Good DFM does not simply make a part cheaper. It preserves function while making the manufacturing and verification route explicit.
Internal corners and tool access
Because milling cutters rotate, internal vertical corners normally require a radius. Increasing the radius relative to pocket depth can permit a larger, more rigid tool. Avoid designing every corner at the same minimum radius; relief or a larger non-critical radius can reduce machining time.
Deep pockets and thin walls
Long tool reach increases vibration and deflection. Deep narrow cavities may require smaller tools and slower cutting. Thin walls can move during machining or measurement, especially in aluminum and engineering plastics. Add local stiffness where possible and identify which wall thickness or profile is function-critical.
Holes and threads
- Specify thread standard, size, class and required depth.
- Distinguish thread depth from drill depth.
- Allow tool clearance beyond the usable thread where geometry permits.
- Call out helicoils, inserts, sealing threads or gauge requirements explicitly.
- Avoid very deep small-diameter holes unless the function requires them.
Tolerances and surface roughness
Apply general tolerances to non-critical features, then call out the interfaces that control assembly, sealing, bearing fit or alignment. Surface roughness is a functional specification—use it for sliding, sealing or optical/cosmetic needs rather than as a blanket note.
| Requirement | Better drawing practice |
|---|---|
| Mating bore | Define size tolerance, datum relationship and surface requirement if functional |
| Cosmetic face | Mark the face and provide an appearance reference or acceptance criteria |
| Threaded hole | State standard, size, class, full thread depth and inspection expectation |
| Coated dimension | State whether the limit applies before or after coating |
Datums and inspectability
A datum scheme should reflect how the part locates in its assembly and how it can be measured. Avoid controlling features to an unstable, unfinished or inaccessible reference. If a geometric tolerance is essential, define the datum structure and material condition correctly.
RFQ checklist
- STEP/STP model matching the drawing revision.
- PDF drawing with critical dimensions, datums, threads and notes.
- Exact material grade or a clear performance requirement.
- Quantity now and expected repeat quantity.
- Surface finish, color, masking and cosmetic zones.
- Required inspection documents, certificates and packaging.
- Delivery destination and target date.
Common questions
Why do internal corners need a radius?
Rotating end mills naturally leave an internal radius. Larger radii often allow stronger tools and more efficient machining.
Should every dimension have a tight tolerance?
No. Reserve tighter limits for features that control fit or function; blanket tight tolerances increase process and inspection cost.
Is a 3D model enough for a quote?
It can support an early estimate, but a drawing is needed when tolerances, threads, surface finish, datums or documentation affect the part.