Bead blasting produces uniform matte finishes on aluminum prototypes with Ra 1.6-3.2 μm surface roughness at $2-8 per part. Polishing creates mirror-like surfaces with Ra 0.05-0.3 μm but costs $15-50 per part with 3-5x longer processing time. For most prototypes requiring professional appearance, bead blasting offers better value. Choose polish only when high-gloss aesthetics justify the premium cost.
Over 12 years producing aluminum prototypes for clients like Haier, Midea, and Xiaomi, we’ve seen teams struggle with this exact decision. The wrong choice adds unnecessary cost or delays your project timeline.
Here’s what you need to know to make the right call.
Quick Comparison: Bead Blast vs Polish
| Parameter | Bead Blast | Polish |
|---|---|---|
| Surface Roughness | Ra 1.6-3.2 μm | Ra 0.05-0.3 μm |
| Visual Appearance | Uniform matte/satin | Mirror-like gloss |
| Cost per Part | $2-8 | $15-50 |
| Lead Time | 2-3 days | 5-7 days |
| Material Removal | 0.005-0.025mm | 0.05-0.15mm |
| Best For | Consumer electronics, cost-sensitive prototypes | Medical devices, high-end products |
| Tolerance Impact | Minimal (±0.01mm) | Moderate (±0.005mm planning needed) |
| Pre-Anodizing Prep | Excellent (creates texture for uniform color) | Good (requires bright dip for best results) |
Both finishes work. But most prototype projects don’t need mirror polish.
Why Surface Finish Matters for Your Prototype
Your prototype’s surface finish affects more than appearance. It influences:
- How well anodizing or powder coating adheres
- Whether machining marks show through colored finishes
- Total project cost and timeline
- Dimensional accuracy of final parts
We’ve machined over 10,000 prototypes across 20+ countries. The teams that specify finish requirements upfront save 40% more time than those who decide later.
Your surface finish choice should match your prototype’s purpose. Testing internal fit? As-machined surface works fine. Presenting to investors or running user testing? You need proper finishing.
Understanding Bead Blast Finish
Bead blasting propels spherical glass beads at 40-60 PSI against aluminum surfaces. Each impact creates a tiny dimple, building up thousands of micro-indentations that scatter light uniformly.
The result? A consistent matte finish that looks similar to Apple’s MacBook housings.
Process specifications:
- Media: Glass beads (110-170 mesh for aluminum)
- Pressure: 40-60 PSI (lower pressure = finer finish)
- Surface roughness: Ra 1.6-3.2 μm (32-125 μin)
- Material removal: 0.005-0.025mm per surface
Bead blasting removes surface contamination and light machining marks while maintaining base dimensions. We hold ±0.01mm tolerances on features that don’t require masking.
The finish feels smooth to touch but has visible texture. It’s not reflective like a mirror, but it’s bright with even light diffusion. Think brushed stainless steel appliances, but with a finer texture.
Common bead blast applications we see:
- Consumer electronics housings (smartphones, speakers, wearables)
- Home appliance control panels
- Automotive interior trim pieces
- Prototype enclosures for user testing
- Parts requiring subsequent anodizing
Processing time for typical prototype batches (1-20 parts) runs 2-3 days including quality inspection.
Understanding Polished Finish
Polishing uses progressive abrasive compounds on rotating wheels to gradually smooth aluminum to a mirror-like surface. It’s a multi-stage process requiring skilled hand work.
Typical polishing sequence:
- Initial sanding (320 grit) to remove machining marks
- Progressive sanding (600, 800, 1200 grit)
- Buffing with cutting compound
- Final buffing with jeweler’s rouge
- Optional bright dip for maximum reflectivity
Each stage removes material and reduces surface roughness. Final polished surfaces achieve Ra 0.05-0.3 μm—up to 60x smoother than bead blast.
Polished aluminum reflects light like a mirror. Hold a polished part next to your face and you’ll see your reflection clearly.
Material removal considerations:
Polishing removes 0.05-0.15mm of material. For parts with ±0.02mm tolerances on critical features, you need to account for this in your CNC machining specifications. We typically add 0.1mm to features that will be polished, then remove it during finishing.
Polish works best for:
- Medical device housings requiring cleanability
- High-end consumer products (luxury goods, jewelry)
- Parts where reflectivity is functional (optical equipment)
- Prototypes matching existing polished production parts
- Applications requiring ASME/BPE surface standards
Processing time for prototype batches runs 5-7 days due to intensive hand labor at each polishing stage.
