Design smarter.
Ship faster.
Spend less.
Every manufacturing process has rules. Break them, and you pay in cost, lead time, or failed parts. Follow them, and your designs manufacture economically, repeatably, and without drama. This is our free DFM guide.
Each process has its own rules.
General DFM principles apply across all processes, but the specific constraints differ dramatically. Design rules for CNC are completely different from injection molding or sheet metal.
CNC Machining
- Internal radii ≥ 0.8 mm
- Depth-to-width ≤ 4:1
- Wall thickness ≥ 1.0 mm
- Thread depth 1.5–3× dia
3D Printing
- Feature size ≥ 0.5 mm
- Wall thickness 1.0+ mm
- Hollow if > 100×100 mm
- Drain holes for SLA/SLS
Injection Molding
- Uniform wall ±10%
- Draft angle 0.5–1.5°
- Fillet ≥ 0.5× wall
- No sharp corners
Sheet Metal
- Bend R ≥ thickness
- Hole-to-edge ≥ 2t
- Hole-to-bend ≥ 3t
- K-factor 0.33–0.40
DFM rules that always apply.
These seven principles work across every manufacturing process. Internalize them, and you\'ll be a better hardware designer regardless of production method.
Specify tolerance by function, not habit
Default to ISO 2768-m (±0.1 mm) unless the feature mates with another part or affects performance. Every ±0.01 mm callout adds $30–80 per part. Tight tolerances should appear on < 10% of features on most drawings.
Keep wall thickness uniform
For injection-molded parts, wall thickness variation > 10% causes warp, sink marks, and ejection problems. For CNC, thin walls (<1 mm) deflect under cutting forces. Aim for constant wall thickness throughout the part.
Avoid sharp internal corners
Internal sharp corners concentrate stress, trap chips in CNC, and require EDM or expensive micro-tools to produce. Use fillets with R ≥ 0.5× wall thickness as a default.
Minimize setups
Every CNC setup costs time and introduces tolerance stack-up. A part machinable in one or two setups is dramatically cheaper than one requiring five setups. Use 4- or 5-axis machining to consolidate setups when cost-effective.
Use standard sizes
Standard fastener sizes, bearing bores, and common stock materials are cheaper and faster. An Ø 10 mm bore is standard; an Ø 10.47 mm bore requires custom tooling or interpolation.
Design for inspection
Features hidden from CMM probes require teardown inspection or special tooling. Leave reference surfaces, add datum features, ensure critical dimensions are accessible for measurement.
Consider assembly
Parts that assemble themselves (self-piloting features, bolt-through holes with chamfers, captive fasteners) save 30–60% of assembly time over parts requiring alignment and care.
Deeper technical references.
Surface Finish Guide
Ra values, finish callouts, and what each finish actually looks like.
Read guideMaterial Selection Guide
Decision matrix for picking the right alloy or plastic for your application.
Read guideTolerance Guide
ISO 2768 classes, GD&T primer, and how tolerance drives cost.
Read guideMaterial Properties
Side-by-side mechanical property comparison of common engineering materials.
Read guide