Internal, not external
A lifter is for a hidden lip. External clips usually want a slider.
Lifters
Mold Lifters: Release Internal Undercuts on Ejection
Use a lifter for internal undercuts that cannot shut off. Redesign first when the hook can bump off or move. DFM review comments on CAD before quoting.
Design guideline
The steel lifts out of an internal undercut
A lifter moves at an angle during ejection to pull steel out of an internal hook or lip. It is not a side action. Aggressive geometry wears steel and marks parts.
Lifter marks and wear show if the geometry is too aggressive. Snap faces that ride the lifter need draft. Undercuts decide whether an action is needed. DFM review comments before steel is cut.
This spoke owns the lifter mechanism. Side actions own external sliders. Cantilever snap fits own the hook. The design guide hub lists every topic.
Roles
Which page answers which release question
Stay here for internal lifter steel. Open a sibling for sliders or the decision.
| Page | Use it for |
|---|---|
| Lifters (this page) | Internal undercut release on ejection |
| Side actions | External sliders and cams |
| Undercuts | Whether any action is needed |
| Cantilever snap fit | The hook the lifter may release |
| Draft angle | Draft on lifter contact faces |
| Venting | Internal pockets still need a gas path |
| Bosses | Internal posts are not lifters |
| Wall thickness | Hook thickness still references a nominal wall |
| DFM review | CAD check before steel |
Checks
What DFM review looks for on lifters
Qualitative checks. No figure on this page is a NetProto specification.
Redesign first
Move the hook, add a through window, or bump off if the resin allows.
Draft on contact faces
Faces that ride the lifter need draft so they do not scuff.
Wear and witness
Aggressive travel marks parts and wears steel. Keep the undercut honest.
Decision
Add a lifter versus remove the internal undercut
Wrong: every internal hook gets a lifter. Right: redesign first, then size the mechanism.
What goes wrong
- Treat a lifter as the same thing as a slide
- Leave a deep internal hook with no draft on the lifter face
- Discover the undercut after quote approval
What to try first
- Use the undercuts page to decide action type
- Add draft on lifter contact faces
- Mark internal hooks on CAD before steel is quoted
RFQ
Send these notes with CAD for a lifter review
The quote can start from CAD alone. These notes make the DFM pass specific.
Internal undercut map
Snap or lip travel, if known
Whether redesign or bump-off was considered
Draft on lifter contact faces
Cosmetic witness tolerance on lifter marks
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 checks internal release before steel.
DFM reviewFAQ
Mold lifters FAQ
What is a mold lifter?
Steel that moves at an angle during ejection to release an internal undercut. It is not a side-action slider.
Are lifters the same as slides?
No. Slides usually move sideways for external undercuts. Lifters lift out of internal hooks as the mold opens.
Can lifters be avoided?
Often. Reorient the hook, add a through window, or bump off a shallow feature on a flexible resin. The undercuts page owns that decision.
Do lifters limit resin choice?
Aggressive geometry and abrasive fills wear steel faster. Name the resin. This page does not publish a wear table.
Will a lifter mark the part?
It can. Call out cosmetic tolerance on those faces. Keep the undercut as small as function allows.
How is this page different from undercuts or side actions?
Undercuts own the decision. Side actions own external sliders. This spoke owns lifter release. DFM review checks CAD.
Next step
Upload CAD for DFM review of lifter features
Share internal hooks, resin, and whether redesign is acceptable so review can check release before quoting.