Metal Finishes in CNC Machining: Your Complete Guide

Metal finish selection. People treat it like an afterthought.

Big mistake.

Your finish determines how long that part lasts. How well it performs. Whether it corrodes in six months or six years. It’s also crucial to consider how the product appears to the customer.

Get this decision wrong and you’re swapping parts way earlier than you planned. Get it right? Parts hold up. Standards get met. Everyone’s happy.

Here’s the breakdown.

Snapshot: Metal Finishes at a Glance

Finish Type	Lifespan	Cost Range	Best For	Materials
Anodizing	5-15 years	$0.50-$3/sq in	Aerospace, electronics, consumer	Aluminum
Powder Coating	7-15 years	$1-5/sq in	Outdoor, industrial, automotive	Steel, aluminum
Electroplating	5-10 years	$0.75-$4/sq in	Electrical, decorative, wear-resistant	Steel, copper, brass
Bead/Sandblasting	N/A (prep step)	$0.25-$1/sq in	Pre-coating, rust removal	Stainless, aluminum
Brushing/Polishing	N/A (decorative)	$0.50-$3/sq in	Luxury, food-grade, medical	Stainless, aluminum
Passivation	10-15 years	$0.50-$2/sq in	Marine, medical, food processing	Stainless steel
Black Oxide	3-7 years	$0.25-$1.50/sq in	Tools, firearms, anti-glare	Steel

Quick reference. Engineers, designers, buyers—compare options fast.

Common Metal Finishes in CNC Machining

Part comes off the machine looking like raw metal. Because it is raw metal.

Finishing changes that. Makes it durable. Makes it look right. Makes it compliant with whatever standards apply to your industry.

Here’s what each method actually does.

1. Anodizing

Electrochemical process. Builds an oxide layer on aluminum that wasn’t there before.

Result? Harder surface. Better corrosion resistance. You can even add color if that matters for your application.

Three types to know:

• Type I: Chromic acid. Thin protective layers.
• Type II: Sulfuric acid. Decorative stuff.
• Type III: Hard anodizing. Industrial-grade wear resistance.

Aerospace, electronics housings, automotive parts—all use anodizing heavily. But here’s the catch. Aluminum only. Won’t work on steel, copper, nothing else.

2. Powder Coating

Electrostatic powder hits the surface. Heat cures it. You get a finish that’s tough and looks good.

What makes it popular:

• Impact resistance that holds up
• Coverage stays uniform
• UV protection. Chemical protection.

Outdoor equipment, machine enclosures, automotive stuff. Anywhere you need durability without babying the part.

3. Electroplating and Metal Plating

Thin metal layer—zinc, nickel, chromium—deposited onto your part.

What you gain:

• Corrosion resistance goes up
• Wear resistance goes up
• Electrical conductivity (gold or silver plating)
• Shiny decorative look if that’s what you’re after

Electrical components love this. Automotive too. Consumer products where appearance matters.

4. Bead Blasting and Sandblasting

High-pressure abrasive streams. Clean surfaces. Smooth them out.

• Bead blasting: Uniform matte look.
• Sandblasting: More aggressive. Strips rust, paint, surface defects.

Usually a prep step. You blast it, then coat it. Works on stainless, aluminum, most alloys you’ll encounter.

5. Brushing and Polishing

• Brushing: Linear satin texture. Appliances, architectural panels, anything decorative.
• Polishing: Mirror finish. High-gloss. Medical equipment, food-grade surfaces, luxury products.

Both look sharp. Both reduce dirt buildup. Hygiene applications love polished surfaces for a reason.

6. Passivation

Chemical treatment. Stainless steel only.

Removes free iron and contaminants sitting on the surface. Corrosion resistance jumps way up.

Medical, marine, food processing—these industries don’t ask if you passivated. They require it.

7. Black Oxide

Chemical conversion coating. Gives you mild corrosion protection and a matte black look.

Cuts glare. Improves lubricity. Common on tools, firearms, industrial machinery.

One thing though. Not for food. Not for medical. Strictly industrial applications.

Choosing the Right Finish

Multiple factors at play here. Think through each one before committing.

• Material compatibility: Anodizing only works on aluminum. Steel or brass? Go with plating or powder coating.
• Environment: Moisture exposure? Chemicals? Temperature extremes? Corrosion resistance becomes the priority.
• Aesthetics: Matte, satin, mirror finish? Know what the end use demands.
• Function: Need electrical conductivity? Insulation? Lower friction?
• Regulations: Aerospace, medical, food—each has specific surface finish requirements. Check before you choose.

Watch out for this. Plating and powder coating add thickness. Design your tolerances accordingly. Learned that one the hard way myself.

Step-by-Step Plan for Finishing CNC Parts

Same process every time. Don’t skip steps.

1. Assess material: What metal? What finishes actually work with it?
2. Define requirements: Function. Appearance. Compliance. All three.
3. Pick the finish: Anodizing, powder coating, plating—match to your needs.
4. Pre-treat the surface: Clean it. Blast it. Polish if needed. Adhesion depends on this.
5. Apply finish: Controlled conditions. Standardized process.
6. Inspect: Thickness, adhesion, uniformity. Check all three.
7. Adjust dimensions: Account for any material the finish added.

Trends in the U.S. Market

Durable finishes are in. Eco-friendly finishes even more so.

Powder coating and hard anodizing lead the pack. Low maintenance, long-lasting, customers love them.

Other stuff happening:

• VOC emissions dropping as coating processes go greener
• Multi-layer finishes—aesthetics plus durability in one
• Automation speeding things up and improving consistency

Local manufacturers want finishes that survive outdoors, handle industrial abuse, and shrug off temperature swings. Makes sense. That’s what the applications demand.

FAQs

Can all metals be anodized?

Nope. Aluminum alloys only. Everything else needs plating or powder coating.

Do finishes change part dimensions?

They do. Electroplating and powder coating both add thin layers. Factor that into your design.

Best finish for outdoor parts?

Powder coating or hard anodizing. Both handle corrosion and UV exposure well.

Can I use black oxide on food equipment?

No. Black oxide is industrial only. Tools, firearms, machinery. Keep it away from food and medical.

How do I maintain brushed or polished surfaces?

Non-abrasive cleaners. Skip the harsh chemicals. Surface quality lasts longer that way.

Which finish lasts longest?

Passivation and powder coating. Both can hit 10-15+ years in the right conditions.

Why Styner Machine Tools

Styner Machine Tools has decades of CNC machining experience. Finishing capabilities to match.

Anodizing. Powder coating. Electroplating. Polishing. We do it all. Every part gets inspected for quality, durability, and appearance.

Aerospace, automotive, medical—industry doesn’t matter. Parts meet strict standards or they don’t ship.

Precision manufacturing. Experienced team. Quality that actually holds up. That’s what Styner delivers.