How to Design Aluminum Parts for CNC Machining: DfM Tips, Wall Thickness, and Keeping Costs Down

CNC aluminum parts are fast to make and don’t cost a fortune. That’s why pretty much everyone picks aluminum: it’s strong, super light, shrugs off rust, and the tools just fly through it. The trick is simple: design it right the first time or watch your bill double for no reason.

DfM isn’t some fancy buzzword; it just means “don’t make the machinist hate you.” Follow a few basic rules up front and you skip the headaches, scrap, and parts that come out different every run.

This is the no-BS list of what actually matters:

· which aluminum to grab

· tolerances that won’t bankrupt you

· walls thick enough to survive the spindle

· how to stop parts from turning into potato chips

· finishes that look good without breaking the bank

· what anodizing really does to your dimensions

· how many pieces make sense to order

Doesn’t matter if you’re doing plane brackets, car bits, or little electronics boxes; these rules keep everything working and keep the price sane.

Which Aluminum Alloy Should I Pick for CNC Machining?

Aluminum is still the top choice for prototypes and small runs. It’s light, cheap, and machines beautifully. CNC is a subtractive process—it starts with a block and removes material until the part matches your drawing.

Here are six popular aluminum grades for CNC work:

· 6061-T6: Machines great and welds nicely. Perfect for everyday parts.

· 6082: A bit stronger than 6061. Often used in Europe for structural pieces.

· 7075-T6: Super strong. Common in aerospace and high-stress jobs.

· 5083: Best-in-class corrosion resistance. Great for boats and salty environments.

· 5052: Easy to form and very corrosion-resistant. Good for enclosures and brackets.

· MIC-6: Cast plate with excellent flatness and stability. Loved for jigs, fixtures, and baseplates.

Quick comparison table

Real-world uses:

· Aerospace → 7075 for wings or landing-gear parts

· Automotive → 6061 or 6082 for suspension arms

· Electronics → MIC-6 for heat sinks or precision plates

· Medical → 5052 for corrosion-proof housings

Key points:

· Match the alloy to your needs (strength vs. corrosion).

· Pick MIC-6 when flatness really matters.

· Remember that material price changes between prototypes and production.

What Tolerances Should I Use Without Exploding the Price?

CNC machines can hit very tight numbers, but tighter = more expensive and slower. Most shops can easily hold ±0.005 mm (±0.002") on aluminum. For normal parts, ±0.01 mm (±0.004") is plenty and keeps the price reasonable.

Only go tighter when you really need it:

· Parts that must line up perfectly

· Press-fits or bearing seats

· High-speed rotating components

ISO 2768 reference (mm)

Real cost example: Asking for ±0.01 mm instead of ±0.05 mm can add 30–50% to the quote. You’ll pay for slower speeds, extra tooling, and more measuring time.

Pro tip: Use one-sided tolerances when possible (example: +0.00 / -0.05 mm). It makes machining easier.

Bottom line:

· Start with standard tolerances.

· Tighten only where it matters.

· Talk to your shop—they’ll tell you what’s realistic.

Key DfM Rules and Minimum Wall Thickness for Aluminum

Wall thickness is super important. Too thin and the part can bend or break while cutting.

Safe minimum wall thickness

Main DfM rules:

· Add ribs or gussets to support thin areas. Keep rib height ≤ 3× wall thickness.

· Don’t make holes or slots smaller than 1 mm unless you have to.

· Put a radius on inside corners—at least half the tool diameter.

· Keep pocket depth ≤ 4× width so the tool doesn’t flex.

· For threads: minimum length = 1× diameter; tapped blind holes ≥ 1.5× diameter.

Quick checklist:

· No long unsupported walls

· Make sure tools can reach everywhere

· Round inside corners

· Add fillets to kill stress points

Will My Aluminum Part Warp During Machining?

Yes, it can—especially with thin walls, big flat areas, or uneven material removal. Aluminum has internal stresses that get released when you cut.

High-risk shapes:

· Long thin plates

· Deep pockets on only one side

· Thin boxes or covers

Seven ways to stop warping

1. Keep the design symmetrical when you can.

2. Ask for stress-relief annealing before roughing.

3. Leave extra material that gets removed later.

4. Choose MIC-6 for big flat parts.

5. Balance the tool paths so material comes off evenly.

6. Use good fixturing or vacuum tables.

7. Add a final stress-relief bake for critical large parts.

Takeaway: Think about warping while you’re still designing, not after the part twists.

What Surface Finish Should I Ask For?

As-machined aluminum usually looks like fine tool marks with Ra 1.6–3.2 μm.

Common options

If the part will be anodized or painted, keep the surface clean and fairly uniform.

Takeaway: Pick the cheapest finish that satisfies appearance and function.

How Does Anodizing Change Dimensions?

Anodizing grows an oxide layer. Roughly half grows outward, half inward.

Typical buildup:

· Type II (regular) → 5–15 μm per surface

· Type III (hardcoat) → about 25 μm per surface

That means a 10 μm Type II coat adds roughly 5 μm to each side.

What to do:

· Design to final (post-anodize) dimensions or tell the shop to leave extra material.

· Mask threads, bores, or any tight-fit areas.

· Accept slight color variation between batches.

Takeaway: Always plan for the coating thickness and tell your shop which surfaces must stay exact.

How Many Parts Should I Order? (Prototyping vs. Low-Volume)

Typical quantities

Setup and programming cost is fixed per batch, so more parts = lower price per piece.

When to think about die casting: Switch when you need 500–1,000+ identical parts and the design won’t change.

Lead-time comparison

Takeaway: Stick with CNC for speed and flexibility until you’re sure the design is final.

Aluminum CNC machining service gives you precision and freedom—if you design with manufacturing in mind. Pick the right alloy, use sensible tolerances, respect wall thickness, fight warping, choose finishes wisely, and plan for anodizing. Do that, and you’ll get strong, beautiful parts without paying extra.

Ready to start your aluminum project? Contact Momaking factory for a free DfM review and quote.

FAQ

Q: What’s the best all-around aluminum for CNC?

A: 6061-T6 wins for most jobs—good strength, great machining, decent corrosion, low price. Go 7075 when you need max strength, MIC-6 when flatness is everything.

Q: What’s a safe minimum wall thickness in CNC machining?

A: 0.8–1.0 mm for small parts, 1.5–2.0 mm for medium, 2.5–3.0 mm for big parts. You can go thinner, but cost and risk go way up.

Q: How much does specifying tight tolerances increase CNC machining cost?

A: Going from ±0.05 mm to ±0.01 mm usually adds 30–70% because of slower speeds and extra checks.