Problem / Question
Most slow or inaccurate CNC quotes are not caused by the shop. They are caused by drawings that leave the important decisions open.
A quotation is a manufacturing plan in disguise: to price it, the supplier must decide which material, which stock, which process and which inspection the part needs.
Engineering context
A machinist reads three things first: the material, the tightest feature, and the quantity. Everything else follows from those.
Key factors
- State the material and temper, not just 'aluminum'.
- Mark only the tolerances that actually matter; a blanket ±0.01 mm across every dimension raises cost without benefit.
- Give a datuming scheme so features are referenced consistently.
- Show thread callouts, surface finish (Ra) and any heat treatment or coating.
- Provide 3D CAD (STEP) alongside the PDF drawing.
Common mistakes
- Title-block material left blank.
- GD&T applied inconsistently or to non-critical features.
- Critical dimensions buried in a model but absent from the drawing.
- No quantity, so the supplier cannot choose between setup-heavy and tooling-heavy routes.
What information a supplier needs
Material and temper, the critical-to-quality features, acceptable finish, quantity and target date. If something is unknown, say so — an engineer can propose it.