Bead Blasting for CNC Parts: Finish Specs and Cost
Short answer: bead blasting gives CNC parts a uniform matte surface, typically around Ra 1.6–3.2 µm with fine glass beads, hides machining marks, and costs roughly $1–$5 per small-to-medium part at batch volumes. Specify it as a cosmetic finish, not a dimensional one: mask threads, ground seats and sealing faces, and know that blasting rounds sharp edges slightly and can embed media in soft aluminum.
Bead blasting is the most popular way to make a machined part look like a product rather than a machining exercise. It is also the most misunderstood line item on a quote, because buyers write "bead blast" on the drawing and assume everyone means the same thing. They do not. Media type, bead size, air pressure, duration and masking all change the result, and a finish spec that says only "bead blast" leaves the outcome to the operator's judgment. This guide gives you the vocabulary to spec it properly.
What Bead Blasting Actually Does
Bead blasting fires round media at the part surface under compressed air, cold-working the surface in thousands of small impacts. The result is a diffuse, low-glare matte texture that evens out the visual differences between machined, ground and stamped surfaces. On CNC parts its main jobs are cosmetic — hiding tool marks, giving a uniform appearance across features — plus light edge blending and the removal of minor burrs. It is not a dimensional process: the material removal is negligible on bulk surfaces, but edges get microscopically rounded and media can lodge in threads, blind holes or soft surfaces, which is why masking decisions matter more than the blast itself.
Surface roughness after blasting depends mainly on media and pressure, not on how smooth the part was before. A finely machined face and a roughly machined face tend to converge toward the same blasted texture, which is exactly why blasting is used to unify appearance. If the drawing needs both a blasted cosmetic surface and a precision feature, the precision feature must be masked or machined after blasting — a sequence question that should be resolved before quoting, not after first article.
Media, Size and the Finish You Get
| Media | Typical size | Typical blasted Ra | Effect and typical use |
|---|---|---|---|
| Glass beads | 0.05–0.15 mm (fine) | ~1.6–2.5 µm | Soft satin on aluminum and stainless; least surface damage |
| Glass beads | 0.15–0.25 mm (standard) | ~2.5–4.0 µm | Uniform matte for cosmetic housings and brackets |
| Aluminum oxide | 0.05–0.20 mm | ~3.2–6.3 µm | More aggressive; faster cut, whiter etch on aluminum |
| Ceramic beads | 0.10–0.30 mm | ~2.5–5.0 µm | Faster than glass with moderate texture |
| Steel shot / grit | 0.20–0.60 mm | 6.3 µm and coarser | Peening or heavy texture; not for cosmetic matte |
Ra values are indicative and method-dependent — the same part measured by stylus and by optical profilometer will differ — but the ordering is reliable: finer media and lower pressure give smoother, softer results; coarser media and higher pressure give rougher, more etched looks. For aluminum cosmetic parts, fine glass beads at moderate pressure are the safest default. Aluminum oxide cuts faster and produces a whiter, more matte appearance, but it embeds more readily in soft aluminum and can create a surface that looks good until handling turns it grey. Stainless steel parts are usually blasted with glass or ceramic beads to get a uniform satin without rust-colored contamination from steel media.
Specifying the Finish So the Shop Cannot Guess
A professional bead blast callout names four things: the media, the surface result, the coverage and the exclusions. Instead of "bead blast", write "fine glass bead blast, uniform matte, no visible machining marks, threads and Ø10 bore masked". If appearance is critical, add a reference: match a supplied sample, or specify against a visual standard. If the part will be anodized afterward, say so — blasting changes how the anodize takes color, and blasted-plus-anodized aluminum is usually described as satin or matte rather than the bright look of machined-and-anodized surfaces. Our anodizing guide covers that interaction in detail, and the surface finish guide explains how Ra maps to what you see.
Coverage needs a decision too. Full blasting treats every exterior face; selective blasting masks logos, datums, precision bores, ground surfaces and threads. Masking is real labor, and on small parts it often costs more than the blasting itself. A part with ten masked features can cost several times more to blast than an identical part blasted everywhere. Where possible, consolidate cosmetic surfaces so masking is simple, or design the part so critical features are machined after blasting rather than masked through it.
| Part size class | Indicative added cost per part, 100–1,000 pcs | Notes |
|---|---|---|
| Small, under 30 mm, blast all over | ~$1–$2 | Minimal handling and masking |
| Medium, 30–150 mm, blast all over | ~$2–$5 | Dominant cost is handling and cleaning |
| Medium with masked threads/bores | ~$4–$8 | Masking labor exceeds blast time |
| Large or selective multi-face blasting | $8+ | Quote per part; handling dominates |
These are indicative ranges from our own quoting experience, not a price list — the geometry, media and masking on your drawing decide the number. What matters is that the quote states media, pressure class and masking so the delivered finish matches the agreed spec, and that the shop cleans parts properly afterward.
