CNC phone case production: the engineering side of custom cases

• 1
  Key takeaways
• 2
  What CNC phone case production actually involves
• 3
  Material choice drives wall thickness and finish
• 4
  Tolerances and features that decide the toolpath
• 5
  When to choose CNC and when to choose molding
• 6
  Surface finishing and the last 0.02 mm
• 7
  What to send for an accurate quote
• 8
  CNC milling vs injection molding for phone cases

A machined case starts as a solid block or a near-net extrusion. The blank is squared, the outer profile is roughed, then the cavity that receives the phone body is cut from the inside. Every pocket, speaker slot, button relief, and camera opening is a separate toolpath with its own tool, feed, and step-down.

The work is subtractive, so the design freedom runs the other way from molding. You can change a wall thickness between prototype and production without paying for a new mold. You can also cut a one-off in a week rather than waiting on steel.

That flexibility has a cost. Each unit takes machine time, and machine time is the dominant term in the price. A case with 14 features and three setups will always cost more than a case with 4 features and one setup.

For a 5-axis mill, most phone cases fit inside a 200 × 100 × 15 mm envelope. GreatLight runs 16 simultaneous 5-axis centers, so a small case body is a comfortable fit well inside the machine travel.

Aluminium 6061-T6 is the default for a machined case. It cuts clean, holds a sharp edge, anodizes predictably, and takes a bead-blasted or brushed finish without smearing. 7075 gives higher strength for a thin frame but anodizes to a darker, less uniform tone.

Titanium TC4 (Ti-6Al-4V) is the premium option. It is roughly three times stiffer than aluminium at the same section, so a 0.5 mm wall feels rigid. The trade-off is cutter wear: tool life drops sharply, and a case that takes 40 minutes in aluminium may take three hours in titanium.

Stainless 316L and 17-4PH are used for hinge plates, screws, and camera bezels rather than whole bodies, because density makes a full stainless case heavy. Plastics such as POM, PC, and carbon fibre laminate are common for prototype shells and for RF-transparent sections.

Pick the material from the requirement, not the look. If the case must survive a 1.5 m drop, stiffness and wall thickness matter more than alloy grade. If it must sit on a wireless charger, keep metal out of the coil area or use a plastic insert.

General machined features on a phone case hold ±0.05 mm without special effort. Critical interfaces, like the camera ring seat or a magnetic array pocket, can be held to ±0.005 mm on a 5-axis center with a controlled temperature shop.

The tightest callout is usually flatness on the back face and parallelism between the front rim and the rear plane. If the back is not flat, the case rocks on a table and the camera bump looks tilted. We check flatness on a granite surface plate, not on the machine.

Corner radii set the tool size, and tool size sets the cycle time. A 0.5 mm internal corner needs a Ø1 mm cutter, which must run at reduced feed to avoid snapping. Keep internal corners at 1 mm or larger unless the feature is cosmetic.

Button cutouts and speaker slots are the features that break. A 0.8 mm wide slot in a 0.7 mm wall leaves almost no material. Reinforce it or widen the slot.

Inspection at GreatLight is 100% before shipment, with raw material check, in-process monitoring, and final inspection. Dimensional reports are available on request. Qualification rate is 99.99%.

Milling is the right answer from one prototype up to a few hundred units, and for any design that is still moving. There is no tooling cost, no mold lead time, and no minimum order quantity at GreatLight. A revision is a new program, not a new mold.

Injection molding becomes cheaper per part somewhere in the thousands, depending on geometry. If the design is frozen and the volume is real, molding wins on unit cost. If the design is frozen but the volume is 50 units, it does not.

A hybrid pattern works well for small brands. Machine the first 20 to 50 units in aluminium, sell them, collect field feedback, then cut steel for the molded version. The machining cost buys you information you cannot get from a simulation.

CNC also covers the parts molding cannot make at all: low-volume titanium, one-piece unibody frames, engraved serial numbers, and cases with metal inlays bonded into a plastic shell.

Anodizing is the most common finish for aluminium cases. Type II clear or colour adds a thin oxide layer that grows both outward and inward, so a part that measures 0.02 mm under nominal before plating usually lands on size. Hardcoat anodize builds a thicker layer and is more abrasion resistant, but it shifts colour.

Bead blasting gives a matte texture that hides small tool marks. Brushing leaves a directional grain, which means the part must be oriented the same way through the finishing line or the grain will run in different directions on the same case.

Laser marking is the usual way to add a logo or serial number. Minimum character height is 1.5 mm for a legible mark on an anodized surface. Anything smaller fills in.

Electroless nickel, zinc, silver, and gold plating are available for stainless and copper parts. Powder coating and black oxide are options when the case is steel. Plan the finish before you set the machining dimension, not after.

Send a STEP or IGES file with the case modeled at final dimension, plus a 2D drawing if any feature has a tolerance or a datum. Renders help us see intent, but they do not define geometry.

Tell us the phone model and whether the case must fit the bare phone or a screen protector as well. A 0.3 mm clearance difference is the most common cause of a case that will not snap on.

State the finish, the target quantity, and any cosmetic zones. Cosmetic zones matter because a tool mark that is acceptable on an internal face is a reject on the outer back.

GreatLight returns a quotation and a free DFM analysis within 12 hours. Production can start within 24 hours of approval, and parts ship in 3–5 days. Uploads are secure and confidential, and an NDA is available on request.