Bead blasting aluminum parts can transform rough machined surfaces into professional-looking components, but it requires careful design planning to avoid tolerance issues and uneven finishes. With years of experience finishing precision parts for aerospace, audio, and medical applications, we’ve learned that successful bead blasting starts with smart design decisions — not just process execution.
Bead blasting removes 0.005-0.015 mm of material from aluminum surfaces, creating a uniform matte finish with Ra values of 1.6-3.2 μm. Critical tolerances must account for this material removal, and certain geometries like deep pockets or sharp internal corners should be avoided for consistent results.
Discover which features suit bead blasting, how to set tolerances, and what to call out on drawings—based on real aluminum housing and bracket examples.
Table of Contents
What features should I avoid if I'm planning to bead blast?
Avoid deep narrow pockets (deeper than 3x width), sharp internal corners under 0.5 mm radius, and thin walls below 1.5 mm thickness when designing for bead blasting. These geometries prevent uniform media coverage and can cause distortion or incomplete finishing.
When you’re looking at your CAD model right now, check for these three red flags:
- Pocket depth-to-width ratio over 3:1 – Measure from part surface to deepest point, then divide by narrowest opening width
- Wall thickness under 1.5 mm – Use thickness analysis on flat sections larger than 20 mm square
- Internal corner radii under 0.5 mm – Check L-shapes, brackets, and load-bearing transitions
The pocket geometry issue is pure physics – glass beads bounce off edges but can’t reach deep corners effectively. We recently processed aluminum audio faceplates where 15 mm deep display cutouts with 4 mm openings (3.75 ratio) left the bottom shiny with visible tool marks while everything else turned uniformly matte. No amount of additional blasting time fixes this mixed finish problem.
Wall thickness creates more expensive failures. During a medical device project, we watched 1.2 mm aluminum walls permanently bow outward 0.2 mm from peening stress. The housing couldn’t assemble afterward and required complete remachining. Any flat area under 1.5 mm thickness risks this permanent distortion, especially without supporting ribs.
Sharp corners cause scattered bright spots across otherwise uniform surfaces. High-velocity media creates stress concentration at corners tighter than 0.5 mm radius, where material fractures differently than surrounding areas. These stress points also trap glass beads that require ultrasonic cleaning to remove.
If your measurements show problems, here are your options ranked by cost and schedule impact:
- Quick design fixes – Add 0.3 mm to corner radii, increase walls to 1.8 mm minimum (1-2 days, minimal cost)
- Selective masking – Protect problem areas with polyurethane tape ($75-150, 3-5 day lead time)
- Alternative finishing – Chemical etching or vibro-finishing for complex geometries (similar cost, different appearance)
- Redesign required – Multiple deep pockets and thin walls need fundamental changes (2-3 weeks, highest cost)
Design Takeaway: Run these three measurements in your CAD model before finalizing the design. Simple adjustments now prevent expensive rework later, and planning for masking is always cheaper than discovering problems during production.
What aluminum grades respond best to bead blasting?
6061-T6 provides the most consistent bead blasting results with uniform texture and minimal cost impact, while 7075-T6 requires more aggressive parameters and costs 15-20% more due to its harder surface. 2024 aluminum should be avoided for cosmetic applications due to poor surface uniformity after blasting.
6061-T6 consistently delivers the best results because its relatively soft, homogeneous structure responds predictably to glass bead media. We typically achieve Ra 1.6-2.4 μm surface finish with standard parameters, and the alloy’s uniform grain structure means no blotchy areas or color variations that plague other grades.
7075-T6 requires 40% longer blast time and higher pressure due to its zinc content and surface hardness, driving up costs by 15-20%. The harder surface creates slightly more aggressive texture, which works for industrial parts but may look harsh on consumer products. If you’re locked into 7075 for strength requirements, use finer media and moderate pressure to avoid overly rough texture.
2024 aluminum creates the most problems for cosmetic applications. Its copper-rich composition responds inconsistently during blasting – some areas turn matte while copper-heavy sections remain shinier, creating an unprofessional spotted appearance. Fine for hidden structural parts, unacceptable for visible surfaces.
Design Takeaway: Choose 6061-T6 unless strength calculations specifically require 7075. Avoid 2024 for any visible applications, and budget extra time and cost if 7075 is unavoidable.
Will bead blasting affect the tolerance or fit of my aluminum part?
