No universal max
Resin, gate, and wall all change the answer. This page has no ratio table.
Flow length ratio
Flow Length to Wall Thickness: Why Long, Thin Paths Short-Fill
Mark the intended gate start and the last thin region. DFM review comments on CAD. This page does not publish a maximum ratio.
Design guideline
The path is long. The wall is thin. Fill gets hard.
Flow length versus wall thickness is a fill-difficulty check, not a published NetProto spec. High L/t makes shorts and hesitation more likely. Geometry still dominates over a high-flow grade.
The flow length to wall thickness ratio is a fill-difficulty check, not a published NetProto spec. Gate at the geometric start of fill helps pack reach the last thin region. Gate location owns that face. Thin wall design owns the light skin. Short shot is the defect when fill dies. DFM review needs resin and intended gate.
This spoke owns the L/t question. Wall thickness owns the nominal wall. The design guide hub lists every topic.
Roles
Which page answers which fill-path question
Stay here for long-path fill risk. Open a sibling for the wall, the gate, the runner, or the defect.
| Page | Use it for |
|---|---|
| Flow length ratio (this page) | Long path through a thin wall |
| Runner design | How melt reaches the gate from the sprue |
| Wall thickness | The nominal wall the path uses |
| Thin wall design | Fill on a light skin |
| Gate location | Where fill should start |
| Short shot | When the path does not fill |
| Uniform wall thickness | Steps that stall the melt |
| Venting | Gas at the end of a long path |
| DFM review | CAD check before steel |
Checks
What DFM review looks for on flow length
Qualitative checks. No figure on this page is a NetProto specification.
Gate at the start
Put the gate where fill should begin, not at the last thin tip.
More gates can help
A second gate shortens the path. It also adds a weld. Mark cosmetics.
Warp follows pack
A long path packs unevenly. The warpage page owns that defect.
Decision
A long thin path versus a shorter gated fill
Wrong: a published max ratio on every resin. Right: mark the path, gate, and last thin region on CAD.
What goes wrong
- A long thin channel with the gate at the far end
- A claimed max ratio with no resin or gate note
- Ignore shorts at the last thin tip
What to try first
- Show the intended gate start
- Open thin-wall and gate-location pages for those jobs
- Name the resin family
RFQ
Send these notes with CAD for a flow-length review
The quote can start from CAD alone. These notes make the DFM pass specific.
Intended gate start
Last thin region that must fill
Resin family
Whether a second gate is acceptable
Cosmetic faces that cannot take a weld
Known short or hesitation 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.
Short shot
When the path does not fill.
Short shotWarpage
Uneven pack on a long path.
WarpageDFM review
How NetProto reads the fill path on CAD.
DFM reviewFAQ
Flow length ratio FAQ
Is there a universal max flow length ratio?
No. Resin, gate, wall, and temperature all change it. NetProto does not publish a max ratio on this page. Upload CAD.
How do I calculate flow length ratio?
Divide the longest flow path from gate to last fill point by the thinnest wall along that path. Both dimensions must come from your CAD model. Mark them on upload so DFM review can assess the risk.
Can multiple gates fix a long flow?
They can shorten the path. They also add a weld. Mark cosmetics. Gate location owns the faces.
Does flow length affect warp?
Yes. A long path packs unevenly. The warpage page owns that defect.
How is this different from thin-wall design?
Thin-wall owns the light skin. This spoke owns how far melt must travel through that skin.
Do I need a flow study?
Not to start a quote. DFM review comments on the path from CAD. A study is a later tooling choice, not a published spec.
How is this page different from wall thickness or short shot?
Wall thickness owns the nominal wall. Short shot owns the defect. This spoke owns the L/t question. DFM review checks CAD.
Next step
Upload CAD for DFM review of your fill path
Share gate start, last thin region, and resin so review can comment on fill before quoting.