External undercut
A clip, barb, or side hole off the draw. Internal lips belong on lifters.
Side actions
Side Actions in Injection Molds: External Undercuts vs Redesign
Eliminate external undercuts with draft, parting line, or assembly when you can. DFM review accepts slides on qualified programs when the feature must stay.
Design guideline
Sideways steel for an external undercut
A side action moves steel sideways to release an external undercut: a clip, barb, or hole off the draw. Redesign first when a shutoff or through window works.
Designers should try draft, a split line, or assembly before adding a slide. NetProto quotes side actions when DFM accepts the complexity. Undercuts own that decision. DFM review comments before steel is cut.
This spoke owns the slider. Lifters own internal release. Cantilever snap fits own the clip. The design guide hub lists every topic.
Roles
Which page answers which side-action question
Stay here for external sliders. Open a sibling for lifters or the decision.
| Page | Use it for |
|---|---|
| Side actions (this page) | External sliders, cams, hydraulic |
| Lifters | Internal lips and snaps |
| Undercuts | Whether any action is needed |
| Cantilever snap fit | The clip a slide may release |
| Draft angle | Draft that can remove a slide |
| Side holes | A hole off draw is often an undercut |
| Through holes | A through window can shut off steel |
| Venting | Slide pockets still need a gas path |
| DFM review | CAD check before steel |
Checks
What DFM review looks for on side actions
Qualitative checks. No figure on this page is a NetProto specification.
Redesign first
Move the feature, change the parting line, or add a through window.
Witness on the split
Slides leave a parting witness. Call out cosmetic tolerance.
Volume and wear
Slides add maintenance. Name volume intent so review can comment.
Decision
Add a slide versus remove the external undercut
Wrong: every side hole gets a slider. Right: lock draw direction, then keep only the actions you need.
What goes wrong
- Add a slider when a shutoff would release the feature
- Discover the undercut after quote approval
- Ignore slide witness on a class-A face
What to try first
- Reorient the feature or move the parting line
- Mark external undercuts on CAD before quoting
- Call out cosmetic tolerance on slide splits
RFQ
Send these notes with CAD for a side-action review
The quote can start from CAD alone. These notes make the DFM pass specific.
External undercut map
Draw or pull direction
Whether redesign was considered
Cosmetic witness tolerance on slide splits
Annual volume intent, qualitatively
Resin family
Related
Related design guidelines
Stay on this spoke for its question. Open a sibling for the neighbor topic or the CAD check.
DFM review
How NetProto accepts slides before steel.
DFM reviewFAQ
Side actions FAQ
What is a side action?
Steel that moves sideways to release an external undercut. Slides, cams, and hydraulic pulls are common forms.
How do I show undercuts on CAD?
Mark features that do not release in the mold-open direction. Lock draw direction. DFM review uses that map.
Do slides change the tool plan?
Yes. They add steel motion and witness. Redesign first when function still works. This page does not publish a price.
Can side actions run on high-volume programs?
Yes when DFM accepts the geometry. Wear and maintenance still matter. Name volume intent qualitatively.
Are side actions the same as lifters?
No. Side actions are usually external. Lifters release internal hooks.
How is this page different from undercuts?
Undercuts own the decision. This spoke owns the slider. DFM review checks CAD.
Next step
Upload CAD for DFM review of side actions
Share external undercuts, draw direction, and cosmetic faces so review can decide redesign versus a slide before quoting.