Bead blasting removes 0.005-0.015 mm of material from aluminum surfaces, requiring tolerance adjustments on critical dimensions and mating surfaces. Always add this material removal to your nominal dimensions or specify post-blast machining for precision fits.
Check your tolerance callouts right now – if you see ±0.01 mm or tighter on dimensions that will be bead blasted, you need to decide before machining. The typical 0.010 mm material removal turns acceptable fits into loose assemblies.
Here’s what happens to common fit scenarios: bearing bores with H7 fits become loose clearance, gasket grooves widen (usually acceptable) but depth changes affect sealing, and press fits lose their interference entirely. External threads become loose with nuts and inserts, while shaft diameters grow enough to affect bearing performance. We learned this during an audio equipment project where faceplate mounting holes grew from 6.2 mm to 6.35 mm, making screws loose in production parts.
Your approach depends on the tolerance you’re working with. For anything looser than ±0.05 mm, proceed normally since material removal won’t affect function. Tolerances between ±0.02-0.05 mm need compensation – add 0.01 mm to your CAD dimensions before machining. For tighter tolerances under ±0.02 mm, mask critical surfaces or plan post-blast final machining.
Communication with your machinist prevents costly mistakes. Add this note to your drawing: “Dimensions shown are post-bead blast. Machine critical features 0.01 mm undersize or mask as indicated.” This ensures proper compensation and eliminates confusion about which dimensions need adjustment.
Design Takeaway: Review every tolerance under ±0.05 mm in your model. Either open the tolerance, adjust dimensions by +0.01 mm, or mask those surfaces. Planning ahead costs less than fixing loose fits after production.
Is bead blasting the best way to remove machining marks from aluminum?
Bead blasting effectively removes visible machining marks and creates uniform matte texture, but it’s not always the most cost-effective solution. For simple cosmetic improvement on non-critical surfaces, hand sanding or vibro-finishing often provides better value.
The real question isn’t whether bead blasting works – it does – but whether your situation actually requires it. Most machining marks that bother engineers during prototype review disappear once parts are anodized or painted.
Bead blasting makes sense for complex geometries where hand finishing can’t reach consistently, production volumes over 50 pieces where setup costs spread reasonably, and visible surfaces that will remain uncoated or receive clear anodizing. Hand sanding with 320-400 grit removes marks from flat surfaces at much lower cost – typically 15 minutes of labor versus $85 setup plus $12 per part for selective blasting.
If you’re unsure whether marks will show through your intended finish, request a test sample. Most anodizing shops can process a prototype part for $25-50 to show how machining marks appear in the final finish, often saving hundreds in unnecessary blast processing.
Design Takeaway: Test whether machining marks will actually be visible in your final application before choosing removal methods. Hand finishing works for simple surfaces, while bead blasting excels when geometry complexity or production volume justifies the setup cost.
Can I bead blast aluminum before anodizing or painting?
Yes, bead blasting before anodizing or painting significantly improves adhesion and creates more uniform finish appearance. The textured surface provides better mechanical bond than smooth machined surfaces, but plan for slightly thicker anodizing buildup.
Bead blasting creates ideal surface preparation for subsequent finishes, but vendor coordination matters more than most engineers realize. The Ra 1.6-2.4 μm texture gives anodizing solutions better surface area for chemical bonding, resulting in more durable color that resists wear. Colors appear richer and more matte, with texture showing through as subtle depth that many designers prefer over flat finishes.
Vendor coordination options:
- Single-source shops – Many anodizers partner with blast services and handle coordination
- Separate vendors – Ship parts in sealed containers, coordinate timing directly
- Package pricing – Often 15-20% less than managing separate quotes and logistics
The process sequence requires careful timing. Always bead blast first, then move to anodizing within 24-48 hours maximum. Aluminum develops oxide films quickly that interfere with coating adhesion. Most anodizing shops understand this timing and can coordinate if you communicate the plan upfront.
Drawing and specification updates:
- Add note: “Bead blast before anodizing, coordinate timing to prevent oxidation”
- Show dimensions as post-blast, post-anodize final size
- Account for additional 0.005-0.010 mm coating thickness from surface texture
- Standard anodizing specs (Type II, Class 1) still apply but expect richer color
Cost considerations often favor the combined approach. While bead blasting adds process steps, it reduces finishing rejects from poor adhesion. Parts that sit too long between processes may need acid etching to restore surface chemistry, adding cost and delay.
