CNC Design for Manufacturability (DFM) Checklist

Geometry

• Internal corner radius ≥ ⅓ pocket depth. Smaller radii force smaller end mills which run slower. Each step down in tool size roughly doubles cycle time.
• Minimum wall thickness ≥ 0.8 mm on aluminum, ≥ 1.5 mm on stainless. Thinner walls chatter or deflect during cutting.
• Maximum hole depth ≤ 4× hole diameter. Deeper requires specialty tooling (gun drills, peck cycles); cost goes up sharply past 4D.
• Avoid square internal corners unless you actually need them — they cost EDM time. If a square corner is functional (e.g. mating part), call it out specifically.
• External corners are free. Round them or leave them sharp — same cost.

Features

• Standard hole sizes preferred. Designing to drill chart sizes (e.g. 6.35 mm = ¼") removes the need for a custom reamer.
• Through-holes faster than blind holes. Especially if blind hole needs a flat bottom (which requires a flat-end mill instead of drill).
• Thread engagement = 1.5× diameter, not more. M6 threads need 9 mm engagement, not 30 mm. Deeper threads are wasted material + slower tap operation.
• Avoid undercuts if 3-axis possible. Undercuts force 4 or 5-axis machining (1.5–3× more expensive). If absolutely needed, dimension them clearly.
• Use standard tap sizes (M3, M4, M5, M6, M8, M10) rather than M3.5, M4.5 — same strength, smaller tap library.

Tolerances

• Apply tight tolerances only where they matter. ±0.025 mm on a clearance hole is wasteful; the hole only needs to clear the screw.
• Tolerance stack carefully. Don't over-tolerance interfaces — if A is ±0.05 mm and B is ±0.05 mm, their assembly is ±0.10 mm; design B to ±0.025 mm only if you really need ±0.05 mm total.
• Surface finish callouts only where needed. "Ra 1.6 everywhere" forces all features to that finish; specify per-feature.

Material + finishing

• Prefer 6061-T6 over 7075-T6 unless you specifically need 7075 strength. 6061 is 3× easier to machine.
• Avoid mixing materials in one part. Multi-material features force two operations or inserts.
• Choose finish before designing. Anodizing builds up 5–25 µm of oxide layer — affects fit on tight tolerances. Account for it in the design.
• Standard finishes are cheaper. Type II clear anodize is industry-default; Type III hard anodize or specific colors add cost + lead time.

Documentation

• Drawing in PDF + 3D in STEP. Both, every time.
• Critical dimensions ballooned on drawing. Helps engineer focus DFM review where it matters.
• Use GD&T for interfaces. Positional, parallelism, perpendicularity — communicates intent better than +/− tolerances alone.

The DFM review

Ginwate runs a free DFM review on every quote (1–12 hours during business hours). We'll flag any rule above that applies to your part, suggest a fix, and re-quote — at no extra cost.

Upload your CAD and we'll send back the DFM notes with the quote.