Guides / Materials
Aluminium or Polycarbonate: What Changes on the Machine
September 27, 2026
Most of this niche’s material comparisons are aluminium against aluminium, or aluminium against another metal. Polycarbonate is a different conversation, because it is not a lighter aluminium alternative, it is a different manufacturing process wearing the same part shape.
Cutting the two materials
Aluminium 6061 and 6063 cut predictably at high spindle speed with standard coolant, and a shop that runs cosmetic aluminium all day has the feeds and speeds for it dialled in.
Polycarbonate is a different job. It has a low melting point relative to the heat a cutting edge generates, so a feed that is fine in aluminium can locally melt PC, leaving a smeared, cloudy mark that no polish removes. Cast acrylic-like plastics also hold internal stress from how the sheet or billet was made, and machining releases it unevenly, which is why a PC case can warp slightly weeks after it measured perfectly. A shop that is good at aluminium is not automatically good at polycarbonate, and the two are worth asking about separately when you choose a manufacturer.
Finishing: a shorter menu
Aluminium’s finishing options are wide: Type II or Type III anodising, e-coating, PVD, cerakote, each changing colour and texture in a different way.
Polycarbonate cannot be anodised at all, because anodising converts a metal surface into an oxide layer. A PC case gets its colour from one of three places: the resin is dyed before moulding or extrusion, a coating is sprayed on afterward, or the surface is left in its natural clear or smoked state and the colour comes from something visible through it, like a PCB or backlighting. A clear or smoked PC top is a genuinely different design move from anything metal offers, and it is the reason some designers pick the material regardless of cost.
Weight and sound
Polycarbonate is roughly half the density of aluminium. A PC case is a noticeably lighter board, which some buyers want and others read as cheap, so know your audience before you commit.
On sound, the lower density and higher internal damping of polycarbonate generally produces a deeper, quieter, less resonant tone than aluminium, which rings brighter and holds a tone longer. Community descriptions and lived experience with both materials both point the same direction here, though the finished sound depends heavily on the mount and the gasket as well, covered in mounting styles from the machinist’s side.
Tolerance and fit
Aluminium holds a tight tolerance well and does not move much with temperature or humidity once machined. Polycarbonate is more dimensionally sensitive: it expands more with heat, absorbs a small amount of moisture over time, and a thin wall section can creep slightly under sustained clamping load, for example where a screw compresses it.
None of this rules polycarbonate out. It means a gasket shelf or a screw boss drawn to an aluminium block tolerance is not automatically safe in polycarbonate, and it is worth widening tolerances slightly or asking the shop what they have seen hold up on prior PC runs.
Cost, honestly
At the raw material line, cast or extruded polycarbonate stock usually costs less per kilogram than 6061 or 6063 billet. That advantage narrows or disappears once you account for slower cycle times from careful feeds, a higher scrap rate while a shop dials in a new material, and a finishing process that does not benefit from the anodising batch economics aluminium enjoys, laid out in what drives a keyboard case’s cost.
The honest comparison is: raw material favours polycarbonate, process risk and finishing options favour aluminium, and the two materials are aimed at different aesthetic and acoustic targets in the first place. Pick the sound and the look you want, then price both, because the cost difference is smaller and less predictable than the material cost alone suggests.
Plastics, wood and composites sit side by side in our guide to keyboard case materials.
Frequently asked questions
Is polycarbonate cheaper than aluminium for a keyboard case?
The raw material is cheaper, but the machining is not always faster, because polycarbonate needs slower feeds and more careful tool paths to avoid melting and stress marks. A raw PC case is often cheaper than a raw aluminium one. A painted or textured PC case can close that gap or lose it entirely.
Can polycarbonate be anodised?
No. Anodising is an electrochemical process specific to aluminium. A polycarbonate case gets colour from the resin itself, from paint, or from a UV coating, and none of those hold a texture or a metallic look the way anodising does.
Does a polycarbonate case sound different from an aluminium one?
Yes, and the difference is one reason designers choose it. Polycarbonate is lower density and more compliant, which most people describe as a softer, deeper sound compared to the brighter, harder tone of aluminium. Neither is more correct, they are different design targets.
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