Surface Roughness: What the Numbers Mean
Surface roughness (Ra) measures average peak-to-valley height across a surface. Lower Ra = smoother surface.
Here’s how different finishes compare:
| Finish Type | Ra (μm) | Ra (μin) | Touch Feel | Visual Appearance |
|---|---|---|---|---|
| As-Machined | 3.2-6.3 | 125-250 | Rough with visible tool marks | Dull with directional marks |
| Bead Blast (Coarse) | 2.4-3.2 | 95-125 | Textured, similar to 320-grit sanded | Uniform matte, low reflectivity |
| Bead Blast (Fine) | 1.6-2.4 | 63-95 | Smooth texture, like 400-grit sanded | Satin appearance, some sheen |
| Rough Polish | 0.4-0.8 | 16-32 | Very smooth with slight texture | Semi-gloss, moderate reflectivity |
| Fine Polish | 0.1-0.3 | 4-12 | Glass-smooth | High gloss, strong reflections |
| Mirror Polish | 0.05-0.1 | 2-4 | Perfectly smooth | Mirror-like reflectivity |
For context, human skin typically measures Ra 20-30 μm. A standard office desk surface runs Ra 1-2 μm.
Industry-specific Ra requirements:
Medical devices often require Ra 0.2-0.6 μm per ASME/BPE standards for surfaces contacting sterile products. Food equipment typically needs Ra 0.8 μm or better (FDA guidance).
Consumer electronics have no strict Ra requirements. Apple’s products use bead blast (Ra 2.0-2.5 μm) before anodizing. Most of our 3C product clients specify similar finishes.
Cost Analysis: What You’ll Actually Pay
Let’s break down real costs for aluminum prototype finishing.
Bead blasting costs:
- Setup: $25-50 per batch
- Processing: $2-8 per part
- Masking (if needed): $5-15 per part
Example project costs:
- 1 part: $27-58 total ($27-58/part)
- 5 parts: $35-90 total ($7-18/part)
- 20 parts: $65-210 total ($3.25-10.50/part)
Bead blast cost scales efficiently. The per-part price drops significantly with batch size.
Polishing costs:
- Setup: $0 (no batching advantage)
- Processing: $15-50 per part (varies with size/complexity)
- Masking: $10-20 per part
Example project costs:
- 1 part: $15-50 total
- 5 parts: $75-250 total ($15-50/part)
- 20 parts: $300-1000 total ($15-50/part)
Polish pricing stays relatively flat. A single prototype costs nearly the same per-part as 20 prototypes.
Where the cost difference comes from:
Bead blasting uses automated equipment. One operator can process multiple parts simultaneously in a blast cabinet. Processing time per part: 5-15 minutes.
Polishing requires skilled hand work at every stage. One operator handles one part at a time. Processing time per part: 45-180 minutes depending on size and desired finish level.
For a typical smartphone-sized housing (100mm x 60mm x 8mm), bead blast costs $4-6 per piece. Polish costs $25-35 per piece.
At our facility, 70% of aluminum prototype projects choose bead blast. The cost savings and faster turnaround make it the practical choice for most applications.
Dimensional Impact: Planning Your Tolerances
Both finishing processes remove material. You need to account for this in your design.
Material removal rates:
| Finish Process | Material Removed | Tolerance Planning Strategy |
|---|---|---|
| Bead Blast | 0.005-0.025mm uniform | Add to non-critical surfaces only |
| Polish | 0.05-0.15mm variable | Add 0.1mm to all polished features |
| Bead + Bright Dip | 0.01-0.04mm | Add to surfaces specified for dipping |
Critical features requiring masking:
- Threaded holes (any thread pitch)
- Press-fit holes with H7 or tighter tolerances
- O-ring grooves and seal surfaces
- Bearing bores
- Mating surfaces with ±0.02mm or tighter specs
A common mistake: Specifying ±0.01mm tolerances, then requesting bead blast without masking callouts. The blasting removes 0.01-0.02mm, potentially pushing critical dimensions out of spec.
Real example from our shop:
Client specified a 10.000mm H7 bearing bore (tolerance +0.015/-0.000mm) on an aluminum housing. They requested bead blast finish with no masking callout.
After blasting, the bore measured 10.018-10.025mm—out of spec and requiring rework. We now catch this in DFM review before starting production.
Best practice: Add “Mask before blast: [list specific features]” note on your technical drawings. We’ll apply rubber plugs or tape to protect critical dimensions during finishing.
