CNC processing telephone case design: from CAD to a machined housing

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  Key takeaways
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  What CNC processing telephone case design changes on the drawing
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  Wall thickness, ribs and the limits of a machined shell
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  Features that decide whether a case is machinable
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  Surface finish and color: what survives handling
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  Prototype or production: choosing the right process
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  Quality checks before a case ships
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  Machining vs casting vs printing for a phone case

A telephone case looks simple until you cut it. The outer shell is a thin curved surface, the inside is a pocket, and the two have to stay parallel within a few hundredths of a millimeter. CNC processing telephone case design means writing the drawing around how a cutter actually reaches the material, not around how the render looks.

On a 5-axis machine the tool can tilt. That single fact removes most of the hand work: undercuts, tapered side walls and camera rings can be milled at an angle instead of being split into two parts and glued. GreatLight runs 16 simultaneous 5-axis machining centers, plus 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers, so the routing can match the geometry rather than the other way around.

The trade-off is clamping. Every extra setup adds a datum shift. If your case needs three setups on a 3-axis machine, the wall thickness at the seam will wander. Design for one or two setups whenever the part allows it.

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  Design around the toolGive every pocket a corner radius at least 1/3 of the cutter diameter.
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  Keep one primary datumPick the face that stays in the vise and dimension everything from it.
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  Model the stockFlat bar or extruded tube changes how much material the first pass removes.

Machined aluminum cases usually land between 0.8 mm and 2.0 mm wall thickness. Below 0.8 mm the part starts to sing during the finishing pass and the floor of the pocket deflects. Above 2.0 mm you are simply adding weight and cycle time. For a 6.1 to 6.7 inch phone body, 1.0–1.5 mm aluminum is the practical band.

Ribs are the cheapest stiffness you can buy. A 0.6 mm rib standing 2 mm off the inner floor can raise the bending stiffness of a flat back panel by a large margin without thickening the whole shell. Cut ribs with a small-diameter end mill and leave 0.1–0.2 mm stock for the finishing pass so the rib top stays flat.

Titanium and stainless cases behave differently. Ti-6Al-4V and 316L resist deflection better than aluminum, so 0.6–0.8 mm walls are possible, but cutting forces rise and tool life drops. Expect longer cycle times and a higher unit cost. PEEK and carbon fiber composites sit in the middle: stiff, light, and hard on cutters.

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  Aluminum 6061-T6Best balance of stiffness, finish and cost for a production case.
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  7075Stronger, machines cleanly, but anodizing color can shift between lots.
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  PC or ABSUse when the case is a fit-check prototype, not a load-bearing shell.

Camera openings, side button slots, speaker holes and charging cutouts are where designs fail. A camera ring with a 0.3 mm chamfer and a sharp internal corner cannot be cut with a standard end mill. Either square the internal corner to a real radius or accept a small relief cut. Speaker hole arrays under 0.6 mm diameter are better laser cut than drilled; laser marking handles character heights down to 1.5 mm.

Threaded inserts and screw bosses need wall material around them. A M2 thread in aluminum wants at least 1.6 mm of surrounding wall, and M1.6 wants about 1.3 mm. If the boss sits on a 1 mm shell, add a local pad rather than thickening the whole panel.

Sealing faces are the one place where tight tolerance pays off. IP-rated or gasket-sealed cases usually need flatness under 0.05 mm and surface finish around Ra 0.8–1.6 μm on the mating lip. Everything else can run at Ra 1.6–3.2 μm as machined.

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  Internal cornersRadius them to match the smallest cutter you are willing to pay for.
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  Deep pocketsKeep depth under 3× the cutter diameter or step up to a longer, thinner tool.
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  Thin slotsBelow 0.8 mm wide, expect multiple light passes and possible wire EDM.

Anodizing is the default for aluminum cases. Clear, colored, hardcoat and conductive variants all change the dimension slightly, so the drawing should state whether the tolerance applies before or after coating. Hardcoat adds roughly 0.025–0.05 mm per surface and is worth it on edges that see keys and coins.

Bead blasting gives a uniform matte look and hides the faint scallops left by a ball nose cutter. Brushing runs in one direction and shows any deviation in the tool path. Polishing removes tool marks entirely, but it also rounds edges, so keep polished surfaces away from mating faces.

Electroless nickel, zinc, silver and gold plating are available when conductivity or wear resistance matters. Powder coating and black oxide suit steel and some stainless grades. On a phone case, laser engraving a logo on a blasted surface reads better than on a mirror polish.

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  Hardcoat anodizeBest abrasion resistance; specify the added thickness in the drawing.
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  Bead blast + clear anodizeStandard premium look, hides tool marks well.
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  Laser markingMinimum character height 1.5 mm for clean, readable text.

A machined prototype is the fastest way to hold a real phone case in your hand. GreatLight can start production within 24 hours of an approved drawing, and parts usually ship in 3–5 days. Quotation and a free DFM analysis come back within 12 hours. There is no minimum order quantity, so a single unit is fine.

For runs above a few thousand pieces, die casting or vacuum casting starts to compete on unit price, but the tooling lead time and the wall thickness limits change the design. Machining holds thin walls, tight tolerances and small undercuts that a die cannot. Many programs machine the first units, validate the fit, then move to tooling with the machined part as the reference.

If the case is a mechanical sample rather than a functional shell, 3D printing is cheaper and faster. Use it for ergonomics and assembly checks, not for drop or ingress testing.

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  1–500 unitsCNC machining, no tooling cost, design can still change.
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  500–5,000 unitsMachining or vacuum casting depending on wall and finish.
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  5,000+ unitsDie casting or injection molding, with a machined reference part.

GreatLight inspects 100% of parts before shipment, with raw material verification, in-process monitoring and a final inspection. Reports are available on request. For a phone case the critical checks are wall thickness at four or more points, flatness of the mating lip, camera opening position, and thread depth on any insert.

Tolerance on critical features is held to ±0.005 mm (±0.0002 in) where the drawing calls for it. That level is realistic on a flat sealing face or a bearing bore, not on a large curved shell. Ask for it only where the function needs it; spreading it across the whole part adds cost without adding value.

The shop holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. For unreleased phone models, an NDA is available on request and uploads are treated as confidential.

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  Wall thicknessMeasure at the thinnest section and near any rib intersection.
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  FlatnessCheck the gasket lip, not the decorative outer surface.
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  ThreadsGo/no-go gauge every tapped hole on functional cases.