Surface finish decisions impact both part performance and production cost. With decades of CNC experience across aerospace and medical sectors, understanding bead blasting’s effects on tolerances and materials is critical for smart design choices.
Bead blasting produces Ra 1.6–6.3 μm finishes while removing 0.005–0.025 mm material. Success depends on proper media selection, controlled air pressure, and substrate compatibility for dimensional accuracy.
Discover material compatibility, tolerance impacts, and cost trade-offs from real CNC production data.
Table of Contents
What Surface Finish Does Bead Blasting Achieve?
Bead blasting produces Ra surface finishes between 1.6–6.3 μm with uniform matte texture. Glass beads achieve Ra 1.6–3.2 μm for cosmetic applications, while ceramic beads create Ra 3.2–6.3 μm textures for improved paint adhesion.
Typical bead blasting surface finishes:
- Glass beads: Ra 1.6–3.2 μm (fine, cosmetic finish)
- Ceramic beads: Ra 3.2–6.3 μm (coarse, paint-ready texture)
- Steel shot: Ra 2.5–5.0 μm (durable, uniform coverage)
We verify bead-blasted finishes using Mitutoyo contact profilometers with 5-point surface sampling to ensure consistency. Glass beads at 40-60 PSI maintain optimal impact energy without media fracturing, consistently delivering Ra 2.5 μm across aluminum surfaces. Higher pressures (80+ PSI) can embed media particles or create surface peening that alters dimensions beyond the typical 0.005–0.025 mm material removal.
For medical housings requiring paint adhesion, ceramic beads at 60-80 PSI create controlled Ra 4.0 μm anchor patterns. The roughened surface increases mechanical bonding area compared to smooth machined surfaces. Audio equipment benefits from glass bead uniformity—it eliminates directional machining marks that create inconsistent light reflection and anodizing color variation.
Media flow dynamics limit coverage in features with depth-to-width ratios exceeding 3:1. Narrow slots or deep pockets require secondary finishing or design modifications for uniform texture.
Design Takeaway: Choose bead blasting when you need consistent matte appearance or paint prep, and can accept 0.005–0.025 mm material removal on non-critical dimensions. Skip it for hidden surfaces or when machining marks don’t affect function.
When Should I Choose Bead Blasting Over Other Finishes?
Choose bead blasting when you need uniform matte appearance, paint preparation, or gentle surface texturing without aggressive material removal. It excels for cosmetic parts requiring consistent light diffusion and surfaces needing mechanical paint adhesion.
Best applications for bead blasting:
- Cosmetic housings requiring uniform matte appearance
- Pre-paint surface preparation for improved adhesion
- Removing machining marks while preserving dimensions
- Creating consistent texture across complex geometries
From machining thousands of audio faceplates, bead blasting consistently outperforms brushed finishes for eliminating directional tool marks. The uniform texture prevents the “zebra striping” effect that brushed aluminum shows under certain lighting angles. For medical device housings requiring paint, we’ve measured 40% better paint adhesion on bead-blasted surfaces compared to as-machined aluminum using standard pull-off testing.
Skip bead blasting for parts with tight tolerances (±0.01 mm or tighter) where the 0.005–0.025 mm material removal creates risk. Chemical etching or anodizing work better for maintaining precise dimensions. Also avoid it for parts with deep pockets, internal channels, or complex undercuts where media coverage becomes inconsistent—these geometries need different approaches like chemical texturing or selective masking.
Design Takeaway: Specify bead blasting for visible surfaces needing consistent matte texture or paint prep, but only when dimensional tolerance allows for slight material removal. For precision features or complex internal geometry, consider alternative finishing methods
Which Materials Work Best with Bead Blasting?
Aluminum alloys (6061, 7075) respond excellently to bead blasting, while stainless steel and mild steel show good results. Avoid bead blasting on soft materials like brass, copper, or thin plastic components that can deform under media impact.
Material compatibility ranking:
- Excellent: 6061-T6, 7075-T6 aluminum (uniform texture, no deformation)
- Good: 304/316 stainless steel, mild steel (harder media required)
- Fair: Titanium, Inconel (specialized media needed)
- Poor: Brass, copper, soft plastics (surface damage risk)
Material compatibility follows established hardness thresholds per ASTM E18 Rockwell testing. Aluminum alloys with hardness ranges 25-87 HRB demonstrate optimal bead blasting response without surface embedding. Stainless steel grades 304/316 at 70-85 HRB require ceramic media and higher pressures due to work hardening characteristics defined in ASTM A240 specifications.
Materials below 35 HRB (brass, copper per ASTM B36/B152) show surface deformation and media embedding under standard glass bead impact. Industry surface preparation guidelines recommend minimum 2:1 hardness ratios between media and substrate to prevent embedding while achieving effective texturing.
ASTM B117 salt spray testing shows bead-blasted aluminum maintains corrosion resistance equivalent to as-machined surfaces when proper media cleanliness standards are maintained. Titanium and Inconel require specialized angular media and controlled atmospheres per aerospace specifications.
Design Takeaway: Stick with aluminum alloys for best bead blasting results. For soft materials, specify alternative texturing methods to avoid surface damage.
What Design Features Should I Avoid with Bead Blasting?
Avoid bead blasting on parts with deep narrow slots, blind holes smaller than 6 mm diameter, or sharp internal corners where media can’t reach effectively. Also skip it for threaded features or complex undercuts requiring uniform coverage.
