should eliminate undercuts with draft, split lines, or assembly before adding slides.
NetProto quotes side actions when DFM accepts complexity on qualified programs.
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.
Strategy
Redesign versus side action
Slides are valid, not free.
Eliminate or split undercut
- Snap or living hinge on a different plane
- Assembly of two molded halves
- Draft plus parting on a hidden edge
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
Design guide hub
All DFM topics on one route.
Design guide hubDFM article
Long form engineer guide.
DFM articleUndercuts
When redesign is preferred.
UndercutsLifters
Angled release for internal undercuts.
LiftersDraft angle
Release before slides.
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
Side action questions
How do I show undercuts on CAD?
Mark external undercuts and desired draw direction on a PDF or view.
Do slides affect piece price?
Tooling amortization and cycle can both move on slide tools.
Can side actions run with high volume?
Yes when maintenance and shutoff design match volume.
Next step
Resolve undercuts in DFM
Upload CAD with undercut map before approving slide tooling.