Design Takeaway: Plan the sequence early and discuss timing with your finisher upfront. Single-source vendors simplify logistics, but separate vendors work fine with proper coordination and sealed transport between processes.
What surface roughness and appearance should I expect after bead blasting?
Bead blasting aluminum typically produces Ra 1.6-3.2 μm surface roughness with uniform matte appearance and reduced reflectivity. The exact finish depends on media type, pressure, and blast time, but results are predictable and consistent across complex geometries.
Standard glass bead blasting creates Ra 1.6-2.4 μm surface finish that feels similar to 400-grit sanded aluminum – smooth to touch but visibly textured. This eliminates machining grain patterns, replacing them with even texture that works well under anodizing or paint. The surface loses mirror-like reflectivity, becoming diffusely reflective with appearance similar to brushed stainless steel appliances.
Aluminum oxide media produces rougher Ra 2.4-3.2 μm finish feeling closer to 320-grit sanded surface. This works well for maximum paint adhesion but may feel too coarse for consumer products where people handle parts directly.
Most customers notice the difference from machined surfaces but find the texture pleasant and intentional-looking rather than rough. For inspection, vendors use portable surface roughness testers for Ra readings. Visual inspection looks for uniform matte appearance without shiny spots (under-blasted) or embedded particles (over-blasted).
Design Takeaway: Expect smooth but textured finish similar to 400-grit sanded surface with glass beads. The uniform matte appearance works well for anodizing and feels intentional rather than rough. Request test samples to verify texture meets expectations before production.
What should I call out in my drawing for bead blasted finish?
Specify surface finish requirements, areas to be blasted, and any masking zones on your drawing to ensure consistent results. Use standard surface finish symbols with Ra values and clear notes about process sequence if other finishes follow.
Use standard surface finish symbols with Ra values – the triangle symbol with “Ra 1.6 μm BEAD BLAST” placed near affected surfaces. This gives vendors measurable targets and inspection criteria.
Essential drawing callouts:
- Surface finish symbol with “Ra 1.6 μm BEAD BLAST”
- Area specification: “BEAD BLAST SURFACES AS SHOWN” with clear zone marking
- Masking notes: “MASK THREADS AND PRECISION BORES ±0.01mm”
- Process sequence: “BEAD BLAST BEFORE ANODIZING” in general notes
Place callouts in general notes and reference with leader lines to specific surfaces. Most CAD systems have standard surface finish symbols in annotation libraries. Add “DIMENSIONS SHOWN ARE POST-BLAST” to prevent confusion about material removal.
When vendors ask for clarification, they typically want blast media type (glass bead vs aluminum oxide), pressure ranges (60-80 PSI), and dimensional references. For quality control, specify “VERIFY Ra WITH PORTABLE ROUGHNESS TESTER” for precision applications.
Design Takeaway: Use standard surface finish symbols with Ra values, clearly mark blast zones, and specify masking requirements. Include process sequence and dimensional notes to prevent miscommunication with vendors.
Conclusion
Bead blasting works best on simple geometries with adequate wall thickness and non-critical tolerances. Account for 0.01 mm material removal on functional surfaces and choose 6061-T6 for consistent results. Contact us to explore manufacturing solutions tailored to your aluminum bead blasting requirements.
Frequently Asked Questions
Bead blasting typically adds $8-15 per part for simple geometries, with $75-150 setup costs for selective masking. Complex parts requiring extensive masking can cost 20-30% more. Volume pricing improves economics – parts over 100 pieces often see per-part costs drop to $5-8 range.
Glass beads create smoother Ra 1.6-2.4 μm finish with less material removal, ideal for cosmetic applications. Aluminum oxide produces rougher Ra 2.4-3.2 μm texture with more aggressive cutting action, better for paint adhesion but harsher appearance on consumer products.
Bead blasting requires line-of-sight access to surfaces. Deep pockets narrower than 6 mm, internal channels with direction changes, and undercuts remain partially unblasted. Consider design modifications or alternative finishing methods for complex internal geometries.
Maintain minimum 1.5 mm wall thickness on flat sections larger than 20 mm to prevent permanent distortion from peening stress. Thinner walls require support fixturing or should be avoided for bead blasting applications.
Bead blast after all machining operations are complete. The process removes 0.005-0.015 mm of material, affecting dimensional accuracy of features machined afterward. Plan final machining only for surfaces requiring post-blast dimensional correction.
