Why drawings matter
A CAD model defines nominal geometry. A drawing defines what must be controlled, measured, and accepted. If a requirement affects function, assembly, safety, cosmetics, or inspection, put it on a drawing instead of relying on assumptions.
What to include
- Part name, revision, units, material, finish, and quantity context.
- Critical dimensions and tolerances for mating features, holes, threads, fits, sealing surfaces, and functional interfaces.
- Thread specifications including size, pitch, depth, class, and inserts when relevant.
- Surface roughness, flatness, perpendicularity, concentricity, or GD&T only where they affect function.
- Inspection requirements such as first article, CMM report, material certificate, or critical-to-quality dimensions.
Tolerance strategy
| Feature type | Recommended tolerance approach | Reason |
|---|---|---|
| Non-critical shape | Use general tolerance or process standard | Controls cost and avoids unnecessary inspection. |
| Mating holes | Specify diameter, position, and fit requirement | Prevents assembly problems. |
| Bearing or shaft seats | Use precise tolerance and surface finish where needed | Controls function and wear. |
| Cosmetic surfaces | Define finish and acceptable appearance | Dimensional tolerance alone does not control cosmetics. |
| Sheet metal bends | Define bend angle and key formed dimensions | Bending has different variation than flat cutting. |
Avoid over-tolerancing
Tight tolerances increase production time, supplier limitations, scrap risk, and inspection effort. A drawing with tight tolerance on every dimension is often more expensive than a drawing that only controls the functional features.
GD&T and datums
Use datums and GD&T when feature relationships matter more than simple plus/minus dimensions. Datums should reflect how the part is assembled, measured, or used. If the inspection setup is unclear, the supplier may need clarification before production.
Quality and inspection
- Mark critical-to-quality dimensions clearly.
- State whether inspection reports are required or whether standard production checks are sufficient.
- Clarify if dimensions apply before or after finishing.
- Include acceptable cosmetic conditions for visible faces where appearance matters.
Uretyco AI workflow
Uretyco can use drawing content to identify critical features, flag expensive tolerance patterns, and ask whether requirements are functional or optional. This helps users avoid paying for controls they do not need while protecting the dimensions that matter.
FAQ
- Do I need GD&T? Only when relationships such as position, flatness, concentricity, or profile are important.
- Should all dimensions be tight? No. Tighten only critical dimensions.
- Can a note override the model? If drawing and model disagree, the order needs clarification before production.
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