DFM Checklist for CNC Machined Parts: 10 Rules to Cut Cost
The 10 most impactful CNC DFM rules: minimum wall 0.8mm aluminum / 0.5mm steel; internal corner radius ≥ 1/3 of pocket depth; standard drill sizes only; standard thread depths (1.5× diameter); avoid deep narrow pockets; tolerance only what matters; consolidate setups; use stock thicknesses; flat datum surfaces; specify finishes only where visible.
Following these 10 design rules typically cuts CNC part cost 20–50% and lead time 1–3 days. They are non-negotiable for engineers serious about manufacturable design.
The 10 Rules
1. **Minimum wall thickness**: 0.8mm aluminum, 0.5mm steel, 1.0mm plastics 2. **Internal corner radius** ≥ 1/3 of pocket depth (radius < depth/3 forces tiny tools, slow cycles) 3. **Use standard drill sizes** (metric: 3, 4, 5, 6, 8, 10mm); custom sizes need special tools 4. **Thread depth** = 1.5× nominal diameter; deeper threads add little strength but lots of cost 5. **Avoid deep narrow pockets** — depth ≤ 4× width is the safe zone 6. **Tolerance only critical features** — default ISO 2768-m everywhere else 7. **Consolidate setups** — design parts machinable in 1–2 setups vs. 4+ 8. **Use stock thicknesses** for plates (3, 5, 6, 8, 10, 12, 15, 20mm) — saves a face-mill operation 9. **Provide flat datum surfaces** for fixturing — avoid round-stock-only designs 10. **Specify finishes only on visible surfaces** — internal anodizing or painting wastes money
Frequently asked questions
- How much can good DFM save?
- Typical cost reduction from applying these rules: 20–50%. Lead time reduction: 1–3 days. The biggest single savings come from relaxing non-critical tolerances.
- Do you offer free DFM review?
- Yes — every FormHub quote includes a free DFM analysis. We flag manufacturability issues and suggest cost-saving design changes before production.
- Can you machine a part that violates these rules?
- Usually yes, but it costs more. We will quote any geometry but will flag rule violations and offer alternatives.