Cleanliness, Masking and the Traps
Three traps cause most bead blast complaints. First, embedded media: fine particles lodge in soft aluminum or in blind features, and unless the part is cleaned — air blow-off, ultrasonic or washing depending on the requirement — those particles later appear as contamination in assembly or as cosmetically dark specks. Cleanliness-critical parts should specify post-blast cleaning and, where needed, confirm the part meets the same cleanliness level as before blasting. Second, edge rounding and dimension drift on delicate features: blasting rounds sharp corners by fractions of a micron to a few microns depending on media and time, which is irrelevant on a housing edge but fatal on a knife-edge seal or a precision land. Mask, or machine such features after blasting. Third, media cross-contamination: a shop that blasts steel and then glass on the same equipment without proper changeover can leave ferrous contamination on stainless parts, which rusts later. Ask how the shop controls media changeover if your parts are stainless or destined for corrosive environments.
Blasting also interacts with the rest of the finishing sequence. Blast before anodize for a satin anodized look; blast after machining but before any precision grinding or honing; never blast a surface that must seal or mate tightly. When a drawing carries both a tight tolerance and a blasted appearance on the same face, the process order — not the tolerance — is what the shop must get right, and the quote should say how. For the full menu of what happens after machining, our secondary finishing guide lays out the options and their cost logic.
At BQUQ we finish CNC parts in-house — blasting, anodizing coordination and cleaning are part of the same ISO9001-controlled flow, so the finish spec on your drawing and the finish on your parts are the same document. Send the drawing with a clear finish callout to sc@bquq.com or WhatsApp +86 13713157787, and the 12-hour quotation will state media, masking and cleaning assumptions before you commit.
Frequently Asked Questions
Q: What surface roughness does bead blasting produce?
A: Indicatively, fine glass beads at moderate pressure give roughly Ra 1.6–2.5 µm, standard glass beads around Ra 2.5–4.0 µm, and aluminum oxide from about Ra 3.2 to 6.3 µm. Results vary with media, pressure and measurement method, which is why a serious spec names the media and the visual result, not just a target Ra.
Q: How much does bead blasting add to a CNC part?
A: Indicatively $1–$2 per small part blasted all over at batch volume, $2–$5 for medium parts, and more when masking is involved — masking labor often exceeds blast time. The geometry, media and coverage on your drawing decide the real number, so the quote should state the assumptions.
Q: Does bead blasting change part dimensions?
A: Negligibly on bulk surfaces, but it rounds sharp edges by microns and can disturb fine features, and media can lodge in threads or blind holes. Critical faces, precision bores and sealing surfaces should be masked or machined after blasting.
Q: Should I bead blast before anodizing?
A: Only if you want the satin or matte anodized appearance. Blasting changes how the anodize layer reads, so machined-and-anodized and blasted-and-anodized parts look clearly different. State the intended final look on the drawing so the finishing sequence is chosen correctly.
Q: Can you blast stainless steel without contaminating it?
A: Yes, when the shop controls media changeover and uses non-ferrous media such as glass or ceramic beads. Ferrous contamination from shared equipment can rust on stainless parts later, so if your parts are stainless or corrosion-critical, specify the media and ask how changeover is managed.
Related Resources
- CNC surface finish Ra guide — what Ra numbers actually look like on machined and blasted surfaces.
- CNC machining services — machining and finishing under one ISO9001 roof in Dongguan.
- About BQUQ — the source factory running CNC, stamping, spring and heat sink lines.
- Contact us — send drawings and finish specs for a quote within 12 working hours.
Authored by the BQUQ Engineering Team. BQUQ is an ISO9001-certified source factory in Dongguan, China, running CNC machining, metal stamping, custom springs, heat sink and collet lines under one roof. Send drawings to sc@bquq.com or WhatsApp +86 13713157787 for a quote within 12 working hours. www.bquq.com
