A DFM (design-for-manufacture) pass before the drawing leaves your desk turns "makeable eventually" into "right first time" — and it costs cents versus a tooling revision. Here are the five fixes that cover most of what goes wrong when a drawing crosses to a Chinese shop.
The most common drawing mistake is over-tolerancing — a blanket ±0.01 mm on every dimension. Every tight tolerance forces inspection, slows the floor, and scraps parts that were functionally fine. Apply tight numbers only to fit and critical surfaces, and let the rest sit at commercial standard. Better still, use GD&T to control what actually matters — the position of a bore — instead of stacking linear tolerances that fight each other.
Each process has limits a drawing ignores at its peril:
Every unique hole size, thread type and chamfer is another toolchange and another chance for error. Pick one standard hole, one thread, one chamfer wherever you can. Fewer unique features means fewer setups, lower cost and better consistency across a batch. Design for the floor, not just for the model.
For cast and extruded parts, draft (1–3°) is what lets the part release from the tool. Put the parting line where it won't land on a cosmetic or sealing surface, and for extrusions design the cross-section to run in a single die pass. Get this wrong and you're revising the tool, not the file.
Vague calls like "anodize" or "Ra fine" are invitations to rework. State the anodize type (II or III), color and thickness; state the actual Ra where it matters and drop it where it doesn't. Every secondary operation is a handling step and a defect opportunity — call out only what the part needs to do its job.
Drawings that travel badly cause more failures than bad designs. Watch for: mixed units (mm vs inch) with no dominant standard, missing datum references, a material called only "aluminum" instead of 6061-T6, and notes in a language the shop can't read. Confirm material grade, units and critical callouts are explicit and bilingual before the file leaves your desk — a five-minute check prevents a container of wrong parts.
I run a DFM pass on your file before it reaches any shop — flagging these five issues and translating your intent into manufacturing language, so the first quote is realistic and the first parts are right. Send the drawing; I'll send back the changes that save the revision.
Send the drawing and target process — I'll return the five fixes that keep the first articles right.