Features that cause bead blasting problems:
- Deep pockets with depth-to-width ratios >3:1 (poor media coverage)
- Internal threads or fine features (media embedding risk)
- Sharp internal corners <0.5 mm radius (stress concentration points)
- Complex undercuts or re-entrant angles (shadow zones)
From manufacturing medical device components, we’ve learned that blind holes under 6 mm diameter trap media particles that become nearly impossible to remove completely. The trapped glass beads can contaminate assemblies or interfere with moving parts. Similarly, internal threads often collect media residue that affects fastener torque specifications and thread engagement.
Sharp internal corners create stress risers where bead impact can initiate micro-cracks, particularly in heat-treated aluminum. We recommend minimum 0.5 mm radii on all internal corners planned for bead blasting. Complex undercuts or re-entrant angles prevent uniform media flow, creating “shadow zones” with inconsistent texture that require secondary hand-finishing operations.
Keyways, splines, and other precision mechanical features lose dimensional accuracy due to selective media impact on edges and corners. These features typically need post-blast machining or complete masking during the process.
Design Takeaway: Design parts with generous radii, accessible surfaces, and keep threaded or mechanical features separate from bead-blasted areas. Consider masking critical surfaces for complex geometries.
How Does Bead Blasting Affect Part Tolerances?
Bead blasting removes 0.005–0.025 mm of material uniformly across surfaces, which can affect tight tolerances. For features requiring ±0.01 mm or tighter, consider the material removal in your tolerance stackup or mask critical surfaces during processing.
We measure dimensional changes using Mitutoyo coordinate measuring machines before and after bead blasting to verify removal rates. On precision aluminum housings with ±0.02 mm tolerances, we consistently see 0.008–0.012 mm material loss that must be accounted for during machining. The removal rate depends on blast pressure, media size, and exposure time—higher pressures or longer cycles increase material loss exponentially.
Critical surfaces like bearing bores, threaded holes, or mating faces typically require masking during bead blasting to maintain dimensional accuracy. Alternatively, leave 0.015 mm stock on these features and finish-machine after blasting. The uniform material removal actually improves surface parallelism and flatness by removing tool marks and surface irregularities from machining operations.
Geometric tolerances like flatness and cylindricity often improve after bead blasting because the process removes high spots and creates more uniform surface contact. However, position tolerances can shift if material removal isn’t uniform across all reference surfaces, particularly on parts with varying wall thicknesses.
Design Takeaway: Add 0.010–0.020 mm to your machining stock allowance for bead-blasted surfaces, and always mask or finish-machine features requiring tolerances tighter than ±0.02 mm.
How Much Does Bead Blasting Cost vs Other Finishes?
Bead blasting typically adds $15–45 per part depending on size and complexity, with 2-3 day lead time impact. It costs less than anodizing ($25–75) but more than as-machined finishes, making it cost-effective for cosmetic improvement without premium finishing expense.
Typical finishing cost comparison (per part):
- As-machined: $0 additional cost
- Bead blasting: $15–45 (size and complexity dependent)
- Anodizing: $25–75 (plus masking and racking costs)
- Powder coating: $20–60 (minimum batch quantities required)
- Chemical etching: $35–85 (hazmat handling and disposal costs)
Cost drivers include part size, surface area, geometric complexity, and batch quantity. Simple aluminum faceplates (100 x 50 mm) typically cost $18–25 for bead blasting, while complex housings with internal features can reach $35–45 due to masking requirements and extended blast times. Setup costs get distributed across batch sizes—single prototypes pay full setup overhead while production runs of 25+ parts see significant per-piece cost reductions.
Lead time impact averages 2-3 business days for standard bead blasting, compared to 5-7 days for anodizing or 7-10 days for powder coating. Rush processing available for additional 25-50% cost premium. Transportation and handling add minimal cost since parts don’t require special packaging like chemically-treated components.
The cost-benefit analysis favors bead blasting when you need improved appearance over as-machined surfaces but don’t require the durability or color options of anodizing or powder coating.
Design Takeaway: Budget $20–40 per part for bead blasting on aluminum components, with 2-3 day lead time addition. It’s the most cost-effective option for improved cosmetic appearance without premium finishing requirements.
Conclusion
Bead blasting delivers consistent Ra 1.6–6.3 μm finishes ideal for cosmetic surfaces and paint preparation, but requires careful tolerance management due to 0.005–0.025 mm material removal. Choose aluminum substrates and avoid complex internal features for best results. Contact us to explore bead blasting and manufacturing solutions tailored to your product requirements.
Frequently Asked Questions
Yes, bead blasting creates uniform surface texture that improves anodizing color consistency and eliminates streaky appearance from machining marks. The Ra 2.5 μm texture provides optimal base for Type II anodizing.
Walls below 1.5 mm thickness risk deflection and warping from blast pressure. Use lower pressure settings (30-40 PSI) or consider alternative texturing methods for thin-walled components to prevent dimensional distortion.
Standard bead blasting adds 2-3 business days to machining lead time. Complex parts requiring masking may need additional 1-2 days for setup and post-blast inspection verification.
Add “BEAD BLAST ALL SURFACES” note with Ra specification (e.g., “Ra 2.5 μm MAX”). Include “MASK” callouts for threaded holes, bearing surfaces, or critical dimensions requiring protection during blasting process.
Add 0.010-0.020 mm stock allowance on surfaces planned for bead blasting. For aluminum, expect 0.008-0.012 mm removal; for stainless steel, plan for 0.015-0.025 mm material loss during processing.
Blind holes require 6 mm minimum diameter for effective media flow and complete removal. Through-holes can go smaller (3-4 mm) since media exits freely without trapping particles.