For parts with many tight-tolerance features, consider as-machined finish on functional surfaces and bead blast only on cosmetic surfaces.
Pre-Anodizing Prep: Which Finish Works Better?
Both finishes work before anodizing, but they produce different final appearances.
Bead blast before anodizing:
Creates uniform texture that accepts anodizing dye evenly. The micro-dimpled surface provides consistent color distribution across the part.
Recommended parameters:
- Glass bead size: 110-170 mesh
- Pressure: 40-60 PSI (lower = smoother finish)
- Type II sulfuric acid anodizing: Excellent compatibility
- Type III hard anodizing: Good compatibility
The matte texture remains visible after anodizing. Black anodize over bead blast produces the classic matte black finish seen on camera bodies and audio equipment.
For our clients doing anodizing after bead blast, we see excellent color uniformity and minimal variation between batches.
Polish before anodizing:
Creates high-gloss appearance after anodizing, but requires careful surface prep. Any remaining polishing compound or contamination causes splotchy color.
Polished then anodized aluminum can look darker than expected. The extremely smooth surface (Ra 0.05-0.3 μm) has fewer pores for dye absorption.
Many teams choose bright dip after polishing, before anodizing. Bright dipping chemically smooths microscopic surface variations, creating maximum reflectivity. This combination produces brilliant anodized finishes.
The hybrid approach (most popular for high-end prototypes):
- Machine part slightly oversize
- Bead blast to create uniform base texture
- Bright dip for increased reflectivity (removes 0.005-0.015mm)
- Anodize per specification
This process costs $10-20 per part—more than bead blast alone, less than full polish. You get 80% of the polish appearance with bead blast’s uniform texture.
Apple uses this approach on many products. The result is a semi-gloss finish with even light reflection and no visible machining marks.
Industry-Specific Recommendations
Different industries have different requirements. Here’s what works in practice:
Consumer Electronics & 3C Products:
Bead blast wins for most applications. It matches user expectations for premium devices while keeping prototype costs reasonable.
Typical specs:
- Surface: Bead blast, Ra 1.6-2.4 μm
- Finish: Clear or black anodize over bead blast
- Cost impact: $4-8 per housing
- Lead time: 7-10 days (machining + finishing + anodizing)
Our electronics clients in Shenzhen consistently choose this route. It delivers the Apple-style aesthetic users expect at prototype-friendly pricing.
Medical Devices:
Polish often required for surfaces contacting patients or sterile products. ASME/BPE standards specify Ra 0.2-0.6 μm for many applications.
Typical specs:
- Surface: Fine polish, Ra 0.2-0.5 μm
- Finish: Passivation or electropolish for corrosion resistance
- Cost impact: $25-50 per part depending on size
- Lead time: 10-14 days
For medical prototypes, the extra cost and time are non-negotiable. Regulatory requirements drive the decision.
Home Appliances:
Bead blast provides cost-effective professional appearance for control panels, trim, and visible housings.
Typical specs:
- Surface: Bead blast, Ra 2.0-3.0 μm
- Finish: Powder coat or anodize
- Cost impact: $3-6 per part
- Lead time: 5-8 days
Midea and Haier projects we handle typically specify bead blast. It hides minor imperfections and provides good paint/powder coat adhesion.
Automotive Interior Trim:
Mixed approach. Visible surfaces get bead blast or polish depending on vehicle segment. Functional surfaces stay as-machined.
Typical specs for premium vehicles:
- Visible surfaces: Bead blast + bright dip, Ra 1.0-2.0 μm
- Hidden surfaces: As-machined
- Finish: Clear anodize or chrome plating
- Cost impact: $8-15 per part
Luxury automotive clients request polish more frequently. The extra cost aligns with premium vehicle positioning.
Common Mistakes to Avoid
1. Specifying impossible surface roughness for bead blast
“Bead blast to Ra 0.5 μm” appears on drawings occasionally. Glass bead blasting can’t achieve this. The process naturally produces Ra 1.6-3.2 μm.
If you need Ra 0.5 μm, specify polish or adjust your requirement to match bead blast capabilities.
2. Forgetting material removal on tight tolerances
As-machined part measures 10.00mm. Bead blast removes 0.015mm. Final dimension: 10.015mm—potentially out of spec.
Always add masking callouts for features with ±0.02mm or tighter tolerances.
3. Choosing finish based solely on appearance
Polish looks impressive, but does your prototype actually need it? For internal testing or early design validation, bead blast works fine and saves budget for other development needs.
