Coordinate tolerancing only
- Ambiguous setup on CMM for complex housings
- Hard to separate warp from size error
- Buyers and molders debate setup each T1
DFM
GD&T for Molded Parts: Injection Molding Design Rules
GD&T on molded parts should define functional datums inspectors can repeat.
DFM
GD&T on molded parts should respect process variation
Datums must be accessible for fixturing and inspection.
Primary datums often land on stable planar features, not on cosmetic texture.
Position tolerances on hole patterns need gate and warp behavior considered.
Mixing metal GD&T habits with plastic shrink causes false failures on inspection reports.
DFM
Quote this rule with your CAD upload
NetProto DFM review flags these geometry patterns before steel is ordered.
- Call out draw direction and cosmetic faces on the model.
- Note resin family even when the grade is not final.
- Tighten tolerances only on mating features that need them.
Inspection
Coordinate dimensions only versus datum referenced GD&T
Plastic parts benefit from explicit datum frames on mates.
GD&T with clear datums
- Repeatable inspection setup
- Focus on functional interfaces
- Easier FAI ballooning on qualified programs
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
Design guide hub
All DFM topics on one route.
Design guide hubDFM article
Long form engineer guide.
DFM articleStandard tolerances
Commercial defaults.
Standard tolerancesTight tolerance strategy
When to tighten.
Tight tolerance strategyQuality assurance
NetProto QA overview.
Quality assuranceVisual reference
Molding context for this rule
Images from the Forge media library illustrate typical programs.
Injection molded part design review on CAD
Injection molded part design review on CAD
Plastic housing with ribs and bosses
Plastic housing with ribs and bosses
Engineer measuring molded component
Engineer measuring molded component
FAQ
GD&T questions
Is GD&T required on RFQs?
Not required, but mates benefit from datum clarity.
Can flatness be tight on large covers?
Large flat parts warp. Flatness callouts need process realism.
Who picks datums?
Product design owns assembly datums. Mold design aligns steel to them.
Next step
Upload GD&T frames on mates
Include datum scheme PDF with 3D CAD for DFM review.