Design for Perfect Sandblasting: A DFM Guide for Precision CNC Parts – Consistent Texture Without Dimensional Loss
1. Geometry Design Rules Before Sandblasting
Three geometry features cause the most trouble.
Blunt Sharp Corners and Edges – Leave a Small Radius
A sharp corner (90° edge) will round over when blasted. The abrasive hits the edge harder than the flat face. After blasting, the edge becomes a soft radius. You cannot control how much.
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Design fix: Add a small radius (0.2‑0.5mm) to all external edges that will be blasted. This gives a predictable, clean result.
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Exception: If you need a sharp edge for a seal or a cutting tool, mask that edge. Do not blast it.
Leave Room for Masking – Protect Threads and Bearing Seats
Sandblasting removes material – about 0.002‑0.008mm from the surface. But the bigger issue is abrasive getting into threads or bearing bores. It scratches the surface and gets stuck.
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Threads: Always mask internal threads before blasting. Use a screw, a silicone plug, or tape. Design the hole with a small counterbore or chamfer to seat the mask.
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Precision bores (bearing fits): Do not blast them. Mask them or machine them after blasting. A blasted bore will never hold tolerance.
Deep Narrow Slots and Blind Holes – Ensure Abrasive Can Reach
Sandblasting works like a spray gun. The abrasive travels in a straight line. If a slot is deeper than 5‑6 times its width, the bottom will not get blasted. It will look different.
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Design fix: Keep slot depth‑to‑width ratio under 5:1 if a uniform finish is needed. For deeper slots, consider a secondary process or accept that the bottom will be less textured.
The table below summarizes design guidelines.
| Feature | Design Rule | Why? |
|---|---|---|
| External edges | Add radius ≥0.2mm | Prevents uncontrolled rounding |
| Threaded holes | Provide mask seat (chamfer or counterbore) | Protects thread from abrasive |
| Precision bore | Do not blast; mask or machine after | Preserves tolerance |
| Deep slot | Depth ≤ 5 x width for full coverage | Allows abrasive to reach bottom |
2. Combined Tolerance and Surface Roughness Callouts
Your drawing must tell the shop what happens before and after blasting.
Mark “Before Blasting” vs “After Blasting”
Blasting removes a thin layer. A Ø10mm shaft will become Ø9.99mm after blasting. That 0.01mm change matters for press fits.
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Rule: On the drawing, put dimensions that must stay exact in a box. Add a note: “Critical dimensions measured after blasting. All other surfaces ±0.05mm before blasting.”
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Better yet: For bearing seats, mask them. They never see abrasive.
Specify the Right Ra Range for Blasted Surfaces
Sandblasting is not polishing. It creates texture. Typical Ra values:
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Fine glass bead: Ra 0.8‑1.6µm (satin, smooth)
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Medium aluminum oxide: Ra 1.6‑3.2µm (uniform matte)
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Coarse grit: Ra 3.2‑6.3µm (rough, for paint grip)
Do not ask for Ra 0.2µm on a blasted surface – that is impossible.
Leave Room for Anodizing or Painting After Blasting
If you anodize after blasting, the anodizing layer (0.005‑0.025mm) adds a tiny amount of thickness. It does not change the texture much. But if you powder coat, the coating thickness (0.05‑0.15mm) will fill in the blast texture. A very rough blast (Ra > 4µm) will still show texture under paint. A fine blast (Ra < 1.5µm) will be completely hidden.
Design tip: For painted parts, specify medium blast (Ra 2‑3µm). For anodized parts, fine blast (Ra 1‑2µm).
3. How Different Materials Respond to Sandblasting
Not all metals blast the same.
| Material | Best Abrasive | Result | Caution |
|---|---|---|---|
| Aluminum (6061, 7075) | Glass bead or fine aluminum oxide | Smooth satin or matte | Soft – low pressure (30‑50 psi) |
| Stainless steel (304, 316) | Glass bead or ceramic bead | Bright, clean satin | Can be blasted at higher pressure |
| Brass / copper | Glass bead (fine) | Warm, matte gold | Soft – do not overblast |
| Titanium | Glass bead (low pressure) or specially cleaned media | Matte gray | Do not use steel or aluminum oxide – can embed and cause galvanic corrosion |
| Magnesium | Do not sandblast | – | Highly flammable dust. Use chemical etching instead. |
Titanium – Special Caution
Titanium is reactive. If you blast it with steel grit or used aluminum oxide (which may contain steel particles), those particles embed in the surface. Later, in service, the steel particles rust and cause pitting. Always use new, clean glass bead or ceramic media for titanium. Specify media certification.
4. Expert Insight: The Masking Rule of Thumb
“I see drawings that say ‘sandblast all surfaces’ – including fine threads and bearing bores. That is a mistake. The abrasive will change the thread fit. You might get a gritty feel. The bearing bore will be oversized. My rule: if a feature would fail from a 0.01mm diameter change, mask it. If it has a sharp edge that must stay sharp, mask it. Blasting is for cosmetic and paint prep surfaces. It is not for precision fits.”
— Surface Finishing Engineer, DongGuan YiTai Electronic Technologies
Send Your Design for a DFM Report Including Sandblasting Feasibility
At DongGuan YiTai Electronic Technologies , we do not just machine your part. We review it for sandblasting success. We check edge radii, maskability, and depth‑to‑width ratios. We recommend the right abrasive, pressure, and Ra target.
Send us your 3D drawing and 2D print. We will reply with a professional DFM report that includes sandblasting recommendations – at no charge.
5. Frequently Asked Questions (FAQ)
Q: Does sandblasting change the dimensions of my part?
A: Yes, but very little. Typically 0.002‑0.008mm per surface. For most parts, this does not matter. For press fits and bearing bores, mask the area. Do not blast them.
Q: What is the best surface finish for anodizing after sandblasting?
A: A fine glass bead blast gives Ra 1.0‑1.6µm . This hides tool marks and gives a soft, even look after anodizing. Do not use coarse grit – the anodizing will not hide the roughness.
Q: Can I sandblast a part with holes smaller than 1mm?
A: Yes, but the abrasive may not go deep into small holes. The inside of a 0.8mm hole will not be blasted. If you need a uniform finish inside small holes, consider a different process (tumbling or chemical etching).
Q: How do I write a sandblasting spec on my drawing?
A: Write a note: “Sandblast all external surfaces except [list masked features]. Use 120‑grit glass bead. Target surface roughness Ra 1.8‑2.2µm. Mask all threaded holes with silicone plugs.”
Q: Is sandblasting safe for thin walls (under 1mm)?
A: Be careful. High pressure can warp thin aluminum. Reduce pressure to 30‑40 psi. Use fine media. For very thin parts (0.5mm), consider a less aggressive finish or mask the thin areas.
Q: Does DongGuan YiTai Electronic Technologies offer sandblasting for all these materials?
A: Yes. We blast aluminum, stainless, brass, titanium, and some plastics. We use dedicated media for each material to avoid cross‑contamination. Send your part for a free feasibility check.
DongGuan YiTai Electronic Technologies Co.,Ltd
DongGuan YiTai Electronic Technologies Co.,Ltd is a manufacturing service provider located in Dongguan, China.
YiTai specialized in CNC turning machining and sheet metal fabrication mainly. As a member of Hung Mou Group, we focus on the overseas marketing development. And based on our parent company’s manufacturing capability and resources, YiTai also expended machining services such as die casting, injection molding, aluminum profile extrusion, 3D printing, which are committed to providing customers with one-stop purchasing services and experience.
CNC MACHINING , CNC MILLING , CNC TURNING , SHEETMETAL , FASTENER , OTHERS
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