4. Not considering downstream processing
Some finishes conflict with later operations. Heavy bead blast texture makes welding difficult. Mirror polish shows every fingerprint and scratch during assembly.
Think about the full prototype lifecycle when selecting finish.
5. Missing masking requirements on drawings
“Bead blast all surfaces” without masking callouts leads to problems. We’ll need to halt production and contact you for clarification.
Add explicit notes: “Mask threaded holes M3 and bearing bore Ø10 H7 before blast.”
6. Using polish pricing as the standard
Teams sometimes budget polish costs, then discover their project doesn’t need it. Start with bead blast as your baseline. Upgrade to polish only when justified.
How to Specify Surface Finish on Your Drawings
Clear callouts prevent miscommunication and rework. Here’s proper notation:
For bead blast finish:
“Surface finish: Glass bead blast, Ra 1.6-2.4 μm (63-95 μin), per ISO 4287. Mask features noted with [M] before blasting.”
Then mark critical features with [M] callout pointing to the feature.
For polished finish:
“Surface finish: Mechanical polish to Ra 0.2 μm (8 μin) max, per ISO 4287. Polish visible surfaces only (see shaded areas on view 2).”
Include a view showing which surfaces need polishing.
Additional helpful notes:
- “Dimensions shown are pre-finish. Account for material removal.”
- “Verify critical dimensions post-finish before anodizing.”
- “Glass bead size: 110-170 mesh preferred.”
- “Post-finish inspection: Ra verification required on indicated surfaces.”
ISO 1302 symbols:
The triangle symbol with Ra value works but isn’t always clear. Written notes provide better communication for prototype finishing.
Getting Started with Your Aluminum Prototype
Now you can make an informed decision between bead blast and polish.
Choose bead blast when:
- Budget and timeline matter
- Your part needs uniform matte/satin appearance
- Subsequent anodizing or powder coating is planned
- Application is consumer electronics, appliances, or general industrial
- Order quantity is 1-100 parts
Choose polish when:
- Mirror-like appearance is required
- Regulatory standards mandate specific Ra values
- Parts represent luxury/premium positioning
- Maximum corrosion resistance is needed (polish + passivation)
- Reflectivity is functional, not just cosmetic
Choose combined approach (bead + bright dip) when:
- You want semi-gloss appearance
- Budget allows moderate premium over basic bead blast
- Parts need better appearance than matte but not full mirror
- Subsequent anodizing should have maximum color vibrancy
At Yanmee, we handle over 10,000 prototype finishing projects annually. Our CMF surface finishing capabilities include both bead blast and polish with single-piece MOQ flexibility.
Upload your CAD file for instant quote, or contact our engineering team to discuss finish requirements for your specific application.
Frequently Asked Questions
Bead blasting creates a uniform matte surface with Ra 1.6-3.2 μm by propelling glass beads at aluminum under pressure. Polishing produces mirror-like surfaces with Ra 0.05-0.3 μm through progressive abrasive compounds. Bead blast costs $2-8 per part with 2-3 day lead time. Polish costs $15-50 per part with 5-7 day lead time due to intensive hand work.
Bead blast works better for most anodizing applications. It creates micro-textured surface that accepts dye evenly, producing uniform color distribution. Use 110-170 mesh glass beads at 40-60 PSI before Type II sulfuric acid anodizing. Polish before anodizing creates high-gloss appearance but requires bright dip step for best results and consistent color.
Bead blasting costs $2-8 per part for typical prototype sizes, with batch pricing improving economics. A 20-part batch runs $3-10 per part. Polishing costs $15-50 per part with minimal batch discount since each part requires individual hand work. For smartphone-sized housing, expect $4-6 for bead blast versus $25-35 for polish.
Yes, bead blasting removes 0.005-0.025mm of material uniformly across blasted surfaces. This impacts tolerances ±0.02mm or tighter. Mask critical features like threaded holes, bearing bores, O-ring grooves, and press-fit surfaces before blasting. Add masking callouts on technical drawings and dimensions marked as post-finish or pre-finish to prevent confusion.
Bead blasting aluminum typically achieves Ra 1.6-3.2 μm (63-125 microinches) depending on glass bead size and pressure. Fine beads (170 mesh) at low pressure (40 PSI) produce Ra 1.6-2.0 μm. Coarse beads (110 mesh) at higher pressure (60 PSI) produce Ra 2.4-3.2 μm. This is 10-60x rougher than polished surfaces at Ra 0.05-0.3 μm.