Balance first
Each cavity should fill and pack together. Uneven runners show as warp or shorts.
Runner design
Runner Design: Balance Fill Across Cavities
Buyers do not size the runner. Mark cosmetics, cavitation intent, and cold versus hot. DFM review comments on CAD before steel is cut.
Design guideline
The runner is tooling, not a part feature you sketch
The runner carries melt from the sprue to each gate. Layout sets how evenly cavities fill and pack. Cold runners leave a tree. Hot runners keep melt in the manifold.
Asymmetric parts may need different runner lengths even when cavities look alike. Cold runner and hot runner define the two systems. Gate location ties the runner to the part. DFM review needs cavitation context.
This spoke owns layout and balance. Cold slug wells own the runner-end pocket. Gate types own how melt enters the cavity. The design guide hub lists every topic.
Roles
Which page answers which runner question
Stay here for layout and balance. Open a sibling for gates, wells, or the glossary.
| Page | Use it for |
|---|---|
| Runner design (this page) | Layout, balance, cold versus hot |
| Runner glossary | What a runner is |
| Cold runner glossary | The cold tree |
| Hot runner glossary | The heated manifold |
| Gate types | How melt enters the cavity |
| Hot tip gates | Drops from a hot system |
| DFM review | CAD check before steel |
Checks
What DFM review looks for on runners
Qualitative checks. No figure on this page is a NetProto specification.
Cold versus hot
Cold leaves a tree. Hot keeps melt in the drop. Name the intent.
Buyer does not size it
The tooling team sizes the runner. Mark cosmetics and cavitation.
Tied to the gate
Runner work without a gate plan is incomplete. Open gate location.
Decision
A buyer-drawn runner versus a balanced tool layout
Wrong: sketch runner diameters on the part. Right: state cavitation and cosmetics, then let tooling size the tree.
What goes wrong
- A runner diameter drawn on the part as a spec
- Family cavities with no balance note
- Ignore how the runner feeds warp
What to try first
- Name cold or hot intent
- Mark cavitation and family-mold parts
- Tie runner work to gate location and type
RFQ
Send these notes with CAD for a runner review
The quote can start from CAD alone. These notes make the DFM pass specific.
Cold runner or hot runner intent
Cavity count or family-mold pairing
Cosmetic faces that cannot take a gate
Resin family
Whether regrind from a cold tree is acceptable
Known fill or warp trouble on similar parts
Related
Related design guidelines
Stay on this spoke for its question. Open a sibling for the neighbor topic or the CAD check.
Runner glossary
What a runner is.
Runner glossaryCold runner glossary
The cold tree and regrind.
Cold runner glossaryHot runner glossary
The heated manifold.
Hot runner glossaryDFM review
How NetProto checks fill balance before steel.
DFM reviewFAQ
Runner design FAQ
What is runner design?
The layout that carries melt from the sprue to each gate so cavities fill and pack together. It is tooling geometry.
Can buyers design the runner?
You mark cosmetics, cavitation, and cold versus hot. The tooling team sizes the runner. This page does not publish a diameter.
Do runners affect warp?
Yes. Uneven fill and pack show as warp. Gate location and wall thickness share that story.
Does a cold runner leave extra plastic?
Yes. A cold tree is trimmed. Hot systems keep melt in the manifold. Name the intent. This page does not discuss quote line items.
How is a runner different from a gate?
The runner feeds the gate. The gate is the last opening into the cavity. Open gate types and gate location.
How is this page different from hot tips or slug wells?
This spoke owns layout. Hot tips own the heated drop. Slug wells own the cold-end pocket. DFM review checks CAD.
Next step
Upload CAD for DFM review of runner intent
Share cavitation, cosmetics, and cold versus hot so review can comment on balance before quoting.