CNC aluminum alloy keyboard manufacturing: how a custom case is actually made

• 1
  What the case has to do before it looks good
• 2
  Alloy selection for a machined keyboard body
• 3
  How the part is held, and why that decides accuracy
• 4
  Which dimensions deserve ±0.005 mm and which do not
• 5
  Anodizing, blasting, and what they do to your dimensions
• 6
  Machined billet vs die cast vs sheet metal case

A keyboard case is a thin-wall box with a flat top face. Those two features fight each other. The top face has to stay flat enough that the plate and PCB sit without rocking, and the walls have to stay thin enough that the board does not feel like a brick. On a 65 percent layout, the case is roughly 320 mm long and 115 mm wide, so a 0.15 mm bow across that span is already visible when you set it on a granite surface plate.

Rigidity matters more than weight. When a user presses a key, the force travels through the plate into the case floor. If the floor flexes, the whole board sounds hollow and the typing feel goes soft. Machined ribs, a thicker floor boss under the spacebar, and a raised perimeter lip all add stiffness without adding much mass. A cast or sheet-metal case usually cannot hold the same wall thickness and rib pattern in one part.

The third job is thermal and acoustic. Aluminum pulls heat away from the PCB, which matters on boards with per-key lighting or a metal plate. It also rings. Deep pockets, rubber gaskets, and a deliberate distribution of mass change the sound signature. None of that is a machining tolerance, but all of it is decided by how the part is modeled and cut.

Interface geometry is where most rework happens. USB-C cutouts, screw bosses, daughterboard standoffs, and the switch plate lip all need to line up with parts you did not machine. We ask for the mating drawings, not just the case model, because a 0.2 mm mismatch at a connector cutout is a scrap part.

Most aluminum keyboard cases are cut from 6061 or 6061-T6. It machines cleanly at 8,000–12,000 rpm with carbide tooling, holds a sharp edge, anodizes to a consistent color, and is available in plate thickness from 6 mm to 40 mm. For a two-piece tray case, 6061-T6 plate in 20 mm or 25 mm stock covers most layouts.

6082 behaves close to 6061 and is common in Europe. 7075 is stronger and stiffer, so it allows a thinner floor, but it is harder on tools, anodizes to a darker and less predictable tone, and costs more. We only suggest 7075 when a customer has a specific stiffness target or a weight limit that 6061 cannot meet.

2024 is a poor fit for visible keyboard parts. It machines well and is strong, but it corrodes readily and needs a protective finish that changes the surface color. 5052 and 5083 are weldable and corrosion resistant, which makes them useful for sheet-metal or hybrid cases rather than a single billet part.

ADC12 is a die-casting alloy, not a billet alloy. It belongs in the conversation when volume reaches the thousands and the design can accept draft angles and thicker nominal walls. For one-off and small-batch custom work it is the wrong process, and a machined billet is cheaper once you count the tooling.

A keyboard case has five or six faces that matter and almost no flat surfaces to grip after the first operation. The usual sequence is: face and square the billet, cut the top pocket and switch plate opening, flip to a soft jaw or fixture, then cut the bottom pockets, screw bosses and connector cutouts. Each flip reintroduces setup error, so we try to keep the number of flips low.

For a two-piece case, the bottom can often be finished in two operations on a three-axis machine with a fixture plate. The top, with its angled side walls and radiused corners, is faster on a four-axis or five-axis mill where the part rotates instead of being re-clamped. Our shop runs 16 simultaneous five-axis centers, 12 four-axis mills, and 27 three-axis machines, so the routing follows the geometry rather than the other way around.

Thin walls move during cutting. As material is removed, internal stress in the plate redistributes and the part can bow. Roughing with 0.3–0.5 mm of stock left, then a stress-relief pause, then a finishing pass at light depth of cut keeps the floor flatter than a single heavy pass. On tall walls, we add temporary support ribs that are cut away last.

Workholding for long parts is the quiet cost driver. A 4,000 mm maximum processing size is available on our large-travel machines at 4,000 × 400 × 150 mm, but a keyboard case never needs that. What it does need is a fixture that repeats. Once a soft-jaw set is made, the second and tenth piece come off the same way as the first.

Specifying ±0.005 mm on every dimension of a keyboard case raises cost and does not improve the product. The tolerance should follow the function. Switch plate openings, PCB standoff heights, and connector cutouts are the critical group. Outer profile, pocket depth, and cosmetic radii are not.

A practical split: switch cutouts at ±0.05 mm so the plate seats without play; standoff heights at ±0.05 mm so the PCB sits parallel to the plate; USB-C opening at +0.1/−0 mm on the width and ±0.1 mm on position; outer profile at ±0.2 mm; pocket depth at ±0.1 mm. Our general machining capability is ±0.005 mm when a drawing calls for it, and surface finish ranges from Ra 0.2–0.8 μm on a fine finish to Ra 1.6–3.2 μm as-machined.

Flatness is usually the forgotten callout. On the case floor, 0.1 mm over 300 mm is a reasonable ask and it is what keeps the board from rocking on a desk. If the drawing says nothing, the shop will chase whatever the machine naturally produces, which may be better or worse than what the design needs.

Threaded holes deserve a note too. M2 and M2.5 threads in 6061 hold well but strip if the boss is under 3.5 mm diameter. We prefer 4 mm bosses for M2 and 5 mm for M2.5, with at least 4 mm of thread depth. Helicoil inserts are an option when the case will be opened repeatedly.

Anodizing builds a layer on the surface, roughly 5–25 μm depending on type. It grows outward and slightly inward, so a hardcoat at 25 μm can add about 0.012 mm per side. On a switch cutout that is already tight, that growth can close the opening enough to bind. We account for it by cutting the pre-finish dimension slightly under nominal when the drawing specifies a thick coating.

Type II clear or colored anodizing at 10–15 μm is the standard for keyboard cases. Hardcoat, at 25–50 μm, is more wear resistant and better on threads and wear surfaces, but it shifts color and can look uneven on large flat faces. Conductive anodizing exists for grounding paths, and it is worth specifying if the case is part of an electrical ground.

Bead blasting sets the texture before anodizing. Fine glass bead gives a matte surface that hides tool marks; a brushed finish runs the other way and shows every scratch. Both change how light reads across a flat top face, which is why two cases with the same alloy and coating can look different.

Laser marking is a common add-on for logos and port labels. Minimum character height is 1.5 mm; below that the mark becomes a smudge on an anodized surface. If the logo has to survive handling, it should be cut into the part before finishing rather than applied after.