Internal versus external
Inside corners need a blend for flow and stress. Outside corners are appearance and witness.
Corner design
Corner Design for Injection Molding: Types, Flow, and Parting Line
Internal and external corners drive flow, stress, and witness. DFM review comments on CAD before steel is cut. This page does not publish a radius number.
Design guideline
Pick the corner type before you pick a number
Corner design is the type decision: internal fillet, external radius or chamfer, and where the parting line can land. It is not the radius-to-wall rule.
External corners can use a small break for polish access. Internal sharp corners stall flow. Parting lines often land on external corners and change witness. Fillets and radii own the radius rule. Sharp corner stress owns why zero radius cracks. DFM review comments on CAD.
This spoke owns the type decision. The design guide hub lists every topic.
Roles
Which page answers which corner question
Stay here for corner type. Open a sibling for the radius rule or the crack mechanism.
| Page | Use it for |
|---|---|
| Corner design (this page) | Types, flow, and parting-line choices |
| Fillets and radii | Radius rules across the part |
| Sharp corner stress | Why zero-radius insides crack |
| Draft angle | Whether a chamfer replaces draft (it does not) |
| Rib design | Corners at rib roots |
| Boss design | Corners at boss roots |
| Gussets | Corners where a brace meets the wall |
| Wall thickness | A large corner blend can hide extra mass |
| DFM review | CAD check before steel |
Checks
What DFM review looks for on corners
Qualitative checks. No figure on this page is a NetProto specification.
Chamfer versus fillet
A chamfer is a straight break. A fillet is a curve. They are not interchangeable on a loaded inside.
Parting-line land
External corners often carry the split. Call out witness.
No universal radius
This page does not publish how large a radius must be. Fillets own that rule.
Decision
A sharp internal pocket versus a radiused corner
Wrong: CNC knife edges inside every pocket. Right: pick the type, then let fillets size the blend.
What goes wrong
- A sharp internal pocket on a loaded wall
- A chamfer used as if it were draft
- A parting line dropped on a class-A corner with no note
What to try first
- Radius loaded insides; keep sharp only where function needs it
- Use draft for release; use a chamfer for a straight lead-in
- Mark parting-line witness on external corners
RFQ
Send these notes with CAD for a corner review
The quote can start from CAD alone. These notes make the DFM pass specific.
Internal versus external corners of interest
Keep-sharp edges versus blend edges
Parting-line intent on external corners
Cosmetic faces that cannot show witness or sink
Loaded corners on ribs, bosses, or snaps
Whether a chamfer is for assembly or for looks
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 corner types before steel.
DFM reviewFAQ
Corner design FAQ
What does corner design cover?
The type decision: internal blend, external radius or chamfer, and where the parting line can land. Not a radius-to-wall number.
Do external chamfers replace draft?
No. Draft releases the face. A chamfer is a straight break. You may need both.
What radius is enough?
It depends on load, resin, and cosmetics. NetProto does not publish a radius on this page. Open fillets and radii, then upload CAD.
Can corners hide gate vestige?
Sometimes a gate sits near a corner. That is a gate-location choice. Mark cosmetics. The gate page owns placement.
When should a corner stay sharp?
Shutoffs, seals, and some snap catches. Flag them. Sharp-corner stress owns why loaded insides should not stay sharp by default.
How is this page different from fillets or sharp-corner stress?
This spoke owns types. Fillets own the radius rule. Sharp-corner stress owns the crack mechanism. DFM review checks CAD.
Next step
Upload CAD for DFM review of your corners
Share loaded corners, keep-sharp edges, and parting-line intent so review can check types before quoting.